Toll-like receptor-targeted anti-tumor therapies: Advances and challenges

Abstract

Toll-like receptors (TLRs) are pattern recognition receptors, originally discovered to stimulate innate immune reactions against microbial infection. TLRs also play essential roles in bridging the innate and adaptive immune system, playing multiple roles in inflammation, autoimmune diseases, and cancer. Thanks to the immune stimulatory potential of TLRs, TLR-targeted strategies in cancer treatment have proved to be able to regulate the tumor microenvironment towards tumoricidal phenotypes. Quantities of pre-clinical studies and clinical trials using TLR-targeted strategies in treating cancer have been initiated, with some drugs already becoming part of standard care. Here we review the structure, ligand, signaling pathways, and expression of TLRs; we then provide an overview of the pre-clinical studies and an updated clinical trial watch targeting each TLR in cancer treatment; and finally, we discuss the challenges and prospects of TLR-targeted therapy.

Introduction

Toll-like receptors (TLRs) are type I transmembrane glycoproteins (1) with evolutionarily conserved structures, existing in a wide variety of species from plants to vertebrates (2). Since the discovery in 1996 of Toll receptor protein that contributes to Drosophila’s anti-fungal response and embryonic development (3, 4), 13 functionally active homologs of Toll receptor-TLRs, have been identified in humans and mice, of which TLR1-9 and TLR11 are conserved in both species (5–7). However, TLR11 is non-functional in human, presented only by a pseudogene (8).TLR12 and 13 do not exist in humans, while TLR10 in mice is non-functional due to a retrovirus insertion (6).

Pattern recognition receptors (PRRs) are key components of innate immunity because of their ability to sense infection, elicit intracellular signaling cascades and initiate immune responses that ultimately eliminate pathogens and infected cells (9). As a group of important PRRs (3), TLRs recognize diverse microbial pathogens (e.g., lipids, peptides, carbohydrates, and nucleic acids) by their conserved molecular patterns, indicated as pathogen-associated molecular patterns (PAMPs), and initiate immune responses (10, 11). Almost all cells of the immune system (e.g., macrophages, B lymphocytes, dendritic cells, mast cells, neutrophils, etc.) as well as epithelial cells, endothelial cells, adipocytes, and cardiomyocytes recognize pathogens via TLRs (9). Recognition of microbial products by TLRs activates the innate immune response and triggers the activation of downstream signaling pathways in which myeloid differentiation factor 88 (MyD88) and toll-IL-1 receptor structural domain (TRIF) lead to the activation of NF-κB and subsequent transcription of pro-inflammatory cytokines including tumor necrosis factor-α (TNF-α), IL-1 and IL-6 (12). TLRs also recognize conserved molecular structures of host-derived molecules, often referred to as damage-associated molecular patterns (DAMPs) (13), derived after cell death and extracellular matrix (ECM) degradation from tissue damage caused by trauma or infection. TLRs have also been found to play critical roles in many other activities, including adaptive immune responses (14), differentiation and development (15, 16), tissue regeneration (17–19), cell cycle regulation (20, 21), and metabolism (22, 23).

As a group of regulators of various cellular functions, it is unsurprising that TLRs also exert their versatility in the process of carcinogenesis and tumor development, where their functions are augmented or dysregulated, resulting in either anti-tumor or pro-tumor responses (24–26). The exploitation of TLR anti-tumor activities has shown great promise in cancer immunotherapies, with some synthesized TLR agonists already approved by FDA for clinical use (27); however, problems still exist relating to their use, including limited translation rate from bench to bedside, possible immunosuppression induced by TLR agonists, and safety issues (28, 29).

In this article, we review the basic features of TLRs. We report on the applications of TLR-targeted treatment in anti-cancer therapies in clinical trials, encompassing various combinatory therapeutic strategies. Lastly, we review the challenges facing TLR-targeted therapy at present.

TLR structures and ligands

TLR structures

TLRs are membrane-spanning proteins (3) with an extracellular N-terminal domain consisting of 19-25 tandem leucine-rich repeat motifs (2), displaying a horseshoe tertiary structure (30, 31), which is responsible for ligand recognition (2). Next to the ectodomain is a transmembrane region (3), connecting the intracellular portion: the Toll/IL-1 receptor (TIR) domain in the C-terminal tail, which is homologous to IL-1 receptor family’s cytoplasmic region (32) and required for downstream signaling (10).

All the TLRs are synthesized in the endoplasmic reticulum (ER), then transferred to Golgi apparatus, and finally migrate to the plasma membrane or intracellular endosomes (33).

Human TLRs can be classified into two groups by sub-cellular localization: 1) the cell surface TLRs, TLR1, 2, 4, 5, 6, and 10, which reside on the plasma membrane (4), traveling to phagosomes when activated (34), 2) the intracellular TLRs, TLR7, 8, 9, which are expressed on endosomes inside the cells, with the LRR domain facing the inner cavity of the compartment, sampling their ligands (31). TLR3 are also primarily expressed on endosomes, yet it has been reported to express on the cell surface of fibroblasts, epithelial cells, and macrophages as well (35, 36).

In the ligand-binding, namely, activated status, TLRs tend to be dimerized (31). TLR2 alternatively forms heterodimers with TLR1, 6, or 10 (37, 38); each combination is associated with the specificity for recognizing a particular group of ligands, making TLR2 the most competent TLR in sensing a diverse range of PAMPs. Other TLRs tend to form homodimers (Figure 1) (39).

Figure 1

LR ligands

TLRs do not necessarily distinguish between self and non-self, but they respond to “danger signals” in general; as long as the “signals” are encompassed within certain molecular patterns, both no matter whether exogenous or endogenous ligands (40).

TLR ligands (TLRLs) primarily fall into three categories (1): natural exogenous ligands (PAMPs) (2); natural endogenous ligands (DAMPs and secreted ligands) (3); synthesized agents.

Exogenous ligands, namely, PAMPs originate from broadly expressed components in bacteria, fungi, protozoa, parasites, and viruses (10, 41, 42); they are common and genetically conserved because of their significance to microbial survival and infectivity (1, 43). As sentinels of the host’s defense system, TLRs sense PAMPs as invading dangers and directly activate the innate immune system (44), meanwhile indirectly activating the adaptive immune system (43), thereby providing indispensable protection against pathogens. Studies on mice lacking each TLR have shown that each TLR has a different function in PAMP recognition and immune response (45). Cell surface TLRs mainly recognize microbial membrane components such as lipids, lipoproteins, and proteins. TLRs expressed in intracellular components, such as endosomes, recognize viral or bacterial nucleic acids (46, 47). Specifically, TLR1/2 recognizes triacylated lipopeptides from Gram negative bacteria (38, 39), TLR2/6 recognizes diacylated lipopeptide from mycoplasma (38, 48), and TLR2/10 recognizes microbial components shared by TLR1 (37). TLR3 ligands are double-stranded RNAs (dsRNAs) emerging from cytosol virus replication (13, 39). TLR4 binds lipopolysaccharide (LPS) from Gram negative bacteria (39, 49) and fungal mannanes (48).TLR5 ligates with bacterial flagellin (13).TLR7 and 8 ligands are both single-stranded RNAs (ssRNAs) from viruses (13, 39).TLR9 recognizes nonmethylated CpG motifs normally found in bacterial and viral DNA (13, 39).

On the other hand, endogenously derived DAMPs from cells and ECM also activate TLRs. DAMPs are generated from cellular components or fragments of extracellular macromolecules, which are typicallyinaccessible to TLR ligand-binding regions in homeostasis, yet exposed to TLRs in the case of cell necrosis (passive release), apoptosis (pulsative release) or extracellular matrix degradation (5, 16, 43, 50) following trauma, inflammation and tissue remodeling during development (43). Specifically, TLR2 recognizes HMGB1, β-defensin-3, serum amyloid A, and biglycan (51);TLR4 recognizes HMGB1, fibrinogen, saturated fatty acids, and hyaluronic acid fragments (51);TLR3 recognizes mRNA (52);TLR7 and TLR8 recognize ssRNA (53) and antiphospholipid antibody (54);TLR9 recognizes IgG-chromatin complexes (55).

In the tumor microenvironment (TME), DAMPs can be abundantly released by solid tumors (5, 56) and have a significant impact in the TME by adopting mechanisms of tissue repair [such as cell proliferation (57, 58), angiogenesis (56), and tissue remodeling (59)], contributing to tumor progression. Alternatively, just as PAMPs, DAMPs can also act as stimulators of immune responses, showing anticancer potential in vitro as well (56).

Synthetic TLRLs on the other hand have varied levels of similarity to natural ligands (41), designed for the purpose of disease treatment by manipulating different aspects of TLR functions. The synthetic TLRLs are in active pre-clinical and clinical investigation. The advances of TLRLs, including synthetic TLRLs, in therapeutic research are reviewed in the following section 5 and Tables 1–3.

TLR signaling

TLR signaling is initiated after TLR-ligand binding, which causes conformational changes, leading to the recruitment of four major adaptor proteins (Figure 1) (41). Each of these proteins contain a TIR domain that is homologous to the intracellular region of TLRs; all TLRs transmit signals through at least one of those proteins: myeloid differentiation factor 88 (MyD88), TIR domain-containing adaptor protein (TIRAP, also identified as MyD88 adaptor-like protein, MAL), TIR domain-containing adaptor protein-inducing interferon (IFN)-β (TRIF, also identified as TIR domain-containing adaptor molecule 1, TICAM1), and TRIF-related adaptor molecule (TRAM, also identified as TICAM2 and TIR-containing protein, TIRP) (1, 10, 41, 224, 225). A fifth TIR-domain exists, containing adaptor protein- sterile alpha and HEAT/armadillo motif protein (SARM), but contrary to the other four adaptors with functions of TLR signaling stimulation, it negatively regulates TLR signaling by inhibiting the downstream of TRIF pathway (225, 226).

TLR signaling can be divided into two pathways according to the TIR-containing adaptor used: the MyD88 pathway (MyD88-dependent pathway) and the TRIF pathway (MyD88-independent pathway) (227). TLR4 is the only TLR that activates both pathways; TLR3 relies only on the TRIF pathway; the remaining TLRs, TLR1-2, TLR5-10, activate solely the MyD88 pathway (10, 24, 37, 227). When initiating these pathways, some TLRs require an accompanying adaptor molecule. TLR4 and TLR2 (after dimerized with TLR1 or TLR6 but not TLR10) require TIRAP to recruit MyD88. TLR4 requires TRAM to bridge to TRIF (227–229). However, TLR5 and TLR7-9 can independently interact with MyD88 (227), and TLR3 depends solely on TRIF (228, 230).

In the MyD88 pathway, a series of downstream molecules are sequentially activated following recruitment of MyD88, including but not limited to interleukin-1 receptor-associated kinases (IRAKs), tumor necrosis factor (TNF) receptor-associated factor 6 (TRAF6), interferon (IFN) regulatory factor 5 (IRF5), receptor-interacting protein kinase 1 (RIP1), nuclear factor κB (NF-κB) inhibitor (IκB) kinase (IKK) complex, finally leading to the activation of mitogen-activated protein kinases (MAPKs) (ERK, JNK, p38) and NF-κB, which induces a wide range of pro-inflammatory cytokines (227, 228). In addition, in a cell-specific manner, following TLR7-9 ligation, the stimulated MyD88 pathway in plasmacytoid dendritic cells (pDCs) can activate IRF7, which subsequently leads to IFNα production (227).

In the TRIF pathway, IRF3 is activated and translocated into the nucleus, consequently resulting in IFNβ induction (227, 228). TLR3 and TLR4 can signal through the IRF3/IFNβ pathway (231, 232). In addition, TRIF can also stimulate RIP1 and TRAF6, leading to activation of MAPKs and NF-κB to induce pro-inflammatory cytokine production (227, 228).

Besides typeIIFN (IFNα, IFNβ) and inflammatory cytokines (TNFα, interleukin-1 (IL-1), IL-6, IL-10, IL-12, etc.), TLRs also induce many different chemokines (IL-8, macrophage inflammatory protein (MIP)-1, IP-10, etc.) and microRNAs (miRNAs) (10, 41, 233–235). In cells, TLR activation may lead to apoptotic, proliferative, or differentiative responses (41). In tissues, TLR signaling can result in inflammation, immune responses, and tissue repair (236).

TLR expression

In humans, TLRs have a broad expression in various tissues, with the most diversity in locations involved in immune function, such as the spleen and peripheral blood, and locations in constant contact with microbes, such as the lung and the gastroenterological tract (237). Other locations expressing TLRs include the female reproductive tract, urinary tract, skin, neural system, and vascular system (238–240).

Specific to cell types, TLRs can typically be found in immune cells, such as DCs, monocytes, macrophages, granulocytes, NK cells, mast cells, and lymphocytes. Other non-immune cells also express TLRs, including endothelial cells, epithelial cells, fibroblasts, glial cells, astrocytes, keratinocytes, vascular smooth muscle cells, and sperm cells (3, 10, 33, 238, 239, 241, 242).

Recent evidence has shown that TLRs are expressed in diverse tumor cell populations (including tumor stem cells) together with cancer-associated fibroblasts, tumor-associated macrophages, myeloid-derived suppressor cells (MDSCs), regulatory T cells (Tregs), and adipocytes in the TME, participating in both promotion and inhibition in tumor growth (4, 10, 243).

During the process of malignant transformation, the level of TLR expression tend to elevate in transformed cells (including tumor cells) (24, 238, 244); meanwhile, the expression of TLR2, 4, 5, which is normally on cell membrane, increases in cytosol in a diffused manner (25, 245).

The expression patterns of TLRs and the downstream molecules are varied and regulated by multiple factors (237). Understanding these factors is vital for better exploitation in pre-clinical/translational research in TLR-targeted anti-tumor therapies.

TLR expression varies among distinctive species. For example, in humans, TLR9 is primarily expressed in B cells, whereas in mice, it can be found in B cells, monocytes, macrophages, and plasmacytoid DCs (pDCs) (246). Thus, cross-species interpretation of TLR research data should be carried out with caution.

Cell differentiation and activation status can also influence TLR expression. The differentiated human monocytic cell line THP-1 expresses increased TLR1, 4, 6, 7, 8, and MyD88 compared to undifferentiated THP-1 cells (33). E. coli-stimulated monocytes and granulocytes present different expression profiles of TLR1-10 (237). Phorbol myristate acetate/ionomycin-activated cytotoxic T cells (CTLs) showed increased TLR2 expression compared to unstimulated CTLs (247).

Ligands are another major factor affecting TLR expression. A specific TLR agonist may influence the expression of the TLR that it is ligating to and other TLRs as well. For example, the TLR4 agonist LPS elevated TLR1-8 expression in THP-1 cells, not just TLR4 (237). In addition, different ligands may differentially regulate the expression of a particular TLR. While TLR3 expression is upregulated by LPS, it is down-regulated by synthetic bacterial lipopeptide - a TLR2 agonist (237). Hence, cell localization related to potential ligand accessibility can impact TLR expression (39). As the case with TLR2 expression in B cells, only a restricted portion of peripheral blood B cells express TLR2 (248), but different developmental stages of tonsillar B cells all express TLR2 (249).

Cytokines are also engaged in the regulation of TLR expression. Many cytokines have been reported to increase TLRs expression level, including IL-6 and IFN-γ (237).

TLR activation can initiate negative feedback on TLR expression (237), and there is also internal balance among different expression of different TLRs (250, 251).

The factors discussed above indicate a complex network regulating TLR expression. This results in varied spectrums of TLR expression in respective cell groups and varied TLR-mediated responses, contributing to the heterogeneity of neoplasia, while also providing the basis for understanding the evidence for both anti-tumor and pro-tumor TLR-mediated activities. TLRs expressing in cancer cells could lead to tumor cell proliferation and induce cytokines that suppress immune activities; TLRs expressing on immune cells, however, could elicit Th1-based immunity, immune memory, and suppress tumor metastasis (252). The TLR expression in different tumor tissues is associated with patients’ outcome. Urban-Wojciuk et al. (252) have reviewed the association. In their review, the same TLR expressing in different types of cancers, could show opposite clinical correlations. TLR5, 7, 8, and 9 correlate with better clinical outcomes (high immune cell marker expression and/or longer survival), while TLR4, 7, and 9 are associated with poorer outcomes (advanced tumor stage, poor differenciation, and shorter survival) (252).

Recent advances of TLR-targeted tumor therapies

TLR-targeted therapies exert anti-tumor effects mainly by exploiting the potential of TLRs in the enhancement of both innate and adaptive immunity, and the induction of apoptosis in TLR-expressing tumor cells (41).

In this section, we introduce advances in pre-clinical (mainly from the past decade) as well as clinical research in tumor therapies targeting TLR. The TLR-targeting strategies and treatment modalities applied in both pre-clinical and clinical tumor therapeutic studies are summarized in Figure 2.

Figure 2

Pre-clinically, classic TLR agonists are being further explored in novel treatment strategies, and newly synthesized or naturally extracted TLR-stimulating agents are reported for improved immune activation ability and lowered toxicity; novel strategies of TLR agonism, aside from TLR agonists, have also been investigated (Table 1).

There have been many clinical trials completed involving TLRs, and some with promising results (Table 2). The ongoing clinical trials are continuously pushing the boundary of TLR-targeted therapy from bench to bedside (Table 3). Recent advances in clinical trials focusing on therapeutic interventions of tumors were summarized from critically reviewing clinicaltrials.gov and ncbi.nlm.nih.gov/pubmed.

TLR 2

In tumors, TLR2 has been found to enhance T cell immunity (253, 254) and suppress the accumulation of immunosuppressive T regulatory cells (Tregs) (62) and MDSCs (255). TLR2 also induces the anti-tumor M1-like macrophage polarization (66). The immune stimulating potential of TLR2 has been utilized in both basic and clinical therapeutic research.

Recently, there has been pre-clinical data (Table 1) demonstrating tumor inhibition effects by different TLR2L, including triacylated lipopeptides, synthetic chemical compounds, glucomannan polysaccharide, naturally extracted compound, and inactivated virus. In those studies, TLR2Ls are either investigated alone or in combination with tumor vaccines, immune checkpoint inhibition (ICB), chemotherapy, photodynamic therapy(PDT), or adoptive cell transfusion (ACT). In general, enhanced immune activation and suppressed tumor cell viability were observed in these studies (Table 1).

The number of clinical trials with sole TLR2 agonism in tumor immunotherapy is limited. It is noteworthy that Amplivant, the modified Pam3CSK4, can conjugate synthetic long peptides (SLPs) and elicit stronger DC and T cell stimulation in preclinical models compared to Pam3CSK4 (63). In 2021 the first-in-human phase I clinical trial NCT02821494 showed HPV16 E6 SLP-conjugated Amplivant induced robust HPV16-specific T cell immunity with good safety profile (187).XS15 is a TLR1/2 agonist, applied as an adjuvant to a multi-peptide vaccine scheme is in currently active phase I trial NCT04688385 (256).

TLR2 agonism has been applied in chimeric antigen receptor T cell (CAR-T) technology. In trial NCT02822326, a TLR2 Toll/IL-1 domain is incorporated in CAR-T, and the results showed that the tumor-targeting CD19-CAR-T2 cells augmented anti-leukemia responses in relapsed or refractory B cell acute lymphoblastic leukemia (B-ALL) patients with extramedullary involvement, competent in the eradication of extramedullary leukemia cells (257). Another similar phase I trial NCT04049513 is currently investigating the efficacy of 1928T2z CAR-T cells in treating B cell lymphoma.

In general, the Amplivant-SLP compounds are promising for further research for their early clinical data in terms of safety and efficacy of immune stimulation. Also, they have a great potential in treating different tumors as SLPs can be highly variable.

Clinical trials with multi-TLR activation, including TLR2, are discussed in the below sections.

TLR 3

TLR3 actively regulates multiple aspects of tumor development. Either directly or indirectly, TLR3 triggers both innate and adaptive immune responses (258, 259);, it suppresses tumor cell proliferation and promotes tumor cell apoptosis (260–262); it regulates tumor angiogenesis (263); it has also been found to enhance chemosensitivity (70) and radiosensitivity (264). By initiating these mechanisms, TLR3 agonists have shown promising therapeutic value.

In recent years, pre-clinical investigations of TLR3-targeted therapy (Table 1) have focused on combination therapy of TLR3 agonism with other treatment modalities, including chemotherapy, tumor vaccines, and ICB. There have also been studies examining nanoparticle incorporated TLR3 targeted therapies. Poly (I:C) has been used in most studies as the TLR3-targeting agent, while ARNAX, a new DNA-capped dsRNA, has also been applied. These treatment strategies aim to improve immune stimulation and reduce treatment side effects, thus achieving better therapeutic results.

Three TLR3 agonists, Poly ICLC (Hiltonol), Rintatolimod (Ampligen), and BO-112 have progressed for assessment in clinical trials (Tables 2 and 3) as cancer treatments.

Poly ICLC is carboxymethylcellulose, polyinosinic-polycytidylic acid, and poly-L-lysine double-stranded RNA, administratedintratumorally (i.t.), intramuscularly (i.m.), or subcutaneously (s.c.) in cancer treatments of different malignant stages, including primary, recurrent, and metastatic. The various types of cancer involved range from hematopoietic malignancies, skin cancers, sarcoma, squamous cell carcinomas, breast cancer, neurological malignancies, gastroenterological tumors, female reproductive tract malignancies, and urinary tumors (Tables 2 and 3). In these cancer treatments, Poly ICLC is mostly used in combination with traditional therapies (surgery, chemotherapy, or radiotherapy), immunotherapies (tumor vaccine, immune co-stimulation, or ICB), or other synthesized anti-tumor agents. Most of the trials are active or undergoing recruitment. One completed phase II trial (NCT02423863) aiming at multiple solid tumors applied Poly ICLC intratumorally (i.t.) or intramuscularly (i.m.), showing good tolerability with local and systemic immune responses, achieving clinical benefit (188). Two trials investigating melanoma have also been completed with available results: in phase I/II trial NCT01079741, poly ICLC was combined with NY-ESO-1 protein vaccine and Montanide to treat melanoma, effectively activating humoral and T cell immunity in patients. In phase I trial NCT01585350, poly ICLC together with peptide vaccine and incomplete Freund’s adjuvant (IFA) markedly enhanced T cell responses (190). Phase I trial NCT01834248 also combined poly ICLC with NY-ESO-1 vaccine and Decitabine in treating myelodysplastic syndrome, which showed success in the induction of NY-ESO-1-specific cytotoxic CD4⁺ and CD8⁺ T cells as well as CD141^Hi cDCs (265). The completed phase I trial NCT03380871 combined Hiltonol with a tumor vaccine, pembrolizumab, and chemotherapy to treat NSCLC, which showed a good safety profile and immune stimulation. Two completed phase I trials investigating either Hiltonol combined with tumor vaccines (NCT02721043) or Hiltonol with a tumor vaccine and Nivolumab (NCT02897765), all showing good treatment safety profile and immunogenicity. In particular, the latter treatment strategy induced intra-tumoral chemotaxis of cytotoxic T cells (191). The phase I trial NCT02544880 recently completed, where Hiltonol and Mucin1 were combined to make the MUC1 vaccine; together with influenza vaccine and PDE5 inhibitor Tadalafil, MUC1 vaccine has been used to treat solid tumors. Published interim results showed that the combination of MUC1 vaccine and Tadalafil was well tolerated and induced immune activation in HNSCC patients, despite the implication of immune evasion after the treatment was also observed (192). However, trial NCT01532960, where Hiltonol was combined with a tumor vaccine in treating breast cancer, was terminated due to the lack of immune stimulation by of Hiltonol for the vaccine (266). Phase II trial NCT02873819, phase I/II trial NCT02643303, and phase I trial NCT03358719 usingHiltonol in combinatory cancer therapies have recently closed, and are awaiting results. In general, Hitonol is well tolerated and can induce immune responses; however, there is a lack of robustdata presenting its competence in bringing clinical benefit.

Rintatolimod is a modified poly (I:C), PolyI: PolyC12U, administratedintravenously (i.v.) or intraperitoneally (i.p.) in gynecological cancers, breast cancer, and colorectal carcinoma. In clinical trials, Rintatolimod is applied used in combination with chemotherapy, a tumor vaccine, ICB, or other immune-modulatory therapies. Phase I/II trial NCT01312389 and phase II trial NCT03403634 using Rintatolimod have been completed, however the results are not yet publicly available.

BO-112 is a nanoplexed form of poly (I:C), which is currently under investigation in melanoma with pembrolizumab (NCT04570332).

In conclusion, pre-clinical data of TLR3 agonists provide promising perspectives for them to move from bench to bedside, yet more research and trials are needed in optimizing TLR3Ls’ clinical effectiveness.

TLR 4

In tumor studies, TLR4 has been reported to enhance the function of antigen-presenting cells (APCs) (267), increase the production of pro-inflammatory cytokines as well as IFNs (268–270), and boost cytotoxic responses of CTLs and NK cells (267, 271). These immune stimulating mechanisms can be initiated by TLR4 agonists in cancer treatment.

Recently, lipopolysaccharide, lipid A derivatives, polysaccharides, and protein TLR4 agonists were investigated in therapeutic studies (Table 1). These TLR4 agonists have been mostly used in combination with tumor vaccines, including DNA-, peptide- and DC-based vaccines; they have also been used in combinationwith radiotherapy and different kinds of immune-stimulating agents. Notably, many TLR4 agonists are engineered into nanoparticles, which have improved drug delivery efficiency and reduced off-target effects (88–91).

Several TLR4 agonists have completed clinical studies(Table 2), including LPS, GLA-SE(G100), IDC-G305, GSK1795091 (CRX-601), and the TriMix DC vaccine.

The completed phase I trial NCT01585350, investigated LPS in combination with a peptide vaccine and incomplete Freund’s adjuvant (IFA) to treat melanoma, which showed that this treatment was well tolerated and stimulated marked T cell responses (190).

GLA-SE is a glucopyranosyl lipid A-stable oil-in-water emulsion, tested in lymphoma, skin cancers, sarcoma, lung cancer, and colorectal cancer, either applied alone or in combination with surgery, chemotherapy, radiotherapy, ICB, or a tumor vaccine. In these trials, GLA-SE is administered i.t. or i.m. A phase I trial NCT02035657 applying GLA-SE in treatment against Merkel cell carcinoma has been completed. Treatment withintratumoral GLA-SE as an adjuvant to surgery and radiotherapy demonstrated safety and feasibility in Merkle cell carcinoma with increased intratumoral infiltration of CD8⁺ and CD4⁺ T cells, activation of immune-related genes, and local tumor regression (193).

IDC-G305 is a combination of NY-ESO-1 recombinant protein and GLA-SE, that has been tested in melanoma, ovarian cancer, renal cell cancer, and non-small cell lung cancer(NSCLC) (NCT02015416). This phase I trial showed that intramuscular administration of IDC-G305 was well-tolerated and can generate antigen-specific immunity (195). On the contrary, another two phase I trials NCT02387125 and NCT02609984, where NY-ESO-1 recombinant protein-GLA-SE was used with a DC-targeting tumor vaccine in treating solid tumors including sarcoma, melanoma, NSCLC, and ovarian cancer, were terminated because of lack of efficacy.

GSK1795091, a synthetic aminoalkyl glucosaminide 4-phosphate, in conjunction with anti-PD-1 pembrolizumab was investigated in advanced solid tumor treatment in trial NCT03447314; the results of this trial are yet to come.

TriMix DCs are autologous DCs incorporating mRNA encoding, CD40 ligand, CD70, and a constitutively active TLR4. The phase I/II trial NCT01530698 showed TriMix DCs, further electroporated with a tumor antigent encoding mRNA, administered intranodally, was safe but with only narrow immunological and clinical response.

In general, recent clinical trials usingTLR4 agonists did show clinical or immune stimulating efficacy in solid tumor treatment. However, there are contradictory results about the same agent in different trials. For those agents that showed promising results in early phase trials, future studies should pay attention to the optimal treatment conditions, including the therapy combination strategy and the route of administration.

TLR 5

TLR5 can be activated by bacterial flagellin and plays a key role in the immune homeostasis of pathogen-host interactions (272, 273). In addition, TLR5 is associated with decreased tumor cell proliferation, invasion, and metastasis (274, 275). Several drugs targeting TLR5 are under investigation.

Recently, protein-based TLR5 agonists have been investigated pre-clinically: in combination with a tumor vaccine (96), incorporated into the adoptive cell therapy (97), or used alone (98). All yielded enhanced therapeutic effects (Table 1).

Entolimod and Mobilan are administrated in two phase I trials (Table 2). Entolimod, namely, CBLB502 is a derivative of Salmonella flagellin. In trial NCT01527136, i.m. or s.c. administration of Entolimod was usedto treat locally advanced or metastatic solid tumors that cannot be removed by surgery. Results of this trial are yet to be available. While having the advantage of avoiding the dangerous inflammatory “cytokine storm” (276), Entolimod has a drawback that it can induce a rapid antibody neutralization (277),leading to its efficacy limitation. Pharmacological modification could be one solution to this problem. Mett et al. (277) identified and eliminated the epitopes leading to Entolimod’s neutralizing immunogenicity and refined its structure to get GP532 as a new TLR5 agonist. GP532 reduced neutralizing antibody response while preserving pro-inflammatory capacity. However, the anti-tumor potential of GP532 has not been verified in any therapeutic studies yet.

To extend the application of TLR5 agonism in TLR5 negative tumors, an adenovirus carrying TLR5 receptor and its agonist’s gene called Mobilan (M-VM3) was designed (276). In preclinical prostate cancer models, Mobilan displayed promising therapeutic efficacy (276).In phase I clinical trial NCT02654938, Mobilan was used intratumorally to treat prostate cancer; no results are available yet. A similar study showed Mobilan was well-tolerated in prostate cancer patients (278); however, more data is needed to verify its clinical benefit.

TLR 7 and TLR 8

TLR 7 and 8 serve as important sentinels in response to infection, which makes them irreplaceable in the activation of mammalian innate immune cells (279). These two receptors have also been found to participate in the regulation of the host adaptive immunity (280–283). The emergence of novel small molecular agents targeting these two receptors in the last decade has greatly facilitated cancer immunotherapy studies by adopting their immune activation potential.

Since many agonists exert dual activation to both TLR7 and TLR8, we will summarize TLR7 and TLR8 agonists together in one section.

Following pre-clinical investigations TLR7 or TLR7/8 agonists can be classified by molecular nature into imidazoquinoline and its derivatives, novel synthetic small molecules, and RNA-based agents (Table 1). These agonists are studied either with traditional therapies, such as chemotherapy, radiotherapy, surgery, or novel therapies, such as tumor vaccines, immune checkpoint blockade, adoptive cell therapy, and photothermal therapy (Table 1). It is noteworthy that nanotechnology has become a hot research topic in the drug delivery of therapies applying TLR7/8 agonists. TLR7/8 agonists are incorporated into multi-functional nanoparticles that overcome drug solubility limitations (120, 122) or improve tumor-specific environment-targeting ability (115, 124, 125), thus improving drug delivery efficiency.

A number of TLR7 agonists that have undergone clinical investigation include imiquimod, TMX-101, RNA-LPX, BNT411, DSP-0509, LHC165, SHR2150, TQ-A3334, and RO7119929 (Tables 2 and 3).

Imiquimod has already been clinically applied in the treatment for genital warts (284), low-risk superficial basal cell carcinoma (285), and Bowen’s disease (cutaneous squamous cell carcinoma in situ) (286).In clinical trials initiated in the decade, Imiquimod has been utilized in a wide range of clinical trials targeting different tumor types. There are studies attempting to widen the utilization of Imiquimod based on the current standard of care.

Many clinical studies of Imiquimod focus on Skin cancer. In basal cell carcinoma, a phase III trial (NCT05212246) is going to use Imiquimod as a single treatment in high risk populations to prevent tumor occurrence; imiquimod is also applied in two active trials in combination with curettage (NCT02242929, phase III), and sonidegib together with surgery (NCT03534947, phase II) to treat basal cell carcinoma. In an active phase I trial (NCT03370406), Imiquimod together with 5-fluorouracil is applied to treat squamous cell carcinoma. Two active phase I trial are investigating melanoma, where Imiquimod is combined with either Pembrolizumab(NCT03276832) or tumor vaccine(NCT04072900). A completed phase III trial NCT02385188 found imiquimod together with paracetamol and lidocaine induced 82.6% response rate in vulvar Paget disease but 80% of patients needed painkiller to mitigate side effects (197).

Imiquimod is also studied in intraepithelial neoplasia. In grade 2/3 cervical intraepithelial neoplasia (CIN), a phase II/III trial (NCT02130323) showed that Imiquimod induced lower HPV clearance rate compared to large loop excision (43% vs 64%), which made conization remain the standard care when intervention is needed (199).However, trial NCT03233412 showed that when adjuvant to the loop excision procedure, weekly application of imiquimod can promote regression of high-grade squamous intraepithelial lesions (200). Two active trials are investigating Imiquimod combining HPV vaccine (phase II, NCT02864147) or topical Fluorouracil (phase I, NCT03196180) in treating CIN2/3. In vaginal intraepithelial neoplasia (VIN), the results of the phase III trial NCT01861535demonstrated that: Imiquimod is safe and effective in treating VIN and should be considered as a first-line treatment alternative to surgery (198).In the active phase III trial NCT02059499, single use of Imiquimod is applied in HIV patients who have anal intraepithelial neoplasia.

In glioma, results of phase I trial NCT02454634 recently published in Nature (202) showed that topical Imiquimod combined with IDH1 peptide vaccine induced 93.3% immune responses in IDH1R132H-mutated patients while adverse effects are within grade I. The immune responses induced by the treatment were represented by enhanced IL-17 production and increased IDH1-specific T cells (202). Trial NCT00899574 focused on breast carcinoma; the results showed that single topical use of imiquimod proved beneficial for breast cancer metastasis to skin/chest wall and has been well-tolerated; additionally, this trial proved that imiquimod could induced a pro-immunogenic TME (201). There are also completed phase I/II trials using Imiquimod with radiotherapy, chemotherapy or tumor vaccine to treat breast cancer (NCT01421017, NCT02276300).

In prostate cancer, Imiquimod is applied topically with different tumor vaccines (NCT02293707, NCT02234921). The phase II trial NCT02293707 showed the combination of Imiquimod, telomerase peptide-based vaccine, and Montanide ISA-51 VG was safe in prostate cancer patients. The number of treatments was positively associated with immunological response (204). Bladder cancer is another type of malignancy where Imiquimod displayed its therapeutic potential. TMX-101 is the intravesical formulation for Imiquimod; single use of TMX-101 induced significant increase in urinary cytokines, including IL-6, IL-18, IL-1β, IL-1 receptor antagonist (IL-1ra), and vascular endothelial growth factor (VEGF), in non-muscle invasive bladder cancer, despite accompanied with mild adverse effects (phase II, NCT01731652) (205).

In general, Imiquimod showedits potential in cancer treatment, and also an increasing number of active trials using it has been initiated.

A trial with RNA-LPX (NCT02410733) showed early results with effective quick induction of IFNα and IP-10, and the induction of de novo antigen-specific T-cell responses. In this study, i.v. administration of RNA-LPX proved to be well-tolerated (116). SHR2150 and RO7119929 are oral TLR7 agonists, currently in trials in combination with other therapies in metastatic solid tumors (SHR2150, NCT04588324), and liver/biliary tract cancer (RO7119929, NCT04338685). BNT411 and DSP-0509 are synthetic small molecular TLR7 agonists administered i.v. that are being investigated in multiple types of tumors. LHC165 is a benzonapthyridine TLR7 agonist, which has been used in combination with anti-PD-1 (PDR001) to treat solid tumors.

TLR8 agonist VTX-2337, also known as Motolimod, has been tested in ovarian cancer and squamous cell cancer patients combined with chemotherapy, ICB, or small molecular inhibitors; in most studies, Motolimod was applied subcutaneously. Four studies have since completed with published results. In the first trial, a phase I trial (NCT01294293) with different histological subtypes of ovarian cancer, Motolimod was combined with doxorubicin, showing 15% patients with a complete response and 53% with stable disease (210). A similar phase II trial (NCT01666444), however, showed that the supplement of Motolimod to doxorubicin did not improve clinical outcomes in patients with recurrent or persistent epithelial ovarian, fallopian tube or primary peritoneal cancer, compared with placebo (207). Motolimod was demonstrated to augment clinical responses in patients with HNSCC of advanced stages, who have also been treated with the epidermal growth factor receptor inhibitor cetuximab (phase I trial NCT01334177) (209). However, in a trial of recurrent or metastatic SCCHN patients, the addition of Motolimod to platinum-based chemotherapy and cetuximab did not improve progression free survival (PFS) or OS; nevertheless, remarkable benefit was presented in HPV-positive patients and those with injection site reaction, suggesting the application potential of Motolimod in subset- and biomarker-selected patients (phase II trial NCT01836029) (287). Recently, a strong TLR8 agonist, combined with a HER2 monoclonal antibody was designed (sbt-6050), aiming to activate myeloid cells with the presence of HER2 positive tumor cells, and it is under investigation now in HER2 positive solid tumors with pembrolizumab (NCT04460456).

In terms of dual TLR7/8 agonists, Resiquimod, TransCon, 852A, BDB001, BDB018, NKTR-262, and BDC-1001 have undergone clinical investigation. Resiquimod has been examined by topical use in melanoma and brain tumors in combination treatment with a tumor vaccine and/or other adjuvants, however the addition of Resiquimod to NY-ESO-1 protein vaccine and IFA failed to elicit steady antigen-specific CD8+ T cell response (NCT00821652) (206). TransCon is a type of Resiquimod prodrug, now under investigation in combination with pembrolizumab in solid tumors (NCT04799054). 852A is also an imidazoquinoline TLR7/8 agonist, which has previously been tested in multiple tumors types (including renal cell carcinoma, melanoma, lung cancer, hematologic malignancies, breast cancer, ovarian cancer, and cervical cancer), showing acceptable tolerability, evident immune stimulation, and clinical benefit in some patients (288–291). The i.v. administered TLR7/8 agonist BDB001 and its refined analog BDB018 (designed to enhance immune stimulation while preserving the safety profile of BDB001) are both investigated in solid tumor treatment (NCT03486301, NCT04196530, NCT04840394). BDC-1001 is an immune stimulating antibody conjugate of an anti-HER2 monoclonal antibody with a TLF7/8 dual agonist, currently recruiting a trial enrolling patients with HER2 positive solid tumors (NCT04278144).

In summary, TLR7/8 agonists have drawn most research attention among other TLR ligands; despite that preclinical data indicate promising prospects, none of the TLR7/8 agonists has gained regulatory approval to treat cancer in human except Imiquimod. Future study could focus on optimizing delivery routes, administration schedule, and the vaccine itself (where vaccines are applied) (292).

TLR 9

TLR9 is preferentially expressed on the endosomal membrane of B cells and plasmacytoid dendritic cells (pDCs), and its primary ligand is unmethylated cytidine phosphoguanosine (CpG) oligonucleotides (ODNs) (293). TLR9 activation can lead to potent activation of innate (133, 294, 295) and adaptive immunity (both cell and humoral immunity) (133).

TLR9 agonists previously evaluated in pre-clinical studies are all DNA-based agents containing non-methylated CpG motifs (Table 1). Most of these agonists are CpG ODNs, while some have more complex DNA structures designed for better protection from drug degradation and enhanced TLR9 stimulation capacity (164–166). The therapeutic enhancing effect of TLR9 agonists has been studied with chemotherapy, photodynamic therapy, radiofrequency ablation, vaccines, ICB, and other immune stimulatory agents. (Table 1) Interestingly, in two studies (139, 140) the CpG motif has been used as myeloid cell targeting sequence, incorporated into decoy ODNs that contain STAT3-specific sequence, which can inhibit STAT3 transcription. Both studies showed the decoy ODNs effectively suppressed tumors in animal models of hematological malignancies. Similar to TLR7/8 agonists, many studies have also looked into the design of nanoparticles for TLR9 agonist drug delivery. These versatile nanoparticles have improved the ability for TME-targeting (159), specific cell-targeting (148, 150, 163), and even sub-cellular compartment-targeting (147); they have also protected against drug degradation (152, 156); plus, some conjugated to drug tracers to monitor drug tracking after administration in vivo (152, 155).

Currently the most clinically investigated TLR9 agonists (Tables 2, 3) are SD-101, CMP-001, IMO-2125. SD-101 is a class C CpG oligonucleotide, applied intratumorally in trials for advanced (metastatic, refractory, or recurrent) malignancies such as pancreatic adenocarcinoma, prostate cancer, liver metastatic uveal melanoma, and multiple lymphoma subtypes. In these early phase trials, SD-101 will be administered in combination with ICB, radiotherapy, small molecular inhibitors, or an anti-OX40 antibody.

Two phase I/II trials applying SD-101 in combination with radiotherapy and immunotherapy in treating lymphoma and other solid tumors just completed, and the results are not yet available. CMP-001, also named as Vidutolimod, is a short DNA piece packaged in protein, mimicking the virus structure. It has been administratedsubcutaneously or intratumorally with ICB, an OX40 agonist, an IgG2 agonist, surgery, and radiotherapy in multiple types of primary and metastatic solid tumors. The completed phase I trial NCT03084640 is completed, which combinedPembrolizumab with CMP-001, and compared the safety together with response rates of CMP-001 administered in different routes in intreating melanoma. Another completed phase I trial NCT03438318 combined CMP-001 with Atezolizumab and radiotherapy to treat NSCLC. In both of the above trials, CMP-001 elicited antitumor-related transcriptional signatures (2022 AACR Abstract #: LB107); more results from trial on CMP-001 are yet to be published. IMO-2125, also known as Tilsotolimod, a synthetic phosphorothioate oligodeoxyribonucleotides, has shown a good safety profile with effective activation of dendritic cells, induction of type I IFN signaling, and up-regulation of multiple immune checkpoint pathways in a phase I trial (NCT03052205) (213), where IMO-2125 was usedas a monotherapy administrated intratumorally in refractory solid tumors. However, a phase III trial (NCT03445533), where IMO-2125 and Ipilimumab were combined for treating melanoma, was terminated for lack of efficacy. Other phase I to II trials with intratumoral administration of IMO-2125 are actively recruiting, either alone or with the combination of ICB in solid tumors (Table 3).

MGN1703 (Lefitolimod) is a DNA-based molecular alternative to a CpG-ODN, administratedsubcutaneously in trials and currently under investigation in combination with anti-CTLA4 in advanced cancers (NCT02668770). In trial NCT02200081, MGN1703 was used with platinum-based chemotherapy in advanced stage small-cell lung cancer where it was well tolerated but showed no impact on the main efficacy of treatment and overall survival of patients (214). DUK-CPG-001 a CpG-based TLR9 agonist is being evaluated in the treatment of myeloid and lymphoid malignancies combined with donor lymphocyte infusion enriched with NK cells in a phase II trial (NCT02452697).

Other TLR9 agonists, all CpG-based, have been assessed in clinical trials, with results available. Inhaled DV281 was tested with anti-PD-1 in advanced NSCLC, with no results publicly available yet (NCT03326752). CpG-MCL vaccine, combining CpG7909 and autologous mantle cell lymphoma-derived tumor cells, was studied to treat mantle cell lymphoma in combination with immunochemotherapy and an autologous hematopoietic stem cell transplant (NCT00490529). The trial showed moderate response to the vaccine among patients (40% developed anti-tumor CD8 T cell response, associated with favorable clinical outcomes), good treatment efficacy (89% were minimal residual disease negative), and a good safety profile (211). CpG7910 was applied in combinationwith local radiotherapy to treat recurrent low-grade lymphoma in a phase I/II trial (NCT00185965), where local administration of this agent systemically induced tumor-reactive memory CD8⁺ T cells. This regimen showed clinical feasibility (212). EMD 1201081 combined with EGFR inhibitor, however, showed no improvement to the clinical efficacy of HNSCC treatment (215).

In summary, despite that there are trials showing the immunogenicity and good tolerability of CpG-based agents, low translational rate remains an issue. This may due to the difference in TLR9 expression in animal models and humans (296). Pre-clinical models of human origins are necessary, such as primary tumor organoids. Also, one safety concern is that CpG motifs are potential to induce autoreactivity (297). There need to be trials with larger sample sizes, longer follow-up durations, and stratified patient subgroups to verify the safety and the suitable patient groups that can benefit from CpG ODN adjuvanted therapies.

Multi-TLR

In addition to single TLR activation, multi-TLR agonism is also under both pre-clinical and clinical investigation for many cancers. Multi-TLR agonism can be realized by a single agent or by a combination of several TLR agonists.

Preclinically, the most studied treatment modality with multi-TLR activation is with tumor vaccines (Table 1). There is also a trend of applying nanotechnology in drug delivery in multi-TLR stimulating treatments for improved APC-targeting (173, 179) and drug tracing (170).

In clinical trials, Bacillus Calmette-Guérin (BCG), an attenuated live Mycobacterium bovis, is the most studied multi-TLR agonist. It can activate TLR2, TLR4, and TLR9 (298); it was originally applied as a vaccine against tuberculosis and later broadened its application as an adjuvant in the standard care of a part of bladder cancer patients (298). Currently, BCG is still investigated in bladder carcinoma patients in combination with other drug treatments, including an anti-PD-1/PD-L1 antibody, small molecule inhibitors, and a neoantigen encoding gene vaccine. A completed trial NCT02753309 combined rapamycin with BCG in bladder cancer treatment, which showed good tolerability in high-grade non-muscle invasive bladder cancer patients and induction of antigen-specific γδ T cell response as well as urinary cytokine production (219). BCG has also been assessed for the treatment of upper or lower urinary tract carcinoma. In treating urinary tract urothelial carcinoma, the trial NCT00794950 investigated combination therapy of BCG and sunitinib, a novel anti-angiogenesis drug. This trial has since been completed, and results showed the combination treatment was associated with a lower rate of progression and recurrence with an acceptable safety profile (218). Besides malignancies in the urinary system, BCG combinedwith chemotherapy, radiofrequency ablation, and GM-CSF have been evaluated in the treatment of liver metastatic colorectal cancer (NCT04062721).

OM-174 is a lipid A analog, which activates both TLR2 and TLR4. In a phase I trial (NCT01800812) with solid tumor patients, OM-174 as a monotherapy was well tolerated and proved to be effective for the induction of IL-8, IL-10, TNF-α, and IL-6 (despite that TNF-αand IL-6 decreased progressively in repeated treatment). Progressively increased NK cells and NK cell activity were observed in patients who received the highest dose, 1000 μg/m² (217). AS-15 is an adjuvant system, comprised of a TLR4 agonism system (MPL and QS-21) and a TLR9 agonist (CpG 7909) in a liposomal formulation. In the completed phase II trial NCT01266603, AS-15 was combined with the MAGE-A3 tumor antigen and high dose IL-2 to treat metastatic melanoma. This treatment achieved 25% response rate, which was associated with increased infiltrating T cells in the primary tumor tissue (222).

TLR3 agonist poly-ICIC and TLR7/8 agonist Resiquimod have been combined with tumor vaccines in the treatment of melanoma (NCT02126579) and advanced tumors refractory to conventional treatment (NCT00948961). In the completed trial NCT00948961, poly-ICIC and/or Resiquimod combined with NY-ESO-1-targeting DC cell vaccine. The combination therapy induced NY-ESO-1–specific IgG titers in 79% patients and NY-ESO-1–specific T cell responses in 56% patients, leading to disease stabilization and tumor regression in 15/70 patients (220).

A phase I trial NCT00068510, where poly-ICLC or imiquimod used in conjunction with an autologous tumor-pulsed DC vaccine, has reported that this regimen was safe and effective in prolonging survival for glioblastoma patients (221).

TLR antagonists

Considering the versatility of TLRs in cancer, some of which can promote tumor growth, there is also rationale for exploring TLR antagonists as a cancer therapy.

In several types of cancers arising from the digestive system, pre-clinical studies have demonstrated the therapeutic potential of TLR antagonists. OPN-301, an inhibitory anti-TLR2 antibody, suppressed tumor initiation and growth in a gastric animal model, which was associated with gene suppression of CXCL2 and TNF-α (183). Another two studies reported that IRS-954, an inhibitory DNA sequence against TLR7 and 9, and chloroquine, which inhibits TLR7 and 9 activation, significantly impeded tumor development and growth in vivo and in vitro in liver cancer (184) and cholangiocarcinoma models (185).

A subset of diffuse large B cell lymphoma patients carry the MyD88 L265P mutation, associated with overactivation of the TLR7/9/MyD88 pathway (186). A TLR7/8/9 antagonist IMO-8400 was previously usedin this subset of lymphoma patients in a completed clinical trial NCT02252146, which, showed limited therapeutic efficacy. Similarly, trial NCT02092909, studying IMO-8400 in treating Waldenstrom’s macroglobulinemia, also showed insufficient efficacy of IMO-8400, and hence it was terminated.

Recently, another synthesized ODN-based TLR7/9 antagonist HJ901 was shown to significantly inhibit tumor cell proliferation and tumor growth in cell lines or animal models carrying the MyD88 L265P mutation (186). However, these data warrant further investigation before it can be translated to the establishment of an early phase trial.

There are obviously fewer published studies on anti-cancer TLR antagonists, which generally showed less efficacy than TLR agonists.

TLR-targeted therapy: Challenges and future perspectives

Simultaneous activation of anti-/pro-tumor mechanisms

As TLRs regulate a wide range of functions, initiating signaling pathways that may lead to both anti-tumor and pro-tumor effects, there is a concern regarding whether the application of TLR agonists will promote tumor growth or whether the anti-tumor effect will be counteracted by the pro-tumor effect they simultaneously initiated. For example, Theodoraki and colleagues have found that TLR3 agonists stimulate the TLR3-TRAF3/IRF3 pathway, which leads to the production of CTL attractants and activate MAVS/helicase pathway, which elicits Treg chemotaxis (299).

Two directions may be feasible for further investigation into this challenge. On one hand, choosing the agonist that specifically activates the anti-tumor pathways but leaves no effect on the pro-tumor pathway could help (Figure 3). Theodoraki et al. (299) further discovered the difference of pathway stimulation potential in different TLR3 agonists: dsRNA Sendai Virus, Poly (I:C), and Rintatolimod. Rintatolimod can activate the TLR3 pathway only, resulting in the induction of CTL attracting cytokines IFNa, ISG-60, and CXCL10, and avoid the initiation of MAVS/helicase pathway, which then prevents Treg accumulation. In the future, more focus to elucidate how drug conformation of TLR-targeting agents influences downstream signaling is necessary, which can then guide future drug synthesis or discovery.

Figure 3

On the other hand, combination therapy is of utmost significance in TLR-targeted therapy. Combined therapies can enhance therapeutic effects in many cases and potentially diminish the pro-tumor impact elicited by TLR agonists. Feng et al. (300) discovered that poly (I:C) could inhibit HCC cell proliferation and lead to cell apoptosis while promoting cell migration and invasion at the same time. When combined with the toad venom constituent bufalin, cell migration and invasion were inhibited, whereas cell apoptosis and suppressed proliferation remained unaffected (300), indicating the potential of combination therapy of the two in eliminating poly (I:C)-initiated pro-tumor effect.

Inefficacy and toxicity

Despite numerous promising results emerging from pre-clinical research with TLR-targeted therapies, many failed to advance to clinical implementation. Lack of efficacy and toxicity has been an issue for TLR-targeting therapy (28, 301).

To address this, first, precise identification and investigation of patient sub-populations that respond to TLR-targeting strategies is important (Figure 3). Some treatments may not have shown significant efficacy in the overall study population, but do in a subset of patients. Monk et al. (207) and Ferris et al. (208) both found in their clinical trial studies that adding Motolimod to chemotherapy did not improve survival in the overall patient population. In contrast, the sub-population with injection site reactions did significantly benefit from Motolimod. The evidence above suggests 1) lack of significance in the overall analysis does not reject the potential of a certain TLR-targeting drug; 2) there are certain groups of patients that may be more responsive to TLR-targeting agents than others. Future work calls for more translational studies incorporated into the trial designs to examine any associations between treatment responsiveness and patient characteristics, including gene expression patterns, biomarker levels, local treatment reaction, etc., thus providing clues for the screening of the target patient population.

Secondly, both lab and clinical research data support that the optimal treatment potency of immunotherapy requires combinatory approaches (27, 28), which continues to be the trend for TLR-targeted therapy. As discussed in section 5 (Tables 1–3), many studies showed that the combination of TLR agonists with other therapies enhanced tumor retardation compared to a single treatment alone. However, there is still a gap in our knowledge regarding the timing and dosing to be applied to each treatment to achieve the optimal therapeutic result. For example, in the combinatory treatment of poly (I:C) and radiation in Lewis lung carcinoma models, Yoshida et al. (264) found using poly (I:C) one day ahead of radiotherapy yielded better tumor suppression than to use after radiation.

Pharmaceutical modification of targeting agents has great potential to improve efficacy and lower toxicity as well. Furthermore, polymer and nanoparticle formulations incorporating TLR agonists are promising avenues to explore as they may potentially increase the specificity of targeting and prevent the drug from early degradation, thereby reducing systemic toxicity. Those formulations can now be designed to load multiple agents and be multi-functional (Figure 3), including but not limited to pH-specific drug-releasing (115, 124), in vivo drug tracing (152, 155), and tumor hypoxia relief (106). The advancement of nanotechnology utilizedin TLR-targeted therapy has been reviewed comprehensively elsewhere (302). However, careful attention should be paid to these new biomaterials as the bioactivities they may incur in vivo remain to be fully elucidated. Meanwhile, reducing the financial and timing costs is also a formidable challenge to face.

Besides refinement of the drug delivery system, choosing a localized delivery route may also have an influence on efficacy. This can avoid systemic inflammation to a great extent and improve intratumoral efficacy (300), especially for solid tumors.

TLR Tolerance

TLR tolerance arises due to the unresponsiveness or hyporesponsiveness of TLRs upon TLR agonist stimulation after repeated, prolonged, or chronic activation, which also includes TLR cross-tolerance, where a pre-used TLR agonist incurs tolerance of another TLR (303, 304). There have been studies showing TLR tolerance in TLR2, 3, 4, 5, 7/8, and 9 (304–309). This mechanism physiologically prevents uncontrolled inflammation and autoimmunity, thus protecting healthy tissues from inflammatory damage (303, 304). In cancer, however, such tolerance leads to impaired tumoricidal effect.

To overcome this phenomenon, Bourquin et al. (310) found cycles of repeated low dose TLR7/8 agonist injection within 24h with intervals every five days, compared to one high dose injection every three days, significantly suppressed tumor growth in a mouse model (310), indicating the potential of circumventing TLR tolerance by adjusting treatment dose and time. Similarly, Tsitoura et al. (311) found the minimum and optimal dosing interval to maintain a TLR agonists’ pharmacological responsiveness. Future research needs to further explore the cyclical changes in specific TLR-TLRL induced responsiveness and consider cross-tolerance as new cancer therapies incorporating multi-TLR agonism continue to emerge (Figure 3).

Discussion

The pattern recognition receptor family of TLRs, widely expressed on both healthy cells and tumor cells, play versatile roles in both physical and pathological conditions. Each TLR influences multiple aspects of tumor development, with both anti- and pro-tumor potentials.

TLR-targeted cancer therapies have been widely studied, with some TLR agonists (Imiquimod and BCG) approved for clinical use to treat cancers (312). Pre-clinical studies are currently focusing on developing novel TLR-targeting agents, incorporating nanotechnology into TLR drug manufacturing and delivery, and novel approaches activating TLRs apart from using agonists (e.g. inactivated virus (67), engineered bacteria (175), and modified T cells (97)).(Figure 2) Increasing evidence demonstrates the insufficiency of single intervention in circumventing immunosuppression incurred by tumor progression, hence leading to both pre-clinical and clinical research focusing on multi-agent and multi-modality treatment at present (312). (Figure 2) In addition, TLR antagonists also showed therapeutic potential in pre-clinical models with tumors in the digestive system, but the potency of this group of agents in human remains to be fully elucidated.

Future research into TLR-targeting therapies must tackle several challenges, including the control of simultaneous activation of both anti- and pro-tumor effect elicited by TLR activation, TLR tolerance, and insufficient efficacy and toxicity. Additionally, due to the heterogenous nature of different types of tumors and the consequent influence on TLR activities in the TME, better research models, which preserve the important genetic mutations that affect tumor growth and treatment response, should be developed (313). Instead of using cell lines, bulk tumors derived from the real patient could be an ideal source for research models (252), from where the primary TME cell components– tumor cells, stromal cells, and immune cells–can be extracted.

Furthermore, with the trend of precision medicine and the deepening of research, there is a need for patient stratification according to their disease profile and treatment responsiveness to treat each patient with the most suitable strategy, providing them with the optimal benefit both therapeutically and economically. We speculate that addressing the challenges described above will elevateTLR-targeted therapies to their full potential and augment the efficacy of immunotherapies for patients.

Funding

This work was supported by the National Natural Science Foundation of China (No. 81821002), National Natural Science Foundation of China (No.81902662), and Sichuan Science and Technology Program 2021YJ0011.

Publisher’s note

All claims expressed in this article are solely those of the authors and do not necessarily represent those of their affiliated organizations, or those of the publisher, the editors and the reviewers. Any product that may be evaluated in this article, or claim that may be made by its manufacturer, is not guaranteed or endorsed by the publisher.

References

• 1

  Rakoff-NahoumSMedzhitovR. Toll-like receptors and cancer. Nat Rev Cancer (2009) 9(1):57–63. doi: 10.1038/nrc2541

  • CrossRef
  • Google Scholar

• 2

  LoiarroMRuggieroVSetteC. Targeting Tlr/Il-1r signalling in human diseases. Mediators Inflammation (2010) 2010:674363. doi: 10.1155/2010/674363

  • CrossRef
  • Google Scholar

• 3

  GnjaticSSawhneyNBBhardwajN. Toll-like receptor agonists: Are they good adjuvants? Cancer J (Sudbury Mass) (2010) 16(4):382–91. doi: 10.1097/PPO.0b013e3181eaca65

  • CrossRef
  • Google Scholar

• 4

  ChangZL. Important aspects of toll-like receptors, ligands and their signaling pathways. Inflammation research: Off J Eur Histamine Res Soc [et al] (2010) 59(10):791–808. doi: 10.1007/s00011-010-0208-2

  • CrossRef
  • Google Scholar

• 5

  PatidarASelvarajSSarodeAChauhanPChattopadhyayDSahaB. Damp-Tlr-Cytokine axis dictates the fate of tumor. Cytokine (2018) 104:114–23. doi: 10.1016/j.cyto.2017.10.004

  • CrossRef
  • Google Scholar

• 6

  KawaiTAkiraS. The role of pattern-recognition receptors in innate immunity: Update on toll-like receptors. Nat Immunol (2010) 11(5):373–84. doi: 10.1038/ni.1863

  • CrossRef
  • Google Scholar

• 7

  AnwarMAShahMKimJChoiS. Recent clinical trends in toll-like receptor targeting therapeutics. Medicinal Res Rev (2019) 39(3):1053–90. doi: 10.1002/med.21553

  • CrossRef
  • Google Scholar

• 8

  RoachJCGlusmanGRowenLKaurAPurcellMKSmithKDet al. The evolution of vertebrate toll-like receptors. Proc Natl Acad Sci U.S.A. (2005) 102(27):9577–82. doi: 10.1073/pnas.0502272102

  • CrossRef
  • Google Scholar

• 9

  TakeuchiOAkiraS. Pattern recognition receptors and inflammation. Cell (2010) 140(6):805–20. doi: 10.1016/j.cell.2010.01.022

  • CrossRef
  • Google Scholar

• 10

  BayraktarRBertilaccioMTSCalinGA. The interaction between two worlds: Micrornas and toll-like receptors. Front Immunol (2019) 10:1053. doi: 10.3389/fimmu.2019.01053

  • CrossRef
  • Google Scholar

• 11

  BourquinCPommierAHotzC. Harnessing the immune system to fight cancer with toll-like receptor and rig-I-Like receptor agonists. Pharmacol Res (2019) 154:104192. doi: 10.1016/j.phrs.2019.03.001

  • CrossRef
  • Google Scholar

• 12

  TakedaKAkiraS. Tlr Signaling Pathways. Seminars in immunology (2004) 16(1):3–9. doi: 10.1016/j.smim.2003.10.003

  • CrossRef
  • Google Scholar

• 13

  HennessyEJParkerAEO’NeillLA. Targeting toll-like receptors: Emerging therapeutics? Nat Rev Drug Discovery (2010) 9(4):293–307. doi: 10.1038/nrd3203

  • CrossRef
  • Google Scholar

• 14

  IwasakiAMedzhitovR. Regulation of adaptive immunity by the innate immune system. Sci (New York NY) (2010) 327(5963):291–5. doi: 10.1126/science.1183021

  • CrossRef
  • Google Scholar

• 15

  HuaZHouB. Tlr signaling in b-cell development and activation. Cell Mol Immunol (2013) 10(2):103–6. doi: 10.1038/cmi.2012.61

  • CrossRef
  • Google Scholar

• 16

  HaageVElmadanyNRollLFaissnerAGutmannDHSemtnerMet al. Tenascin c regulates multiple microglial functions involving Tlr4 signaling and Hdac1. Brain behavior Immun (2019) 81:470–83. doi: 10.1016/j.bbi.2019.06.047

  • CrossRef
  • Google Scholar

• 17

  SekiETsutsuiHIimuroYNakaTSonGAkiraSet al. Contribution of toll-like Receptor/Myeloid differentiation factor 88 signaling to murine liver regeneration. Hepatol (Baltimore Md) (2005) 41(3):443–50. doi: 10.1002/hep.20603

  • CrossRef
  • Google Scholar

• 18

  ChenYSunR. Toll-like receptors in acute liver injury and regeneration. Int Immunopharmacol (2011) 11(10):1433–41. doi: 10.1016/j.intimp.2011.04.023

  • CrossRef
  • Google Scholar

• 19

  KimDChenRSheuMKimNKimSIslamNet al. Noncoding dsrna induces retinoic acid synthesis to stimulate hair follicle regeneration Via Tlr3. Nat Commun (2019) 10(1):2811. doi: 10.1038/s41467-019-10811-y

  • CrossRef
  • Google Scholar

• 20

  HasanUATrinchieriGVlachJ. Toll-like receptor signaling stimulates cell cycle entry and progression in fibroblasts. J Biol Chem (2005) 280(21):20620–7. doi: 10.1074/jbc.M500877200

  • CrossRef
  • Google Scholar

• 21

  HariPMillarFRTarratsNBirchJQuintanillaARinkCJet al. The innate immune sensor toll-like receptor 2 controls the senescence-associated secretory phenotype. Sci Adv (2019) 5(6):eaaw0254. doi: 10.1126/sciadv.aaw0254

  • CrossRef
  • Google Scholar

• 22

  MogilenkoDAHaasJTL’HommeLFleurySQuemenerSLevavasseurMet al. Metabolic and innate immune cues merge into a specific inflammatory response Via the upr. Cell (2019) 177(5):1201–16.e19. doi: 10.1016/j.cell.2019.03.018

  • CrossRef
  • Google Scholar

• 23

  KrawczykCMHolowkaTSunJBlagihJAmielEDeBerardinisRJet al. Toll-like receptor-induced changes in glycolytic metabolism regulate dendritic cell activation. Blood (2010) 115(23):4742–9. doi: 10.1182/blood-2009-10-249540

  • CrossRef
  • Google Scholar

• 24

  PradereJPDapitoDHSchwabeRF. The yin and yang of toll-like receptors in cancer. Oncogene (2014) 33(27):3485–95. doi: 10.1038/onc.2013.302

  • CrossRef
  • Google Scholar

• 25

  HuangBZhaoJUnkelessJCFengZHXiongH. Tlr signaling by tumor and immune cells: A double-edged sword. Oncogene (2008) 27(2):218–24. doi: 10.1038/sj.onc.1210904

  • CrossRef
  • Google Scholar

• 26

  ConroyHMarshallNAMillsKH. Tlr ligand suppression or enhancement of treg cells? a double-edged sword in immunity to tumours. Oncogene (2008) 27(2):168–80. doi: 10.1038/sj.onc.1210910

  • CrossRef
  • Google Scholar

• 27

  SmithMGarcia-MartinezEPitterMRFucikovaJSpisekRZitvogelLet al. Trial watch: Toll-like receptor agonists in cancer immunotherapy. Oncoimmunology (2018) 7(12):e1526250. doi: 10.1080/2162402x.2018.1526250

  • CrossRef
  • Google Scholar

• 28

  GuhaM. Anticancer tlr agonists on the ropes. Nat Rev Drug Discovery (2012) 11(7):503–5. doi: 10.1038/nrd3775

  • CrossRef
  • Google Scholar

• 29

  LuH. Tlr agonists for cancer immunotherapy: Tipping the balance between the immune stimulatory and inhibitory effects. Front Immunol (2014) 5:83. doi: 10.3389/fimmu.2014.00083

  • CrossRef
  • Google Scholar

• 30

  CarpenterSO’NeillLA. Recent insights into the structure of toll-like receptors and post-translational modifications of their associated signalling proteins. Biochem J (2009) 422(1):1–10. doi: 10.1042/BJ20090616

  • CrossRef
  • Google Scholar

• 31

  LeeBLBartonGM. Trafficking of endosomal toll-like receptors. Trends Cell Biol (2014) 24(6):360–9. doi: 10.1016/j.tcb.2013.12.002

  • CrossRef
  • Google Scholar

• 32

  HedayatMTakedaKRezaeiN. Prophylactic and therapeutic implications of toll-like receptor ligands. Medicinal Res Rev (2012) 32(2):294–325. doi: 10.1002/med.20214

  • CrossRef
  • Google Scholar

• 33

  PatraMCShahMChoiS. Toll-like receptor-induced cytokines as immunotherapeutic targets in cancers and autoimmune diseases. Semin Cancer Biol (2019) 64:61–82. doi: 10.1016/j.semcancer.2019.05.002

  • CrossRef
  • Google Scholar

• 34

  BlanderJMMedzhitovR. On regulation of phagosome maturation and antigen presentation. Nat Immunol (2006) 7(10):1029–35. doi: 10.1038/ni1006-1029

  • CrossRef
  • Google Scholar

• 35

  MurakamiYFukuiRMotoiYKannoAShibataTTanimuraNet al. Roles of the cleaved n-terminal Tlr3 fragment and cell surface Tlr3 in double-stranded rna sensing. J Immunol (Baltimore Md: 1950) (2014) 193(10):5208–17. doi: 10.4049/jimmunol.1400386

  • CrossRef
  • Google Scholar

• 36

  MatsumotoMSeyaT. Tlr3: Interferon induction by double-stranded rna including Poly(I:C). Advanced Drug delivery Rev (2008) 60(7):805–12. doi: 10.1016/j.addr.2007.11.005

  • CrossRef
  • Google Scholar

• 37

  GuanYRanoaDRJiangSMuthaSKLiXBaudryJet al. Human tlrs 10 and 1 share common mechanisms of innate immune sensing but not signaling. J Immunol (Baltimore Md: 1950) (2010) 184(9):5094–103. doi: 10.4049/jimmunol.0901888

  • CrossRef
  • Google Scholar

• 38

  TakeuchiOSatoSHoriuchiTHoshinoKTakedaKDongZet al. Cutting edge: Role of toll-like receptor 1 in mediating immune response to microbial lipoproteins. J Immunol (Baltimore Md: 1950) (2002) 169(1):10–4. doi: 10.4049/jimmunol.169.1.10

  • CrossRef
  • Google Scholar

• 39

  MansellAJenkinsBJ. Dangerous liaisons between interleukin-6 cytokine and toll-like receptor families: A potent combination in inflammation and cancer. Cytokine Growth factor Rev (2013) 24(3):249–56. doi: 10.1016/j.cytogfr.2013.03.007

  • CrossRef
  • Google Scholar

• 40

  KhanAAKhanZWarnakulasuriyaS. Cancer-associated toll-like receptor modulation and insinuation in infection susceptibility: Association or coincidence? Ann oncology: Off J Eur Soc Med Oncol (2016) 27(6):984–97. doi: 10.1093/annonc/mdw053

  • CrossRef
  • Google Scholar

• 41

  KanzlerHBarratFJHesselEMCoffmanRL. Therapeutic targeting of innate immunity with toll-like receptor agonists and antagonists. Nat Med (2007) 13(5):552–9. doi: 10.1038/nm1589

  • CrossRef
  • Google Scholar

• 42

  Khajeh Alizadeh AttarMAnwarMAEskianMKeshavarz-FathiMChoiSRezaeiN. Basic understanding and therapeutic approaches to target toll-like receptors in cancerous microenvironment and metastasis. Medicinal Res Rev (2018) 38(5):1469–84. doi: 10.1002/med.21480

  • CrossRef
  • Google Scholar

• 43

  MedvedevAE. Toll-like receptor polymorphisms, inflammatory and infectious diseases, allergies, and cancer. J Interferon Cytokine research: Off J Int Soc Interferon Cytokine Res (2013) 33(9):467–84. doi: 10.1089/jir.2012.0140

  • CrossRef
  • Google Scholar

• 44

  TakedaKAkiraS. Toll-like receptors in innate immunity. Int Immunol (2005) 17(1):1–14. doi: 10.1093/intimm/dxh186

  • CrossRef
  • Google Scholar

• 45

  SatohTAkiraS. Toll-like receptor signaling and its inducible proteins. Microbiol Spectr (2016) 4(6):4.6.41. doi: 10.1128/microbiolspec.MCHD-0040-2016

  • CrossRef
  • Google Scholar

• 46

  BlasiusALBeutlerB. Intracellular toll-like receptors. Immunity (2010) 32(3):305–15. doi: 10.1016/j.immuni.2010.03.012

  • CrossRef
  • Google Scholar

• 47

  FitzgeraldKAKaganJC. Toll-like receptors and the control of immunity. Cell (2020) 180(6):1044–66. doi: 10.1016/j.cell.2020.02.041

  • CrossRef
  • Google Scholar

• 48

  LaRueHAyariCBergeronAFradetY. Toll-like receptors in urothelial cells–targets for cancer immunotherapy. Nat Rev Urol (2013) 10(9):537–45. doi: 10.1038/nrurol.2013.153

  • CrossRef
  • Google Scholar

• 49

  WardillHRGibsonRJLoganRMBowenJM. Tlr4/Pkc-mediated tight junction modulation: A clinical marker of chemotherapy-induced gut toxicity? Int J Cancer (2014) 135(11):2483–92. doi: 10.1002/ijc.28656

  • CrossRef
  • Google Scholar

• 50

  BasithSManavalanBYooTHKimSGChoiS. Roles of toll-like receptors in cancer: A double-edged sword for defense and offense. Arch pharmacal Res (2012) 35(8):1297–316. doi: 10.1007/s12272-012-0802-7

  • CrossRef
  • Google Scholar

• 51

  PiccininiAMMidwoodKS. Dampening inflammation by modulating tlr signalling. Mediators Inflammation (2010) 2010:672395. doi: 10.1155/2010/672395

  • CrossRef
  • Google Scholar

• 52

  KarikoKNiHPCapodiciJLamphierMWeissmanD. Mrna is an endogenous ligand for toll-like receptor 3. J Biol Chem (2004) 279(13):12542–50. doi: 10.1074/jbc.M310175200

  • CrossRef
  • Google Scholar

• 53

  VollmerJTlukSSchmitzCHammSJurkMForsbachAet al. Immune stimulation mediated by autoantigen binding sites within small nuclear rnas involves toll-like receptors 7 and 8. J Exp Med (2005) 202(11):1575–85. doi: 10.1084/jem.20051696

  • CrossRef
  • Google Scholar

• 54

  HurstJPrinzNLorenzMBauerSChapmanJLacknerKJet al. Tlr7 and Tlr8 ligands and antiphospholipid antibodies show synergistic effects on the induction of il-1beta and caspase-1 in monocytes and dendritic cells. Immunobiology (2009) 214(8):683–91. doi: 10.1016/j.imbio.2008.12.003

  • CrossRef
  • Google Scholar

• 55

  LeadbetterEARifkinIRHohlbaumAMBeaudetteBCShlomchikMJMarshak-RothsteinA. Chromatin-igg complexes activate b cells by dual engagement of igm and toll-like receptors. Nature (2002) 416(6881):603–7. doi: 10.1038/416603a

  • CrossRef
  • Google Scholar

• 56

  LotfiREisenbacherJSolgiGFuchsKYildizTNienhausCet al. Human mesenchymal stem cells respond to native but not oxidized damage associated molecular pattern molecules from necrotic (Tumor) material. Eur J Immunol (2011) 41(7):2021–8. doi: 10.1002/eji.201041324

  • CrossRef
  • Google Scholar

• 57

  SzczepanskiMJCzystowskaMSzajnikMHarasymczukMBoyiadzisMKruk-ZagajewskaAet al. Triggering of toll-like receptor 4 expressed on human head and neck squamous cell carcinoma promotes tumor development and protects the tumor from immune attack. Cancer Res (2009) 69(7):3105–13. doi: 10.1158/0008-5472.Can-08-3838

  • CrossRef
  • Google Scholar

• 58

  FonteEAgathangelidisAReverberiDNtoufaSScarfoLRanghettiPet al. Toll-like receptor stimulation in splenic marginal zone lymphoma can modulate cell signaling, activation and proliferation. Haematologica (2015) 100(11):1460–8. doi: 10.3324/haematol.2014.119933

  • CrossRef
  • Google Scholar

• 59

  MiceraABalzaminoBODi ZazzoABiamonteFSicaGBoniniS. Toll-like receptors and tissue remodeling: The Pro/Cons recent findings. J Cell Physiol (2016) 231(3):531–44. doi: 10.1002/jcp.25124

  • CrossRef
  • Google Scholar

• 60

  CenXZhuGYangJYangJGuoJJinJet al. Tlr1/2 specific small-molecule agonist suppresses leukemia cancer cell growth by stimulating cytotoxic T lymphocytes. Advanced Sci (Weinheim Baden-Wurttemberg Germany) (2019) 6(10):1802042. doi: 10.1002/advs.201802042

  • CrossRef
  • Google Scholar

• 61

  QuachHRotivalMPothlichetJLohYEDannemannMZidaneNet al. Genetic adaptation and neandertal admixture shaped the immune system of human populations. Cell (2016) 167(3):643–56.e17. doi: 10.1016/j.cell.2016.09.024

  • CrossRef
  • Google Scholar

• 62

  SharmaNVacherJAllisonJP. Tlr1/2 ligand enhances antitumor efficacy of ctla-4 blockade by increasing intratumoral treg depletion. Proc Natl Acad Sci U.S.A. (2019) 116(21):10453–62. doi: 10.1073/pnas.1819004116

  • CrossRef
  • Google Scholar

• 63

  ZomGGWillemsMKhanSvan der SluisTCKleinovinkJWCampsMGMet al. Novel Tlr2-binding adjuvant induces enhanced T cell responses and tumor eradication. J immunotherapy Cancer (2018) 6(1):146. doi: 10.1186/s40425-018-0455-2

  • CrossRef
  • Google Scholar

• 64

  WangYSuLMorinMDJonesBTMifuneYShiHet al. Adjuvant effect of the novel Tlr1/Tlr2 agonist diprovocim synergizes with anti-Pd-L1 to eliminate melanoma in mice. Proc Natl Acad Sci U.S.A. (2018) 115(37):E8698–e706. doi: 10.1073/pnas.1809232115

  • CrossRef
  • Google Scholar

• 65

  FengYMuRWangZXingPZhangJDongLet al. A toll-like receptor agonist mimicking microbial signal to generate tumor-suppressive macrophages. Nat Commun (2019) 10(1):2272. doi: 10.1038/s41467-019-10354-2

  • CrossRef
  • Google Scholar

• 66

  MengYQuYWuWChenLSunLTaiGet al. Galactan isolated from cantharellus cibarius modulates antitumor immune response by converting tumor-associated macrophages toward M1-like phenotype. Carbohydr polymers (2019) 226:115295. doi: 10.1016/j.carbpol.2019.115295

  • CrossRef
  • Google Scholar

• 67

  SamudioIRezvaniKShaimHHofsENgomMBuLet al. Uv-inactivated hsv-1 potently activates nk cell killing of leukemic cells. Blood (2016) 127(21):2575–86. doi: 10.1182/blood-2015-04-639088

  • CrossRef
  • Google Scholar

• 68

  SalemMLAttiaZIGalalSM. Acute inflammation induces immunomodulatory effects on myeloid cells associated with anti-tumor responses in a tumor mouse model. J advanced Res (2016) 7(2):243–53. doi: 10.1016/j.jare.2015.06.001

  • CrossRef
  • Google Scholar

• 69

  AznarMAPlanellesLPerez-OlivaresMMolinaCGarasaSEtxeberriaIet al. Immunotherapeutic effects of intratumoral nanoplexed poly I:C. J immunotherapy Cancer (2019) 7(1):116. doi: 10.1186/s40425-019-0568-2

  • CrossRef
  • Google Scholar

• 70

  DingLRenJZhangDLiYHuangXJiJet al. The Tlr3 agonist inhibit drug efflux and sequentially consolidates low-dose cisplatin-based chemoimmunotherapy while reducing side effects. Mol Cancer Ther (2017) 16(6):1068–79. doi: 10.1158/1535-7163.MCT-16-0454

  • CrossRef
  • Google Scholar

• 71

  AlkurdiLVirardFVanbervlietBWeberKToscanoFBonninMet al. Release of c-flip brake selectively sensitizes human cancer cells to Tlr3-mediated apoptosis. Cell Death Dis (2018) 9(9):874. doi: 10.1038/s41419-018-0850-0

  • CrossRef
  • Google Scholar

• 72

  ZemekRMDe JongEChinWLSchusterISFearVSCaseyTHet al. Sensitization to immune checkpoint blockade through activation of a Stat1/Nk axis in the tumor microenvironment. Sci Transl Med (2019) 11(501):eaav7816. doi: 10.1126/scitranslmed.aav7816

  • CrossRef
  • Google Scholar

• 73

  AzumaMTakedaYNakajimaHSugiyamaHEbiharaTOshiumiHet al. Biphasic function of Tlr3 adjuvant on tumor and spleen dendritic cells promotes tumor T cell infiltration and regression in a vaccine therapy. Oncoimmunology (2016) 5(8):e1188244. doi: 10.1080/2162402x.2016.1188244

  • CrossRef
  • Google Scholar

• 74

  NimanongSOstroumovDWingerathJKnockeSWollerNGurlevikEet al. Cd40 signaling drives potent cellular immune responses in heterologous cancer vaccinations. Cancer Res (2017) 77(8):1918–26. doi: 10.1158/0008-5472.Can-16-2089

  • CrossRef
  • Google Scholar

• 75

  ChenYLChangMCChiangYCLinHWSunNYChenCAet al. Immuno-modulators enhance antigen-specific immunity and anti-tumor effects of mesothelin-specific chimeric DNA vaccine through promoting dc maturation. Cancer Lett (2018) 425:152–63. doi: 10.1016/j.canlet.2018.03.032

  • CrossRef
  • Google Scholar

• 76

  ZhaoJZhangZXueYWangGChengYPanYet al. Anti-tumor macrophages activated by ferumoxytol combined or surface-functionalized with the Tlr3 agonist poly (I: C) promote melanoma regression. Theranostics (2018) 8(22):6307–21. doi: 10.7150/thno.29746

  • CrossRef
  • Google Scholar

• 77

  LiuLHeHLiangRYiHMengXChenZet al. Ros-inducing micelles sensitize tumor-associated macrophages to Tlr3 stimulation for potent immunotherapy. Biomacromolecules (2018) 19(6):2146–55. doi: 10.1021/acs.biomac.8b00239

  • CrossRef
  • Google Scholar

• 78

  KimSYNohYWKangTHKimJEKimSUmSHet al. Synthetic vaccine nanoparticles target to lymph node triggering enhanced innate and adaptive antitumor immunity. Biomaterials (2017) 130:56–66. doi: 10.1016/j.biomaterials.2017.03.034

  • CrossRef
  • Google Scholar

• 79

  RahimianSFransenMFKleinovinkJWChristensenJRAmidiMHenninkWEet al. Polymeric nanoparticles for Co-delivery of synthetic long peptide antigen and poly ic as therapeutic cancer vaccine formulation. J Controlled release: Off J Controlled Release Soc (2015) 203:16–22. doi: 10.1016/j.jconrel.2015.02.006

  • CrossRef
  • Google Scholar

• 80

  LuoZWangCYiHLiPPanHLiuLet al. Nanovaccine loaded with poly I:C and Stat3 sirna robustly elicits anti-tumor immune responses through modulating tumor-associated dendritic cells in vivo. Biomaterials (2015) 38:50–60. doi: 10.1016/j.biomaterials.2014.10.050

  • CrossRef
  • Google Scholar

• 81

  TakedaYKataokaKYamagishiJOgawaSSeyaTMatsumotoM. A Tlr3-specific adjuvant relieves innate resistance to pd-L1 blockade without cytokine toxicity in tumor vaccine immunotherapy. Cell Rep (2017) 19(9):1874–87. doi: 10.1016/j.celrep.2017.05.015

  • CrossRef
  • Google Scholar

• 82

  NelsonMHBowersJSBaileySRDivenMAFugleCWKaiserADet al. Toll-like receptor agonist therapy can profoundly augment the antitumor activity of adoptively transferred Cd8(+) T cells without host preconditioning. J immunotherapy Cancer (2016) 4:6. doi: 10.1186/s40425-016-0110-8

  • CrossRef
  • Google Scholar

• 83

  AtukoralePURaghunathanSPRaguveerVMoonTJZhengCBieleckiPAet al. Nanoparticle encapsulation of synergistic immune agonists enables systemic codelivery to tumor sites and ifnbeta-driven antitumor immunity. Cancer Res (2019) 79(20):5394–406. doi: 10.1158/0008-5472.Can-19-0381

  • CrossRef
  • Google Scholar

• 84

  HaroMADyevoichAMPhippsJPHaasKM. Activation of b-1 cells promotes tumor cell killing in the peritoneal cavity. Cancer Res (2019) 79(1):159–70. doi: 10.1158/0008-5472.Can-18-0981

  • CrossRef
  • Google Scholar

• 85

  TangACRahaviSMFungSYLuHYYangHLimCJet al. Combination therapy with proteasome inhibitors and tlr agonists enhances tumour cell death and il-1beta production. Cell Death Dis (2018) 9(2):162. doi: 10.1038/s41419-017-0194-1

  • CrossRef
  • Google Scholar

• 86

  GablehFSaeidiMHematiSHamdiKSoleimanjahiHGorjiAet al. Combination of the toll like receptor agonist and alpha-galactosylceramide as an efficient adjuvant for cancer vaccine. J Biomed Sci (2016) 23:16. doi: 10.1186/s12929-016-0238-3

  • CrossRef
  • Google Scholar

• 87

  ZamaniPNavashenaqJGNikpoorARHatamipourMOskueeRKBadieeAet al. Mpl nano-liposomal vaccine containing P5 Her2/Neu-derived peptide pulsed padre as an effective vaccine in a mice tubo model of breast cancer. J Controlled release: Off J Controlled Release Soc (2019) 303:223–36. doi: 10.1016/j.jconrel.2019.04.019

  • CrossRef
  • Google Scholar

• 88

  BoksMAAmbrosiniMBruijnsSCKalayHvan BlooisLStormGet al. Mpla incorporation into dc-targeting glycoliposomes favours anti-tumour T cell responses. J Controlled release: Off J Controlled Release Soc (2015) 216:37–46. doi: 10.1016/j.jconrel.2015.06.033

  • CrossRef
  • Google Scholar

• 89

  ZhuangXWuTZhaoYHuXBaoYGuoYet al. Lipid-enveloped zinc phosphate hybrid nanoparticles for codelivery of h-2k(B) and h-2d(B)-Restricted antigenic peptides and monophosphoryl lipid a to induce antitumor immunity against melanoma. J Controlled release: Off J Controlled Release Soc (2016) 228:26–37. doi: 10.1016/j.jconrel.2016.02.035

  • CrossRef
  • Google Scholar

• 90

  GuoYWangDSongQWuTZhuangXBaoYet al. Erythrocyte membrane-enveloped polymeric nanoparticles as nanovaccine for induction of antitumor immunity against melanoma. ACS Nano (2015) 9(7):6918–33. doi: 10.1021/acsnano.5b01042

  • CrossRef
  • Google Scholar

• 91

  WafaEIGearySMRossKAGoodmanJTNarasimhanBSalemAK. Pentaerythritol-based lipid a bolsters the antitumor efficacy of a polyanhydride particle-based cancer vaccine. Nanomedicine: nanotechnology biology Med (2019) 21:102055. doi: 10.1016/j.nano.2019.102055

  • CrossRef
  • Google Scholar

• 92

  XuLKwakMZhangWZengLLeePCJinJO. Rehmannia glutinosa polysaccharide induces toll-like receptor 4 dependent spleen dendritic cell maturation and anti-cancer immunity. Oncoimmunology (2017) 6(7):e1325981. doi: 10.1080/2162402x.2017.1325981

  • CrossRef
  • Google Scholar

• 93

  VillanuevaLSilvaLLlopizDRuizMIglesiasTLozanoTet al. The toll like receptor 4 ligand cold-inducible rna-binding protein as vaccination platform against cancer. Oncoimmunology (2018) 7(4):e1409321. doi: 10.1080/2162402x.2017.1409321

  • CrossRef
  • Google Scholar

• 94

  KimYSParkHJParkJHHongEJJangGYJungIDet al. A novel function of Api5 (Apoptosis inhibitor 5), Tlr4-dependent activation of antigen presenting cells. Oncoimmunology (2018) 7(10):e1472187. doi: 10.1080/2162402x.2018.1472187

  • CrossRef
  • Google Scholar

• 95

  WeiFYangDTewaryPLiYLiSChenXet al. The alarmin Hmgn1 contributes to antitumor immunity and is a potent immunoadjuvant. Cancer Res (2014) 74(21):5989–98. doi: 10.1158/0008-5472.Can-13-2042

  • CrossRef
  • Google Scholar

• 96

  LeeSEHongSHVermaVLeeYSDuongTNJeongKet al. Flagellin is a strong vaginal adjuvant of a therapeutic vaccine for genital cancer. Oncoimmunology (2016) 5(2):e1081328. doi: 10.1080/2162402x.2015.1081328

  • CrossRef
  • Google Scholar

• 97

  GengDKaczanowskaSTsaiAYoungerKOchoaARapoportAPet al. Tlr5 ligand-secreting T cells reshape the tumor microenvironment and enhance antitumor activity. Cancer Res (2015) 75(10):1959–71. doi: 10.1158/0008-5472.Can-14-2467

  • CrossRef
  • Google Scholar

• 98

  BrackettCMKojouharovBVeithJGreeneKFBurdelyaLGGollnickSOet al. Toll-like receptor-5 agonist, entolimod, suppresses metastasis and induces immunity by stimulating an nk-Dendritic-Cd8+ T-cell axis. Proc Natl Acad Sci U.S.A. (2016) 113(7):E874–83. doi: 10.1073/pnas.1521359113

  • CrossRef
  • Google Scholar

• 99

  DoorduijnEMSluijterMSalvatoriDCSilvestriSMaasSArensRet al. Cd4(+) T cell and nk cell interplay key to regression of mhc class I(Low) tumors upon Tlr7/8 agonist therapy. Cancer Immunol Res (2017) 5(8):642–53. doi: 10.1158/2326-6066.Cir-16-0334

  • CrossRef
  • Google Scholar

• 100

  SoongRSSongLTrieuJKnoffJHeLTsaiYCet al. Toll-like receptor agonist imiquimod facilitates antigen-specific Cd8+ T-cell accumulation in the genital tract leading to tumor control through ifngamma. Clin Cancer research: an Off J Am Assoc Cancer Res (2014) 20(21):5456–67. doi: 10.1158/1078-0432.Ccr-14-0344

  • CrossRef
  • Google Scholar

• 101

  WeiJLongYGuoRLiuXTangXRaoJet al. Multifunctional polymeric micelle-based chemo-immunotherapy with immune checkpoint blockade for efficient treatment of orthotopic and metastatic breast cancer. Acta Pharm Sin B (2019) 9(4):819–31. doi: 10.1016/j.apsb.2019.01.018

  • CrossRef
  • Google Scholar

• 102

  NuhnLDe KokerSVan LintSZhongZCataniJPCombesFet al. Nanoparticle-conjugate Tlr7/8 agonist localized immunotherapy provokes safe antitumoral responses. Advanced materials (Deerfield Beach Fla) (2018) 30(45):e1803397. doi: 10.1002/adma.201803397

  • CrossRef
  • Google Scholar

• 103

  XuJXuLWangCYangRZhuangQHanXet al. Near-Infrared-Triggered photodynamic therapy with multitasking upconversion nanoparticles in combination with checkpoint blockade for immunotherapy of colorectal cancer. ACS Nano (2017) 11(5):4463–74. doi: 10.1021/acsnano.7b00715

  • CrossRef
  • Google Scholar

• 104

  GeRLiuCZhangXWangWLiBLiuJet al. Photothermal-activatable Fe3o4 superparticle nanodrug carriers with pd-L1 immune checkpoint blockade for anti-metastatic cancer immunotherapy. ACS Appl materials interfaces (2018) 10(24):20342–55. doi: 10.1021/acsami.8b05876

  • CrossRef
  • Google Scholar

• 105

  ChenQXuLLiangCWangCPengRLiuZ. Photothermal therapy with immune-adjuvant nanoparticles together with checkpoint blockade for effective cancer immunotherapy. Nat Commun (2016) 7:13193. doi: 10.1038/ncomms13193

  • CrossRef
  • Google Scholar

• 106

  ChenQChenJYangZXuJXuLLiangCet al. Nanoparticle-enhanced radiotherapy to trigger robust cancer immunotherapy. Advanced materials (Deerfield Beach Fla) (2019) 31(10):e1802228. doi: 10.1002/adma.201802228

  • CrossRef
  • Google Scholar

• 107

  YangRXuJXuLSunXChenQZhaoYet al. Cancer cell membrane-coated adjuvant nanoparticles with mannose modification for effective anticancer vaccination. ACS Nano (2018) 12(6):5121–9. doi: 10.1021/acsnano.7b09041

  • CrossRef
  • Google Scholar

• 108

  ZhouZYuXZhangJTianZZhangC. Tlr7/8 agonists promote nk-dc cross-talk to enhance nk cell anti-tumor effects in hepatocellular carcinoma. Cancer Lett (2015) 369(2):298–306. doi: 10.1016/j.canlet.2015.09.017

  • CrossRef
  • Google Scholar

• 109

  KumaiTLeeSChoHISultanHKobayashiHHarabuchiYet al. Optimization of peptide vaccines to induce robust antitumor Cd4 T-cell responses. Cancer Immunol Res (2017) 5(1):72–83. doi: 10.1158/2326-6066.Cir-16-0194

  • CrossRef
  • Google Scholar

• 110

  HosoyaTSato-KanekoFAhmadiAYaoSLaoFKitauraKet al. Induction of oligoclonal Cd8 T cell responses against pulmonary metastatic cancer by a phospholipid-conjugated Tlr7 agonist. Proc Natl Acad Sci U.S.A. (2018) 115(29):E6836–e44. doi: 10.1073/pnas.1803281115

  • CrossRef
  • Google Scholar

• 111

  NarayananJSSRayPHayashiTWhisenantTCVicenteDCarsonDAet al. Irreversible electroporation combined with checkpoint blockade and Tlr7 stimulation induces antitumor immunity in a murine pancreatic cancer model. Cancer Immunol Res (2019) 7(10):1714–26. doi: 10.1158/2326-6066.Cir-19-0101

  • CrossRef
  • Google Scholar

• 112

  VascottoFPetschenkaJWalzerKCVormehrMBrkicMStroblSet al. Intravenous delivery of the toll-like receptor 7 agonist Sc1 confers tumor control by inducing a Cd8+ T cell response. Oncoimmunology (2019) 8(7):1601480. doi: 10.1080/2162402x.2019.1601480

  • CrossRef
  • Google Scholar

• 113

  WiedemannGMJacobiSJChaloupkaMKrachanAHammSStroblSet al. A novel Tlr7 agonist reverses nk cell anergy and cures rma-s lymphoma-bearing mice. Oncoimmunology (2016) 5(7):e1189051. doi: 10.1080/2162402x.2016.1189051

  • CrossRef
  • Google Scholar

• 114

  ZhuJHeSDuJWangZLiWChenXet al. Local administration of a novel toll-like receptor 7 agonist in combination with doxorubicin induces durable tumouricidal effects in a murine model of T cell lymphoma. J Hematol Oncol (2015) 8:21. doi: 10.1186/s13045-015-0121-9

  • CrossRef
  • Google Scholar

• 115

  HuangZGanJLongZGuoGShiXWangCet al. Targeted delivery of let-7b to reprogramme tumor-associated macrophages and tumor infiltrating dendritic cells for tumor rejection. Biomaterials (2016) 90:72–84. doi: 10.1016/j.biomaterials.2016.03.009

  • CrossRef
  • Google Scholar

• 116

  KranzLMDikenMHaasHKreiterSLoquaiCReuterKCet al. Systemic rna delivery to dendritic cells exploits antiviral defence for cancer immunotherapy. Nature (2016) 534(7607):396–+. doi: 10.1038/nature18300

  • CrossRef
  • Google Scholar

• 117

  PilchZToneckaKBraniewskaASasZSkorzynskiMBoonLet al. Antitumor activity of Tlr7 is potentiated by Cd200r antibody leading to changes in the tumor microenvironment. Cancer Immunol Res (2018) 6(8):930–40. doi: 10.1158/2326-6066.Cir-17-0454

  • CrossRef
  • Google Scholar

• 118

  CheadleEJLipowska-BhallaGDovediSJFagnanoEKleinCHoneychurchJet al. A Tlr7 agonist enhances the antitumor efficacy of obinutuzumab in murine lymphoma models Via nk cells and Cd4 T cells. Leukemia (2017) 31(7):1611–21. doi: 10.1038/leu.2016.352

  • CrossRef
  • Google Scholar

• 119

  ParkCGHartlCASchmidDCarmonaEMKimHJGoldbergMS. Extended release of perioperative immunotherapy prevents tumor recurrence and eliminates metastases. Sci Transl Med (2018) 10(433):eaar1916. doi: 10.1126/scitranslmed.aar1916

  • CrossRef
  • Google Scholar

• 120

  LuRGroerCKleindlPAMoulderKRHuangAHuntJRet al. Formulation and preclinical evaluation of a toll-like receptor 7/8 agonist as an anti-tumoral immunomodulator. J Controlled release: Off J Controlled Release Soc (2019) 306:165–76. doi: 10.1016/j.jconrel.2019.06.003

  • CrossRef
  • Google Scholar

• 121

  SchmidDParkCGHartlCASubediNCartwrightANPuertoRBet al. T Cell-targeting nanoparticles focus delivery of immunotherapy to improve antitumor immunity. Nat Commun (2017) 8(1):1747. doi: 10.1038/s41467-017-01830-8

  • CrossRef
  • Google Scholar

• 122

  RodellCBArlauckasSPCuccareseMFGarrisCSAhmedRLMSKohlerRHet al. Tlr7/8-Agonist-Loaded nanoparticles promote the polarization of tumour-associated macrophages to enhance cancer immunotherapy. Nat Biomed Eng (2018) 2(8):578–+. doi: 10.1038/s41551-018-0236-8

  • CrossRef
  • Google Scholar

• 123

  KimSYKimSKimJELeeSNShinIWShinHSet al. Lyophilizable and multifaceted toll-like receptor 7/8 agonist-loaded nanoemulsion for the reprogramming of tumor microenvironments and enhanced cancer immunotherapy. ACS Nano (2019) 13:12671–86. doi: 10.1021/acsnano.9b04207

  • CrossRef
  • Google Scholar

• 124

  KimHSehgalDKucabaTAFergusonDMGriffithTSPanyamJ. Acidic ph-responsive polymer nanoparticles as a Tlr7/8 agonist delivery platform for cancer immunotherapy. Nanoscale (2018) 10(44):20851–62. doi: 10.1039/c8nr07201a

  • CrossRef
  • Google Scholar

• 125

  KimHNiuLLarsonPKucabaTAMurphyKAJamesBRet al. Polymeric nanoparticles encapsulating novel Tlr7/8 agonists as immunostimulatory adjuvants for enhanced cancer immunotherapy. Biomaterials (2018) 164:38–53. doi: 10.1016/j.biomaterials.2018.02.034

  • CrossRef
  • Google Scholar

• 126

  PersanoSGuevaraMLLiZMaiJFerrariMPompaPPet al. Lipopolyplex potentiates anti-tumor immunity of mrna-based vaccination. Biomaterials (2017) 125:81–9. doi: 10.1016/j.biomaterials.2017.02.019

  • CrossRef
  • Google Scholar

• 127

  LiuMO’ConnorRSTrefelySGrahamKSnyderNWBeattyGL. Metabolic rewiring of macrophages by cpg potentiates clearance of cancer cells and overcomes tumor-expressed Cd47-mediated ‘Don’t-Eat-Me’ signal. Nat Immunol (2019) 20(3):265–75. doi: 10.1038/s41590-018-0292-y

  • CrossRef
  • Google Scholar

• 128

  LinYCHsuCYHuangSKFanYHHuangCHYangCKet al. Induction of liver-specific intrahepatic myeloid cells aggregation expands Cd8 T cell and inhibits growth of murine hepatoma. Oncoimmunology (2018) 7(12):e1502129. doi: 10.1080/2162402x.2018.1502129

  • CrossRef
  • Google Scholar

• 129

  BenbenishtyAGadrichMCottarelliALubartAKainDAmerMet al. Prophylactic Tlr9 stimulation reduces brain metastasis through microglia activation. PloS Biol (2019) 17(3):e2006859. doi: 10.1371/journal.pbio.2006859

  • CrossRef
  • Google Scholar

• 130

  Sagiv-BarfiICzerwinskiDKLevySAlamISMayerATGambhirSSet al. Eradication of spontaneous malignancy by local immunotherapy. Sci Trans Med (2018) 10(426):eaan4488. doi: 10.1126/scitranslmed.aan4488

  • CrossRef
  • Google Scholar

• 131

  Sagiv-BarfiIKohrtHEBurckhardtLCzerwinskiDKLevyR. Ibrutinib enhances the antitumor immune response induced by intratumoral injection of a Tlr9 ligand in mouse lymphoma. Blood (2015) 125(13):2079–86. doi: 10.1182/blood-2014-08-593137

  • CrossRef
  • Google Scholar

• 132

  JordanMWaxmanDJ. Cpg-1826 immunotherapy potentiates chemotherapeutic and anti-tumor immune responses to metronomic cyclophosphamide in a preclinical glioma model. Cancer Lett (2016) 373(1):88–96. doi: 10.1016/j.canlet.2015.11.029

  • CrossRef
  • Google Scholar

• 133

  GallottaMAssiHDegagnéÉKannanSKCoffmanRLGuiducciC. Inhaled Tlr9 agonist renders lung tumors permissive to pd-1 blockade by promoting optimal Cd4(+) and Cd8(+) T-cell interplay. Cancer Res (2018) 78(17):4943–56. doi: 10.1158/0008-5472.Can-18-0729

  • CrossRef
  • Google Scholar

• 134

  WangSCamposJGallottaMGongMCrainCNaikEet al. Intratumoral injection of a cpg oligonucleotide reverts resistance to pd-1 blockade by expanding multifunctional Cd8+ T cells. Proc Natl Acad Sci U.S.A. (2016) 113(46):E7240–e9. doi: 10.1073/pnas.1608555113

  • CrossRef
  • Google Scholar

• 135

  MarabelleAKohrtHSagiv-BarfiIAjamiBAxtellRCZhouGet al. Depleting tumor-specific tregs at a single site eradicates disseminated tumors. J Clin Invest (2013) 123(6):2447–63. doi: 10.1172/jci64859

  • CrossRef
  • Google Scholar

• 136

  NieYHeJShirotaHTrivettALYangDDMKet al. Blockade of Tnfr2 signaling enhances the immunotherapeutic effect of cpg odn in a mouse model of colon cancer. Sci Signaling (2018) 11(511):eaan0790. doi: 10.1126/scisignal.aan0790

  • CrossRef
  • Google Scholar

• 137

  XuAZhangLYuanJBabikrFFreywaldAChibbarRet al. Tlr9 agonist enhances radiofrequency ablation-induced ctl responses, leading to the potent inhibition of primary tumor growth and lung metastasis. Cell Mol Immunol (2019) 16(10):820–32. doi: 10.1038/s41423-018-0184-y

  • CrossRef
  • Google Scholar

• 138

  BehmBDi FazioPMichlPNeureiterDKemmerlingRHahnEGet al. Additive antitumour response to the rabbit Vx2 hepatoma by combined radio frequency ablation and toll like receptor 9 stimulation. Gut (2016) 65(1):134–43. doi: 10.1136/gutjnl-2014-308286

  • CrossRef
  • Google Scholar

• 139

  ZhangQHossainDMDuttaguptaPMoreiraDZhaoXWonHet al. Serum-resistant cpg-Stat3 decoy for targeting survival and immune checkpoint signaling in acute myeloid leukemia. Blood (2016) 127(13):1687–700. doi: 10.1182/blood-2015-08-665604

  • CrossRef
  • Google Scholar

• 140

  ZhaoXZhangZMoreiraDSuYLWonHAdamusTet al. B cell lymphoma immunotherapy using Tlr9-targeted oligonucleotide Stat3 inhibitors. Mol therapy: J Am Soc Gene Ther (2018) 26(3):695–707. doi: 10.1016/j.ymthe.2018.01.007

  • CrossRef
  • Google Scholar

• 141

  FendLGatard-ScheiklTKintzJGantzerMSchaedlerERittnerKet al. Intravenous injection of mva virus targets Cd8+ lymphocytes to tumors to control tumor growth upon combinatorial treatment with a Tlr9 agonist. Cancer Immunol Res (2014) 2(12):1163–74. doi: 10.1158/2326-6066.Cir-14-0050

  • CrossRef
  • Google Scholar

• 142

  HumbertMGueryLBrighouseDLemeilleSHuguesS. Intratumoral cpg-b promotes antitumoral neutrophil, cdc, and T-cell cooperation without reprograming tolerogenic pdc. Cancer Res (2018) 78(12):3280–92. doi: 10.1158/0008-5472.Can-17-2549

  • CrossRef
  • Google Scholar

• 143

  BabaerDAmaraSMcAdoryBSJohnsonOMylesELZentRet al. Oligodeoxynucleotides odn 2006 and M362 exert potent adjuvant effect through tlr-9/-6 synergy to exaggerate mammaglobin-a peptide specific cytotoxic Cd8+T lymphocyte responses against breast cancer cells. Cancers (2019) 11(5):672. doi: 10.3390/cancers11050672

  • CrossRef
  • Google Scholar

• 144

  KramerKShieldsNJPoppeVYoungSLWalkerGF. Intracellular cleavable cpg oligodeoxynucleotide-antigen conjugate enhances anti-tumor immunity. Mol therapy: J Am Soc Gene Ther (2017) 25(1):62–70. doi: 10.1016/j.ymthe.2016.10.001

  • CrossRef
  • Google Scholar

• 145

  Domingos-PereiraSGallivertiGHanahanDNardelli-HaefligerD. Carboplatin/Paclitaxel, E7-vaccination and intravaginal cpg as tri-therapy towards efficient regression of genital Hpv16 tumors. J immunotherapy Cancer (2019) 7(1):122. doi: 10.1186/s40425-019-0593-1

  • CrossRef
  • Google Scholar

• 146

  DuraiswamyJFreemanGJCoukosG. Therapeutic pd-1 pathway blockade augments with other modalities of immunotherapy T-cell function to prevent immune decline in ovarian cancer. Cancer Res (2013) 73(23):6900–12. doi: 10.1158/0008-5472.Can-13-1550

  • CrossRef
  • Google Scholar

• 147

  HaabethOAWBlakeTRMcKinlayCJWaymouthRMWenderPALevyR. Mrna vaccination with charge-altering releasable transporters elicits human T cell responses and cures established tumors in mice. Proc Natl Acad Sci U.S.A. (2018) 115(39):E9153–e61. doi: 10.1073/pnas.1810002115

  • CrossRef
  • Google Scholar

• 148

  HanSWangWWangSWangSJuRPanZet al. Multifunctional biomimetic nanoparticles loading baicalin for polarizing tumor-associated macrophages. Nanoscale (2019) 11:20206–20. doi: 10.1039/c9nr03353j

  • CrossRef
  • Google Scholar

• 149

  MochizukiSMorishitaHKobiyamaKAoshiTIshiiKJSakuraiK. Immunization with antigenic peptides complexed with beta-glucan induces potent cytotoxic T-lymphocyte activity in combination with cpg-odns. J Controlled release: Off J Controlled Release Soc (2015) 220(Pt A):495–502. doi: 10.1016/j.jconrel.2015.11.008

  • CrossRef
  • Google Scholar

• 150

  YoshizakiYYubaESakaguchiNKoiwaiKHaradaAKonoK. Ph-sensitive polymer-modified liposome-based immunity-inducing system: Effects of inclusion of cationic lipid and cpg-DNA. Biomaterials (2017) 141:272–83. doi: 10.1016/j.biomaterials.2017.07.001

  • CrossRef
  • Google Scholar

• 151

  GuoLYanDDYangDLiYWangXZalewskiOet al. Combinatorial photothermal and immuno cancer therapy using chitosan-coated hollow copper sulfide nanoparticles. ACS Nano (2014) 8(6):5670–81. doi: 10.1021/nn5002112

  • CrossRef
  • Google Scholar

• 152

  ZhuGLiuYYangXKimYHZhangHJiaRet al. DNA-Inorganic hybrid nanovaccine for cancer immunotherapy. Nanoscale (2016) 8(12):6684–92. doi: 10.1039/c5nr08821f

  • CrossRef
  • Google Scholar

• 153

  LinSIHuangMHChangYWChenIHRofflerSChenBMet al. Chimeric peptide containing both b and T cells epitope of tumor-associated antigen L6 enhances anti-tumor effects in hla-A2 transgenic mice. Cancer Lett (2016) 377(2):126–33. doi: 10.1016/j.canlet.2016.04.031

  • CrossRef
  • Google Scholar

• 154

  LuYYangYGuZZhangJSongHXiangGet al. Glutathione-depletion mesoporous organosilica nanoparticles as a self-adjuvant and Co-delivery platform for enhanced cancer immunotherapy. Biomaterials (2018) 175:82–92. doi: 10.1016/j.biomaterials.2018.05.025

  • CrossRef
  • Google Scholar

• 155

  Ruiz-de-AnguloAZabaletaAGomez-VallejoVLlopJMareque-RivasJC. Microdosed lipid-coated (67)Ga-magnetite enhances antigen-specific immunity by image tracked delivery of antigen and cpg to lymph nodes. ACS Nano (2016) 10(1):1602–18. doi: 10.1021/acsnano.5b07253

  • CrossRef
  • Google Scholar

• 156

  MunakataLTanimotoYOsaAMengJHasedaYNaitoYet al. Lipid nanoparticles of type-a cpg D35 suppress tumor growth by changing tumor immune-microenvironment and activate Cd8 T cells in mice. J Controlled release: Off J Controlled Release Soc (2019) 313:106–19. doi: 10.1016/j.jconrel.2019.09.011

  • CrossRef
  • Google Scholar

• 157

  YanSRolfeBEZhangBMohammedYHGuWXuZP. Polarized immune responses modulated by layered double hydroxides nanoparticle conjugated with cpg. Biomaterials (2014) 35(35):9508–16. doi: 10.1016/j.biomaterials.2014.07.055

  • CrossRef
  • Google Scholar

• 158

  WuCGuanXXuJZhangYLiuQTianYet al. Highly efficient cascading synergy of cancer photo-immunotherapy enabled by engineered graphene quantum Dots/Photosensitizer/Cpg oligonucleotides hybrid nanotheranostics. Biomaterials (2019) 205:106–19. doi: 10.1016/j.biomaterials.2019.03.020

  • CrossRef
  • Google Scholar

• 159

  ZhongXZhangYTanLZhengTHouYHongXet al. An aluminum adjuvant-integrated nano-mof as antigen delivery system to induce strong humoral and cellular immune responses. J Controlled release: Off J Controlled Release Soc (2019) 300:81–92. doi: 10.1016/j.jconrel.2019.02.035

  • CrossRef
  • Google Scholar

• 160

  KadiyalaPLiDNunezFMAltshulerDDohertyRKuaiRet al. High-density lipoprotein-mimicking nanodiscs for chemo-immunotherapy against glioblastoma multiforme. ACS Nano (2019) 13(2):1365–84. doi: 10.1021/acsnano.8b06842

  • CrossRef
  • Google Scholar

• 161

  AhmedKKGearySMSalemAK. Surface engineering tumor cells with adjuvant-loaded particles for use as cancer vaccines. J Controlled release: Off J Controlled Release Soc (2017) 248:1–9. doi: 10.1016/j.jconrel.2016.12.036

  • CrossRef
  • Google Scholar

• 162

  ZengQLiHJiangHYuJWangYKeHet al. Tailoring polymeric hybrid micelles with lymph node targeting ability to improve the potency of cancer vaccines. Biomaterials (2017) 122:105–13. doi: 10.1016/j.biomaterials.2017.01.010

  • CrossRef
  • Google Scholar

• 163

  XuXJinZLiuYGongHSunQZhangWet al. Carbohydrate-based adjuvants activate tumor-specific Th1 and Cd8(+) T-cell responses and reduce the immunosuppressive activity of mdscs. Cancer Lett (2019) 440-441:94–105. doi: 10.1016/j.canlet.2018.10.013

  • CrossRef
  • Google Scholar

• 164

  KappKVolzBCurranMAOswaldDWittigBSchmidtM. Enandim - a novel family of l-Nucleotide-Protected Tlr9 agonists for cancer immunotherapy. J immunotherapy Cancer (2019) 7(1):5. doi: 10.1186/s40425-018-0470-3

  • CrossRef
  • Google Scholar

• 165

  KooJEShinSWUmSHLeeJY. X-Shaped DNA potentiates therapeutic efficacy in colitis-associated colon cancer through dual activation of Tlr9 and inflammasomes. Mol Cancer (2015) 14:104. doi: 10.1186/s12943-015-0369-2

  • CrossRef
  • Google Scholar

• 166

  VolzBSchmidtMHeinrichKKappKSchroffMWittigB. Design and characterization of the tumor vaccine Mgn1601, allogeneic fourfold gene-modified vaccine cells combined with a tlr-9 agonist. Mol Ther oncolytics (2016) 3:15023. doi: 10.1038/mto.2015.23

  • CrossRef
  • Google Scholar

• 167

  RosaliaRACruzLJvan DuikerenSTrompATSilvaALJiskootWet al. Cd40-targeted dendritic cell delivery of plga-nanoparticle vaccines induce potent anti-tumor responses. Biomaterials (2015) 40:88–97. doi: 10.1016/j.biomaterials.2014.10.053

  • CrossRef
  • Google Scholar

• 168

  CaisovaVLiLGuptaGJochmanovaIJhaAUherOet al. The significant reduction or complete eradication of subcutaneous and metastatic lesions in a pheochromocytoma mouse model after immunotherapy using mannan-bam, tlr ligands, and anti-Cd40. Cancers (2019) 11(5):654. doi: 10.3390/cancers11050654

  • CrossRef
  • Google Scholar

• 169

  ShojaeiHObergHHJurickeMMarischenLKunzMMundhenkeCet al. Toll-like receptors 3 and 7 agonists enhance tumor cell lysis by human gammadelta T cells. Cancer Res (2009) 69(22):8710–7. doi: 10.1158/0008-5472.Can-09-1602

  • CrossRef
  • Google Scholar

• 170

  Bocanegra GondanAIRuiz-de-AnguloAZabaletaAGomez BlancoNCobaleda-SilesBMGarcia-GrandaMJet al. Effective cancer immunotherapy in mice by polyic-imiquimod complexes and engineered magnetic nanoparticles. Biomaterials (2018) 170:95–115. doi: 10.1016/j.biomaterials.2018.04.003

  • CrossRef
  • Google Scholar

• 171

  Le NociVTortoretoMGulinoAStortiCBianchiFZaffaroniNet al. Poly(I:C) and cpg-odn combined aerosolization to treat lung metastases and counter the immunosuppressive microenvironment. Oncoimmunology (2015) 4(10):e1040214. doi: 10.1080/2162402x.2015.1040214

  • CrossRef
  • Google Scholar

• 172

  Le NociVSommarivaMTortoretoMZaffaroniNCampiglioMTagliabueEet al. Reprogramming the lung microenvironment by inhaled immunotherapy fosters immune destruction of tumor. Oncoimmunology (2016) 5(11):e1234571. doi: 10.1080/2162402x.2016.1234571

  • CrossRef
  • Google Scholar

• 173

  SilvaJMZupancicEVandermeulenGOliveiraVGSalgadoAVideiraMet al. In vivo delivery of peptides and toll-like receptor ligands by mannose-functionalized polymeric nanoparticles induces prophylactic and therapeutic anti-tumor immune responses in a melanoma model. J Controlled release: Off J Controlled Release Soc (2015) 198:91–103. doi: 10.1016/j.jconrel.2014.11.033

  • CrossRef
  • Google Scholar

• 174

  ZhangLDewanVYinH. Discovery of small molecules as multi-Toll-Like receptor agonists with proinflammatory and anticancer activities. J medicinal Chem (2017) 60(12):5029–44. doi: 10.1021/acs.jmedchem.7b00419

  • CrossRef
  • Google Scholar

• 175

  ZhengJHNguyenVHJiangS-NParkS-HTanWHongSHet al. Two-step enhanced cancer immunotherapy with engineered salmonella typhimurium secreting heterologous flagellin. Sci Trans Med (2017) 9(376):eaak9537. doi: 10.1126/scitranslmed.aak9537

  • CrossRef
  • Google Scholar

• 176

  ZhuDHuCFanFQinYHuangCZhangZet al. Co-Delivery of antigen and dual agonists by programmed mannose-targeted cationic lipid-hybrid polymersomes for enhanced vaccination. Biomaterials (2019) 206:25–40. doi: 10.1016/j.biomaterials.2019.03.012

  • CrossRef
  • Google Scholar

• 177

  ZhangLWuSQinYFanFZhangZHuangCet al. Targeted codelivery of an antigen and dual agonists by hybrid nanoparticles for enhanced cancer immunotherapy. Nano Lett (2019) 19(7):4237–49. doi: 10.1021/acs.nanolett.9b00030

  • CrossRef
  • Google Scholar

• 178

  ZhuMDingXZhaoRLiuXShenHCaiCet al. Co-Delivery of tumor antigen and dual toll-like receptor ligands into dendritic cell by silicon microparticle enables efficient immunotherapy against melanoma. J Controlled release: Off J Controlled Release Soc (2018) 272:72–82. doi: 10.1016/j.jconrel.2018.01.004

  • CrossRef
  • Google Scholar

• 179

  SainzVMouraLIFPeresCMatosAIVianaASWagnerAMet al. Alpha-galactosylceramide and peptide-based nano-vaccine synergistically induced a strong tumor suppressive effect in melanoma. Acta biomaterialia (2018) 76:193–207. doi: 10.1016/j.actbio.2018.06.029

  • CrossRef
  • Google Scholar

• 180

  KuaiRSunXYuanWOchylLJXuYHassani NajafabadiAet al. Dual tlr agonist nanodiscs as a strong adjuvant system for vaccines and immunotherapy. J Controlled release: Off J Controlled Release Soc (2018) 282:131–9. doi: 10.1016/j.jconrel.2018.04.041

  • CrossRef
  • Google Scholar

• 181

  MacedoRRochefortJGuillot-DelostMTanakaKLe MoignicANoizatCet al. Intra-cheek immunization as a novel vaccination route for therapeutic vaccines of head and neck squamous cell carcinomas using plasmo virus-like particles. Oncoimmunology (2016) 5(7):e1164363. doi: 10.1080/2162402x.2016.1164363

  • CrossRef
  • Google Scholar

• 182

  Sato-KanekoFYaoSAhmadiAZhangSSHosoyaTKanedaMMet al. Combination immunotherapy with tlr agonists and checkpoint inhibitors suppresses head and neck cancer. JCI Insight (2017) 2(18):e93397. doi: 10.1172/jci.insight.93397

  • CrossRef
  • Google Scholar

• 183

  TyeHKennedyCLNajdovskaMMcLeodLMcCormackWHughesNet al. Stat3-driven upregulation of Tlr2 promotes gastric tumorigenesis independent of tumor inflammation. Cancer Cell (2012) 22(4):466–78. doi: 10.1016/j.ccr.2012.08.010

  • CrossRef
  • Google Scholar

• 184

  MohamedFEAl-JehaniRMMinogueSSAndreolaFWinstanleyAOlde DaminkSWet al. Effect of toll-like receptor 7 and 9 targeted therapy to prevent the development of hepatocellular carcinoma. Liver international: Off J Int Assoc Study Liver (2015) 35(3):1063–76. doi: 10.1111/liv.12626

  • CrossRef
  • Google Scholar

• 185

  MohamedFEZJalanRMinogueSAndreolaFHabtesionAHallAet al. Inhibition of Tlr7 and Tlr9 reduces human cholangiocarcinoma cell proliferation and tumor development. Digestive Dis Sci (2021) 67:1806–21. doi: 10.1007/s10620-021-06973-9

  • CrossRef
  • Google Scholar

• 186

  AnBZhuSLiTWuJZangGLvXet al. A dual Tlr7/Tlr9 inhibitor Hj901 inhibits abc-dlbcl expressing the Myd88 L265p mutation. Front Cell Dev Biol (2020) 8:262. doi: 10.3389/fcell.2020.00262

  • CrossRef
  • Google Scholar

• 187

  SpeetjensFMWeltersMJPSlingerlandMde Vos van SteenwijkPRoozenICFMBoekestijnSet al. Phase I trial to determine safety and immunogenicity of amplivant, a synthetic toll-like receptor 2 ligand, conjugated to two Hpv16 E6 synthetic long peptides. J Clin Oncol (2021) 39(15_suppl):2614. doi: 10.1200/JCO.2021.39.15_suppl.2614

  • CrossRef
  • Google Scholar

• 188

  KyiCRoudkoVSabadoRSaengerYLogingWMandeliJet al. Therapeutic immune modulation against solid cancers with intratumoral poly-iclc: A pilot trial. Clin Cancer research: an Off J Am Assoc Cancer Res (2018) 24(20):4937–48. doi: 10.1158/1078-0432.Ccr-17-1866

  • CrossRef
  • Google Scholar

• 189

  AwadMMGovindanRSpigelDRGaronEBKohlerVVyasamneniRet al. Abstract 73: A personal neoantigen vaccine neo-Pv-01 in combination with chemotherapy and pembrolizumab induces broad De novo immune responses in first-line non-squamous nsclc: Associations with clinical outcomes. Cancer Res (2021) 81(13_Supplement):73. doi: 10.1158/1538-7445.Am2021-73

  • CrossRef
  • Google Scholar

• 190

  MelssenMMPetroniGRChianese-BullockKAWagesNAGroshWWVarhegyiNet al. A multipeptide vaccine plus toll-like receptor agonists lps or polyiclc in combination with incomplete freund’s adjuvant in melanoma patients. J immunotherapy Cancer (2019) 7(1):163. doi: 10.1186/s40425-019-0625-x

  • CrossRef
  • Google Scholar

• 191

  OttPAHu-LieskovanSChmielowskiBGovindanRNaingABhardwajNet al. A phase ib trial of personalized neoantigen therapy plus anti-Pd-1 in patients with advanced melanoma, non-small cell lung cancer, or bladder cancer. Cell (2020) 183(2):347–62.e24. doi: 10.1016/j.cell.2020.08.053

  • CrossRef
  • Google Scholar

• 192

  WeedDTZilioSReisIMSargiZAbouyaredMGomez-FernandezCRet al. The reversal of immune exclusion mediated by tadalafil and an anti-tumor vaccine also induces Pdl1 upregulation in recurrent head and neck squamous cell carcinoma: Interim analysis of a phase I clinical trial. Front Immunol (2019) 10:1206. doi: 10.3389/fimmu.2019.01206

  • CrossRef
  • Google Scholar

• 193

  BhatiaSMillerNJLuHLonginoNVIbraniDShinoharaMMet al. Intratumoral G100, a Tlr4 agonist, induces antitumor immune responses and tumor regression in patients with merkel cell carcinoma. Clin Cancer research: an Off J Am Assoc Cancer Res (2019) 25(4):1185–95. doi: 10.1158/1078-0432.Ccr-18-0469

  • CrossRef
  • Google Scholar

• 194

  SeoYDZhouJMorseKPatinoJMackaySKimEYet al. Effect of intratumoral (It) injection of the toll-like receptor 4 (Tlr4) agonist G100 on a clinical response and Cd4 T-cell response locally and systemically. J Clin Oncol. (2018) 36:71. doi: 10.1200/JCO.2018.36.5_suppl.71

  • CrossRef
  • Google Scholar

• 195

  MahipalAEjadiSGnjaticSKim-SchulzeSLuHTer MeulenJHet al. First-in-Human phase 1 dose-escalating trial of G305 in patients with advanced solid tumors expressing ny-Eso-1. Cancer immunology immunotherapy: CII (2019) 68(7):1211–22. doi: 10.1007/s00262-019-02331-x

  • CrossRef
  • Google Scholar

• 196

  BolKFFigdorCGAarntzenEHWelzenMEvan RossumMMBlokxWAet al. Intranodal vaccination with mrna-optimized dendritic cells in metastatic melanoma patients. Oncoimmunology (2015) 4(8):e1019197–e. doi: 10.1080/2162402X.2015.1019197

  • CrossRef
  • Google Scholar

• 197

  van der LindenMMeeuwisKvan HeesCvan DorstEBultenJBosseTet al. P191 paget trial: Topical 5% imiquimod for vulvar paget disease, first results of clinical efficacy. Int J Gynecologic Cancer (2019) 29(Suppl 4):A170. doi: 10.1136/ijgc-2019-ESGO.248

  • CrossRef
  • Google Scholar

• 198

  TrutnovskyGReichOJouraEAHolterMCiresa-KönigAWidschwendterAet al. Topical imiquimod versus surgery for vulvar intraepithelial neoplasia: A multicentre, randomised, phase 3, non-inferiority trial. Lancet (London England) (2022) 399(10337):1790–8. doi: 10.1016/s0140-6736(22)00469-x

  • CrossRef
  • Google Scholar

• 199

  PolterauerSReichOWidschwendterAHadjariLBognerGReinthallerAet al. Topical imiquimod compared with conization to treat cervical high-grade squamous intraepithelial lesions: Multicenter, randomized controlled trial. Gynecologic Oncol (2022) 165(1):23–9. doi: 10.1016/j.ygyno.2022.01.033

  • CrossRef
  • Google Scholar

• 200

  FonsecaBOPossati-ResendeJCSalcedoMPSchmelerKMAccorsiGSFregnaniJet al. Topical imiquimod for the treatment of high-grade squamous intraepithelial lesions of the cervix: A randomized controlled trial. Obstet Gynecol (2021) 137(6):1043–53. doi: 10.1097/aog.0000000000004384

  • CrossRef
  • Google Scholar

• 201

  AdamsSKozhayaLMartiniukFMengTCChiribogaLLiebesLet al. Topical Tlr7 agonist imiquimod can induce immune-mediated rejection of skin metastases in patients with breast cancer. Clin Cancer research: an Off J Am Assoc Cancer Res (2012) 18(24):6748–57. doi: 10.1158/1078-0432.Ccr-12-1149

  • CrossRef
  • Google Scholar

• 202

  PlattenMBunseLWickABunseTLe CornetLHartingIet al. A vaccine targeting mutant Idh1 in newly diagnosed glioma. Nature (2021) 592(7854):463–8. doi: 10.1038/s41586-021-03363-z

  • CrossRef
  • Google Scholar

• 203

  PlattenMSchillingDBunseLWickABunseTRiehlDet al. A mutation-specific peptide vaccine targeting Idh1r132h in patients with newly diagnosed malignant astrocytomas: A first-in-Man multicenter phase I clinical trial of the German neurooncology working group (Noa-16). J Clin Oncol (2018) 36(15_suppl):2001. doi: 10.1200/JCO.2018.36.15_suppl.2001

  • CrossRef
  • Google Scholar

• 204

  FilaciGFenoglioDNolèFZanardiETomaselloLAgliettaMet al. Telomerase-based Gx301 cancer vaccine in patients with metastatic castration-resistant prostate cancer: A randomized phase ii trial. Cancer immunology immunotherapy: CII (2021) 70(12):3679–92. doi: 10.1007/s00262-021-03024-0

  • CrossRef
  • Google Scholar

• 205

  DoninNMChamieKLenisATPantuckAJReddyMKivlinDet al. A phase 2 study of tmx-101, intravesical imiquimod, for the treatment of carcinoma in situ bladder cancer. Urologic Oncol (2017) 35(2):39. doi: 10.1016/j.urolonc.2016.09.006

  • CrossRef
  • Google Scholar

• 206

  SabadoRLPavlickAGnjaticSCruzCMVengcoIHasanFet al. Resiquimod as an immunologic adjuvant for ny-Eso-1 protein vaccination in patients with high-risk melanoma. Cancer Immunol Res (2015) 3(3):278–87. doi: 10.1158/2326-6066.Cir-14-0202

  • CrossRef
  • Google Scholar

• 207

  MonkBJBradyMFAghajanianCLankesHARizackTLeachJet al. A phase 2, randomized, double-blind, placebo- controlled study of chemo-immunotherapy combination using motolimod with pegylated liposomal doxorubicin in recurrent or persistent ovarian cancer: A gynecologic oncology group partners study. Ann oncology: Off J Eur Soc Med Oncol (2017) 28(5):996–1004. doi: 10.1093/annonc/mdx049

  • CrossRef
  • Google Scholar

• 208

  FerrisRLSabaNFGitlitzBJHaddadRSukariANeupanePet al. Effect of adding motolimod to standard combination chemotherapy and cetuximab treatment of patients with squamous cell carcinoma of the head and neck: The Active8 randomized clinical trial. JAMA Oncol (2018) 4(11):1583–8. doi: 10.1001/jamaoncol.2018.1888

  • CrossRef
  • Google Scholar

• 209

  DietschGNLuHYangYMorishimaCChowLQDisisMLet al. Coordinated activation of toll-like Receptor8 (Tlr8) and Nlrp3 by the Tlr8 agonist, vtx-2337, ignites tumoricidal natural killer cell activity. PloS One (2016) 11(2):e0148764. doi: 10.1371/journal.pone.0148764

  • CrossRef
  • Google Scholar

• 210

  MonkBJFacciabeneABradyWEAghajanianCAFracassoPMWalkerJLet al. Integrative development of a Tlr8 agonist for ovarian cancer chemoimmunotherapy. Clin Cancer research: an Off J Am Assoc Cancer Res (2017) 23(8):1955–66. doi: 10.1158/1078-0432.Ccr-16-1453

  • CrossRef
  • Google Scholar

• 211

  FrankMJKhodadoustMSCzerwinskiDKHaabethOAWChuMPMiklosDBet al. Autologous tumor cell vaccine induces antitumor T cell immune responses in patients with mantle cell lymphoma: A phase I/Ii trial. J Exp Med (2020) 217(9):e20191712. doi: 10.1084/jem.20191712

  • CrossRef
  • Google Scholar

• 212

  BrodyJDAiWZCzerwinskiDKTorchiaJALevyMAdvaniRHet al. In situ vaccination with a Tlr9 agonist induces systemic lymphoma regression: A phase I/Ii study. J Clin Oncol (2010) 28(28):4324–32. doi: 10.1200/jco.2010.28.9793

  • CrossRef
  • Google Scholar

• 213

  BabikerHBorazanciESubbiahVMaguireORahimianSMindermanHet al. 1195p - safety, efficacy, and immune effects of intratumoral tilsotolimod in patients with refractory solid tumours: Updated results from illuminate-101. Ann Oncol (2019) 30:v487. doi: 10.1093/annonc/mdz253.021

  • CrossRef
  • Google Scholar

• 214

  ThomasMPonce-AixSNavarroARiera-KnorrenschildJSchmidtMWiegertEet al. Immunotherapeutic maintenance treatment with toll-like receptor 9 agonist lefitolimod in patients with extensive-stage small-cell lung cancer: Results from the exploratory, controlled, randomized, international phase ii impulse study. Ann oncology: Off J Eur Soc Med Oncol (2018) 29(10):2076–84. doi: 10.1093/annonc/mdy326

  • CrossRef
  • Google Scholar

• 215

  RuzsaASenMEvansMLeeLWHideghetyKRotteySet al. Phase 2, open-label, 1:1 randomized controlled trial exploring the efficacy of emd 1201081 in combination with cetuximab in second-line cetuximab-naive patients with recurrent or metastatic squamous cell carcinoma of the head and neck (R/M scchn). Investigational New Drugs (2014) 32(6):1278–84. doi: 10.1007/s10637-014-0117-2

  • CrossRef
  • Google Scholar

• 216

  GaronESpiraAIJohnsonMBazhenovaLLeachJCandiaAet al. Abstract Ct224: Phase Ib/Ii, open label, multicenter study of inhaled Dv281, a toll-like receptor 9 agonist, in combination with nivolumab in patients with advanced or metastatic non small cell lung cancer (Nsclc). Cancer Res (2019) 79(13 Supplement):CT224–CT. doi: 10.1158/1538-7445.Am2019-ct224

  • CrossRef
  • Google Scholar

• 217

  IsambertNFumoleauPPaulCFerrandCZanettaSBauerJet al. Phase I study of om-174, a lipid a analogue, with assessment of immunological response, in patients with refractory solid tumors. BMC Cancer (2013) 13:172. doi: 10.1186/1471-2407-13-172

  • CrossRef
  • Google Scholar

• 218

  HelfandAMLeeCTHafezKHussainMLiebertMDaignaultSet al. Phase ii clinical trial of intravesical bacillus calmette-guerin (Bcg) followed by sunitinib for the treatment of high-risk nonmuscle-invasive bladder cancer (Nmibc). J Clin Oncol (2015) 33(7_suppl):293. doi: 10.1200/jco.2015.33.7_suppl.293

  • CrossRef
  • Google Scholar

• 219

  JiNMukherjeeNReyesRMGelfondJJavorsMMeeksJJet al. Rapamycin enhances bcg-specific Γδ T cells during intravesical bcg therapy for non-muscle invasive bladder cancer: A randomized, double-blind study. J immunotherapy Cancer (2021) 9(3):e001941. doi: 10.1136/jitc-2020-001941

  • CrossRef
  • Google Scholar

• 220

  DhodapkarMVSznolMZhaoBWangDCarvajalRDKeohanMLet al. Induction of antigen-specific immunity with a vaccine targeting ny-Eso-1 to the dendritic cell receptor Dec-205. Sci Trans Med (2014) 6(232):232ra51. doi: 10.1126/scitranslmed.3008068

  • CrossRef
  • Google Scholar

• 221

  PrinsRMSotoHKonkankitVOdesaSKEskinAYongWHet al. Gene expression profile correlates with T-cell infiltration and relative survival in glioblastoma patients vaccinated with dendritic cell immunotherapy. Clin Cancer Res (2011) 17(6):1603–15. doi: 10.1158/1078-0432.Ccr-10-2563

  • CrossRef
  • Google Scholar

• 222

  McQuadeJLHomsiJTorres-CabalaCABassettRPopuriRMJamesMLet al. A phase ii trial of recombinant mage-A3 protein with immunostimulant As15 in combination with high-dose interleukin-2 (Hdil2) induction therapy in metastatic melanoma. BMC Cancer (2018) 18(1):1274. doi: 10.1186/s12885-018-5193-9

  • CrossRef
  • Google Scholar

• 223

  NeilEEatonALunnSNelsonKGreengardEMoertelCet al. Ctim-15. first-in-Human phase 1 study of Cd200 activation receptor-ligand (Cd200ar-l) and allogeneic tumor lysate vaccine immunotherapy for recurrent glioblastoma: Initial results from an ongoing clinical trial. Neuro-oncology (2021) 23(Supplement_6):vi52–vi3. doi: 10.1093/neuonc/noab196.207

  • CrossRef
  • Google Scholar

• 224

  AndreakosESacreSMSmithCLundbergAKiriakidisSStonehouseTet al. Distinct pathways of lps-induced nf-kappa b activation and cytokine production in human myeloid and nonmyeloid cells defined by selective utilization of Myd88 and Mal/Tirap. Blood (2004) 103(6):2229–37. doi: 10.1182/blood-2003-04-1356

  • CrossRef
  • Google Scholar

• 225

  FitzgeraldKARoweDCGolenbockDT. Endotoxin recognition and signal transduction by the Tlr4/Md2-complex. Microbes Infect (2004) 6(15):1361–7. doi: 10.1016/j.micinf.2004.08.015

  • CrossRef
  • Google Scholar

• 226

  CartyMGoodbodyRSchroderMStackJMoynaghPNBowieAG. The human adaptor sarm negatively regulates adaptor protein trif-dependent toll-like receptor signaling. Nat Immunol (2006) 7(10):1074–81. doi: 10.1038/ni1382

  • CrossRef
  • Google Scholar

• 227

  JenkinsKAMansellA. Tir-containing adaptors in toll-like receptor signalling. Cytokine (2010) 49(3):237–44. doi: 10.1016/j.cyto.2009.01.009

  • CrossRef
  • Google Scholar

• 228

  KawaiTAkiraS. Tlr signaling. Semin Immunol (2007) 19(1):24–32. doi: 10.1016/j.smim.2006.12.004

  • CrossRef
  • Google Scholar

• 229

  HasanUChaffoisCGaillardCSaulnierVMerckETancrediSet al. Human Tlr10 is a functional receptor, expressed by b cells and plasmacytoid dendritic cells, which activates gene transcription through Myd88. J Immunol (Baltimore Md: 1950) (2005) 174(5):2942–50. doi: 10.4049/jimmunol.174.5.2942

  • CrossRef
  • Google Scholar

• 230

  SchroderMBowieAG. Tlr3 in antiviral immunity: Key player or bystander? Trends Immunol (2005) 26(9):462–8. doi: 10.1016/j.it.2005.07.002

  • CrossRef
  • Google Scholar

• 231

  ZhaoWQiJWangLZhangMWangPGaoC. Ly294002 inhibits Tlr3/4-mediated ifn-B production Via inhibition of Irf3 activation with a Pi3k-independent mechanism. FEBS Lett (2012) 586(6):705–10. doi: 10.1016/j.febslet.2012.01.016

  • CrossRef
  • Google Scholar

• 232

  EskanMARoseBGBenakanakereMRLeeMJKinaneDF. Sphingosine 1-phosphate 1 and Tlr4 mediate ifn-beta expression in human gingival epithelial cells. J Immunol (Baltimore Md: 1950) (2008) 180(3):1818–25. doi: 10.4049/jimmunol.180.3.1818

  • CrossRef
  • Google Scholar

• 233

  BalaSPetrasekJMundkurSCatalanoDLevinIWardJet al. Circulating micrornas in exosomes indicate hepatocyte injury and inflammation in alcoholic, drug-induced, and inflammatory liver diseases. Hepatol (Baltimore Md) (2012) 56(5):1946–57. doi: 10.1002/hep.25873

  • CrossRef
  • Google Scholar

• 234

  GalliRPaoneAFabbriMZanesiNCaloreFCascioneLet al. Toll-like receptor 3 (Tlr3) activation induces microrna-dependent reexpression of functional rarbeta and tumor regression. Proc Natl Acad Sci U.S.A. (2013) 110(24):9812–7. doi: 10.1073/pnas.1304610110

  • CrossRef
  • Google Scholar

• 235

  LusterAD. The role of chemokines in linking innate and adaptive immunity. Curr Opin Immunol (2002) 14(1):129–35. doi: 10.1016/s0952-7915(01)00308-9

  • CrossRef
  • Google Scholar

• 236

  SabroeIParkerLCDowerSKWhyteMK. The role of tlr activation in inflammation. J Pathol (2008) 214(2):126–35. doi: 10.1002/path.2264

  • CrossRef
  • Google Scholar

• 237

  ZaremberKAGodowskiPJ. Tissue expression of human toll-like receptors and differential regulation of toll-like receptor mrnas in leukocytes in response to microbes, their products, and cytokines. J Immunol (2002) 168(2):554–61. doi: 10.4049/jimmunol.168.2.554

  • CrossRef
  • Google Scholar

• 238

  RidnourLAChengRYSwitzerCHHeineckeJLAmbsSGlynnSet al. Molecular pathways: Toll-like receptors in the tumor microenvironment–poor prognosis or new therapeutic opportunity. Clin Cancer research: an Off J Am Assoc Cancer Res (2013) 19(6):1340–6. doi: 10.1158/1078-0432.Ccr-12-0408

  • CrossRef
  • Google Scholar

• 239

  FellnerLIrschickRSchandaKReindlMKlimaschewskiLPoeweWet al. Toll-like receptor 4 is required for alpha-synuclein dependent activation of microglia and astroglia. Glia (2013) 61(3):349–60. doi: 10.1002/glia.22437

  • CrossRef
  • Google Scholar

• 240

  AyariCBergeronALaRueHMenardCFradetY. Toll-like receptors in normal and malignant human bladders. J Urol (2011) 185(5):1915–21. doi: 10.1016/j.juro.2010.12.097

  • CrossRef
  • Google Scholar

• 241

  KadowakiNHoSAntonenkoSMalefytRDKasteleinRABazanFet al. Subsets of human dendritic cell precursors express different toll-like receptors and respond to different microbial antigens. J Exp Med (2001) 194(6):863–9. doi: 10.1084/jem.194.6.863

  • CrossRef
  • Google Scholar

• 242

  FujitaYMiharaTOkazakiTShitanakaMKushinoRIkedaCet al. Toll-like receptors (Tlr) 2 and 4 on human sperm recognize bacterial endotoxins and mediate apoptosis. Hum Reprod (Oxford England) (2011) 26(10):2799–806. doi: 10.1093/humrep/der234

  • CrossRef
  • Google Scholar

• 243

  ChenXChengFLiuYZhangLSongLCaiXet al. Toll-like receptor 2 and toll-like receptor 4 exhibit distinct regulation of cancer cell stemness mediated by cell death-induced high-mobility group box 1. EBioMedicine (2019) 40:135–50. doi: 10.1016/j.ebiom.2018.12.016

  • CrossRef
  • Google Scholar

• 244

  YuLChenS. Toll-like receptors expressed in tumor cells: Targets for therapy. Cancer immunology immunotherapy: CII (2008) 57(9):1271–8. doi: 10.1007/s00262-008-0459-8

  • CrossRef
  • Google Scholar

• 245

  JouhiLRenkonenSAtulaTMakitieAHaglundCHagstromJ. Different toll-like receptor expression patterns in progression toward cancer. Front Immunol (2014) 5:638. doi: 10.3389/fimmu.2014.00638

  • CrossRef
  • Google Scholar

• 246

  DuthieMSWindishHPFoxCBReedSG. Use of defined tlr ligands as adjuvants within human vaccines. Immunol Rev (2011) 239(1):178–96. doi: 10.1111/j.1600-065X.2010.00978.x

  • CrossRef
  • Google Scholar

• 247

  SobekVBirknerNFalkIWurchAKirschningCJWagnerHet al. Direct toll-like receptor 2 mediated Co-stimulation of T cells in the mouse system as a basis for chronic inflammatory joint disease. Arthritis Res Ther (2004) 6(5):R433–46. doi: 10.1186/ar1212

  • CrossRef
  • Google Scholar

• 248

  Ganley-LealLMLiuXWetzlerLM. Toll-like receptor 2-mediated human b cell differentiation. Clin Immunol (2006) 120(3):272–84. doi: 10.1016/j.clim.2006.04.571

  • CrossRef
  • Google Scholar

• 249

  ManssonAAdnerMHockerfeltUCardellLO. A distinct toll-like receptor repertoire in human tonsillar b cells, directly activated by pamcsk, r-837 and cpg-2006 stimulation. Immunology (2006) 118(4):539–48. doi: 10.1111/j.1365-2567.2006.02392.x

  • CrossRef
  • Google Scholar

• 250

  WangJShaoYBennettTAShankarRAWightmanPDReddyLG. The functional effects of physical interactions among toll-like receptors 7, 8, and 9. J Biol Chem (2006) 281(49):37427–34. doi: 10.1074/jbc.M605311200

  • CrossRef
  • Google Scholar

• 251

  FukuiRSaitohSMatsumotoFKozuka-HataHOyamaMTabetaKet al. Unc93b1 biases toll-like receptor responses to nucleic acid in dendritic cells toward DNA- but against rna-sensing. J Exp Med (2009) 206(6):1339–50. doi: 10.1084/jem.20082316

  • CrossRef
  • Google Scholar

• 252

  Urban-WojciukZKhanMMOylerBLFåhraeusRMarek-TrzonkowskaNNita-LazarAet al. The role of tlrs in anti-cancer immunity and tumor rejection. Front Immunol (2019) 10:2388. doi: 10.3389/fimmu.2019.02388

  • CrossRef
  • Google Scholar

• 253

  LoweELCrotherTRRabizadehSHuBWangHChenSet al. Toll-like receptor 2 signaling protects mice from tumor development in a mouse model of colitis-induced cancer. PloS One (2010) 5(9):e13027. doi: 10.1371/journal.pone.0013027

  • CrossRef
  • Google Scholar

• 254

  AsproditesNZhengLGengDVelasco-GonzalezCSanchez-PerezLDavilaE. Engagement of toll-like receptor-2 on cytotoxic T-lymphocytes occurs in vivo and augments antitumor activity. FASEB journal: Off Publ Fed Am Societies Exp Biol (2008) 22(10):3628–37. doi: 10.1096/fj.08-108274

  • CrossRef
  • Google Scholar

• 255

  LiSSunRChenYWeiHTianZ. Tlr2 limits development of hepatocellular carcinoma by reducing Il18-mediated immunosuppression. Cancer Res (2015) 75(6):986–95. doi: 10.1158/0008-5472.CAN-14-2371

  • CrossRef
  • Google Scholar

• 256

  NeldeAMaringerYBilichTSalihHRRoerdenMHeitmannJSet al. Immunopeptidomics-guided warehouse design for peptide-based immunotherapy in chronic lymphocytic leukemia. Front Immunol (2021) 12:705974. doi: 10.3389/fimmu.2021.705974

  • CrossRef
  • Google Scholar

• 257

  WengJLaiPQinLLaiYJiangZLuoCet al. A novel generation 1928zt2 car T cells induce remission in extramedullary relapse of acute lymphoblastic leukemia. J Hematol Oncol (2018) 11(1):25. doi: 10.1186/s13045-018-0572-x

  • CrossRef
  • Google Scholar

• 258

  MatsumotoMTakedaYTatematsuMSeyaT. Toll-like receptor 3 signal in dendritic cells benefits cancer immunotherapy. Front Immunol (2017) 8:1897. doi: 10.3389/fimmu.2017.01897

  • CrossRef
  • Google Scholar

• 259

  TakemuraRTakakiHOkadaSShimeHAkazawaTOshiumiHet al. Polyi:C-induced, Tlr3/Rip3-dependent necroptosis backs up immune effector-mediated tumor elimination in vivo. Cancer Immunol Res (2015) 3(8):902–14. doi: 10.1158/2326-6066.Cir-14-0219

  • CrossRef
  • Google Scholar

• 260

  FanLZhouPHongQChenAXLiuGYYuKDet al. Toll-like receptor 3 acts as a suppressor gene in breast cancer initiation and progression: A two-stage association study and functional investigation. Oncoimmunology (2019) 8(6):e1593801. doi: 10.1080/2162402x.2019.1593801

  • CrossRef
  • Google Scholar

• 261

  YonedaKSugimotoKShirakiKTanakaJBeppuTFukeHet al. Dual topology of functional toll-like receptor 3 expression in human hepatocellular carcinoma: Differential signaling mechanisms of Tlr3-induced nf-kappab activation and apoptosis. Int J Oncol (2008) 33(5):929–36. doi: 10.3892/ijo_00000080

  • CrossRef
  • Google Scholar

• 262

  GambaraGDesideriMStoppacciaroAPadulaFDe CesarisPStaraceDet al. Tlr3 engagement induces irf-3-Dependent apoptosis in androgen-sensitive prostate cancer cells and inhibits tumour growth in vivo. J Cell Mol Med (2015) 19(2):327–39. doi: 10.1111/jcmm.12379

  • CrossRef
  • Google Scholar

• 263

  BergéMBonninPSulpiceEVilarJAllanicDSilvestreJSet al. Small interfering rnas induce target-independent inhibition of tumor growth and vasculature remodeling in a mouse model of hepatocellular carcinoma. Am J Pathol (2010) 177(6):3192–201. doi: 10.2353/ajpath.2010.100157

  • CrossRef
  • Google Scholar

• 264

  YoshidaSShimeHTakedaYNamJMTakashimaKMatsumotoMet al. Toll-like receptor 3 signal augments radiation-induced tumor growth retardation in a murine model. Cancer Sci (2018) 109(4):956–65. doi: 10.1111/cas.13543

  • CrossRef
  • Google Scholar

• 265

  GriffithsEASrivastavaPMatsuzakiJBrumbergerZWangESKocentJet al. Ny-Eso-1 vaccination in combination with decitabine induces antigen-specific T-lymphocyte responses in patients with myelodysplastic syndrome. Clin Cancer research: an Off J Am Assoc Cancer Res (2018) 24(5):1019–29. doi: 10.1158/1078-0432.Ccr-17-1792

  • CrossRef
  • Google Scholar

• 266

  DillonPMPetroniGRSmolkinMEBreninDRChianese-BullockKASmithKTet al. A pilot study of the immunogenicity of a 9-peptide breast cancer vaccine plus poly-iclc in early stage breast cancer. J immunotherapy Cancer (2017) 5(1):92. doi: 10.1186/s40425-017-0295-5

  • CrossRef
  • Google Scholar

• 267

  ApetohLGhiringhelliFTesniereAObeidMOrtizCCriolloAet al. Toll-like receptor 4-dependent contribution of the immune system to anticancer chemotherapy and radiotherapy. Nat Med (2007) 13(9):1050–9. doi: 10.1038/nm1622

  • CrossRef
  • Google Scholar

• 268

  NaseemuddinMIqbalANastiTHGhandhiJLKapadiaADYusufN. Cell mediated immune responses through Tlr4 prevents dmba-induced mammary carcinogenesis in mice. Int J Cancer (2012) 130(4):765–74. doi: 10.1002/ijc.26100

  • CrossRef
  • Google Scholar

• 269

  OkamotoMOshikawaTTanoTOheGFuruichiSNishikawaHet al. Involvement of toll-like receptor 4 signaling in interferon-gamma production and antitumor effect by streptococcal agent ok-432. J Natl Cancer Inst (2003) 95(4):316–26. doi: 10.1093/jnci/95.4.316

  • CrossRef
  • Google Scholar

• 270

  YusufNNastiTHLongJANaseemuddinMLucasAPXuHet al. Protective role of toll-like receptor 4 during the initiation stage of cutaneous chemical carcinogenesis. Cancer Res (2008) 68(2):615–22. doi: 10.1158/0008-5472.CAN-07-5219

  • CrossRef
  • Google Scholar

• 271

  D’AgostiniCPicaFFebbraroGGrelliSChiavaroliCGaraciE. Antitumour effect of om-174 and cyclophosphamide on murine B16 melanoma in different experimental conditions. Int Immunopharmacol (2005) 5(7-8):1205–12. doi: 10.1016/j.intimp.2005.02.013

  • CrossRef
  • Google Scholar

• 272

  HussainSJohnsonCGSciurbaJMengXStoberVPLiuCet al. Tlr5 participates in the Tlr4 receptor complex and promotes Myd88-dependent signaling in environmental lung injury. Elife (2020) 9:e50458. doi: 10.7554/eLife.50458

  • CrossRef
  • Google Scholar

• 273

  FaberETedinKSpeidelYBrinkmannMMJosenhansC. Functional expression of Tlr5 of different vertebrate species and diversification in intestinal pathogen recognition. Sci Rep (2018) 8(1):11287. doi: 10.1038/s41598-018-29371-0

  • CrossRef
  • Google Scholar

• 274

  JiangWHanYLiangTZhangCGaoFHouG. Down-regulation of toll-like receptor 5 (Tlr5) increased vegfr expression in triple negative breast cancer (Tnbc) based on radionuclide imaging. Front Oncol (2021) 11:708047. doi: 10.3389/fonc.2021.708047

  • CrossRef
  • Google Scholar

• 275

  ShiDLiuWZhaoSZhangCLiangTHouG. Tlr5 is a new reporter for triple-negative breast cancer indicated by radioimmunoimaging and fluorescent staining. J Cell Mol Med (2019) 23(12):8305–13. doi: 10.1111/jcmm.14707

  • CrossRef
  • Google Scholar

• 276

  MettVKomarovaEAGreeneKBespalovIBrackettCGillardBet al. Mobilan: A recombinant adenovirus carrying toll-like receptor 5 self-activating cassette for cancer immunotherapy. Oncogene (2018) 37(4):439–49. doi: 10.1038/onc.2017.346

  • CrossRef
  • Google Scholar

• 277

  MettVKurnasovOVBespalovIAMolodtsovIBrackettCMBurdelyaLGet al. A deimmunized and pharmacologically optimized toll-like receptor 5 agonist for therapeutic applications. Commun Biol (2021) 4(1):466–. doi: 10.1038/s42003-021-01978-6

  • CrossRef
  • Google Scholar

• 278

  EreminaNVKazeyVIMishuginSVLeonenkovRVPushkarDYMettVLet al. First-in-Human study of anticancer immunotherapy drug candidate mobilan: Safety, pharmacokinetics and pharmacodynamics in prostate cancer patients. Oncotarget (2020) 11(14):1273–88. doi: 10.18632/oncotarget.27549

  • CrossRef
  • Google Scholar

• 279

  McGowanDC. Latest advances in small molecule tlr 7/8 agonist drug research. Curr Top Med Chem (2019) 19(24):2228–38. doi: 10.2174/1568026619666191009165418

  • CrossRef
  • Google Scholar

• 280

  SpanerDEShiYWhiteDMenaJHammondCTomicJet al. Immunomodulatory effects of toll-like receptor-7 activation on chronic lymphocytic leukemia cells. Leukemia (2006) 20(2):286–95. doi: 10.1038/sj.leu.2404061

  • CrossRef
  • Google Scholar

• 281

  ClarkRAHuangSJMurphyGFMolletIGHijnenDMuthukuruMet al. Human squamous cell carcinomas evade the immune response by down-regulation of vascular e-selectin and recruitment of regulatory T cells. J Exp Med (2008) 205(10):2221–34. doi: 10.1084/jem.20071190

  • CrossRef
  • Google Scholar

• 282

  MichaelisKANorgardMAZhuXLevasseurPRSivagnanamSLiudahlSMet al. The Tlr7/8 agonist R848 remodels tumor and host responses to promote survival in pancreatic cancer. Nat Commun (2019) 10(1):4682. doi: 10.1038/s41467-019-12657-w

  • CrossRef
  • Google Scholar

• 283

  YeJMaCHsuehECDouJMoWLiuSet al. Tlr8 signaling enhances tumor immunity by preventing tumor-induced T-cell senescence. EMBO Mol Med (2014) 6(10):1294–311. doi: 10.15252/emmm.201403918

  • CrossRef
  • Google Scholar

• 284

  ParkIUIntrocasoCDunneEF. Human papillomavirus and genital warts: A review of the evidence for the 2015 centers for disease control and prevention sexually transmitted diseases treatment guidelines. Clin Infect diseases: an Off Publ Infect Dis Soc America (2015) 61 Suppl 8:S849–55. doi: 10.1093/cid/civ813

  • CrossRef
  • Google Scholar

• 285

  PerisKFargnoliMCGarbeCKaufmannRBastholtLSeguinNBet al. Diagnosis and treatment of basal cell carcinoma: European consensus-based interdisciplinary guidelines. Eur J Cancer (Oxford England: 1990) (2019) 118:10–34. doi: 10.1016/j.ejca.2019.06.003

  • CrossRef
  • Google Scholar

• 286

  PatelGKGoodwinRChawlaMLaidlerPPricePEFinlayAYet al. Imiquimod 5% cream monotherapy for cutaneous squamous cell carcinoma in situ (Bowen’s disease): A randomized, double-blind, placebo-controlled trial. J Am Acad Dermatol (2006) 54(6):1025–32. doi: 10.1016/j.jaad.2006.01.055

  • CrossRef
  • Google Scholar

• 287

  ChowLQMMorishimaCEatonKDBaikCSGoulartBHAndersonLNet al. Phase ib trial of the toll-like receptor 8 agonist, motolimod (Vtx-2337), combined with cetuximab in patients with recurrent or metastatic scchn. Clin Cancer research: an Off J Am Assoc Cancer Res (2017) 23(10):2442–50. doi: 10.1158/1078-0432.Ccr-16-1934

  • CrossRef
  • Google Scholar

• 288

  DummerRHauschildABeckerJCGrobJJSchadendorfDTebbsVet al. An exploratory study of systemic administration of the toll-like receptor-7 agonist 852a in patients with refractory metastatic melanoma. Clin Cancer research: an Off J Am Assoc Cancer Res (2008) 14(3):856–64. doi: 10.1158/1078-0432.Ccr-07-1938

  • CrossRef
  • Google Scholar

• 289

  GellerMACooleySArgentaPADownsLSCarsonLFJudsonPLet al. Toll-like receptor-7 agonist administered subcutaneously in a prolonged dosing schedule in heavily pretreated recurrent breast, ovarian, and cervix cancers. Cancer immunology immunotherapy: CII (2010) 59(12):1877–84. doi: 10.1007/s00262-010-0914-1

  • CrossRef
  • Google Scholar

• 290

  WeigelBJCooleySDeForTWeisdorfDJPanoskaltsis-MortariAChenWet al. Prolonged subcutaneous administration of 852a, a novel systemic toll-like receptor 7 agonist, to activate innate immune responses in patients with advanced hematologic malignancies. Am J Hematol (2012) 87(10):953–6. doi: 10.1002/ajh.23280

  • CrossRef
  • Google Scholar

• 291

  DudekAZYunisCHarrisonLIKumarSHawkinsonRCooleySet al. First in human phase I trial of 852a, a novel systemic toll-like receptor 7 agonist, to activate innate immune responses in patients with advanced cancer. Clin Cancer research: an Off J Am Assoc Cancer Res (2007) 13(23):7119–25. doi: 10.1158/1078-0432.Ccr-07-1443

  • CrossRef
  • Google Scholar

• 292

  FregaGWuQLe NaourJVacchelliEGalluzziLKroemerGet al. Trial watch: Experimental Tlr7/Tlr8 agonists for oncological indications. Oncoimmunology (2020) 9(1):1796002. doi: 10.1080/2162402x.2020.1796002

  • CrossRef
  • Google Scholar

• 293

  KumagaiYTakeuchiOAkiraS. Tlr9 as a key receptor for the recognition of DNA. Advanced Drug delivery Rev (2008) 60(7):795–804. doi: 10.1016/j.addr.2007.12.004

  • CrossRef
  • Google Scholar

• 294

  KangTHMaoCPKimYSKimTWYangALamBet al. Tlr9 acts as a sensor for tumor-released DNA to modulate anti-tumor immunity after chemotherapy. J immunotherapy Cancer (2019) 7(1):260. doi: 10.1186/s40425-019-0738-2

  • CrossRef
  • Google Scholar

• 295

  KriegAM. Toll-like receptor 9 (Tlr9) agonists in the treatment of cancer. Oncogene (2008) 27(2):161–7. doi: 10.1038/sj.onc.1210911

  • CrossRef
  • Google Scholar

• 296

  KayrakliogluNHoruluogluBKlinmanDM. Cpg oligonucleotides as vaccine adjuvants. Methods Mol Biol (2021) 2197:51–85. doi: 10.1007/978-1-0716-0872-2_4

  • CrossRef
  • Google Scholar

• 297

  LeonardJPLinkBKEmmanouilidesCGregorySAWeisdorfDAndreyJet al. Phase I trial of toll-like receptor 9 agonist pf-3512676 with and following rituximab in patients with recurrent indolent and aggressive non hodgkin’s lymphoma. Clin Cancer research: an Off J Am Assoc Cancer Res (2007) 13(20):6168–74. doi: 10.1158/1078-0432.Ccr-07-0815

  • CrossRef
  • Google Scholar

• 298

  van PuffelenJHKeatingSTOosterwijkEvan der HeijdenAGNeteaMGJoostenLABet al. Trained immunity as a molecular mechanism for bcg immunotherapy in bladder cancer. Nat Rev Urol (2020) 17(9):513–25. doi: 10.1038/s41585-020-0346-4

  • CrossRef
  • Google Scholar

• 299

  TheodorakiMNYerneniSSarkarSNOrrBMuthuswamyRVoytenJet al. Helicase-driven activation of nfκb-Cox2 pathway mediates the immunosuppressive component of dsrna-driven inflammation in the human tumor microenvironment. Cancer Res (2018) 78(15):4292–302. doi: 10.1158/0008-5472.Can-17-3985

  • CrossRef
  • Google Scholar

• 300

  FengYChenYMengYCaoQLiuQLingCet al. Bufalin suppresses migration and invasion of hepatocellular carcinoma cells elicited by poly (I:C) therapy. Oncoimmunology (2018) 7(5):e1426434. doi: 10.1080/2162402x.2018.1426434

  • CrossRef
  • Google Scholar

• 301

  GalluzziLVacchelliEEggermontAFridmanWHGalonJSautès-FridmanCet al. Trial watch. Oncoimmunology (2012) 1(5):699–739. doi: 10.4161/onci.20696

  • CrossRef
  • Google Scholar

• 302

  TranTHTranTTPTruongDHNguyenHTPhamTTYongCSet al. Toll-like receptor-targeted particles: A paradigm to manipulate the tumor microenvironment for cancer immunotherapy. Acta biomaterialia (2019) 94:82–96. doi: 10.1016/j.actbio.2019.05.043

  • CrossRef
  • Google Scholar

• 303

  KondoTKawaiTAkiraS. Dissecting negative regulation of toll-like receptor signaling. Trends Immunol (2012) 33(9):449–58. doi: 10.1016/j.it.2012.05.002

  • CrossRef
  • Google Scholar

• 304

  BhagchandaniSJohnsonJAIrvineDJ. Evolution of toll-like receptor 7/8 agonist therapeutics and their delivery approaches: From antiviral formulations to vaccine adjuvants. Advanced Drug delivery Rev (2021) 175:113803. doi: 10.1016/j.addr.2021.05.013

  • CrossRef
  • Google Scholar

• 305

  BagchiAHerrupEAWarrenHSTrigilioJShinHSValentineCet al. Myd88-dependent and Myd88-independent pathways in synergy, priming, and tolerance between tlr agonists. J Immunol (Baltimore Md: 1950) (2007) 178(2):1164–71. doi: 10.4049/jimmunol.178.2.1164

  • CrossRef
  • Google Scholar

• 306

  MichaelisKANorgardMALevasseurPROlsonBBurfeindKGBuenafeACet al. Persistent toll-like receptor 7 stimulation induces behavioral and molecular innate immune tolerance. Brain behavior Immun (2019) 82:338–53. doi: 10.1016/j.bbi.2019.09.004

  • CrossRef
  • Google Scholar

• 307

  HayashiTGrayCSChanMTawataoRIRonacherLMcGargillMAet al. Prevention of autoimmune disease by induction of tolerance to toll-like receptor 7. Proc Natl Acad Sci U.S.A. (2009) 106(8):2764–9. doi: 10.1073/pnas.0813037106

  • CrossRef
  • Google Scholar

• 308

  ButcherSKO’CarrollCEWellsCACarmodyRJ. Toll-like receptors drive specific patterns of tolerance and training on restimulation of macrophages. Front Immunol (2018) 9:933(933). doi: 10.3389/fimmu.2018.00933

  • CrossRef
  • Google Scholar

• 309

  NahidMASatohMChanEK. Microrna in tlr signaling and endotoxin tolerance. Cell Mol Immunol (2011) 8(5):388–403. doi: 10.1038/cmi.2011.26

  • CrossRef
  • Google Scholar

• 310

  BourquinCHotzCNoerenbergDVoelklAHeideggerSRoetzerLCet al. Systemic cancer therapy with a small molecule agonist of toll-like receptor 7 can be improved by circumventing tlr tolerance. Cancer Res (2011) 71(15):5123. doi: 10.1158/0008-5472.CAN-10-3903

  • CrossRef
  • Google Scholar

• 311

  TsitouraDAmberyCPriceMPowleyWGarthsideSBiggadikeKet al. Early clinical evaluation of the intranasal Tlr7 agonist Gsk2245035: Use of translational biomarkers to guide dosing and confirm target engagement. Clin Pharmacol Ther (2015) 98(4):369–80. doi: 10.1002/cpt.157

  • CrossRef
  • Google Scholar

• 312

  Vanpouille-BoxCHoffmannJAGalluzziL. Pharmacological modulation of nucleic acid sensors - therapeutic potential and persisting obstacles. Nat Rev Drug Discovery (2019) 18:845–67. doi: 10.1038/s41573-019-0043-2

  • CrossRef
  • Google Scholar

• 313

  MitraAMishraLLiS. Technologies for deriving primary tumor cells for use in personalized cancer therapy. Trends Biotechnol (2013) 31(6):347–54. doi: 10.1016/j.tibtech.2013.03.006

  • CrossRef
  • Google Scholar