Abstract
Influenza A viruses (IAVs) circulate widely among different mammalian and avian hosts and sometimes give rise to zoonotic infections. Vaccination is a mainstay of IAV prevention and control. However, the efficacy of IAV vaccines is often suboptimal because of insufficient cross-protection among different IAV genotypes and subtypes as well as the inability to keep up with the rapid molecular evolution of IAV strains. Much attention is focused on improving IAV vaccine efficiency using adjuvants, which are substances that can modulate and enhance immune responses to co-administered antigens. The current review is focused on a non-traditional approach of adjuvanting IAV vaccines by therapeutically targeting the immunomodulatory functions of a rare population of innate-like T lymphocytes called invariant natural killer T (iNKT) cells. These cells bridge the innate and adaptive immune systems and are capable of stimulating a wide array of immune cells that enhance vaccine-mediated immune responses. Here we discuss the factors that influence the adjuvant effects of iNKT cells for influenza vaccines as well as the obstacles that must be overcome before this novel adjuvant approach can be considered for human or veterinary use.
Introduction
Influenza A viruses (IAVs) are a genetically diverse group of segmented RNA viruses capable of infecting birds and mammals, including swine, bats, and humans (1–3). IAV infections result in a highly contagious acute respiratory disease that is capable of causing substantial morbidity but usually low mortality (4, 5). IAVs are a significant burden to human and animal health and have the potential to occasionally cause pandemics. Vaccination is a cornerstone of IAV mitigation. However, the high genetic/antigenic diversity of IAVs, which is a result of (i) the rapid IAV mutation rates (“genetic drift”) and (ii) the reassortment ability between genetically different IAV strains (“genetic shift”), inherently limits vaccine effectiveness (6). The genetic evolution of IAVs by genetic drift and shift associated with the heterogeneous and complex immune response to influenza vaccines requires annual updates of human IAV vaccines and often results in vaccine failure (2, 7). For example, the 2018–2019 influenza vaccines for humans were reported to have an estimated vaccine effectiveness of 29% (8), based on the relative difference in influenza risk between vaccinated and unvaccinated participants (9). This low effectiveness was due to the circulation of an influenza H3N2 virus which was antigenically drifted from the H3N2 virus isolate included in the vaccine (8). The use of adjuvants that increase the scope, scale, and quality of innate and adaptive immune responses can improve the effectiveness of IAV vaccines significantly (10). Most adjuvants fall into two categories. The first is delivery systems that enhance antigen release, stability, and uptake (11). The second uses immune stimulatory molecules, such as Toll-like receptor ligands, that induce the release of cytokines and chemokines from innate immune cells, which drives antigen-presenting cell (APC) maturation and licensing and, therefore, improves immunogenicity of the respective antigens (12).
Although conventional adjuvants can stimulate cellular and humoral immune responses and reduce the antigen dose required in the vaccine, they seldom improve long-term immunity and cross-reactivity against heterologous (i.e., belong to the same subtype but are genetically different IAV isolates) and heterosubtypic (i.e., belong to different IAV subtypes) IAV strains, which is greatly needed (13). This has led researchers to explore using non-traditional adjuvants to improve vaccine efficacy, including the powerful immunoregulatory effects of innate T lymphocyte populations, such as γδT cells, and CD1- and MR-1-resticted T cells. Unlike the major histocompatibility complex (MHC)-restricted T cells, these cells possess a restricted repertoire of T cell receptors (TCR), perform rapid effector responses, and recognize a limited selection of non-peptide molecules, including small metabolites and lipids (14). Currently, the innate T cell population with the most potential to enhance vaccines is natural killer T (NKT) cells, which recognize lipid and glycolipid ligands presented by the MHC class I-like molecule CD1d (14). These cells have phenotypic characteristics of both T cells and NK cells and express a semi-invariant TCR (14). Upon activation, NKT cells rapidly release large quantities of multiple cytokines and chemokines capable of boosting adaptive immune responses. Importantly, a subset of NKT cells known as type I or invariant NKT (iNKT) cells that express an invariant αβ TCR, can be globally and specifically activated using derivatives of the prototypic antigen known as (2S,3S,4R)-1-O-(α-D-galactopyranosyl)-N-hexacosanoyl-2-amino-1,3,4-octadecanetriol, also called α-galactosylceramide (α-GalCer), which was first isolated from a marine sponge (Agelas mauritianus) (15, 16). Activation with α-GalCer induces iNKT cells to generate a potent immune response to a wide range of co-delivered antigens.
Since the discovery of α-GalCer, numerous studies have explored how iNKT cell responses can adjuvant vaccines against different infectious diseases [reviewed in (17–20)]. However, most of these studies have used the mouse model of IAV infection, largely because it is well-established and easy to work with. These studies have almost invariably reported that iNKT cells are capable of substantially enhancing the quality and the scale of IAV vaccine responses (21–33). In this review, we summarize the current knowledge about therapeutically harnessing iNKT cell activities to improve IAV vaccines in mice and other animal models. We also address important factors that influence the adjuvant effects of therapeutically activated iNKT cells, which must be considered to safely and effectively exploit the adjuvant potential of iNKT cells for human or livestock vaccines.
NKT Cell Characteristics
Although the name “natural killer T cell” first appeared in the literature in 1995 (34), these cells were first described in 1987 as a subset of T cells with moderate levels of αβ TCRs and NK1.1, a marker characteristic of natural killer cells (35–38). Over the subsequent decade, it was established that NKT cells express a highly restricted TCR repertoire (39), produce developmentally regulated Th1 and Th2 cytokines (40), bind CD1d as their antigen presenting molecule (41), and recognize glycolipid/lipid ligands (15, 42). It was further discovered that NKT cells can be divided into two functionally distinct classes: type I and type II NKT cells (43). Type I NKT or iNKT cells express a highly restricted TCR repertoire which recognizes CD1d-bound α-GalCer (44, 45). Type II NKT cells, also known as diverse NKT cells, express a less restricted TCR repertoire and recognize different glycolipids than iNKT cells, such as sulfatides (46). This review will discuss iNKT cells as it is this subset which can be therapeutically targeted using glycolipid antigens.
iNKT cells recognize both endogenous and exogenous ligands (42). Their recognition of endogenous ligands enables iNKT cells to interact with inflamed or injured tissues which overexpress lipid molecules (47). Most exogenous iNKT cell antigens are glycolipid and phospholipid components of bacterial cell walls, such as mycobacterial phosphatidylinositolmannosides and monoglycosylceramides from gram-negative bacteria (42, 48). iNKT cells also respond to antigens from protozoan parasites, including phospholipids from Leishmania and glycophosphatidylinositol from Plasmodium and Trypanosoma (49, 50). iNKT cells in most species react to α-GalCer and its synthetic analog KRN7000 (51–53). These molecules have been widely used to study iNKT cell function since they strongly activate these cells. α-GalCer stimulated mouse iNKT cells produce a wide variety of cytokines, including IFN-γ, IL-2, IL-3, IL-4, IL-5, IL-9, IL-10, IL-13, IL-17, IL-21, IL-22, and tumor necrosis factor (TNF)-α and -β (54–57). Stimulated mouse iNKT cells also secrete chemokines, including RANTES (regulated on activation, normal T cell expressed and secreted), monocyte chemoattractant protein (MCP)-1, eotaxins, and macrophage inflammatory protein (MIP)-1α and MIP-1β (58–61). Many of these cytokines modulate cellular and humoral immune responses against foreign antigens, which is why α-GalCer activated iNKT cells can enhance the scale and the scope of vaccine responses against a wide variety of pathogens.
iNKT CELL-CD1d System in Mammals
The defining feature of iNKT cells is the expression of a TCR with an invariant Vα chain rearrangement and limited Vβ chain usage. Mouse iNKT cells express a single α chain (Vα14-Jα18) that is paired with a limited number of Vβ chains (Vβ2, Vβ7, or Vβ8.2) (39, 62, 63). Rats use a homologous Vα14-Jα18 rearrangement paired with Vβ8.2 chains but have four Vα14 genes with differential tissue expression (64). The human invariant receptor is composed of a Vα24-Jα18 rearrangement paired with Vβ11 (39, 65, 66), while the porcine iNKT TCR is composed of a Vα10-Jα18 chain paired with a Vβ25-chain, both of which are highly homologous to the human Vα24-Jα18 and Vβ11 TCR chains (67). A consequence of the remarkably conserved nature of the TCR-CD1d system is that CD1d tetramers often cross-react among different animal species. For instance, human CD1d tetramers cross-react with mouse iNKT cells and vice versa (45), and both mouse and human CD1d tetramers cross-react with pig iNKT cells (68). Interestingly, rat iNKT cells are only partially identified by mouse CD1d tetramers and require the use of rat CD1d molecules in glycolipid-loaded tetramers (69). Overall, the CD1d-mediated recognition of α-GalCer by iNKT cells is highly conserved through mammalian evolution (70). This has the advantage that many aspects of glycolipid therapy research in preclinical mouse models can be directly translated to target animal species, including humans.
Not all mammals harbor CD1d genes in their genomes, and some that do, do not express functional transcripts and/or CD1d proteins that are capable of interacting with iNKT cells. Humans (71), primates (72, 73), mice (15), rats (64), cotton rats (74), pigs (75, 76), and dogs (77) have been reported to possess functional iNKT cell-CD1d systems and iNKT cells that react to α-GalCer. Ruminants were thought to harbor two copies of CD1d that are pseudogenes (CD1d1 and CD1d2) due to a mutated start codon and a first intron that cannot be translated into functional proteins (78, 79). However, it was later discovered that the bovine CD1d1 gene has an alternative start codon that produces CD1d proteins capable of being expressed on the cell surface (80). Interestingly, the antigen binding site in bovine CD1d1 is smaller than in human and mouse CD1d proteins, which prohibits α-GalCer from binding. Instead, bovine CD1d1 appears to present glycolipids with shorter alkyl chains than α-GalCer (80, 81). The sequences of the equine iNKT invariant α-chain TCR and CD1d have conserved residues that align with their human and mouse counterparts. Nevertheless, equine iNKT cells have yet to be isolated and horses do not respond to synthetic glycolipids that activate iNKT cells in other species (82).
Mechanisms of iNKT Cell Activation
iNKT cells can be directly activated by TCR signaling after engaging CD1d-bound glycolipid antigens, or indirectly via cytokines from pathogen recognition receptor-stimulated APCs. Indirect activation sometimes involves weak TCR signals from low-affinity microbial or self-lipid antigens but can also occur in the absence of TCR stimulation (83–88). Directly activated mouse iNKT cells secrete a mixture of Th1 and Th2 cytokines, which differs from iNKT cells indirectly activated through pro-inflammatory cytokines that mainly produce Th1-type cytokines (89, 90). The variety and the quantity of cytokines produced by directly activated iNKT cells depend on the strength of the interactions between the iNKT TCR and the lipid-CD1d complex (43, 83, 91, 92). However, additional factors, including different iNKT cell subsets, the half-life of TCR-ligand binding, ligand density, and the uptake and presentation of iNKT cell-activating glycolipids by APCs, may play a role in determining their cytokine bias (93–97). α-GalCer strongly activates iNKT cells, which induces the rapid upregulation of T cell activation markers and the secretion of several cytokines, especially IFN-γ, IL-2, and IL-4 within hours after stimulation. α-GalCer activated iNKT cells also proliferate and may expand up to 10-fold in some organs by 4 days post-treatment, after which they contract to baseline levels (98, 99). Unlike conventional T cells, iNKT cells do not possess memory functions. In fact, secondary α-GalCer administration actually results in a significantly weaker iNKT cell response compared to primary stimulation with this antigen, characterized by reduced proliferation and cytokine secretion (100, 101). This hyporesponsive state lasts for at least 1 month after initial activation (101–103). The same hyporesponsive state has been reported in mice challenged with bacterial pathogens (104–106), toxins (107), and TLR agonists (104). The response of iNKT cells to α-GalCer have been studied most extensively in mice. However, in vivo studies in humans, chimpanzees, macaques, swine, and cotton rats have found that α-GalCer can stimulate iNKT cell activities in a wide variety of mammals.
iNKT cells indirectly activated by APCs participate in immune responses against numerous microorganisms that lack cognate lipid antigens. Various pathogen-associated molecular patterns (PAMPs) and some danger-associated molecular patterns (DAMPs) have been shown to induce iNKT cell-activating cytokines (108–112), such as type I interferons, IL-12, IL-18, and IL-33 (88, 90, 113–115). Interleukin-12 signaling appears to be particularly important as iNKT cells express high baseline levels of the IL-12 receptor (116). Many bacterial and viral infections stimulate sufficient IL-12 to activate iNKT cells with low-affinity endogenous ligands or without TCR signaling (88, 89, 113, 117, 118). Indirect iNKT cell activation may also be induced by IFN-α and IFN-β from TLR-7- and TLR-9-activated APCs (113) or by a combination of IL-12 and IL-18, which are produced by TLR-4- and TLR-9-stimulated APCs (88, 90, 114). iNKT cells can also be activated via their NK receptors that provide both activation and regulation signals in response to stress-induced ligands (119–121). Indirectly activated iNKT cells develop distinct effector functions compared to directly activated iNKT cells. One important difference is that a large fraction of cytokine-activated iNKT cells acquire the ability to express perforin that may allow them to carry out cytolytic functions in vivo (54). Furthermore, indirectly activated iNKT cells secrete large quantities of IFN-γ without IL-4, whereas directly activated iNKT cells often produce both cytokines simultaneously (122). The weak TCR signaling that occurs during indirect iNKT cell activation promotes IFN-γ production by inducing histone H4 acetylation near the IFN-γ locus. This enables iNKT cells to produce IFN-γ upon subsequent exposure to IL-12 and IL-18 without concurrent TCR stimulation (114). Unlike during direct activation, iNKT cells remain motile during stimulation with cytokines, which may enable them to disseminate IFN-γ as they migrate, amplifying their impact on immune responses (114). It is likely that IAV vaccines trigger several indirect activation-mediated iNKT cell effector functions and that some of these responses will support (or perhaps counteract) the direct activation effects of co-delivered glycolipid antigens. In this scenario, achieving optimal IAV vaccine immunity will require studies to evaluate combining different dosages of iNKT cell agonists and IAV vaccines.
Helper Functions of iNKT Cells
iNKT cells are capable of generating immune responses that in many ways mirror conventional CD4+ T cell help (Figure 1). Activated iNKT cells induce APCs to mature when they engage antigen-bound CD1d on their surface (123). These iNKT cell-conditioned APCs, in turn, produce cytokines and T cell costimulatory molecules that further prime iNKT cells, causing them to upregulate CD40L, and secrete IFN-γ and granulocyte-macrophage colony-stimulating factor. This induces surrounding APCs to mature and activate additional iNKT cells (113, 123, 124). iNKT cell-licensed APCs prime conventional CD4+ T cells against co-delivered peptide antigens, which results in enhanced cytotoxic CD8+ T cell responses and induces CD4+ T cells to become follicular helper T (TFH) cells. iNKT cell-conditioned APCs also acquire the ability to cross-present peptide antigens to CD8+ T cells (125–127). The mechanisms through which iNKT cells enhance humoral immune responses have been extensively reviewed (128–132). One mode involves iNKT cells directly interacting with B cells presenting glycolipid ligands on CD1d, which is referred to as cognate B cell help. Initially, iNKT cells recognize glycolipid antigens on dendritic cells (DCs) and differentiate into iNKT follicular helper (iNKTFH) cells that adopt a phenotype similar to TFH cells (133, 134). These iNKTFH cells then activate B cells specific for protein antigens through a process that requires CD1d expression by B cells, B7-1/B7-2, and CD40 ligation by the iNKT cells and the secretion of IFN-γ and IL-21. Cognate B cell help stimulates plasmablast expansion, germinal center formation, antibody class switching, and moderate affinity maturation (135, 136). iNKT cells can also provide non-cognate B cell help which occurs when iNKT cells indirectly activate B cells by inducing TFH cells specific for protein antigens displayed by B cells (137). This mode of activation is thought to drive enhanced antibody production when α-GalCer is co-administered with immunizing antigens; protein and α-GalCer are internalized by DCs that simultaneously present peptide fragments of the protein antigen on MHC class II to naïve CD4+ T cells and α-GalCer on CD1d to iNKT cells. The TFH cells that result provide CD1d-independent antigen-specific help for the proliferation of B cells in germinal centers, antibody class switching, affinity maturation, and the generation of plasma cells and memory B cells. In addition, activated iNKT cells trans-activate NK cells to produce large quantities of IFN-γ that stimulate B cells to secrete IgG (138). Non-cognate B cell help is probably important after virus exposure when iNKT cells may shape B cell responses by producing an early wave of IL-4 that seeds germinal centers and activates antigen-experienced B cells (139).
Figure 1
Invariant natural killer T cells activate and regulate innate and adaptive immune responses that enhance influenza A virus (IAV) vaccine immunity. The co-administered IAV vaccine antigens and the selected α-GalCer analog are internalized by dendritic cells that simultaneously present the α-GalCer analog on CD1d to iNKT cells and IAV epitopes on major histocompatibility complex (MHC) II to CD4+ T cells. Cytokines secreted by iNKT cells increase MHC class II and CD40 presentation to naïve CD4+ T cells, which generates follicular T helper cells (TFH) that provide non-cognate help to B cells. iNKT cells also undergo indirect activation in response to proinflammatory cytokines released by IAV-stimulated antigen-presenting cells (APCs), with or without engagement of the iNKT TCR by CD1d-presented self-antigens. iNKT cell-licensed dendritic cells (DCs) generate vaccine-specific CD8+ T cells which become further activated by cytokines secreted by α-GalCer and IAV-stimulated APCs as well as iNKT cells and CD4+ T cells. The iNKT cells recognizing α-GalCer on DCs differentiate into iNKT follicular helper (iNKTFH) cells that provide cognate help to B cells specific for vaccine antigens. iNKT cells also boost humoral immunity by trans-activating natural killer cells that can stimulate B cells to secrete immunoglobulin G.
The benefit of eliciting T helper responses via iNKT cells compared to CD4+ T cells is that iNKT cells constitute a much greater fraction of total T cells than any antigen-specific CD4+ T cell clone (140, 141). Furthermore, iNKT cells can be globally and specifically activated using α-GalCer analogs due to the highly non-polymorphic CD1d molecule (67, 78, 142). Conversely, conventional CD4+ T cells are restricted by the high level of inter-individual MHC class II polymorphism, which limits the efficacy of peptide-based vaccines in outbred populations. Co-administering iNKT cell ligands with vaccines that induce a wide array of conventional T helper cell responses has the potential to induce wide-ranging cellular and humoral immune responses capable of greatly improving the durability and the cross-protection of vaccines, including against IAVs.
Role of iNKT Cells in Immunity to IAV Infections
Mice lacking iNKT cells are more susceptible to IAV infections than iNKT cell-intact mice (143–146), indicating that these cells contribute to IAV immunity. iNKT cell activation is likely through the indirect pathway as IAVs contain no known iNKT cell ligands. Nevertheless, stimulation may be enhanced by interactions with CD1d-bound endogenous glycolipids which often increase after viral infection (147). iNKT cells migrate to the lungs during the early stages of IAV infections, alongside the recruitment of neutrophils and the rapid induction of pro- and anti-inflammatory cytokines that prime immune cells, including iNKT cells (146, 148). Mouse studies have reported that airway-resident iNKT cells prevent virus replication and limit lung damage through a combination of (i) reducing the suppressive capacity of myeloid-derived suppressor cells that inhibit influenza-specific immune responses (143), (ii) activating lung-resident NK cells (145), and (iii) directly lysing IAV-infected monocytes (144). In addition, iNKT cells stimulated by IL-1β and IL-23 produce large amounts of IL-22 that protects the lung epithelium from influenza-mediated damage (149). iNKT cells have also been investigated for their role in shaping pre-existing immunity against re-infections with the same or heterologous influenza viruses. Benton et al. showed that CD1d knockout mice previously infected with A/Puerto Rico/8/34 (H1N1) or A/Philippines/2/82/X-79 (H3N2) and re-infected after 4 weeks with the correspondent homologous or heterologous H1N1 or H3N2 viruses were just as susceptible to re-infection as wildtype mice (150). These findings suggest that iNKT cell responses might be superfluous for generating immune memory or cross-protection after a natural IAV infection. This contrasts with other studies showing that therapeutically activated iNKT cells improve pre-existing immunity from IAV vaccination and suggests that immunity generated by iNKT cells might differ depending on whether they are activated indirectly during an IAV infection or via glycolipid antigens.
Studies Using iNKT Cell Agonists With IAV Vaccines
At least 17 publications have reported the effects of iNKT cell agonists for adjuvanting IAV vaccines (Table 1). Most of these studies have used mice because they are relatively inexpensive and compatible with a wide variety of vaccine formats. However, swine and non-human primates [pigtail macaques (Macaca nemestrina)] have also been tested. To our knowledge, Ko et al. were the first group to explore adjuvanting IAV vaccines with iNKT cell agonists (26). They reported that BALB/c mice intranasally co-administered with three doses (1 week apart) of α-GalCer and HA antigen derived from the mouse-adapted A/PR/8/34 (PR8, H1N1) IAV were much better protected from a lethal dose of the homologous virus than mice immunized with vaccine alone. α-GalCer induced greater levels of mucosal and systemic IgA and IgG antibodies. The same group later demonstrated that a single intranasal vaccination with inactivated PR8 and α-GalCer was sufficient to induce long-lasting PR8-specific IgG and IgA that protected mice from PR8 infection 3 months after the vaccination (22).
Table 1
| Animal model | Vaccination | Vaccine format | iNKT cell agonist (dose per animal) | Mode of action | References | |
|---|---|---|---|---|---|---|
| Route | Strain/subunit | |||||
| Mouse (BALB/c) | i.n. | H1N1 PR8 | Immunization with PR8 HA antigen with α-GalCer three times at 1-week intervals. Infection with 20 LD50 PR8 2 weeks after final immunization. | α-GalCer (0.125, 0.5, 2 μg) | α-GalCer induced mucosal secretory IgA as well as systemic IgG antibody responses against virus-derived antigen and reduced clinical signs. | (26) |
| Mouse (BALB/c) | i.n. | H1N1 PR8 | Immunization with inactivated PR8 with α-GalCer. Infection with 20 LD50 PR8 2 weeks and 3 months after immunization. | α-GalCer (0.5 μg) | α-GalCer induced both mucosal and systemic antibody responses, provided protective immunity against challenge with live PR8 and induced cytotoxic CD8+ T cells. | (22) |
| Mouse (BALB/c) | i.n./i.m. | H1N1 PR8 H1N1A/Yamagata H3N2A/Guizhou B/Ibaraki | Immunization with PR8, A/Yamagata, A/Guizhou, or B/Ibaraki HA vaccine with α-GalCer twice at 4 weeks apart. Infection with 40 LD50 PR8 2 weeks after the second immunization. | α-GalCer (2 μg) | i.n., not i.m., vaccination (PR8 and A/Yamagata) with α-GalCer boosted IgA and IgG and cross-protection against heterosubtypic virus infection. | (23) |
| Mouse (BALB/c) | i.n. | H1N1 PR8 | Immunization with PR8 with α-GalCer twice at 4 weeks apart. Infection with 40 LD50 A/Yamagata, A/Guizhou, or B/Ibaraki 2 weeks after the second immunization. | α-GalCer (2 μg) | i.n. vaccination with α-GalCer protected against challenge with homologous (A/PR8) and heterologous (A/Yamagata) viruses. | (23) |
| Mouse (BALB/c) | i.n. | H5N1 NIBRG14 | Immunization with NIBRG14 (H5N1) inactivated vaccine with α-GalCer twice, 4 weeks apart. Infection with 103 PFU of A/Vietnam (H5N1) or A/HK483 (H5N1) influenza virus 2 weeks after the second immunization. | α-GalCer (2 μg) | i.n. vaccination with α-GalCer increased nasal IgA and serum IgG and induced cross-protection against H5N1 influenza infection. | (23) |
| Mouse (BALB/c) | i.n. | H1N1 rNS1 1-73 | Immunization with live attenuated rNS1 1-73 with different amounts of α-C-GalCer. Infection with 100 LD50 PR8 3 weeks after the immunization. | α-C-GalCer (0.11, 0.33, 1, 2, 3, 4 μg) | α-C-GalCer used between 0.1 and 1 μg per mouse reduced mortality and morbidity. The adjuvant also increased the amount of influenza virus-specific total IgG, IgG1, and IgG2a antibodies as well as IFN-γ secreting CD8+ T cells. | (27) |
| Mouse (BALB/c) | i.n. | H1N1 PR8 | Immunization with inactivated PR8 with α-GalCer or α-GalCer analogs. Infection with 5 LD50 PR8 4 weeks after the immunization or 100 LD50 PR8 5 weeks after immunization. | α-GalCer (0.5 μg); KBC-007 (0.5 μg); KBC-009 (0.5 μg) | Co-immunization with α-GalCer, KBC-007 and KBC-009 increased PR8-specific systemic IgG and mucosal IgA. α-GalCer and KBC-009 (but not KBC-007) increased antigen-specific lymphocyte proliferation, cytokine production, and cytotoxic CD8+ T cell activity and induced complete protection from live virus infection. | (32) |
| Mouse (C57BL/6) | i.v. | H1N1 PR8-OVA257 | Immunization with SLP-conjugated vaccine PR8-OVA257 with α-GalCer. Infection with 104 PFU HKx31-OVA257 6–8 weeks after the immunization. | α-GalCer (76 ng) | α-GalCer-peptide conjugates induced OVA-specific T cell responses and protected against IAV infection. | (28) |
| Mice (C57BL/6) | i.m. | HA/NA from H3N2 PNM07 | Immunization with PNM07 protein and α-GalCer twice at 2 weeks apart. | α-GalCer (0.1 μg) | Immunization with H3N2 PNM07 plus α-GalCer increased titers of H3N2-specific antibodies. | (30) |
| Mouse (C57BL/6) | i.m. | HA/NA from H1N1 NC20 | Immunization with NC20 protein with α-GalCer twice at 2 weeks apart. Infection with 100 LD50 H1N1 A/WS/33 2 weeks after the second immunization. | α-GalCer (0.1 μg) | α-GalCer increased the survival rate after challenge. | (30) |
| Mouse (C57BL/6) | i.m. | H3N2 PNM07 | Immunization with H3N2 PNM07 protein with α-GalCer twice at 0 and 2 weeks, boosted with PNM07 at 30 weeks. | α-GalCer (0.1 μg) | Immunization with H3N2 PNM07 plus α-GalCer resulted in a higher antibody response and increased expansion of the antigen-specific memory B cells. | (30) |
| Mouse (C57BL/6) | s.c. | H1N1 PR8 | Immunization with inactivated PR8 with α-GalCer. Infection with 104 PFU of live H3N2 HKx31 6 weeks after immunization. | α-GalCer (1 μg) | Vaccination with α-GalCer increased the survival of long-lived memory cytotoxic CD8+ T cell populations capable of boosting protection against heterologous IAV challenge. | (24) |
| Mouse (BALB/c) | i.m. | pCHA5 for H5N1 | Immunization with pCHA5 with C34 twice at 3 weeks apart. Infection with 200 LD50 NIBRG14 (a reassortant H5N1 virus) 2 weeks after the immunization. | C34 (2 μg) | C34 increased titers of HA-specific antibodies and T cells and improved survival after challenge. | (31) |
| Mouse (C57BL/6) | i.v. | H1N1 PR8 | Immunization with PR8 HA mRNA-transfected CD1d-allogeneic cells loaded with α-GalCer (aAVC-HA). Infection with 103 PFU PR8 2 weeks after the immunization. | 5 × 105 aAVC-HA precultured with α-GalCer (500 ng/mL) | Vaccination with aAVC-HA preserved body weight, increased survival after infection, and increased titers of HA-specific IgG. | (29) |
| Mouse (BALB/c) | i.p. | M2e peptide | Immunization with M2e peptide with α-GalCer twice at 3 weeks apart. Infection with 103 PFU H5N1 3 weeks after the final immunization. | α-GalCer (1 μg) | α-GalCer co-administered with M2e peptide reduced morbidity, mortality and up-regulated IFN-γ, IL-4 after challenge. | (25) |
| Mouse (BALB/c) | i.m. | DNA vaccine encoding M2 | Immunization with DNA vaccine encoding M2 with α-GalCer three times at 2-week intervals. Infection with 1 LD90 PR8 2 weeks after the final immunization. | α-GalCer (1 μg) | α-GalCer increased M2-specific IgG; lymphocyte proliferation; IFN-γ and IL-12 and IL-4 production; and survival rate after virus challenge. | (21) |
| Mouse (BALB/c) | i.m. | H1N1 CA07, A/Hong Kong (H3N2), B/Phuket, and B/Texas | Immunization with split influenza HA vaccine with 7DW8-5 twice at 2-week intervals. Infection with 10 MLD50 H1N1 CA04 3 weeks after the final immunization. | 7DW8-5 (1 μg or 10 μg) | 7DW8-5 was sufficient to protect the mice from lethal infection but did not completely prevent virus replication. | (33) |
| Pig | i.n. | H1N1 OH07 | Immunization with inactivated SwIV OH07 with α-GalCer once. Infection with homologous SwIV OH07 (106 TCID50 per pig) 3 weeks after the immunization. | α-GalCer (50 or 250 μg) | α-GalCer increased IAV-specific mucosal IgA and upregulated the expression of BAFF. | (151) |
| Pig | i.n. | H1N1 OH07 | Immunization with inactivated SwIV OH07 with α-GalCer once. Infection with homologous SwIV OH07 (106 TCID50 per pig) 3 weeks after the immunization. | α-GalCer (50 or 250 μg) | α-GalCer (250 μg) administration reduced pulmonary viral load and increased SwIV-specific IgA secretion both in the lungs and the airways. | (152) |
| Pig | i.m. | H1N1 CA04 | Immunization with inactivated H1N1 CA04 with α-GalCer twice at 16-day intervals. Infection with 106 TCID50 CA04 16 days after the immunization. | α-GalCer (100 μg/kg) | Vaccination with α-GalCer enhanced both systemic and mucosal influenza-specific antibodies and inhibited viral replication in the upper and the lower respiratory tracts. | (153) |
| Pigtail macaques | i.v. | Live-attenuated IAV encoding three distinct SIV epitopes (flu-SIV) | A single dose of α-GalCer pulsed onto whole blood for 2 h and re-infused with flu-SIV; additional vaccinations without α-GalCer on days 28, 56, and 119. | α-GalCer (5 μg) | α-GalCer reduced vaccine-specific CD8+T cells and had no effect on the frequency of iNKT cells or IAV-specific antibodies; reduced influenza-specific CD8+ T cells. | (72) |
Summary of studies on modulating immune responses to influenza A virus (IAV) using invariant natural killer T (iNKT) cell agonists.
PR8, H1N1 strain A/Puerto Rico/8/34; NC20, H1N1 strain A/New Caledonia/20/99; A/WS/33, H1N1 strain A/Wilson-Smith/1933; PNM07, H3N2 strain A/Panama/2007/99; A/Yamagata, H1N1 strain A/Yamagata/120/86; A/Guizhou, H3N2 strain A/Guizhou/54/89; B/Ibaraki, B/Ibaraki/2/85; rNS1 1-73, a PR8 mutant virus expressing only the first 73 amino acids in the NS1 gene; NIBRG-14, reassortant virus derived from PR8 and A/Vietnam/1194/2004 (H5N1) virus (in which the polybasic HA cleavage site has been excised); M2e, ectodomain of M2 protein; CA07, A/California/07/2009 (H1N1) virus; A/Hong Kong, A/Hong Kong/4801/2014 (H3N2) virus; B/ Phuket, B/Phuket/3073/2013 (Yamagata lineage) virus; B/Texas, B/Texas/2/2013 (Victoria lineage) virus; OH07, a zoonotic SwIV H1N1 (Sw/OH/24366/07); CA04, H1N1pdm09 strain A/California/04/2009; α-C-GalCer, alpha-C galactosylceramide; α-GalCer, alpha-galactosylceramide; 7DW8-5, 4-fluorophenylundecanoyl-alpha-galactosylceramide; aAVC-HA, HA-expressing artificial adjuvant vector cells; i.m., intramuscular; i.n., intranasal; i.p., intraperitoneal; s.c., subcutaneous; i.v., intravenous; WB, whole blood.
iNKT cell agonists have also been assessed for their ability to improve vaccine-mediated cross-protection against heterologous and heterosubtypic virus infections. Kamijuku et al. administered α-GalCer to BALB/c mice in combination with HA-based vaccines derived from a variety of IAV strains. Strong protection was induced against heterologous IAV strains within the same HA vaccine subtype and partial protection was generated against the heterosubtypic strains (23). A follow-up study demonstrated that an inactivated whole-virion vaccine of H5N1 IAV generated robust cross-protection against a heterologous H5N1 IAV strain when administered intranasally with, but not without, α-GalCer. The cross-protective effects of iNKT cell activation were found to be mediated by mucosal IgA production and effector responses that require IL-4, but not IFN-γ (23).
Other strategies that have been tested include a study where the α-GalCer derivative α-C-galactosylceramide (α-C-GalCer) enhanced the immune response elicited by a live attenuated A/PR/8/34 virus expressing only the first 73 amino acids in the NS1 gene; NS1 is needed to inhibit critical innate host immune factors (27). BALB/c mice were co-administered the live attenuated virus (LAV) vaccine with different doses of α-C-GalCer ranging from 0 to 4 μg/mouse. Interestingly, only mice that received low doses of α-C-GalCer survived, while mice treated with the 4 μg dose or the LAV vaccine alone were not protected. This finding suggests that activating iNKT cells too strongly may be detrimental for LAV vaccine applications since their limited replication capacity might be abolished by iNKT cell-mediated innate immune responses before they have had an opportunity to induce vaccine-specific immunity. α-GalCer has also been used to adjuvant the normally poorly immunogenic IAV M2 ectodomain (M2e); BALB/c mice co-immunized with M2e and α-GalCer were fully protected against a highly pathogenic H5N1 avian IAV infection and exhibited significantly reduced morbidity and lung viral titers compared to mice that were immunized without α-GalCer (25). The enhanced protection was associated with augmented IgG1 and IgG2 antibody levels and greater IFN-γ and IL-4 upregulation after infection. Another study tested the efficacy of α-GalCer-peptide conjugated vaccines composed of synthetic long peptides (SLP) containing an immunogenic peptide covalently attached to α-GalCer by a cleavable linker (28). This ensures that the vaccine peptide and α-GalCer are delivered to the same APC and enables iNKT cells to license the same APCs involved in stimulating conventional CD4+ and CD8+ T cell responses against the vaccine antigen. C57BL/6 mice were vaccinated with α-GalCer conjugated SLPs composed of an immunogenic peptide of chicken ovalbumin and challenged 6 weeks later with a recombinant ovalbumin expressing IAV. The SLP vaccine provided much greater protection than previous infection with the backbone virus. However, it remains to be determined whether this approach provides protection against non-OVA-expressing IAVs. Another strategy used an “adjuvant vector cell” (aAVC) system comprised of CD1d+ HA mRNA-transfected cell lines (NIH3T3 for mice and HEK293 cells for humans) loaded with α-GalCer. C57BL6/J mice immunized with aAVC-HA were protected from a lethal dose of PR8 2 weeks later. The efficacy of this approach seemed to depend on the formation of germinal centers and TFH cells and was more effective than a co-administration of free antigen and α-GalCer (29).
Many articles reporting the adjuvant activities of iNKT cells for IAV vaccines have used the intranasal delivery route of administering α-GalCer because of the importance of this site for pulmonary immunity. α-GalCer administered by this route remains localized to the nasal-associated lymphoid tissues and cervical lymph nodes where it becomes concentrated in the intracellular vesicles of DCs. These DCs co-localize with iNKT cells that accumulate in these tissues through a process that requires the chemokine receptor CXCR6 and its ligand CXCL16 (23). α-GalCer can also induce effective immunity when delivered to tissues beyond the site of infection. For instance, Galli et al. showed that mice immunized via the intramuscular route with α-GalCer admixed with HA/NA subunits from human influenza viruses generated antibody titers that were 1–2 logs higher than mice immunized with protein alone and greatly enhanced survival after a lethal IAV infection (30).
iNKT cell responses have also shown promise for generating cross-reactive CD8+ T cells against serologically distinct IAV subtypes, which is a major shortcoming of current IAV vaccines. Guillonneau et al. examined cytotoxic CD8+ T cell responses in C57BL/6 mice subcutaneously immunized with an inactivated PR8 vaccine, with and without α-GalCer, that were infected with a heterosubtypic H3N2 IAV 6 weeks later (24). iNKT cell activation enhanced the survival of long-lived memory cytotoxic CD8+ T cells capable of clearing virus from the lungs while paradoxically diminishing acute phase cytotoxic T cell responses through iNKT cell-dependent production of indoleamine 2,3-dioxygenase, an immune suppressive enzyme (24). The induction of long-lasting CD8+ T cells was associated with the upregulation of Bcl-2, which is a pro-survival gene. The adjuvant effects of iNKT cells have also shown potential to improve DNA-based vaccines, which stimulate only modest immunity in humans. Two studies have demonstrated that vaccinating mice with α-GalCer derivatives and DNA vaccines encoding an HA consensus sequence of an H5N1 IAV or the IAV M2 protein induces M2-specific cellular and humoral immune responses and protection from virus challenge (21, 31).
Although mouse models have demonstrated that iNKT cell activities can greatly enhance IAV vaccines, it remains unclear whether the same approach would be successful in humans as mice are not natural IAV hosts and mouse and human iNKT cells differ considerably in frequency, subsets, and tissue distribution. Therapeutically activating iNKT cells failed to improve anti-IAV cellular and humoral immune responses when attempted in pigtail macaques, which are considered a good translational model for human IAV infections (72). Nevertheless, we previously reported that α-GalCer substantially increased the efficacy of a killed pandemic 2009 H1N1 IAV vaccine in pigs that were challenged with the homologous virus. Protection was associated with higher levels of vaccine-specific antibodies and T cells and reduced viral replication in the upper and lower respiratory tract compared to pigs that received the vaccine alone (153). Similar results were obtained in studies by Dwivedi et al. and Renu et al., who showed that intranasal co-administration of α-GalCer with UV-inactivated H1N1 vaccines increased mucosal IgA levels, upregulated lung expression of the B cell activation factor BAFF, and substantially reduced virus loads in pigs (151, 152). Collectively, these results are encouraging as swine and human iNKT cells share several key characteristics, and like humans, pigs are natural hosts of IAVs. Furthermore, there may also be potential to use iNKT cell antigens for vaccines against swine influenza and other pig pathogens.
Factors That Influence the Adjuvant Potential of iNKT Cells
Studies in mice have established that the effects of iNKT cell activation are influenced by a variety of interacting parameters, which should be considered when attempting to use these agents to adjuvant vaccines. Some of the main factors are discussed below.
iNKT Cell Subsets
The iNKT cell compartment consists of multiple subsets that play distinct roles during pathogen-host interactions and which produce different effector functions after glycolipid stimulation. Subset development occurs through a linear differentiation process characterized by sequential changes in surface markers and transcription factors. Human iNKT cells develop into CD4− or CD4+ subsets that secrete Th1 or a mixture of Th1 and Th2 cytokines upon activation, respectively (54, 154). However, these differences in cytokine production are less apparent for mouse iNKT cells (85). Another difference is that the CD4+ subset of iNKT cells predominates in mice (155), while human iNKT cells are mostly CD4− (54, 156, 157). Like humans, iNKT cells in pigs are mainly CD4− (52, 68, 75, 153), and both humans and pigs contain a subset of CD8+ iNKT cells which is absent in mice (54, 68, 75, 156, 157).
Mouse iNKT cell subsets can be classified according to their development lineages that are acquired during thymic selection (Table 2). These are composed of the three major functionally distinct subsets, NKT1, NKT2, and NKT17, which express the master transcription factors T-bet, GATA-3, and RORγt that also, respectively, engender the fate of Th1, Th2, and Th17 T helper cell subsets as well as ILC1, ILC2, and ILC3 innate lymphoid cells (95, 158–161, 163–165). Each iNKT subset expresses different levels of the transcription factor PLZF, which is critical for the development and the innate functions of iNKT cells (168–170). Additional iNKT cell subsets that differentiate extrathymically have been identified, including NKTFH and NKT10 cells. NKTFH cells are characterized by the expression of Bcl-6 and the secretion of IL-21 and are located in the germinal centers of lymphoid organs. NKTFH cells provide help to B cells during the formation of germinal centers and drive the affinity maturation of antibodies toward lipid antigens (134, 135). NKT10 cells are equivalent to type-1 regulatory T cells (TREGS) and produce IL-10 and IL-2. This subset induces the differentiation of anti-inflammatory macrophages and provides help to TREGS. Instead of expressing PLZF like other NKT cells, NKT10 express E4BP4, a transcription factor associated with IL-10 production (166).
Table 2
| iNKT cell subset | Transcription factor | Signature cytokines | Tissue distribution | References |
|---|---|---|---|---|
| NKT1 | T-bet, PLZFlow | IL-4, IFN-γ | Liver, spleen, lung, small intestine | (56, 95, 158–162) |
| NKT2 | GATA3, PLZFhi | IL-4, IL-5, IL-13 | Lung, spleen, mesenteric lymph nodes | (56, 159–163) |
| NKT17 | RORγt, PLZFint | IL-17, IL-22 | Lymph nodes, lung, skin | (56, 159–162, 164, 165) |
| NKTFH | Bcl-6 | IL-21 | Germinal centers of lymphoid organs | (134, 135) |
| NKT10 | E4BP4, PLZF− | IL-10, IL-2 | Adipose tissue | (166, 167) |
Key characteristics of the main invariant natural killer T (iNKT) cell subsets.
Individual iNKT cell subsets differentially accumulate in lymphoid and non-lymphoid tissues (171). In mice, most liver iNKT cells are NKT1 cells, while NKT2 cells predominate in the lung, spleen, and mesenteric lymph nodes (56, 162, 171). NKT17 cells are most plentiful in the lymph nodes, lung, and skin (56, 162, 171), while NKT10 cells preferentially accumulate in adipose tissue (167, 171) and NKTFH cells localize in germinal centers, especially in the spleen (134, 135). The effector functions of each subset are distinct and range from NKT1 cells that stimulate proinflammatory responses capable of suppressing cancer and infectious agents (83, 172) to tolerogenic NKT2 and NKT10 cells that inhibit autoimmune diseases (173–175). Such diversity in function needs to be considered when targeting the adjuvant activities of iNKT cell agonists because, depending on the route of vaccinations, some subsets may have more influence on shaping anti-IAV immune responses than others, which could considerably affect the quality and the durability of protection. Another consideration is the extensive variability in iNKT cell subset ratios among inbred mouse strains and genetically outbred humans and animals, which can result in extensive variability in outcomes. Indeed different ratios of NKT1/NKT2 subsets are thought to underlie the dimorphic responses that α-GalCer treatment elicits in C57BL/6 and BALB/c mice for a host of different diseases (95). Currently, a unifying model linking iNKT cell transcription factors and functions is lacking for humans (and other species). Nevertheless, iNKT cells are probably comprised of functionally distinct subsets in all species that expresses these cells. Accordingly, the variability in iNKT cell subsets should be considered a potential source of variation in people or animals administered glycolipids to stimulate iNKT cell adjuvant activities.
iNKT Cell Agonists
Since α-GalCer is the first iNKT cell ligand to be discovered and strongly activates iNKT cells, this agent and its synthetic derivative KRN7000 have been widely used to study the therapeutic potential of iNKT cells, including their adjuvant activities (18, 19, 176). α-GalCer is a glycosylceramide molecule, composed of an α-anomeric sugar linked to a 26-carbon-long fatty acid chain and an 18-carbon-long sphingosine base (15). While this glycolipid induces a mixed Th1/Th2 cytokine response, various structural analogs of α-GalCer that skew iNKT cell cytokine production toward a Th1 or Th2 response have been developed. These modifications include altering the length, saturation level, and branching of the alkyl and sphingosine chains, while other derivatives contain modifications at the glycosyl head (96, 97, 173, 177–181).
In general, α-GalCer analogs with truncated fatty acid chains or the addition of double bonds in the acyl chain, such as OCH ((2S,3S,4R)-1-O-(α-D-galactopyranosyl)-N-tetracosanoyl-2-amino-1,3,4-non-anetriol) and C20:2, skew iNKT cells toward producing Th2 cytokines (173, 177). In contrast, iNKT cells can be preferentially activated to produce Th1-like cytokines by (i) α-GalCer derivatives that contain a CH2 group in place of the glycosidic oxygen (180), (ii) α-C-GalCer analogs that contain an oxygen residue in the galactose sugar ring (182), and (iii) 7DW8-5 and C34 analogs that, respectively, possess methylene and aromatic residues inserted into their fatty acid chains (183, 184). Most studies on the adjuvant activities of iNKT cells use α-GalCer, which generates potent cellular and humoral immunity due to the mixed Th1/Th2 cytokines elicited. However, several Th1-inducing reagents, including 7DW8-5 and C-glycoside, substantially enhance vaccine responses against malaria, HIV, and IAV vaccines in mice (33, 180, 183). Some studies have reported that these agents are superior to α-GalCer for boosting vaccine-mediated immune responses due to a greater ability to trans-activate other immune cells, especially NK cells, to produce IFN-γ (92, 183).
The burgeoning list of synthetic iNKT cell ligands provides new opportunities to tune iNKT cell responses for a desired vaccine-supporting immune outcome. For IAV vaccines, the most promising iNKT cell-stimulating antigens are those which polarize mouse iNKT cells to produce Th1 cytokines or a mixture of Th1 and Th2 cytokines, which are naturally important for antiviral immune responses. Nevertheless, many of these reagents do not polarize human iNKT cells to the same degree as mouse iNKT cells due partially to the structural differences in mouse and human CD1d molecules that affect TCR/CD1d/antigen interactions (91, 92, 178). This is an important consideration for translating preclinical animal vaccine studies to humans.
Vaccine Format
Studies with different disease models have shown that α-GalCer treatment can have diverse immune effects depending on the timing, route, and dose of α-GalCer administration. Understanding how these parameters affect the adjuvant activities of therapeutically activated iNKT cells is critical for optimizing iNKT cell-adjuvanted IAV vaccines. The timing of α-GalCer treatment is a concern for prime-boost vaccination strategies that administer more than one α-GalCer dose. This is because the strong activation from a primary vaccination may render iNKT cells hypo-responsive to an additional stimulation. Most studies on the adjuvant activities of iNKT cell agonists for IAV vaccines employ multiple vaccine applications (Table 1) even though iNKT cells are reported to remain anergic to restimulation within 3 months after the initial stimulation. These reports seldom assess whether increases in immune responses are from the effects of iNKT cells stimulation or from the vaccine antigen alone. However, it has been shown that the intramuscular delivery of α-GalCer avoids iNKT cell anergy in both mice and pigs (21, 30, 52, 153), suggesting that the risk of iNKT cell hypo-responsiveness may be low if prime-boost vaccination strategies were employed with IAV vaccines using the i.m. route.
Studies that have employed inactivated IAV vaccines, viral peptides, and DNA vaccines have used a variety of immunization routes, although intramuscular injection is the most common. In contrast, iNKT-adjuvanted live attenuated IAV vaccines have mostly been delivered intranasally to induce protective immunity at the site of infection. In general, the systemic routes of vaccine and α-GalCer co-administration globally activate iNKT cells in a way that greatly enhances neutralizing antibodies (21, 23, 30). However, this route is not as effective as intranasal administration at inducing secretory IgA antibodies necessary for cross-protection against heterologous virus strains (23). Studies that have compared the efficacy of different vaccination sites include the report by Galli et al. which showed that the intraperitoneal, subcutaneous, intramuscular, and intravenous immunization routes were equally effective and better than intranasal administration at inducing vaccine-specific antibodies (30). Another study showed that BALB/c mice intranasally vaccinated with α-GalCer in combination with HA antigen derived either from A/PR8 (H1N1) or A/Yamagata (H1N1) were protected from subsequent infection with A/PR8 (H1N1) live virus and that the A/Yamagata HA antigen vaccine induced anti-PR8 HA IgA and IgG antibodies. In contrast, the same vaccines administered by the intramuscular route failed to induce IgA antibodies and did not provide cross-protective immunity (23). The same study compared the effect of intraperitoneally and intranasally delivered α-GalCer on an intranasally delivered A/PR8 (H1N1) vaccine. Despite strongly activating splenic and hepatic iNKT cells, intraperitoneally delivered α-GalCer did not induce anti-PR8 IgA and IgG antibodies as a response to the A/PR8 HA antigen vaccine administered intranasally, indicating that iNKT cell ligands must be co-administered with viral antigens to enhance an intranasally delivered vaccine (23).
The adjuvant effects of glycolipid-stimulated iNKT cells enhance immune responses to a wide variety of vaccine formats. Such versatility stems from the powerful immunoregulatory properties of iNKT cells, which affect almost every branch of the immune system and which are generally more diverse than the immunomodulatory effects induced by traditional adjuvants. A drawback of this potency is that iNKT cell responses can reduce the efficacy of live attenuated virus vaccines by inducing antiviral host responses that eliminate the weakened vaccine virus before it has had a chance to induce adaptive immunity. Consequently, it will be necessary to carefully titrate each glycolipid ligand to find a dose that increases, rather than decreases, immunity against live attenuated virus vaccines. Dosage is less important for non-attenuated vaccines, although high doses of glycolipid ligands may render iNKT cells anergic to secondary activation.
Potential Pitfalls
Several obstacles must be overcome before the immunomodulatory activities of iNKT cells can be used for human or livestock vaccines. Of paramount concern is the safety of this strategy as the potent cytokine responses generated by therapeutically activated iNKT cells can sometimes result in immunopathological inflammation and/or disease exacerbation (185–187). This includes reports that α-GalCer administration can induce acute airway hyper-reactivity in mice (188), non-human primates (189), and pigs (76). In addition, the co-administration of α-GalCer and the model antigen ovalbumin resulted in allergic airway inflammation in mice (190). These results should serve as a note of caution that combining α-GalCer with intranasally administered IAV vaccines could cause potentially life-threatening airway inflammation. Another concern is that α-GalCer-stimulated iNKT cells may increase the risk of vaccine-associated enhanced respiratory disease. This phenomenon occurs when inactivated IAV vaccines include a virus strain of the same hemagglutinin subtype as a subsequent challenge virus, but with substantial antigenic shift (191). This occasionally generates IgG antibodies that cross-react with the heterologous virus proteins but lack the ability to neutralize the heterologous virus effectively. These antibodies might instead bind epitopes in the HA stem region (HA2) of the heterologous virus, which facilitates infection of host cells by enhancing virus fusion activity (191). As iNKT cell activation boosts the size and the complexity of humoral responses, it is possible that they will also increase non-neutralizing antibody responses against heterologous viruses. Another concern is the potential that immunity from iNKT cell-adjuvanted vaccines will be inconsistent and unpredictable due to the high interindividual variability in iNKT cell frequency and function in genetically outbred species, including humans (192, 193). Indeed some studies have reported that only patients with high iNKT cell frequencies were likely to benefit from iNKT cell-based treatments (194, 195). It is currently difficult to predict whether an individual's iNKT cells will produce an immunogenic or tolerogenic response to stimulation, and the danger exists that iNKT cell activation might actually reduce the efficacy of IAV vaccines. This is further complicated by the phenomenon that iNKT cells undergo substantial age-related alterations in concentration and effector functions that are likely to impact their response to glycolipid antigens (196–200). Finally, it is important to consider that most studies in this field were conducted using mouse models which, although they have provided extensive knowledge about the fundamental role of iNKT cells during IAV infections, do not closely mirror humans for iNKT cell physiology. Furthermore, mice are not natural hosts of IAV infections and usually develop much more severe disease than humans when infected with mouse-adapted IAV strains (201). Thus, another obstacle is the need for more studies in valid preclinical animal models to translate iNKT cell-adjuvanted vaccination to the clinic.
Concluding Remarks
Durable and broadly protective IAV vaccines are greatly needed to counteract the growing threats of morbidity, mortality, and economic losses from seasonal and pandemic IAV infections. Current vaccine formulations do not provide long-lasting and cross-protective immunity, partly because they do not induce sufficient T cell help from virus-specific T cells. iNKT cells may help to overcome this limitation because they can be uniformly and specifically activated by therapeutic glycolipid antigens to supply a universal form of T cell help capable of expanding virus-specific antibodies and CD8+ T cells. Nevertheless, significant hurdles remain before the adjuvant activities of iNKT cells can be utilized in humans and livestock for vaccines against IAV and other pathogens. Future research should focus on testing this approach using preclinical animal models with high human translational potential, such as swine and non-human primates. Such studies will help determine the translatability of iNKT cell-adjuvanted vaccines for other respiratory diseases which have shown promise in mouse models (202).
Statements
Author contributions
JD and JR contributed to the conceptualization, writing, review, and editing. DC, WG, and BA contributed to the writing. All authors contributed to the article and approved the submitted version.
Funding
This work was supported by U.S. Department of Agriculture Grant 2016-09448 (to JD), National Institutes of Health Grant HD092286 (to JD and JR), the NIAID-funded Center of Excellence for Influenza Research and Surveillance (CEIRS, #HHSN272201400006C; JR), and the U.S. Department of Homeland Security under Grant Award Number DHS-2010-ST-061-AG0001 (JR) for the Center of Excellence for Emerging and Zoonotic Animal Disease (CEEZAD).
Conflict of interest
The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.
References
1.
TaubenbergerJKKashJC. Influenza virus evolution, host adaptation, pandemic formation. Cell Host Microbe. (2010) 7:440–51. 10.1016/j.chom.2010.05.009
2.
MedinaRAGarcía-SastreA. Influenza A viruses: new research developments. Nat Rev Microbiol. (2011) 9:590–603. 10.1038/nrmicro2613
3.
WuYTefsenBShiYGaoGF. Bat-derived influenza-like viruses H17N10 and H18N11. Trends Microbiol. (2014) 22:183–91. 10.1016/j.tim.2014.01.010
4.
KasowskiEJGartenRJBridgesCB. Influenza pandemic epidemiologic and virologic diversity: reminding ourselves of the possibilities. Clin Infect Dis. (2011) 52(Suppl. 1):S44–9. 10.1093/cid/ciq010
5.
GBD2017 Influenza Collaborators. Mortality, morbidity, and hospitalisations due to influenza lower respiratory tract infections, 2017: an analysis for the Global burden of disease study 2017. Lancet Respir Med. (2019) 7:69–89. 10.1016/S2213-2600(18)30496-X
6.
BouvierNMPaleseP. The biology of influenza viruses. Vaccine. (2008) 26(Suppl.4):D49–53. 10.1016/j.vaccine.2008.07.039
7.
KiddM. Influenza viruses: update on epidemiology, clinical features, treatment and vaccination. Curr Opin Pulm Med. (2014) 20:242–6. 10.1097/MCP.0000000000000049
8.
FlanneryBKondorRJGChungJRGaglaniMReisMZimmermanRKet al. Spread of antigenically drifted Influenza A(H3N2) viruses and vaccine effectiveness in the United States during the 2018-2019 season. J Infect Dis. (2020) 221:8–15. 10.1093/infdis/jiz543
9.
JacksonMLNelsonJC. The test-negative design for estimating influenza vaccine effectiveness. Vaccine. (2013) 31:2165–8. 10.1016/j.vaccine.2013.02.053
10.
ReedSGOrrMTFoxCB. Key roles of adjuvants in modern vaccines. Nat Med. (2013) 19:1597–608. 10.1038/nm.3409
11.
Henriksen-LaceyMChristensenDBramwellVWLindenstrømTAggerEMAndersenPet al. Liposomal cationic charge and antigen adsorption are important properties for the efficient deposition of antigen at the injection site and ability of the vaccine to induce a CMI response. J Control Release. (2010) 145:102–8. 10.1016/j.jconrel.2010.03.027
12.
MaisonneuveCBertholetSPhilpottDJde GregorioE. Unleashing the potential of NOD- and toll-like agonists as vaccine adjuvants. Proc Natl Acad Sci USA. (2014) 111:12294–9. 10.1073/pnas.1400478111
13.
Van ReethKVan GuchtSPensaertM. Investigations of the efficacy of European H1N1- and H3N2-based swine influenza vaccines against the novel H1N2 subtype. Vet Rec. (2003) 153:9–13. 10.1136/vr.153.1.9
14.
GodfreyDIUldrichAPMcCluskeyJRossjohnJMoodyDB. The burgeoning family of unconventional T cells. Nat Immunol. (2015) 16:1114–23. 10.1038/ni.3298
15.
KawanoTCuiJKoezukaYTouraIKanekoYMotokiKet al. CD1d-restricted and TCR-mediated activation of valpha14 NKT cells by glycosylceramides. Science. (1997) 278:1626–9. 10.1126/science.278.5343.1626
16.
NatoriTKoezukaYHigaT. Agelasphins, novel alpha-galactosylceramides from the marine sponge agelas-mauritianus. Tetrahedron Lett. (1993) 34:5591–2. 10.1016/S0040-4039(00)73889-5
17.
CarreñoLJKharkwalSSPorcelliSA. Optimizing NKT cell ligands as vaccine adjuvants. Immunotherapy. (2014) 6:309–20. 10.2217/imt.13.175
18.
SpeirMHermansIFWeinkoveR. Engaging natural killer T cells as 'universal helpers' for vaccination. Drugs. (2017) 77:1–15. 10.1007/s40265-016-0675-z
19.
SilkJDHermansIFGileadiUChongTWShepherdDSalioMet al. Utilizing the adjuvant properties of CD1d-dependent NK T cells in T cell-mediated immunotherapy. J Clin Invest. (2004) 114:1800–11. 10.1172/JCI200422046
20.
CerundoloVSilkJDMasriSHSalioM. Harnessing invariant NKT cells in vaccination strategies. Nat Rev Immunol. (2009) 9:28–38. 10.1038/nri2451
21.
FotouhiFShaffifarMFarahmandBShirianSSaeidiMTabarraeiAet al. Adjuvant use of the NKT cell agonist alpha-galactosylceramide leads to enhancement of M2-based DNA vaccine immunogenicity and protective immunity against influenza A virus. Arch Virol. (2017) 162:1251–60. 10.1007/s00705-017-3230-7
22.
YounHJKoSYLeeKAKoHJLeeYSFujihashiKet al. A single intranasal immunization with inactivated influenza virus and alpha-galactosylceramide induces long-term protective immunity without redirecting antigen to the central nervous system. Vaccine. (2007) 25:5189–98. 10.1016/j.vaccine.2007.04.081
23.
KamijukuHNagataYJiangXIchinoheTTashiroTMoriKet al. Mechanism of NKT cell activation by intranasal coadministration of alpha-galactosylceramide, which can induce cross-protection against influenza viruses. Mucosal Immunol. (2008) 1:208–18. 10.1038/mi.2008.2
24.
GuillonneauCMinternJDHubertFXHurtACBesraGSPorcelliSet al. Combined NKT cell activation and influenza virus vaccination boosts memory CTL generation and protective immunity. Proc Natl Acad Sci USA. (2009) 106:3330–5. 10.1073/pnas.0813309106
25.
LiKLuoJWangCHeH. α-Galactosylceramide potently augments M2e-induced protective immunity against highly pathogenic H5N1 avian influenza virus infection in mice. Vaccine. (2011) 29:7711–7. 10.1016/j.vaccine.2011.07.136
26.
KoSYKoHJChangWSParkSHKweonMNKangCY. alpha-Galactosylceramide can act as a nasal vaccine adjuvant inducing protective immune responses against viral infection and tumor. J Immunol. (2005) 175:3309–17. 10.4049/jimmunol.175.5.3309
27.
Kopecky-BrombergSAFraserKAPicaNCarneroEMoranTMFranckRWet al. Alpha-C-galactosylceramide as an adjuvant for a live attenuated influenza virus vaccine. Vaccine. (2009) 27:3766–74. 10.1016/j.vaccine.2009.03.090
28.
AndersonRJLiJKedzierskiLComptonBJHaymanCMOsmondTLet al. Augmenting influenza-specific T cell memory generation with a natural killer T cell-dependent glycolipid-peptide vaccine. ACS Chem Biol. (2017) 12:2898–905. 10.1021/acschembio.7b00845
29.
YamasakiSShimizuKKometaniKSakuraiMKawamuraMFujiiSI. In vivo dendritic cell targeting cellular vaccine induces CD4. Sci Rep. (2016) 6:35173. 10.1038/srep35173
30.
GalliGPittoniPTontiEMalzoneCUematsuYTortoliMet al. Invariant NKT cells sustain specific B cell responses and memory. Proc Natl Acad Sci USA. (2007) 104:3984–9. 10.1073/pnas.0700191104
31.
HungJTTsaiYCLinWDJanJTLinKHHuangJRet al. Potent adjuvant effects of novel NKT stimulatory glycolipids on hemagglutinin based DNA vaccine for H5N1 influenza virus. Antiviral Res. (2014) 107:110–8. 10.1016/j.antiviral.2014.04.007
32.
LeeYSLeeKALeeJYKangMHSongYCBaekDJet al. An α-GalCer analogue with branched acyl chain enhances protective immune responses in a nasal influenza vaccine. Vaccine. (2011) 29:417–25. 10.1016/j.vaccine.2010.11.005
33.
FengHNakajimaNWuLYamashitaMLopesTJSTsujiMet al. A glycolipid adjuvant, 7DW8-5, enhances the protective immune response to the current split influenza vaccine in mice. Front Microbiol. (2019) 10:2157. 10.3389/fmicb.2019.02157
34.
MakinoYKannoRItoTHigashinoKTaniguchiM. Predominant expression of invariant V alpha 14+ TCR alpha chain in NK1.1+ T cell populations. Int Immunol. (1995) 7:1157–61. 10.1093/intimm/7.7.1157
35.
BuddRCMiescherGCHoweRCLeesRKBronCMacDonaldHR. Developmentally regulated expression of T cell receptor beta chain variable domains in immature thymocytes. J Exp Med. (1987) 166:577–82. 10.1084/jem.166.2.577
36.
FowlkesBJKruisbeekAMTon-ThatHWestonMAColiganJESchwartzRHet al. A novel population of T-cell receptor alpha beta-bearing thymocytes which predominantly expresses a single V beta gene family. Nature. (1987) 329:251–4. 10.1038/329251a0
37.
CeredigRLynchFNewmanP. Phenotypic properties, interleukin 2 production, and developmental origin of a “mature” subpopulation of Lyt-2- L3T4- mouse thymocytes. Proc Natl Acad Sci USA. (1987) 84:8578–82. 10.1073/pnas.84.23.8578
38.
SykesM. Unusual T cell populations in adult murine bone marrow. Prevalence of CD3+CD4-CD8- and alpha beta TCR+NK1.1+ cells. J Immunol. (1990) 145:3209–15.
39.
LantzOBendelacA. An invariant T cell receptor alpha chain is used by a unique subset of major histocompatibility complex class I-specific CD4+ and CD4-8- T cells in mice and humans. J Exp Med. (1994) 180:1097–6. 10.1084/jem.180.3.1097
40.
MoodycliffeAMMaitiSUllrichSE. Splenic NK1.1-negative, TCR alpha beta intermediate CD4+ T cells exist in naive NK1.1 allelic positive and negative mice, with the capacity to rapidly secrete large amounts of IL-4 and IFN-gamma upon primary TCR stimulation. J Immunol. (1999) 162:5156–63.
41.
BendelacALantzOQuimbyMEYewdellJWBenninkJRBrutkiewiczRR. CD1 recognition by mouse NK1+ T lymphocytes. Science. (1995) 268:863–5. 10.1126/science.7538697
42.
MattnerJDebordKLIsmailNGoffRDCantuCZhouDet al. Exogenous and endogenous glycolipid antigens activate NKT cells during microbial infections. Nature. (2005) 434:525–9. 10.1038/nature03408
43.
RossjohnJPellicciDGPatelOGapinLGodfreyDI. Recognition of CD1d-restricted antigens by natural killer T cells. Nat Rev Immunol. (2012) 12:845–57. 10.1038/nri3328
44.
BenlaghaKWeissABeavisATeytonLBendelacA. In vivo identification of glycolipid antigen-specific T cells using fluorescent CD1d tetramers. J Exp Med. (2000) 191:1895–903. 10.1084/jem.191.11.1895
45.
MatsudaJLNaidenkoOVGapinLNakayamaTTaniguchiMWangCRet al. Tracking the response of natural killer T cells to a glycolipid antigen using CD1d tetramers. J Exp Med. (2000) 192:741–54. 10.1084/jem.192.5.741
46.
RhostSLofbomLRynmarkBMPeiBManssonJETenebergSet al. Identification of novel glycolipid ligands activating a sulfatide-reactive, CD1d-restricted, type II natural killer T lymphocyte. Eur J Immunol. (2012) 42:2851–60. 10.1002/eji.201142350
47.
MempelMRonetCSuarezFGilleronMPuzoGVan KaerLet al. Natural killer T cells restricted by the monomorphic MHC class 1b CD1d1 molecules behave like inflammatory cells. J Immunol. (2002) 168:365–71. 10.4049/jimmunol.168.1.365
48.
FischerKScotetENiemeyerMKoebernickHZerrahnJMailletSet al. Mycobacterial phosphatidylinositol mannoside is a natural antigen for CD1d-restricted T cells. Proc Natl Acad Sci USA. (2004) 101:10685–90. 10.1073/pnas.0403787101
49.
AmpreyJLImJSTurcoSJMurrayHWIllarionovPABesraGSet al. A subset of liver NKT cells is activated during Leishmania donovani infection by CD1d-bound lipophosphoglycan. J Exp Med. (2004) 200:895–904. 10.1084/jem.20040704
50.
SchofieldLMcConvilleMJHansenDCampbellASFraser-ReidBGrusbyMJet al. CD1d-restricted immunoglobulin G formation to GPI-anchored antigens mediated by NKT cells. Science. (1999) 283:225–9. 10.1126/science.283.5399.225
51.
LiuYGoffRDZhouDMattnerJSullivanBAKhuranaAet al. A modified alpha-galactosyl ceramide for staining and stimulating natural killer T cells. J Immunol Methods. (2006) 312:34–9. 10.1016/j.jim.2006.02.009
52.
ArtiagaBLWhitenerRLStaplesCRDriverJP. Adjuvant effects of therapeutic glycolipids administered to a cohort of NKT cell-diverse pigs. Vet Immunol Immunopathol. (2014) 162:1–13. 10.1016/j.vetimm.2014.09.006
53.
KobayashiEMotokiKUchidaTFukushimaHKoezukaY. KRN7000, a novel immunomodulator, and its antitumor activities. Oncol Res. (1995) 7:529–34.
54.
GumperzJEMiyakeSYamamuraTBrennerMB. Functionally distinct subsets of CD1d-restricted natural killer T cells revealed by CD1d tetramer staining. J Exp Med. (2002) 195:625–36. 10.1084/jem.20011786
55.
CoquetJMChakravartiSKyparissoudisKMcNabFWPittLAMcKenzieBSet al. Diverse cytokine production by NKT cell subsets and identification of an IL-17-producing CD4-NK1.1- NKT cell population. Proc Natl Acad Sci USA. (2008) 105:11287–92. 10.1073/pnas.0801631105
56.
LeeYJWangHStarrettGJPhuongVJamesonSCHogquistKA. Tissue-specific distribution of iNKT cells impacts their cytokine response. Immunity. (2015) 43:566–78. 10.1016/j.immuni.2015.06.025
57.
GotoMMurakawaMKadoshima-YamaokaKTanakaYNagahiraKFukudaYet al. Murine NKT cells produce Th17 cytokine interleukin-22. Cell Immunol. (2009) 254:81–4. 10.1016/j.cellimm.2008.10.002
58.
ChangYJHuangJRTsaiYCHungJTWuDFujioMet al. Potent immune-modulating and anticancer effects of NKT cell stimulatory glycolipids. Proc Natl Acad Sci USA. (2007) 104:10299–304. 10.1073/pnas.0703824104
59.
KimJHChungDH. CD1d-restricted IFN-γ-secreting NKT cells promote immune complex-induced acute lung injury by regulating macrophage-inflammatory protein-1α production and activation of macrophages and dendritic cells. J Immunol. (2011) 186:1432–41. 10.4049/jimmunol.1003140
60.
BilenkiLYangJFanYWangSYangX. Natural killer T cells contribute to airway eosinophilic inflammation induced by ragweed through enhanced IL-4 and eotaxin production. Eur J Immunol. (2004) 34:345–54. 10.1002/eji.200324303
61.
FaunceDEStein-StreileinJ. NKT cell-derived RANTES recruits APCs and CD8+ T cells to the spleen during the generation of regulatory T cells in tolerance. J Immunol. (2002) 169:31–8. 10.4049/jimmunol.169.1.31
62.
OhtekiTMacDonaldHR. Stringent V beta requirement for the development of NK1.1+ T cell receptor-alpha/beta+ cells in mouse liver. J Exp Med. (1996) 183:1277–82. 10.1084/jem.183.3.1277
63.
AraseHAraseNOgasawaraKGoodRAOnoéK. An NK1.1+ CD4+8- single-positive thymocyte subpopulation that expresses a highly skewed T-cell antigen receptor V beta family. Proc Natl Acad Sci USA. (1992) 89:6506–10. 10.1073/pnas.89.14.6506
64.
MatsuuraAKinebuchiMChenHZKatabamiSShimizuTHashimotoYet al. NKT cells in the rat: organ-specific distribution of NKT cells expressing distinct V alpha 14 chains. J Immunol. (2000) 164:3140–8. 10.4049/jimmunol.164.6.3140
65.
ExleyMGarciaJBalkSPPorcelliS. Requirements for CD1d recognition by human invariant Valpha24+ CD4-CD8- T cells. J Exp Med. (1997) 186:109–20. 10.1084/jem.186.1.109
66.
DellabonaPPadovanECasoratiGBrockhausMLanzavecchiaA. An invariant V alpha 24-J alpha Q/V beta 11 T cell receptor is expressed in all individuals by clonally expanded CD4-8- T cells. J Exp Med. (1994) 180:1171–6. 10.1084/jem.180.3.1171
67.
YangGArtiagaBLLomelinoCLJayaprakashADSachidanandamRMckennaRet al. Next generation sequencing of the pig αβ TCR repertoire identifies the porcine invariant NKT cell receptor. J Immunol. (2019) 202:1981–91. 10.4049/jimmunol.1801171
68.
YangGArtiagaBLLewisSTDriverJP. Characterizing porcine invariant natural killer T cells: a comparative study with NK cells and T cells. Dev Comp Immunol. (2017) 76:343–51. 10.1016/j.dci.2017.07.006
69.
PyzENaidenkoOMiyakeSYamamuraTBerberichICardellSet al. The complementarity determining region 2 of BV8S2 (V beta 8.2) contributes to antigen recognition by rat invariant NKT cell TCR. J Immunol. (2006) 176:7447–55. 10.4049/jimmunol.176.12.7447
70.
BrossayLChiodaMBurdinNKoezukaYCasoratiGDellabonaPet al. CD1d-mediated recognition of an alpha-galactosylceramide by natural killer T cells is highly conserved through mammalian evolution. J Exp Med. (1998) 188:1521–8. 10.1084/jem.188.8.1521
71.
SpadaFMKoezukaYPorcelliSA. CD1d-restricted recognition of synthetic glycolipid antigens by human natural killer T cells. J Exp Med. (1998) 188:1529–34. 10.1084/jem.188.8.1529
72.
FernandezCSJegaskandaSGodfreyDIKentSJ. In-vivo stimulation of macaque natural killer T cells with α-galactosylceramide. Clin Exp Immunol. (2013) 173:480–92. 10.1111/cei.12132
73.
MotsingerAAzimzadehAStanicAKJohnsonRPVan KaerLJoyceSet al. Identification and simian immunodeficiency virus infection of CD1d-restricted macaque natural killer T cells. J Virol. (2003) 77:8153–8. 10.1128/JVI.77.14.8153-8158.2003
74.
FichtnerASPalettaDStarickLSchumannRFNiewieskSHerrmannT. Function and expression of CD1d and invariant natural killer T-cell receptor in the cotton rat (Sigmodon hispidus). Immunology. (2015) 146:618–29. 10.1111/imm.12532
75.
ThierryARobinAGiraudSMinoufletSBarraABridouxFet al. Identification of invariant natural killer T cells in porcine peripheral blood. Vet Immunol Immunopathol. (2012) 149:272–9. 10.1016/j.vetimm.2012.06.023
76.
RenukaradhyaGJManickamCKhatriMRaufALiXTsujiMet al. Functional invariant NKT cells in pig lungs regulate the airway hyperreactivity: a potential animal model. J Clin Immunol. (2011) 31:228–39. 10.1007/s10875-010-9476-4
77.
YasudaNMasudaKTsukuiTTengAIshiiY. Identification of canine natural CD3-positive T cells expressing an invariant T-cell receptor alpha chain. Vet Immunol Immunopathol. (2009) 132:224–31. 10.1016/j.vetimm.2009.08.002
78.
Looringh van BeeckFAReininkPHermsenRZajoncDMLavenMJFunATroskieMet al. Functional CD1d and/or NKT cell invariant chain transcript in horse, pig, African elephant and guinea pig, but not in ruminants. Mol Immunol. (2009) 46:1424–31. 10.1016/j.molimm.2008.12.009
79.
Van RhijnIKoetsAPImJSPiebesDReddingtonFBesraGSPorcelliSAet al. The bovine CD1 family contains group 1 CD1 proteins, but no functional CD1d. J Immunol. (2006) 176:4888–93. 10.4049/jimmunol.176.8.4888
80.
NguyenTKKoetsAPVordermeierMJervisPJCoxLRGrahamSPet al. The bovine CD1D gene has an unusual gene structure and is expressed but cannot present alpha-galactosylceramide with a C26 fatty acid. Int Immunol. (2013) 25:91–8. 10.1093/intimm/dxs092
81.
WangJGuillaumeJPauwelsNVan CalenberghSVan RhijnIZajoncDM. Crystal structures of bovine CD1d reveal altered alphaGalCer presentation and a restricted A' pocket unable to bind long-chain glycolipids. PLoS ONE. (2012) 7:e47989. 10.1371/journal.pone.0047989
82.
DossaRGAlperinDCGarzonDMealeyRHBrownWCJervisPJet al. In contrast to other species, alpha-Galactosylceramide (alpha-GalCer) is not an immunostimulatory NKT cell agonist in horses. Dev Comp Immunol. (2015) 49:49–58. 10.1016/j.dci.2014.11.005
83.
BrennanPJBriglMBrennerMB. Invariant natural killer T cells: an innate activation scheme linked to diverse effector functions. Nat Rev Immunol. (2013) 13:101–17. 10.1038/nri3369
84.
BrennanPJTatituriRVBriglMKimEYTuliASandersonJPet al. Invariant natural killer T cells recognize lipid self antigen induced by microbial danger signals. Nat Immunol. (2011) 12:1202–11. 10.1038/ni.2143
85.
Van KaerLParekhVVWuL. Invariant natural killer T cells: bridging innate and adaptive immunity. Cell Tissue Res. (2011) 343:43–55. 10.1007/s00441-010-1023-3
86.
MatsudaJLMallevaeyTScott-BrowneJGapinL. CD1d-restricted iNKT cells, the ‘Swiss-Army knife’ of the immune system. Curr Opin Immunol. (2008) 20:358–68. 10.1016/j.coi.2008.03.018
87.
TupinEKinjoYKronenbergM. The unique role of natural killer T cells in the response to microorganisms. Nat Rev Microbiol. (2007) 5:405–17. 10.1038/nrmicro1657
88.
TyznikAJTupinENagarajanNAHerMJBenedictCAKronenbergM. Cutting edge: the mechanism of invariant NKT cell responses to viral danger signals. J Immunol. (2008) 181:4452–6. 10.4049/jimmunol.181.7.4452
89.
BriglMBryLKentSCGumperzJEBrennerMB. Mechanism of CD1d-restricted natural killer T cell activation during microbial infection. Nat Immunol. (2003) 4:1230–7. 10.1038/ni1002
90.
NagarajanNAKronenbergM. Invariant NKT cells amplify the innate immune response to lipopolysaccharide. J Immunol. (2007) 178:2706–13. 10.4049/jimmunol.178.5.2706
91.
BirkholzANemčovičMYuEDGirardiEWangJKhuranaAet al. Lipid and carbohydrate modifications of α-galactosylceramide differently influence mouse and human type I natural killer T cell activation. J Biol Chem. (2015) 290:17206–17. 10.1074/jbc.M115.654814
92.
SullivanBANagarajanNAWingenderGWangJScottITsujiMet al. Mechanisms for glycolipid antigen-driven cytokine polarization by Valpha14i NKT cells. J Immunol. (2010) 184:141–53. 10.4049/jimmunol.0902880
93.
CarreñoLJRiquelmeEMGonzálezPAEspagnolleNRiedelCAValituttiSet al. T-cell antagonism by short half-life pMHC ligands can be mediated by an efficient trapping of T-cell polarization toward the APC. Proc Natl Acad Sci USA. (2010) 107:210–5. 10.1073/pnas.0911258107
94.
GonzálezPACarreñoLJCoombsDMoraJEPalmieriEGoldsteinBet al. T cell receptor binding kinetics required for T cell activation depend on the density of cognate ligand on the antigen-presenting cell. Proc Natl Acad Sci USA. (2005) 102:4824–9. 10.1073/pnas.0500922102
95.
LeeYJHolzapfelKLZhuJJamesonSCHogquistKA. Steady-state production of IL-4 modulates immunity in mouse strains and is determined by lineage diversity of iNKT cells. Nat Immunol. (2013) 14:1146–54. 10.1038/ni.2731
96.
YuKOImJSMolanoADutroncYIllarionovPAForestierCet al. Modulation of CD1d-restricted NKT cell responses by using N-acyl variants of alpha-galactosylceramides. Proc Natl Acad Sci USA. (2005) 102:3383–8. 10.1073/pnas.0407488102
97.
ImJSAroraPBricardGMolanoAVenkataswamyMMBaineIet al. Kinetics and cellular site of glycolipid loading control the outcome of natural killer T cell activation. Immunity. (2009) 30:888–98. 10.1016/j.immuni.2009.03.022
98.
WilsonMTJohanssonCOlivares-VillagómezDSinghAKStanicAKWangCRet al. The response of natural killer T cells to glycolipid antigens is characterized by surface receptor down-modulation and expansion. Proc Natl Acad Sci USA. (2003) 100:10913–8. 10.1073/pnas.1833166100
99.
CroweNYUldrichAPKyparissoudisKHammondKJHayakawaYSidobreSet al. Glycolipid antigen drives rapid expansion and sustained cytokine production by NKT cells. J Immunol. (2003) 171:4020–7. 10.4049/jimmunol.171.8.4020
100.
FujiiSShimizuKKronenbergMSteinmanRM. Prolonged IFN-gamma-producing NKT response induced with alpha-galactosylceramide-loaded DCs. Nat Immunol. (2002) 3:867–74. 10.1038/ni827
101.
ParekhVVWilsonMTOlivares-VillagómezDSinghAKWuLWangCRet al. Glycolipid antigen induces long-term natural killer T cell anergy in mice. J Clin Invest. (2005) 115:2572–83. 10.1172/JCI24762
102.
UldrichAPCroweNYKyparissoudisKPellicciDGZhanYLewAMet al. NKT cell stimulation with glycolipid antigen in vivo: costimulation-dependent expansion, Bim-dependent contraction, and hyporesponsiveness to further antigenic challenge. J Immunol. (2005) 175:3092–101. 10.4049/jimmunol.175.5.3092
103.
SullivanBAKronenbergM. Activation or anergy: NKT cells are stunned by alpha-galactosylceramide. J Clin Invest. (2005) 115:2328–9. 10.1172/JCI26297
104.
KimSLalaniSParekhVVVincentTLWuLVan KaerL. Impact of bacteria on the phenotype, functions, and therapeutic activities of invariant NKT cells in mice. J Clin Invest. (2008) 118:2301–15. 10.1172/JCI33071
105.
ChibaADascherCCBesraGSBrennerMB. Rapid NKT cell responses are self-terminating during the course of microbial infection. J Immunol. (2008) 181:2292–302. 10.4049/jimmunol.181.4.2292
106.
ChoiHJXuHGengYColmoneAChoHWangCR. Bacterial infection alters the kinetics and function of iNKT cell responses. J Leukoc Biol. (2008) 84:1462–71. 10.1189/jlb.0108038
107.
JoshiSKLangGALarabeeJLDeveraTSAyeLMShahHBet al. Bacillus anthracis lethal toxin disrupts TCR signaling in CD1d-restricted NKT cells leading to functional anergy. PLoS Pathog. (2009) 5:e1000588. 10.1371/journal.ppat.1000588
108.
RafteryMJWinauFGieseTKaufmannSHSchaibleUESchönrichG. Viral danger signals control CD1d de novo synthesis and NKT cell activation. Eur J Immunol. (2008) 38:668–79. 10.1002/eji.200737233
109.
MontoyaCJJieHBAl-HarthiLMulderCPatiñoPJRugelesMTet al. Activation of plasmacytoid dendritic cells with TLR9 agonists initiates invariant NKT cell-mediated cross-talk with myeloid dendritic cells. J Immunol. (2006) 177:1028–39. 10.4049/jimmunol.177.2.1028
110.
KarmakarSBhaumikSKPaulJDeT. TLR4 and NKT cell synergy in immunotherapy against visceral leishmaniasis. PLoS Pathog. (2012) 8:e1002646. 10.1371/journal.ppat.1002646
111.
ChenTGuoJHanCYangMCaoX. Heat shock protein 70, released from heat-stressed tumor cells, initiates antitumor immunity by inducing tumor cell chemokine production and activating dendritic cells via TLR4 pathway. J Immunol. (2009) 182:1449–59. 10.4049/jimmunol.182.3.1449
112.
SharmaAKLaParDJStoneMLZhaoYKronILLaubachVE. Receptor for advanced glycation end products (RAGE) on iNKT cells mediates lung ischemia-reperfusion injury. Am J Transplant. (2013) 13:2255–67. 10.1111/ajt.12368
113.
PagetCMallevaeyTSpeakAOTorresDFontaineJSheehanKCet al. Activation of invariant NKT cells by toll-like receptor 9-stimulated dendritic cells requires type I interferon and charged glycosphingolipids. Immunity. (2007) 27:597–609. 10.1016/j.immuni.2007.08.017
114.
WangXBishopKAHegdeSRodenkirchLAPikeJWGumperzJE. Human invariant natural killer T cells acquire transient innate responsiveness via histone H4 acetylation induced by weak TCR stimulation. J Exp Med. (2012) 209:987–1000. 10.1084/jem.20111024
115.
FerhatMHRobinABarbierLThierryAGombertJMBarbarinAet al. The impact of invariant NKT cells in sterile inflammation: the possible contribution of the alarmin/cytokine IL-33. Front Immunol. (2018) 9:2308. 10.3389/fimmu.2018.02308
116.
KitamuraHIwakabeKYahataTNishimuraSOhtaAOhmiYet al. The natural killer T (NKT) cell ligand alpha-galactosylceramide demonstrates its immunopotentiating effect by inducing interleukin (IL)-12 production by dendritic cells and IL-12 receptor expression on NKT cells. J Exp Med. (1999) 189:1121–8. 10.1084/jem.189.7.1121
117.
BriglMTatituriRVWattsGFBhowruthVLeadbetterEABartonNet al. Innate and cytokine-driven signals, rather than microbial antigens, dominate in natural killer T cell activation during microbial infection. J Exp Med. (2011) 208:1163–77. 10.1084/jem.20102555
118.
WesleyJDTessmerMSChaukosDBrossayL. NK cell-like behavior of Valpha14i NK T cells during MCMV infection. PLoS Pathog. (2008) 4:e1000106. 10.1371/journal.ppat.1000106
119.
BendelacASavagePBTeytonL. The biology of NKT cells. Annu Rev Immunol. (2007) 25:297–336. 10.1146/annurev.immunol.25.022106.141711
120.
Bendelac. Mouse NK1+ T cells. Curr Opin Immunol. (1995) 7:367–74. 10.1016/0952-7915(95)80112-X
121.
KuylenstiernaCBjörkströmNKAnderssonSKSahlströmPBosnjakLPaquin-ProulxDet al. NKG2D performs two functions in invariant NKT cells: direct TCR-independent activation of NK-like cytolysis and co-stimulation of activation by CD1d. Eur J Immunol. (2011) 41:1913–23. 10.1002/eji.200940278
122.
BriglMBrennerMB. How invariant natural killer T cells respond to infection by recognizing microbial or endogenous lipid antigens. Semin Immunol. (2010) 22:79–86. 10.1016/j.smim.2009.10.006
123.
SalioMSpeakAOShepherdDPolzellaPIllarionovPAVeerapenNet al. Modulation of human natural killer T cell ligands on TLR-mediated antigen-presenting cell activation. Proc Natl Acad Sci USA. (2007) 104:20490–5. 10.1073/pnas.0710145104
124.
YangOORackeFKNguyenPTGauslingRSeverinoMEHortonHFet al. CD1d on myeloid dendritic cells stimulates cytokine secretion from and cytolytic activity of V alpha 24J alpha Q T cells: a feedback mechanism for immune regulation. J Immunol. (2000) 165:3756–62. 10.4049/jimmunol.165.7.3756
125.
YooJKBracialeTJ. IL-21 promotes late activator APC-mediated T follicular helper cell differentiation in experimental pulmonary virus infection. PLoS ONE. (2014) 9:e105872. 10.1371/journal.pone.0105872
126.
TarabanVYMartinSAttfieldKEGlennieMJElliottTElewautDet al. Invariant NKT cells promote CD8+ cytotoxic T cell responses by inducing CD70 expression on dendritic cells. J Immunol. (2008) 180:4615–20. 10.4049/jimmunol.180.7.4615
127.
HermansIFSilkJDGileadiUSalioMMathewBRitterGet al. NKT cells enhance CD4+ and CD8+ T cell responses to soluble antigen in vivo through direct interaction with dendritic cells. J Immunol. (2003) 171:5140–7. 10.4049/jimmunol.171.10.5140
128.
FujiiSIYamasakiSSatoYShimizuK. Vaccine designs utilizing invariant NKT-licensed antigen-presenting cells provide NKT or T cell help for B cell responses. Front Immunol. (2018) 9:1267. 10.3389/fimmu.2018.01267
129.
LangML. How do natural killer T cells help B cells?Expert Rev Vaccines. (2009) 8:1109–21. 10.1586/erv.09.56
130.
DohertyDGMeloAMMoreno-OliveraASolomosAC. Activation and regulation of B cell responses by invariant natural killer T cells. Front Immunol. (2018) 9:1360. 10.3389/fimmu.2018.01360
131.
Vomhof-DeKreyEEYatesJLeadbetterEA. Invariant NKT cells provide innate and adaptive help for B cells. Curr Opin Immunol. (2014) 28:12–7. 10.1016/j.coi.2014.01.007
132.
DellabonaPAbrignaniSCasoratiG. iNKT-cell help to B cells: a cooperative job between innate and adaptive immune responses. Eur J Immunol. (2014) 44:2230–7. 10.1002/eji.201344399
133.
BarralPEckl-DornaJHarwoodNEde SantoCSalioMIllarionovPet al. B cell receptor-mediated uptake of CD1d-restricted antigen augments antibody responses by recruiting invariant NKT cell help in vivo. Proc Natl Acad Sci USA. (2008) 105:8345–50. 10.1073/pnas.0802968105
134.
ChangPPBarralPFitchJPratamaAMaCSKalliesAet al. Identification of Bcl-6-dependent follicular helper NKT cells that provide cognate help for B cell responses. Nat Immunol. (2012) 13:35–43. 10.1038/ni.2166
135.
KingILFortierATigheMDibbleJWattsGFVeerapenNet al. Invariant natural killer T cells direct B cell responses to cognate lipid antigen in an IL-21-dependent manner. Nat Immunol. (2012) 13:44–50. 10.1038/ni.2172
136.
LeadbetterEABriglMIllarionovPCohenNLuteranMCPillaiSet al. NK T cells provide lipid antigen-specific cognate help for B cells. Proc Natl Acad Sci USA. (2008) 105:8339–44. 10.1073/pnas.0801375105
137.
TontiEGalliGMalzoneCAbrignaniSCasoratiGDellabonaP. NKT-cell help to B lymphocytes can occur independently of cognate interaction. Blood. (2009) 113:370–6. 10.1182/blood-2008-06-166249
138.
GrayJDHorwitzDA. Activated human NK cells can stimulate resting B cells to secrete immunoglobulin. J Immunol. (1995) 154:5656–64.
139.
GayaMBarralPBurbageMAggarwalSMontanerBWarren NaviaAet al. Initiation of antiviral B cell immunity relies on innate signals from spatially positioned NKT cells. Cell. (2017) 172:517–33.e20. 10.1016/j.cell.2017.11.036
140.
BerzinsSPCochraneADPellicciDGSmythMJGodfreyDI. Limited correlation between human thymus and blood NKT cell content revealed by an ontogeny study of paired tissue samples. Eur J Immunol. (2005) 35:1399–407. 10.1002/eji.200425958
141.
LongHMChagouryOLLeeseAMRyanGBJamesEMortonLTet al. MHC II tetramers visualize human CD4+ T cell responses to Epstein-Barr virus infection and demonstrate atypical kinetics of the nuclear antigen EBNA1 response. J Exp Med. (2013) 210:933–49. 10.1084/jem.20121437
142.
YuKKQWilburnDBHackneyJADarrahPAFouldsKEJamesCAet al. Conservation of molecular and cellular phenotypes of invariant NKT cells between humans and non-human primates. Immunogenetics. (2019) 71:465–78. 10.1007/s00251-019-01118-9
143.
De SantoCSalioMMasriSHLeeLYDongTSpeakAOet al. Invariant NKT cells reduce the immunosuppressive activity of influenza A virus-induced myeloid-derived suppressor cells in mice and humans. J Clin Invest. (2008) 118:4036–48. 10.1172/JCI36264
144.
KokWLDenneyLBenamKColeSClellandCMcMichaelAJet al. Pivotal advance: invariant NKT cells reduce accumulation of inflammatory monocytes in the lungs and decrease immune-pathology during severe influenza A virus infection. J Leukoc Biol. (2012) 91:357–68. 10.1189/jlb.0411184
145.
IshikawaHTanakaKKutsukakeEFukuiTSasakiHHataAet al. IFN-γ production downstream of NKT cell activation in mice infected with influenza virus enhances the cytolytic activities of both NK cells and viral antigen-specific CD8+ T cells. Virology. (2010) 407:325–32. 10.1016/j.virol.2010.08.030
146.
PagetCIvanovSFontaineJBlancFPichavantMRennesonJet al. Potential role of invariant NKT cells in the control of pulmonary inflammation and CD8+ T cell response during acute influenza A virus H3N2 pneumonia. J Immunol. (2011) 186:5590–602. 10.4049/jimmunol.1002348
147.
KulkarniRRHaeryfarSMSharifS. The invariant NKT cell subset in anti-viral defenses: a dark horse in anti-influenza immunity?J Leukoc Biol. (2010) 88:635–43. 10.1189/jlb.0410191
148.
HoLPDenneyLLuhnKTeohDClellandCMcMichaelAJ. Activation of invariant NKT cells enhances the innate immune response and improves the disease course in influenza A virus infection. Eur J Immunol. (2008) 38:1913–22. 10.1002/eji.200738017
149.
PagetCIvanovSFontaineJRennesonJBlancFPichavantMet al. Interleukin-22 is produced by invariant natural killer T lymphocytes during influenza A virus infection: potential role in protection against lung epithelial damages. J Biol Chem. (2012) 287:8816–29. 10.1074/jbc.M111.304758
150.
BentonKAMisplonJALoCYBrutkiewiczRRPrasadSAEpsteinSL. Heterosubtypic immunity to influenza A virus in mice lacking IgA, all Ig, NKT cells, or gamma delta T cells. J Immunol. (2001) 166:7437–45. 10.4049/jimmunol.166.12.7437
151.
RenuSDhakalSKimEGoodmanJLakshmanappaYSWannemuehlerMJet al. Intranasal delivery of influenza antigen by nanoparticles, but not NKT-cell adjuvant differentially induces the expression of B-cell activation factors in mice and swine. Cell Immunol. (2018) 329:27–30. 10.1016/j.cellimm.2018.04.005
152.
DwivediVManickamCDhakalSBinjawadagiBOuyangKHiremathJet al. Adjuvant effects of invariant NKT cell ligand potentiates the innate and adaptive immunity to an inactivated H1N1 swine influenza virus vaccine in pigs. Vet Microbiol. (2016) 186:157–63. 10.1016/j.vetmic.2016.02.028
153.
ArtiagaBLYangGHackmannTJLiuQRichtJASalek-ArdakaniSet al. α-Galactosylceramide protects swine against influenza infection when administered as a vaccine adjuvant. Sci Rep. (2016) 6:23593. 10.1038/srep23593
154.
LeePTBenlaghaKTeytonLBendelacA. Distinct functional lineages of human V(alpha)24 natural killer T cells. J Exp Med. (2002) 195:637–41. 10.1084/jem.20011908
155.
ChenYGTsaihSWSerrezeDV. Genetic control of murine invariant natural killer T-cell development dynamically differs dependent on the examined tissue type. Genes Immun. (2012) 13:164–74. 10.1038/gene.2011.68
156.
GadolaSDDulphyNSalioMCerundoloV. Valpha24-JalphaQ-independent V, CD1d-restricted recognition of alpha-galactosylceramide by human CD4(+) and CD8alphabeta(+) T lymphocytes. J Immunol. (2002) 168:5514–20. 10.4049/jimmunol.168.11.5514
157.
TakahashiTChibaSNiedaMAzumaTIshiharaSShibataYet al. Cutting edge: analysis of human V alpha 24+CD8+ NK T cells activated by alpha-galactosylceramide-pulsed monocyte-derived dendritic cells. J Immunol. (2002) 168:3140–4. 10.4049/jimmunol.168.7.3140
158.
TownsendMJWeinmannASMatsudaJLSalomonRFarnhamPJBironCAet al. T-bet regulates the terminal maturation and homeostasis of NK and Valpha14i NKT cells. Immunity. (2004) 20:477–94. 10.1016/S1074-7613(04)00076-7
159.
EngelISeumoisGChavezLSamaniego-CastruitaDWhiteBChawlaAet al. Innate-like functions of natural killer T cell subsets result from highly divergent gene programs. Nat Immunol. (2016) 17:728–39. 10.1038/ni.3437
160.
GeorgievHRavensIBenarafaCFörsterRBernhardtG. Distinct gene expression patterns correlate with developmental and functional traits of iNKT subsets. Nat Commun. (2016) 7:13116. 10.1038/ncomms13116
161.
LeeYJStarrettGJLeeSTYangRHenzlerCMJamesonSCet al. Lineage-specific effector signatures of invariant NKT cells are shared amongst γδ T, innate lymphoid, Th cells. J Immunol. (2016) 197:1460–70. 10.4049/jimmunol.1600643
162.
ConstantinidesMGBendelacA. Transcriptional regulation of the NKT cell lineage. Curr Opin Immunol. (2013) 25:161–7. 10.1016/j.coi.2013.01.003
163.
KimPJPaiSYBriglMBesraGSGumperzJHoIC. GATA-3 regulates the development and function of invariant NKT cells. J Immunol. (2006) 177:6650–9. 10.4049/jimmunol.177.10.6650
164.
DoisneJMBecourtCAmniaiLDuarteNLe LuduecJBEberlGet al. Skin and peripheral lymph node invariant NKT cells are mainly retinoic acid receptor-related orphan receptor (gamma)t+ and respond preferentially under inflammatory conditions. J Immunol. (2009) 183:2142–9. 10.4049/jimmunol.0901059
165.
JaiswalAKSadasivamMHamadARA. Syndecan-1-coating of interleukin-17-producing natural killer T cells provides a specific method for their visualization and analysis. World J Diabetes. (2017) 8:130–4. 10.4239/wjd.v8.i4.130
166.
LynchLMicheletXZhangSBrennanPJMosemanALesterCet al. Regulatory iNKT cells lack expression of the transcription factor PLZF and control the homeostasis of T(reg) cells and macrophages in adipose tissue. Nat Immunol. (2015) 16:85–95. 10.1038/ni.3047
167.
WingenderGSagDKronenbergM. NKT10 cells: a novel iNKT cell subset. Oncotarget. (2015) 6:26552–3. 10.18632/oncotarget.5270
168.
SavageAKConstantinidesMGHanJPicardDMartinELiBet al. The transcription factor PLZF directs the effector program of the NKT cell lineage. Immunity. (2008) 29:391–403. 10.1016/j.immuni.2008.07.011
169.
KovalovskyDUcheOUEladadSHobbsRMYiWAlonzoEet al. The BTB-zinc finger transcriptional regulator PLZF controls the development of invariant natural killer T cell effector functions. Nat Immunol. (2008) 9:1055–64. 10.1038/ni.1641
170.
KovalovskyDAlonzoESUcheOUEidsonMNicholsKESant'AngeloDB. PLZF induces the spontaneous acquisition of memory/effector functions in T cells independently of NKT cell-related signals. J Immunol. (2010) 184:6746–55. 10.4049/jimmunol.1000776
171.
CrosbyCMKronenbergM. Tissue-specific functions of invariant natural killer T cells. Nat Rev Immunol. (2018) 18:559–74. 10.1038/s41577-018-0034-2
172.
WolfBJChoiJEExleyMA. Novel approaches to exploiting invariant NKT cells in cancer immunotherapy. Front Immunol. (2018) 9:384. 10.3389/fimmu.2018.00384
173.
MiyamotoKMiyakeSYamamuraT. A synthetic glycolipid prevents autoimmune encephalomyelitis by inducing TH2 bias of natural killer T cells. Nature. (2001) 413:531–4. 10.1038/35097097
174.
BaevDVCaielliSRonchiFCocciaMFacciottiFNicholsKEet al. Impaired SLAM-SLAM homotypic interaction between invariant NKT cells and dendritic cells affects differentiation of IL-4/IL-10-secreting NKT2 cells in nonobese diabetic mice. J Immunol. (2008) 181:869–77. 10.4049/jimmunol.181.2.869
175.
SagDKrausePHedrickCCKronenbergMWingenderG. IL-10-producing NKT10 cells are a distinct regulatory invariant NKT cell subset. J Clin Invest. (2014) 124:3725–40. 10.1172/JCI72308
176.
YuKOPorcelliSA. The diverse functions of CD1d-restricted NKT cells and their potential for immunotherapy. Immunol Lett. (2005) 100:42–55. 10.1016/j.imlet.2005.06.010
177.
OkiSChibaAYamamuraTMiyakeS. The clinical implication and molecular mechanism of preferential IL-4 production by modified glycolipid-stimulated NKT cells. J Clin Invest. (2004) 113:1631–40. 10.1172/JCI200420862
178.
OkiSTomiCYamamuraTMiyakeS. Preferential T(h)2 polarization by OCH is supported by incompetent NKT cell induction of CD40L and following production of inflammatory cytokines by bystander cells in vivo. Int Immunol. (2005) 17:1619–29. 10.1093/intimm/dxh342
179.
McCarthyCShepherdDFleireSStrongeVSKochMIllarionovPAet al. The length of lipids bound to human CD1d molecules modulates the affinity of NKT cell TCR and the threshold of NKT cell activation. J Exp Med. (2007) 204:1131–44. 10.1084/jem.20062342
180.
SchmiegJYangGFranckRWTsujiM. Superior protection against malaria and melanoma metastases by a C-glycoside analogue of the natural killer T cell ligand alpha-Galactosylceramide. J Exp Med. (2003) 198:1631–41. 10.1084/jem.20031192
181.
WunKSCameronGPatelOPangSSPellicciDGSullivanLCet al. A molecular basis for the exquisite CD1d-restricted antigen specificity and functional responses of natural killer T cells. Immunity. (2011) 34:327–39. 10.1016/j.immuni.2011.02.001
182.
TashiroTSekine-KondoEShigeuraTNakagawaRInoueSOmori-MiyakeMet al. Induction of Th1-biased cytokine production by alpha-carba-GalCer, a neoglycolipid ligand for NKT cells. Int Immunol. (2010) 22:319–28. 10.1093/intimm/dxq012
183.
LiXFujioMImamuraMWuDVasanSWongCHet al. Design of a potent CD1d-binding NKT cell ligand as a vaccine adjuvant. Proc Natl Acad Sci USA. (2010) 107:13010–5. 10.1073/pnas.1006662107
184.
LinKHLiangJJHuangWILin-ChuSYSuCYLeeYLet al. In vivo protection provided by a synthetic new alpha-galactosyl ceramide analog against bacterial and viral infections in murine models. Antimicrob Agents Chemother. (2010) 54:4129–36. 10.1128/AAC.00368-10
185.
OsmanYKawamuraTNaitoTTakedaKVan KaerLOkumuraKet al. Activation of hepatic NKT cells and subsequent liver injury following administration of alpha-galactosylceramide. Eur J Immunol. (2000) 30:1919–28. 10.1002/1521-4141(200007)30:7<1919::AID-IMMU1919>3.0.CO;2-3
186.
KimHYKimSChungDH. FcgammaRIII engagement provides activating signals to NKT cells in antibody-induced joint inflammation. J Clin Invest. (2006) 116:2484–92. 10.1172/JCI27219
187.
Miellot-GafsouABitonJBourgeoisEHerbelinABoissierMCBessisN. Early activation of invariant natural killer T cells in a rheumatoid arthritis model and application to disease treatment. Immunology. (2010) 130:296–306. 10.1111/j.1365-2567.2009.03235.x
188.
MeyerEHGoyaSAkbariOBerryGJSavagePBKronenbergMet al. Glycolipid activation of invariant T cell receptor+ NK T cells is sufficient to induce airway hyperreactivity independent of conventional CD4+ T cells. Proc Natl Acad Sci USA. (2006) 103:2782–7. 10.1073/pnas.0510282103
189.
MatangkasombutPPichavantMYasumiTHendricksCSavagePBDekruyffRHet al. Direct activation of natural killer T cells induces airway hyperreactivity in nonhuman primates. J Allergy Clin Immunol. (2008) 121:1287–9. 10.1016/j.jaci.2008.02.006
190.
KimJOKimDHChangWSHongCParkSHKimSet al. Asthma is induced by intranasal coadministration of allergen and natural killer T-cell ligand in a mouse model. J Allergy Clin Immunol. (2004) 114:1332–8. 10.1016/j.jaci.2004.09.004
191.
KhuranaSLovingCLManischewitzJKingLRGaugerPCHenningsonJet al. Vaccine-induced anti-HA2 antibodies promote virus fusion and enhance influenza virus respiratory disease. Sci Transl Med. (2013) 5:200ra114. 10.1126/scitranslmed.3006366
192.
RymarchykSLLowensteinHMayetteJFosterSRDambyDEHoweIWet al. Widespread natural variation in murine natural killer T-cell number and function. Immunology. (2008) 125:331–43. 10.1111/j.1365-2567.2008.02846.x
193.
BerninHFehlingHMarggraffCTannichELotterH. The cytokine profile of human NKT cells and PBMCs is dependent on donor sex and stimulus. Med Microbiol Immunol. (2016) 205:321–32. 10.1007/s00430-016-0449-y
194.
MetelitsaLSWuHWWangHYangYWarsiZAsgharzadehSet al. Natural killer T cells infiltrate neuroblastomas expressing the chemokine CCL2. J Exp Med. (2004) 199:1213–21. 10.1084/jem.20031462
195.
SchneidersFLde BruinRCvan den EertweghAJScheperRJLeemansCRBrakenhoffRHet al. Circulating invariant natural killer T-cell numbers predict outcome in head and neck squamous cell carcinoma: updated analysis with 10-year follow-up. J Clin Oncol. (2012) 30:567–70. 10.1200/JCO.2011.38.8819
196.
DelaRosaOTarazonaRCasadoJGAlonsoCOstosBPeñaJet al. Valpha24+ NKT cells are decreased in elderly humans. Exp Gerontol. (2002) 37:213–7. 10.1016/S0531-5565(01)00186-3
197.
TsukaharaASekiSIiaiTMorodaTWatanabeHSuzukiSet al. Mouse liver T cells: their change with aging and in comparison with peripheral T cells. Hepatology. (1997) 26:301–9. 10.1002/hep.510260208
198.
FaunceDEPalmerJLPaskowiczKKWittePLKovacsEJ. CD1d-restricted NKT cells contribute to the age-associated decline of T cell immunity. J Immunol. (2005) 175:3102–9. 10.4049/jimmunol.175.5.3102
199.
MocchegianiEGiacconiRCiprianoCGaspariniNBernardiniGMalavoltaMet al. The variations during the circadian cycle of liver CD1d-unrestricted NK1.1+TCR gamma/delta+ cells lead to successful ageing. Role of metallothionein/IL-6/gp130/PARP-1 interplay in very old mice. Exp Gerontol. (2004) 39:775–88. 10.1016/j.exger.2004.01.014
200.
MocchegianiEGiacconiRMutiERogoCBracciMMuzzioliMet al. Zinc, immune plasticity, aging, and successful aging: role of metallothionein. Ann NY Acad Sci. (2004) 1019:127–34. 10.1196/annals.1297.023
201.
StarbækSMRBrogaardLDawsonHDSmithADHeegaardPMHLarsenLEet al. Animal models for Influenza A virus infection incorporating the involvement of innate host defenses: enhanced translational value of the porcine model. ILAR J. (2018) 59:323–37. 10.1093/ilar/ily009
202.
BaiLDengSRebouletRMathewRTeytonLSavagePBet al. Natural killer T (NKT)-B-cell interactions promote prolonged antibody responses and long-term memory to pneumococcal capsular polysaccharides. Proc Natl Acad Sci USA. (2013) 110:16097–102. 10.1073/pnas.1303218110
Summary
Keywords
natural killer T (NKT) cells, influenza A virus, vaccines, immune modulation, adjuvant
Citation
Driver JP, de Carvalho Madrid DM, Gu W, Artiaga BL and Richt JA (2020) Modulation of Immune Responses to Influenza A Virus Vaccines by Natural Killer T Cells. Front. Immunol. 11:2172. doi: 10.3389/fimmu.2020.02172
Received
30 May 2020
Accepted
10 August 2020
Published
20 October 2020
Volume
11 - 2020
Edited by
Jordi Ochando, Icahn School of Medicine at Mount Sinai, United States
Reviewed by
Mark L. Lang, University of Oklahoma Health Sciences Center, United States; Estanislao Nistal-Villan, San Pablo CEU University, Spain
Updates
Copyright
© 2020 Driver, de Carvalho Madrid, Gu, Artiaga and Richt.
This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY). The use, distribution or reproduction in other forums is permitted, provided the original author(s) and the copyright owner(s) are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms.
*Correspondence: Jürgen A. Richt jricht@ksu.edu
This article was submitted to Vaccines and Molecular Therapeutics, a section of the journal Frontiers in Immunology
Disclaimer
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.