Introduction: New vaccines would benefit from more defined compositions that provide modular control over specific immune pathways. Recent studies show that polymer carriers such as poly(lactide-co-glycolide) can exhibit intrinsic immunogenic characteristics that can complicate rationale design since the carrier itself can alter how the immune system processes vaccines[1]. We hypothesize that self-assembly of immune signals into polyelectrolyte multilayers (PEMs) might provide a route for simple, “carrier-free” vaccines assembled entirely from antigens and adjuvants. The immune-PEMs (iPEMs) are assembled in a layer-by-layer (LBL) manner from peptide antigens modified with cationic amino acids and an anionic, nucleic-acid based toll-like receptor agonist (TLRa) that serves as an adjuvant[2],[3]. iPEM capsules provide a high density of antigens and adjuvants since no carriers are involved, while also mimicking features of polymers such as tunable sizes and co-delivery.
Materials and Methods: iPEMs were assembled from PolyIC, a dsRNA TLR3 agonist, and a model antigen, SIINFEKL, modified with arginine residues as a cationic component. PEMs were assembled by alternately exposing CaCO3 to these two vaccine components. EDTA was then used to remove the core. Particle diameters were measured as a function of pH, and flow cytometry was used to assess dendritic cell (DC) activation and T cell proliferation. Mice were immunized intra-dermally and boosted at Day 15 or 28. SIINFEKL-specific T cells was measured in blood using MHC-I tetramer and lymph nodes (LNs) were analyzed by histology. For tumor studies, mice were challenged with 1x106 B16-OVA cells on Day 36.
Results and Discussion: iPEM capsules exhibited tunable sizes across nano- and micro-scales by varying the pH of the EDTA solution (Fig. 1A). Importantly, these sizes were maintained upon transfer to PBS (Fig. 1B), and were stable during incubation in PBS, media, and serum-containing media (Figure 1C). These materials offer tunable sizes for vaccination. In mice, iPEM capsules drove a significant expansion of antigen-specific T cells with a potent recall response that was 4.7-fold greater than that induced by admixed vaccines (i.e., free) containing the same dose of antigen and adjuvant (Fig. 2A). These effects were driven by co-localization of antigen and adjuvant in draining LNs (yellow signal, Fig. 2B) and efficient antigen presentation that induce greater proliferation in SIIN-specific CD8+ T during ex-vivo co-culture (Fig. 2C). Tumor challenge in mice revealed a significant increase in median survival, with a value of 25 days for mice immunized with iPEM capsules, and 16 days and 13 days for soluble vaccine and untreated mice, respectively (Figure 2D).
Conclusions: iPEMs eliminate carrier and supports but offer many useful features of biomaterials. These structures generate functional, antigen-specific T cell responses in mice and could serve as a simple, modular platform for studying and programming immunity.
A. Beaven at the University of Maryland Imaging Core Facility for assistance in confocal microscopy.
References:
[1] F.A. Sharp,PNAS, 2009. 106(3): 870-5.
[2] P.C. DeMuth, .Advanced Materials, 2010. 22(43):4851-56
[3] P. Zhang, ACS Nano, 2015. 9(6): 6465-77