In-Situ Self-Assembling Oligomeric Collagen Scaffold Enhances Vaccine Retention and Vaccine-Induced Humoral Immunity

<b>Background/Objectives</b>: Subunit vaccines composed of purified proteins and adjuvants offer excellent safety, but often generate short-lived immunity due to rapid antigen clearance and limited antigen-presenting cell engagement. Sustained, localized delivery of antigen and adjuvant may improve the magnitude and durability of the immune response without compromising safety. This study evaluated an in-situ polymerizing type I oligomeric collagen (Oligomer) scaffold to localize antigen/adjuvant at the injection site and prolong antigen presentation. <b>Methods</b>: Mice were immunized intramuscularly with ovalbumin (OVA) and CpG oligonucleotide adjuvant delivered alone or co-formulated with Oligomer. Antibody response and inflammation at the injection site were assessed post-booster at early (Day 32) and late (Day 68) time points. Antigen retention and dendritic cell trafficking to draining lymph nodes were evaluated using fluorescently labeled OVA. <b>Results</b>: The Oligomer scaffold retained vaccine antigen at the injection site without eliciting a material-mediated foreign body response. Co-delivery of OVA and CpG within the scaffold enhanced germinal center activity, increased follicular helper T cells and germinal center B cells, and skewed CD4⁺ T cells toward a Th1 phenotype. Humoral responses were greater and more durable, with higher OVA-specific IgG, IgG1, and IgG2a titers and an increased number of bone marrow antibody-secreting cells persisting through Day 68. Antigen-positive dendritic cells, including both resident and migratory subsets, were elevated in draining lymph nodes, indicating enhanced antigen transport. No anti-mouse collagen I antibodies were detected, confirming the maintenance of collagen self-tolerance. <b>Conclusions</b>: The Oligomer delivery platform functioned as a localized, immunotolerant vaccine depot, sustaining antigen availability and immune cell engagement. This spatiotemporal control enhanced germinal center responses and generated a more robust, durable humoral immune response, supporting its potential to improve subunit vaccine efficacy while maintaining an excellent safety profile.