Sustained antigen availability during germinal center initiation enhances antibody responses to vaccination.

Natural infections expose the immune system to escalating antigen and inflammation over days to weeks, whereas nonlive vaccines are single bolus events. We explored whether the immune system responds optimally to antigen kinetics most similar to replicating infections, rather than a bolus dose. Using HIV antigens, we found that administering a given total dose of antigen and adjuvant over 1-2 wk through repeated injections or osmotic pumps enhanced humoral responses, with exponentially increasing (exp-inc) dosing profiles eliciting >10-fold increases in antibody production relative to bolus vaccination post prime. Computational modeling of the germinal center response suggested that antigen availability as higher-affinity antibodies evolve enhances antigen capture in lymph nodes. Consistent with these predictions, we found that exp-inc dosing led to prolonged antigen retention in lymph nodes and increased Tfh cell and germinal center B-cell numbers. Thus, regulating the antigen and adjuvant kinetics may enable increased vaccine potency.

Generation of effector memory T cell-based mucosal and systemic immunity with pulmonary nanoparticle vaccination.

Many pathogens infiltrate the body and initiate infection via mucosal surfaces. Hence, eliciting cellular immune responses at mucosal portals of entry is of great interest for vaccine development against mucosal pathogens. We describe a pulmonary vaccination strategy combining Toll-like receptor (TLR) agonists with antigen-carrying lipid nanocapsules [interbilayer-crosslinked multilamellar vesicles (ICMVs)], which elicit high-frequency, long-lived, antigen-specific effector memory T cell responses at multiple mucosal sites. Pulmonary immunization using protein- or peptide-loaded ICMVs combined with two TLR agonists, polyinosinic-polycytidylic acid (polyI:C) and monophosphoryl lipid A, was safe and well tolerated in mice, and led to increased antigen transport to draining lymph nodes compared to equivalent subcutaneous vaccination. This response was mediated by the vast number of antigen-presenting cells (APCs) in the lungs. Nanocapsules primed 13-fold more T cells than did equivalent soluble vaccines, elicited increased expression of mucosal homing integrin α4ß7⁺, and generated long-lived T cells in both the lungs and distal (for example, vaginal) mucosa strongly biased toward an effector memory (T(EM)) phenotype. These T(EM) responses were highly protective in both therapeutic tumor and prophylactic viral vaccine settings. Together, these data suggest that targeting cross-presentation-promoting particulate vaccines to the APC-rich pulmonary mucosa can promote robust T cell responses for protection of mucosal surfaces.