ACTIVE AND PASSIVE VACCINATION STRATEGIES AGAINST SARS-COV-2

Abstract

The COVID-19 pandemic underscored the urgent need for innovative vaccine platforms capable of addressing rapidly evolving SARS-CoV-2 variants and enhancing pandemic preparedness. Current intramuscularly administered vaccines, which solely target the spike protein, face diminished efficacy against antibody-escaping variants and provide limited protection for high-risk populations. This thesis presents three studies aimed at improving active and passive mucosal vaccination strategies against SARS-CoV-2. First, we developed and evaluated trivalent human (HuAd) and chimpanzee (ChAd) adenovirus-vectored COVID-19 vaccines encoding the spike, nucleocapsid, and RdRP antigens. In murine models, respiratory mucosal (RM) immunization induced robust tripartite immunity comprised of local and systemic antibody responses, mucosal tissue-resident memory T cells, and trained innate immunity. Moreover, RM vaccination conferred protection against both ancestral SARS-CoV-2 and emerging variants of concern (V oCs), highlighting the potential of Ad-vectored mucosal vaccines as next-generation solutions to address shortcomings in first-generation COVID-19 vaccines. In the second study, we extended this platform to human volunteers, revealing that repeated intramuscular mRNA immunization alone fails to elicit sufficient RM immunity, even in individuals with prior breakthrough infection. To bridge this gap, we administered our next- generation SARS-CoV-2 vaccine candidates via inhaled aerosol which was safe and well- tolerated. A single aerosolized dose induced airway T cell, antibodies, and innate immune memory, with cross-reactive T cells and antibodies against SARS-CoV-2 XBB.1.5. We also explored peripheral biomarkers that may serve as surrogates for the induction of robust RM immunity. Finally, in a complementary approach, we investigated aptamer nanomaterials based on TMSA52, a homotrimeric DNA aptamer engineered for broad neutralization of SARS-CoV- 2 VoC. When RM administered to mice, TMSA52 showed protective efficacy comparable to a monoclonal antibody, offering a cost-effective, scalable alternative for passive immunization. Together, these studies underscore the promise of RM vaccination strategies as critical innovations to enhance global pandemic preparedness.