Cytomegalovirus-Based Viral Vectors Elicit Robust Systemic and Tissue-Resident Immune Response Against SARS-CoV-2...

Current COVID-19 vaccines face challenges such as waning immunity and limited mucosal protection. These limitations highlight the importance of developing next-generation vaccines that can induce strong tissue-specific and systemic immune responses. Cytomegalovirus (CMV) represents a promising vaccine vector due to its ability to elicit robust and durable immunity. In this study, we generated murine CMV (MCMV)-based vaccine vectors expressing the SARS-CoV-2 spike (S) protein using either a wild-type or immunologically attenuated viral strain. By comparing intraperitoneal (IP) and intranasal (IN) immunization with both MCMV vectors, we show that IP administration induced higher, long-lasting S-specific antibody levels in serum. Both routes elicited strong systemic S-specific CD8⁺ T cell responses; however, CD8⁺ T cell responses induced by different immunization routes differed notably in their kinetics and phenotype. Importantly, IN immunization with recombinant MCMV vector expressing NKG2D ligand, RAE-1γ, resulted in a robust accumulation of lung-resident S-specific CD8⁺ T cells, surpassing even the levels induced by licensed COVID-19 vaccines. Overall, we demonstrate the potential of CMV-based vector vaccines to fine-tune immune responses by combining vector design with the route of delivery. By leveraging these variables, it is possible to influence both the magnitude and the quality of the immunity induced.