Characterization of the Anti-Viral and Vaccine-Specific CD8⁺ T Cell Composition upon Treatment with the Cancer...

Numerous factors influence the magnitude and effector phenotype of vaccine-induced CD8⁺ T cells, thereby potentially impacting treatment efficacy. Here, we investigate the effect of vaccination dose, route of immunization, presence of a target antigen-expressing tumor, and heterologous prime-boost with peptide vaccine partner following vaccination with antigen-armed VSV-GP. Our results indicate that a higher vaccine dose increases antigen-specific CD8⁺ T cell proportions while altering the phenotype. The intravenous route induces the highest proportion of antigen-specific CD8⁺ T cells together with the lowest anti-viral response followed by the intraperitoneal, intramuscular, and subcutaneous routes. Moreover, the presence of a B16-OVA tumor serves as pre-prime, thereby increasing OVA-specific CD8⁺ T cells upon vaccination and thus altering the ratio of anti-tumor versus anti-viral CD8⁺ T cells. Interestingly, tumor-specific CD8⁺ T cells exhibit a different phenotype compared to bystander anti-viral CD8⁺ T cells. Finally, the heterologous combination of peptide and viral vaccine elicits the highest proportion of antigen-specific CD8⁺ T cells in the tumor and tumor-draining lymph nodes. In summary, we provide a basic immune characterization of various factors that affect anti-viral and vaccine target-specific CD8⁺ T cell proportions and phenotypes, thereby enhancing our vaccinology knowledge for future vaccine regimen designs.