Induction of multivalent and balanced T cell responses by modular nanoshell vaccine technology

After the outbreak of COVID-19, cellular immunity has been shown to provide protection especially in breakthrough infection and B cell-deficient patients. Furthermore, durable cellular immunity targets conserved epitopes among SARS-CoV-2 variants or different coronavirus then inspiring an attractive strategy for vaccine development. However, how to simultaneously induce balanced T cell responses against multiple epitopes still needs to be elucidated. In this study, we sought to design a T cell-based vaccine that can adjust valency against different T cell epitopes. We selected seven SARS-CoV-2 specific short peptides as antigens, including I-Ab/H-2Kb/H-2Db restricted epitopes. Furthermore, we used PLGA nanoparticle as vaccine platform to achieve the precise loading of the indicated peptides. Mice were immunized with different combinations of peptides and splenocytes were used to access epitope specific-IFN gamma expressing CD8+ or CD4+ T cell responses. First, we confirmed the robust immunogenicity of each peptide. We then combined an equal amount of indicated epitope peptides and accessed the immunogenicity of each epitope in the combination. The results showed peptides compete with each other to induce T cell responses regardless of MHC allele and MHC class. In addition, dominant epitopes significantly suppressed the immunogenicity of the subdominant epitopes. Finally, by optimizing the antigen dose, nanoparticle vaccine induced more balanced T responses against all seven epitopes. Taking advantage of nanoparticle, our results reveal a viable strategy to induce multivalent T cell response. Furthermore, the result suggests that competition of T cell epitopes is one of the factors controlling cellular immunity.