A dual-antigen self-amplifying RNA SARS-CoV-2 vaccine induces potent humoral and cellular immune responses and protects against SARS-CoV-2 variants through T cell-mediated immunity

Self-amplifying RNA vaccines may induce equivalent or more potent immune responses at lower doses compared to non-repli-
cating mRNA vaccines via amplified antigen expression. In this paper, we demonstrate that 1 mg of an LNP-formulated dual-
antigen self-amplifying RNA vaccine (ZIP1642), encoding both the S-RBD and N antigen, elicits considerably higher neutral-
izing antibody titers against Wuhan-like Beta B.1.351 and Delta B.1.617.2 SARS-CoV-2 variants compared to those of convales- cent patients. In addition, ZIP1642 vaccination in mice expanded both S- and N-specific CD3+ CD4+ and CD3+
CD8+ T cells and caused a Th1 shifted cytokine response. We demon- strate that the induction of such dual antigen-targeted cell-medi- ated immune response may provide better protection against variants displaying highly mutated Spike proteins, as infectious viral loads of both Wuhan-like and Beta variants were decreased after challenge of ZIP1642 vaccinated hamsters. Supported by these results, we encourage redirecting focus toward the induc- tion of multiple antigen-targeted cell-mediated immunity in addition to neutralizing antibody responses to bypass waning antibody responses and attenuate infectious breakthrough and disease severity of future SARS-CoV-2 variants.