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 might induce equivalent or more potent immune responses at lower doses compared to non-replicating mRNA vaccines via amplified antigen expression. In this paper we demonstrate that 1 μg of a LNP formulated dual-antigen self-amplifying RNA vaccine (ZIP1642), encoding both the S-RBD and N antigen, elicits considerably higher neutralizing antibody titers against Wuhan-like, beta B.1.351 and delta B.1.617.2 SARS-CoV-2 variants compared to those of convalescent patients. Additionally, 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 demonstrate that induction of such dual-antigen-targeted cell-mediated immune response might 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 towards the induction 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