IMMUNOGENICITY OF EPIGRAPH ANTIGENS IN VACCINATION AGAINST SARS-COV-2 IN MICE

Abstract

The ongoing COVID-19 pandemic continues to rapidly evolve, remaining one of the leading public health concerns worldwide and making the development of a safe and effective vaccine a global priority. Most currently-available vaccines target the spike protein of wild-type SARS-CoV-2. However, new variants continue to emerge, which can evade pre-existing immunity and reduce vaccine efficacy, highlighting the urgent need for more generalizable vaccine platforms. Epigraph, a recently developed graph-based optimization algorithm, generates an artificial peptide sequence by measuring relative frequencies of peptide epitopes within a sampled population, and has previously shown efficacy in generating cross-reactive influenza and pan-filovirus vaccine candidates. Here, we apply this algorithm to the spike protein of SARS-CoV-2, and analyze the immunogenicity of epigraph-based vaccines in mice. Here, we have generated four RhAd52 vectors, each utilizing one of four different epigraph antigens, and we assess their immunogenicity in mice against vectors encoding ancestral, alpha, beta, and delta variant spike sequences. Here, we show with a MesoScale Discovery (MSD) antibody-binding assay comparable antibody responses against both SARS-CoV-2 full-length native spike and RBD, and a slight decrease of response kinetics. We observed similar results in pseudovirus neutralization assays, with neutralization titers comparable in mice vaccinated with epigraph antigens and natural antigens at week 4-post vaccination. Moreover, cellular immunogenicity of epigraph-vaccinated mice, as measured at week 4-post vaccination, demonstrated similar TNFa+/IFNg+ CD8+ T cell responses to those vaccinated with natural antigens, indicating appreciable immunogenicity of epigraph antigens. While studies assessing the in-vivo protective efficacy have yet to be completed, the present studies investigating the cross-neutralizing efficacy of a computationally-predicted antigen have profound implications for the fields of public health and vaccine development.