Increased antibody diversification in mice vaccinated with a self-amplifying RNA versus mRNA directed against SARS-CoV-2 spike protein 9225

Abstract Description Generating effective neutralizing antibodies is the goal of RNA-based vaccine platforms. We evaluated the comparative efficacy of antibody responses in C57BL/6 mice vaccinated at days 0 and 28 with a first-generation self-amplifying RNA (saRNA) versus a conventional mRNA directed against the SARS-CoV-2 spike protein. Analysis of circulating antibody titers at day 42 showed a significantly higher level of total spike-specific IgG in the mRNA-vaccinated mice (mRNA: 574.4 mg/mL vs saRNA: 169 mg/mL, p = 0.0003). Our measurement of the individual IgG subclass titers revealed mRNA IgG to be primarily composed of IgG1 (IgG1: 99%, IgG2a: 0.02%, IgG2b: 0.8%, IgG3: 0.2%), while the saRNA-vaccinated mice had a greater diversity of IgG subclasses (IgG1: 33%, IgG2a: 0.7%, IgG2b: 56%, IgG3: 10%). We found the greatest neutralization activity in the IgG2b subclass of the saRNA-vaccinated mice (saRNA: 17.5%, mRNA: 0.8%, expressed per microgram of IgG2b; p > 0.0001). By contrast, IgG1 (1 µg) from either vaccinated group showed similar neutralizing activity (saRNA: 7.2%, mRNA: 6.5%; p = NS). B cell repertoire analysis by scRNAseq showed increased BCR somatic hypermutation and clonal diversity in saRNA-vaccinated mice. These results suggest that single vaccination and boost by an saRNA vaccine, while generating less total antibody than a comparable mRNA vaccine targeting the SARS-CoV-2 spike protein, generates a greater diversity of IgG subclasses with higher neutralization activity. Funding Sources Ludwig Foundation Mathers Foundation Topic Categories Vaccines and Immunotherapy (VAC)