Evaluation of the long-term anti-Spike immune response following a novel coronavirus vaccine (CORVax): electroporation of SARS-CoV-2 Spike plasmid DNA plus IL12 plasmid DNA

Abstract

Abstract The global SARS-CoV-2 (CoV2) pandemic has focused efforts to generate effective vaccines that induce potent and persistent immunity. Recently, we described a novel vaccine approach using electroporation (EP) of a plasmid encoding a prefusion stabilized CoV2 spike protein (CORVax) plus plasmid Interleukin-12 (IL-12). IL-12 is an effective vaccine adjuvant that increases Th1 and Th2 antibodies in the serum. Here we examine the persistence of anti-Spike antibodies present in the serum of mice one year following CORVax vaccination. C57BL/6 and BALB/c were vaccinated intramuscular (IM) and/or intradermal (ID) with a plasmid encoding the CoV2 spike protein with or without plasmid-encoded murine IL-12. Mice received plasmid EP immediately following injection. Splenocytes and serum were harvested at various time points to interrogate virus-specific cellular responses as well anti-spike antibody titers. Anti-Spike IgG antibodies were elicited by EP of CORVax (IC50 = 1/2112), as well as EP of CORVax combined with IL-12 (IC50 = 1/4214) approximately 40 days after the booster vaccination. These anti-Spike IgG titers decayed over time but were still present 1 year after vaccination: CORVax (IC50 = 1/351 day 146, IC50 = 1/208 day 383); CORVax + IL12 (IC50 = 1/590 day 146, IC50 = 1/266 day 383). Our data shows that EP of CORVax induces IgG responses to CoV2 Spike and the CoV2 Spike receptor binding domain. At one year following vaccination the anti-Spike IgG titers were higher in mice that received CORVax plus IL-12, however the rate at which the titers waned from their initial peak was comparable whether the mice received IL-12 or not. Additional studies are ongoing to determine whether the addition of IL-12 will enhance an anti-Spike memory response. Generous support from The Chiles Foundation, Nancy Lematta, and the Providence Medical Foundation.