ABSTRACT
We have previously reported that the SARS-CoV-2 neutralizing antibody, STI-2020, potently inhibits cytopathic effects of infection by genetically diverse clinical SARS-CoV-2 pandemic isolates in vitro, and has demonstrated efficacy in a hamster model of COVID-19 when administered by the intravenous route immediately following infection. We now have extended our in vivo studies of STI-2020 to include disease treatment efficacy, profiling of biodistribution of STI-2020 in mice when antibody is delivered intranasally (IN) or intravenously (IV), as well as pharmacokinetics in mice following IN antibody administration. Importantly, SARS-CoV-2-infected hamsters were treated with STI-2020 using these routes, and treatment effects on severity and duration of COVID-19-like disease in this model were evaluated. In SARS-CoV-2 infected hamsters, treatment with STI-2020 12 hours post-infection using the IN route led to a decrease in severity of clinical disease signs and a more robust recovery during 9 days of infection as compared to animals treated with an isotype control antibody. Treatment via the IV route using the same dose and timing regimen resulted in a decrease in the average number of consecutive days that infected animals experienced weight loss, shortening the duration of disease and allowing recovery to begin more rapidly in STI-2020 treated animals. Following IN administration in mice, STI-2020 was detected within 10 minutes in both lung tissue and lung lavage. The half-life of STI-2020 in lung tissue is approximately 25 hours. We are currently investigating the minimum effective dose of IN-delivered STI-2020 in the hamster model as well as establishing the relative benefit of delivering neutralizing antibodies by both IV and IN routes.
ABSTRACT
Vaccination efficacy is enhanced by targeting the antigen-presenting cell compartment. Here, we show that S1-Fc antigen delivery targeting the Fc{gamma}R+ antigen-presenting cell compartment elicits anti-SARS-CoV-2 S1-antigen specific IgG production in vivo exerting biologically functional and protective activity against live virus infection, assessed in a stringent experimental virus challenge assay in vitro. The S1-domain of the SARS-CoV-2 spike protein was genetically fused to a human immunoglobulin Fc moiety, which contributes to mediate S1-Fc cellular internalization by Fc{gamma}R+ antigen-presenting cells. Immediately upon administration intramuscularly, our novel vaccine candidate recombinant rS1-Fc homes to lymph nodes in vivo where Fc{gamma}R+ antigen-presenting cells reside. Seroconversion is achieved as early as day 7, mounting considerably increased levels of anti-S1 IgGs in vivo. Interestingly, immunization at elevated doses with non-expiring S1-Fc encoding dsDNA favors the education of a desired antigen-specific adaptive T cell response. However, low-dose immunization, safeguarding patient safety, using recombinant rS1-Fc, elicits a considerably elevated protection amplitude against live SARS-CoV-2 infection. Our promising findings on rS1-Fc protein immunization prompted us to further develop an affordable and safe product for delivery to our communities in need for COVID-19 vaccinations.
