Chimeric mRNA based COVID-19 vaccine elicits potent neutralizing antibodies and protection against Omicron and Delta (preprint)

The emerging SARS-CoV-2 variants of concern (VOCs) exhibit enhanced transmission and immune escape, reducing the efficacy and effectiveness of the two FDA-approved mRNA vaccines currently in use. Here, we explored various strategies to develop mRNA vaccines that offer potentially safer and wider coverage of VOCs. The initial mouse vaccination results showed that the individual VOC mRNAs carrying furin cleavage mutation induced the generation of neutralizing antibody in a VOC-specific manner. Moreover, we discovered that the antibodies produced from mice immunized with Beta-Furin and Washington (WA)-Furin mRNAs cross-reacted with other VOCs. The broad spectrum of generated nAb was further confirmed when vaccinated mice were challenged with the respective live viruses. However, neither WA-Furin nor Beta-Furin mRNA elicited potent neutralizing activity against the omicron variant. Interestingly, in a mix-and-match booster experiment, omicron-Furin and WA-Furin mRNA elicited comparable protection against omicron. Finally, we tested the concept of bivalent vaccine by introducing the RBD of Delta strain into the intact S antigen of Omicron. The chimeric mRNA induces potent and broadly acting nAb against Omicron and Delta, which paves the way to develop vaccine candidate to target emerging variants in the future.

Discovery of a SARS-CoV-2 Broadly-Acting Neutralizing Antibody with Activity against Omicron and Omicron + R346K Variants (preprint)

The continual emergence of SARS-CoV-2 variants of concern, in particular the newly emerged Omicron (B.1.1.529) variant, has rendered ineffective a number of previously EUA approved SARS-CoV-2 neutralizing antibody therapies. Furthermore, even those approved antibodies with neutralizing activity against Omicron are reportedly ineffective against the subset of Omicron variants that contain a R346K substitution, demonstrating the continued need for discovery and characterization of candidate therapeutic antibodies with the breadth and potency of neutralizing activity required to treat newly diagnosed COVID-19 linked to recently emerged variants of concern. Following a campaign of antibody discovery based on the vaccination of Harbour H2L2 mice with defined SARS-CoV-2 spike domains, we have characterized the activity of a large collection of Spike-binding antibodies and identified a lead neutralizing human IgG1 LALA antibody, STI-9167. STI-9167 has potent, broad-spectrum neutralizing activity against the current SARS-COV-2 variants of concern and retained activity against the Omicron and Omicron + R346K variants in both pseudotype and live virus neutralization assays. Furthermore, STI-9167 nAb administered intranasally or intravenously provided protection against weight loss and reduced virus lung titers to levels below the limit of quantitation in Omicron-infected K18-hACE2 transgenic mice. With this established activity profile, a cGMP cell line has been developed and used to produce cGMP drug product intended for use in human clinical trials.