(251a) Engineering Dually Adjuvanted Sars-CoV2 mRNA Vaccines

The successful development of mRNA-based vaccines against SARS-CoV-2 has provoked broad interest in RNA-based technologies and demonstrated the promising potential of mRNA as a new vaccine class for combating infectious diseases. Although two mRNA vaccines have been authorized for use against SARS-CoV2 and many more mRNA vaccines for other infectious diseases are in clinical trials, the widespread clinical translation of this technology requires overcoming certain limitations including eliciting a sufficiently potent immune response to the expressed antigen at a safely tolerable dose. To further improve the safety and efficacy of mRNA vaccines, we here develop a dually self-adjuvanted mRNA vaccine system whereby both the encapsulating lipid nanoparticle as well as the mRNA are designed to potentiate the immune response to an encoded antigen. We first screened a combinatorial library of 480 biodegradable ionizable lipids as part of LNP formulations for vaccine potential, identifying a top ionizable lipid capable of enhanced immune stimulation leading to a potentiated immune response when compared to the FDA-approved ionizable lipid MC3. We then designed an adjuvanted mRNA to encode a fusion protein consisting of a SARS-CoV2 antigen and a bio-inspired adjuvanting peptide (AP), within a single transcript. Compared to the mRNA encoding viral antigens alone, the inclusion of the AP in the mRNA transcript increased the magnitude of antigen-specific antibody titers by at least ten-fold in mouse sera for both wild-type SARS-CoV2 and Delta variant antigens. Vaccination with LNPs combining the dually adjuvanted ionizable lipid and mRNA transcript resulted in synergistic immune responses to the Delta variant of SARS-CoV2 for both intramuscular and intranasal administrations. In addition to significantly improving total antigen-specific IgG titers, vaccination with the dually-adjuvanting system also resulted in antibodies with higher levels of Fc-receptor binding which has recently been shown to be a predictor of resolution of severe COVID-19. Our results demonstrate that a dually-adjuvanted system holds great potential in improving the efficacy, safety, and ease of administration of mRNA vaccines.