Combined adjuvant approaches for enhancement of SARS-CoV-2 vaccine efficacy

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PROJECT SUMMARY/ABSTRACT The high morbidity and mortality associated with Covid-19 continues to underscore the importance of effective vaccines against SARS-CoV-2. While a few promising candidates have received EUAs, the emergence of more transmissible variants which have impacted vaccine efficacy highlight the fact that several challenges remain. A successful vaccine must: 1. induce robust long-lasting protection when natural infection with coronaviruses generally leads to relatively short-lived immunity, 2. impart broad immunity as viral mutations accumulate, 3. provide potent immunity in the elderly, and 4. be safe in light of enhanced disease observed with past coronavirus vaccines. To address these challenges, this proposal aims to develop a safe, effective, and rapidly translatable adjuvant system for SARS-CoV-2 vaccines using a rationally designed combination adjuvant to target an array of key innate receptor pathways involved in antiviral immunity. Adjuvants are powerful tools for promoting fast, durable and qualitative responses most effective for a particular pathogen, especially in immune-challenged individuals. Natural viral infection stimulates strong immune responses through activation of Toll-, RIG-I-, and NOD-like receptors (TLRs, RLRs, NLRs). As induction of appropriate innate responses is crucial for long-lasting adaptive immunity and for shaping the correct types of immune responses, we will test the hypothesis that using a combination of agonists that integrate these pathways will lead to improved humoral and cellular responses towards SARS-CoV-2. To achieve this, we will combine a nanoemulsion-based adjuvant (NE) that activates TLRs and NLRP3 with an RNA agonist of RIG-I (IVT DI). We have demonstrated that simultaneous activation of TLRs, RIG-I, and NLRP3 with NE/IVT DI induces a synergistic immune response with magnified TH1-biased cellular immunity. Guided by strong preliminary data demonstrating the effectiveness of this combined adjuvant approach for improving influenza virus vaccination, and our initial studies with SARS-CoV-2 antigens, we will develop this adjuvant for use in a SARS-CoV-2 vaccine in two specific aims. In Aim 1, we will profile the immune responses elicited by NE/IVT DI with multiple SARS-CoV-2 antigens through parenteral and mucosal routes to optimize formulations and vaccination routes. In Aim 2, we will determine the protective efficacy and safety of the optimized lead vaccine platforms in challenge models of SARS-CoV-2 and define key correlates of protection. Increasing data suggests that SARS-CoV-2 elicits a weak innate response, with poor activation of critical antiviral pathways, which likely contributes to the large variability in magnitude and durability of immune responses in recovered patients. With this targeted approach, we expect to drive more robust and durable immunity while avoiding immune responses promoting vaccine related pathology. The NE adjuvant and several RIG-I agonists have demonstrated good safety profiles in phase I human trials. Thus, we expect that successful completion of this work will lead to a rapidly translatable and deliverable adjuvant compatible with multiple SARS-CoV-2 vaccine candidates, and provide much needed insight on the key effectors of protective SARS-CoV-2 immunity.