Self-Assembling Spike-EBR Nanoparticles as a Vaccine Platform Technology Against SARS-CoV-2 and Future Pandemic Coronaviruses.

Project Summary/Abstract The COVID-19 pandemic represents the 3rd outbreak caused by zoonotic transmission of a beta-coronavirus (beta-CoV) in the last 20 years. Hence there is an urgent need for new vaccine strategies to control the ongoing pandemic and prevent future CoV outbreaks. mRNA vaccines have emerged as an ideal platform for the development of rapid-response vaccines, but clinical studies have shown that neutralizing antibody titers elicited by mRNA vaccines are ~10-fold lower than titers elicited by protein nanoparticle (NP) vaccines. This is a concern with regards to the emergence of SARS-CoV-2 variants of concern (VOCs) that are less sensitive to vaccine- induced antibodies. In addition, less than 25% of the world population is fully vaccinated. Thus, rapid-response vaccine technologies are needed that elicit potent antibody responses with a single injection and/or lower doses, to ensure lasting protection against VOCs, reduce costs, and accelerate global distribution. Moreover, prevention of future CoV pandemics requires the development of a universal CoV vaccine that elicits cross-reactive immune responses against a broad spectrum of CoV strains by focusing responses to conserved epitopes. The scope of the proposed research is to design and evaluate new vaccine strategies to enhance the potency of mRNA-based rapid-response vaccines and facilitate universal CoV vaccine development. The proposal is based on the EBR NP technology, which modifies membrane proteins such as CoV spike (S) proteins to self-assemble into virus- resembling NPs that bud from the cell surface. NP assembly is induced by inserting a short amino acid sequence into the cytoplasmic tail designed to recruit proteins from the endosomal sorting complex required for transport (ESCRT) pathway. Initial studies in mice showed that low-dose injections of EBR NPs presenting the SARS- CoV-2 S protein elicited 10-fold higher neutralizing antibody titers than soluble S protein and protein-based NPs that displayed the receptor-binding domain (RBD) of the S protein. The EBR NP technology will be applied to accomplish three goals: i) Design a hybrid mRNA vaccine encoding the modified SARS-CoV-2 S-EBR construct that would be expressed at the cell surface and self-assemble into virus-resembling NPs to elicit more potent antibody responses than the approved Pfizer/Moderna vaccines, while retaining the manufacturing properties and T-cell activation of mRNA vaccines. ii) Engineer S-EBR NPs to package and deliver S or S-EBR mRNA vaccines as an alternative to lipid NPs. This delivery approach would enhance mRNA vaccine potency as S proteins presented on S-EBR NPs induce potent antibody responses, facilitate efficient intracellular delivery, and target mRNA vaccines to tissues that are naturally infected by SARS-CoV-2 to induce local immune responses. iii) Design and evaluate mosaic S-EBR NP-based universal CoV vaccine candidates that present full-length membrane-associated S proteins from multiple CoV strains to elicit cross-reactive immune responses against a broad spectrum of CoVs and protect against future outbreaks. The proposed vaccine strategies could have direct impact on the COVID-19 global health crisis and advance our emergency preparedness for the next pandemic.