Mechanisms of protective memory CD8 T-cell induction by mRNA-LNP vaccines

Summary CD8 T-cells recognize and kill virus-infected cells displaying at the cell surface short viral peptides bound to major histocompatibility (MHC) class I molecules (MHC-I). CD8 T-cells contribute to the clearance of many viral infections. After an infection subsides, an expanded population of "memory" CD8 T-cells (M CD8 T-cells) may contribute to more rapidly controlling a secondary infection with the virus. Vaccines can mimic this process. Modified mRNA (mmRNA) encapsulated in lipid nanoparticles (mmRNA-LNP) have emerged as a powerful vaccine platform. mmRNA-LNPs have many advantages as vaccines: 1) They can be focused on the antigen of interest. 2) They are highly immunogenic. 3) they are easy to make. 4) They can be mass-produced rapidly. 5) They are relatively inexpensive. The swift development and approval of the mmRNA-LNP vaccines to combat SARS-CoV-2 attest to their potential. While it is known that mmRNA-LNPs induce CD8 T-cell responses, most of the work on their protection mechanisms has focused on Abs. The mCD8 T-cells induced by mmRNA- LNP can potentially complement Ab protection or may provide most of the protection for viruses that are refractory to Ab-mediated control. mmRNA-LNPs could also be used to induce CD8 T-cells against cancer. We have published that the mCD8 T-cell responses induced by mmRNA-LNPs protect mice from highly lethal mousepox, a systemic viral disease of the mouse caused by the Orthopoxvirus (OPV) ectromelia virus (ECTV). ECTV is an outstanding model for systemic viral infections in general and for OPVs that can infect humans, such as the eradicated variola virus (virus of smallpox) and for monkeypox virus (MPXV), which recently caused a major outbreak. In still unpublished experiments, we also found that M CD8 T-cells induced by a mini- mmRNA vaccine encoding for only the minimal, highly conserved CD8 T-cell epitope VNFNFNGL of the SARS- CoV-2 Spike protein protects wild-type mice from lethal respiratory infection with the mouse-adapted SARS- CoV-2 strain MA30, an outstanding model for SARS-CoV-2 and other grave respiratory infections. Here we propose elucidating the mechanisms whereby mmRNA-LNPs induce protective mCD8 T-cells using the ECTV systemic and the MA30 SARS-CoV-2 respiratory mouse models. Our Specific Aims are to: A) Specific Aim 1. Investigate the Mechanisms of MHC-I antigen presentation after mmRNA-LNP vaccination. B) Specific Aim 2. Investigate the roles of Type I interferon (IFN-I) and other proinflammatory cytokines in protective M CD8 T-cell development after mRNA-LNP vaccination.