The roles of Type I interferon subtypes and signaling in mRNA lipid nanoparticle vaccine-induced CD8 T-cell protective immunity.

Introduction/Rationale: The modification of RNA by the incorporation of N-methyl pseudo-uridine (N1mΨ) renders the mRNA less inflammatory, resulting in durable cellular and humoral responses. Interestingly, mRNA-LNP vaccines still elicit strong innate immune activation and stimulate the production of type I interferons (IFN-I) by antigen-presenting cells (APCs). IFN-I is critical in the induction of CD8 T-cell responses to mRNA vaccines; however, the mechanisms underlying this process are poorly understood.

Methods: We determined protection from lethal infection with ectromelia virus in mice with cell-specific deletion of IFNAR1, as well as in mice deficient in specific IFN-I, following vaccination with a previously described EVM158 mRNA-LNP vaccine containing an immunodominant CD8 T-cell epitope.

Results: We demonstrate that the optimal induction of CD8 T-cells requires IFN-I signaling in multiple myeloid cell types, not just in CD8 T-cells, dendritic cells, or monocytes. We also show that at optimal vaccine doses, IFN-β- and IFN-α-deficient mice generate protective CD8 T-cell responses. However, at suboptimal doses, male mice deficient in IFN-β and in IFN-α4, which are regulated by constitutive transcription factors, do not generate completely protective CD8 T cells. Moreover, mice deficient in the NF-κB binding site in the IFN-β promoter and the transcription factor IRF7 generate poorly protective responses.

Conclusion: Our results indicate that optimal induction of protective CD8 T-cell responses by mRNA LNP vaccines requires IFN-I signaling in myeloid cells but not in CD8 T-cells, that IFN-β and IFN-α can individually provide the signals required for protection, and that regulation of IFN-β by NF-κB and all IFN-I subtypes by IRF is required to induce protective CD8 T-cells.