A novel self-adjuvanted mRNA vaccine expressing the Antigen-85B-p25 epitope of <i>Mycobacterium tuberculosis</i> protects mice against tuberculosis

Abstract Mycobacterium tuberculosis (Mtb) is a leading cause of death due to infections. BCG is the most used vaccine despite having partial efficacy against the tuberculosis. We have developed a synthetic mRNA vaccine, SelmRp25-C5, which expresses the p25 epitope of Mtb-derived Antigen-85B and a TLR-2 stimulating C5 adjuvant peptide from CFP-10 protein. We evaluated its efficacy both ex vivo and in mice. Methods Mouse and human macrophages (MΦ) and mouse dendritic cells (DCs) were treated with SelmRp25-C5 vaccine or EGFP-mRNA control followed by antigen presentation assays and assessment of cytokine secretion. C57Bl/6 mice were vaccinated subcutaneously with two doses (5μg per mouse) of SelmRp25-C5 vaccine, or EGFP-mRNA and one dose of subcutaneous BCG (106 CFU per mouse) as a control, followed by aerosol infection with Mtb. Four weeks after Mtb challenge, mice were sacrificed, and organs were analyzed for Mtb CFU, RNAseq, Ag85B-p25 tetramer-specific CD4 T cells and memory T cells. Results SelmRp25-C5 vaccine induced robust antigen presentation to T cells in both mouse MΦs and DCs and in human MΦs, and enhanced Th1 cytokine secretion. Two doses of SelmRp25-C5 vaccine protected mice by reducing Mtb burden by 1log10. Protection induced by SelmRp25-C5 vaccine was associated with an increase in Ag85B-p25-specific CD4 T cells, increased IFN-γ and IL-2 secreting T cells and CD4 effector memory T cells. Lung and spleens of protected mice showed an upregulation of Spleen tyrosine kinase (Syk) and genes of the C-type lectin receptor-pathway compared to control mice. Conclusions We propose that the new generation self-adjuvanted mRNA vaccine strengthen both innate and adaptive immunity to provide protection against tuberculosis. Supported by NIAID, NIH AI122070, AI138587; AI161015.