An LNP-mRNA vaccine modulates innate cell trafficking and promotes polyfunctional Th1 CD4⁺ T cell responses to enhance BCG-induced protective immunity against Mycobacterium tuberculosis

Background Mycobacterium tuberculosis remains the largest infectious cause of mortality worldwide, even with over a century of widespread administration of the only licenced tuberculosis (TB) vaccine, Bacillus Calmette-Guérin (BCG). mRNA technology remains an underexplored approach for combating chronic bacterial infections such as TB. Methods We have developed a lipid nanoparticle (LNP)-mRNA vaccine, termed mRNA CV2 , encoding for the M. tuberculosis CysVac2 fusion protein, which we have previously formulated as an adjuvanted subunit vaccine. This LNP-mRNA vaccine was administered intramuscularly to female C57BL/6 mice as a standalone vaccine or as booster to BCG to assess immunogenicity and efficacy of the construct. Findings Vaccination with mRNA CV2 induced high frequencies of polyfunctional, antigen-specific Th1 CD4 + T cells in the blood and lungs, which was associated with the rapid recruitment of both innate and adaptive immune cells to lymph nodes draining the site of immunisation. mRNA CV2 vaccination also provided significant pulmonary protection in M. tuberculosis-infected mice, reducing bacterial load and inflammatory infiltration in the lungs. Importantly, mRNA CV2 enhanced immune responses and long-term protection when used to boost BCG-primed mice. Interpretation These findings of a protective LNP-mRNA vaccine for TB highlight the potential of the LNP-mRNA platform for TB control and support further research to facilitate translation to humans. Funding This work was supported by the NHMRC Centre of Research Excellence in Tuberculosis Control to JAT and WJB (APP1153493), and MRFF mRNA Clinical Trial Enabling Infrastructure grant to CWP and HAW (MRFCTI000006).