RNA-based vaccine demonstrates prophylactic efficacy against Mycobacterium tuberculosis challenge in a mouse model

Mycobacterium tuberculosis (Mtb) is an opportunistic bacterial pathogen that causes tuberculosis disease (TB) and exerts an extensive burden on global health. The complex intra- and extracellular nature of this bacterium, coupled with different disease stages have made mechanistic studies evaluating the contributions of innate and adaptive host immunity challenging. In this work we leveraged two delivery platforms as prophylactic vaccines to assess immunity and subsequent efficacy against low dose and ultra-low dose aerosol challenge with Mtb H37Rv in C57BL/6 mice. Our proof-of-concept TB vaccine candidate ID91 was produced as a fusion protein formulated with a synthetic TLR4 agonist (glucopyranosyl lipid adjuvant in a stable emulsion) or as a replicating-RNA (repRNA) formulated in a nanostructured lipid carrier (NLC). Results from this work demonstrate that protein subunit- and RNA-based vaccines preferentially elicit cellular immune responses to different ID91 epitopes. In a single prophylactic immunization screen, both platforms reduced pulmonary bacterial burden compared to controls. Excitingly, in prime-boost strategies, groups that received heterologous RNA-prime, protein-boost or combination (simultaneous in different sites) immunizations demonstrated the greatest reduction in bacterial burden and a unique humoral and cellular immune response profile. These data are the first to report that repRNA platforms are a viable system for TB vaccines and should be pursued with high priority Mtb antigens containing CD4+ and CD8+ T cell epitopes.