Impact of untranslated mRNA sequences on immunogenicity of mRNA vaccines against M. tuberculosis in mice

Vaccination is among the most effective measures to reduce tuberculosis morbidity and mortality. In 1974, BCG vaccination was included in the Expanded Program on Immunization. Today, it covers 80% of all children around the globe. Unfortunately, BCG vaccine provides no protection against pulmonary tuberculosis, the most prevalent form of tuberculosis. It is necessary to urgently develop new vaccination strategies to stop large-scale dissemination of infection caused by the multidrugresistant pathogen. The study was aimed to compare the capabilities of three variants of mRNA vaccines encoding Esat6 epitopes of stimulating adaptive immune response formation in C57BL/6 mice (ELISpot, delayed hypersensitivity, IgG titers), as well as of protecting I/St mice against M. tuberculosis infection. Efficacy of mRNA vaccines comprising different untranslated regions packaged in lipid nanoparticles was compared with that of BCG vaccine. The 5'-TPL-Esat6-3'-Mod vaccine demonstrated the highest efficacy in our experimental model. Thus, the 5'-TPL-Esat6-3'-Mod mRNA vaccine can be considered as a candidate vaccine for further optimization, improving efficacy and subsequent use for prevention of tuberculosis.