Abstract: Objective The purpose of this study is to examine the immunogenicity and protective efficacy of PE31, which is a PE-PPE family protein that is under the control of the PhoPR two-component system and Lsr2 global regulator, against Mycobacterium tuberculosis(MTB); and to evaluate its potential in subunit vaccine development. Methods The sequence of PE31 was analyzed for potential CD4⁺ and CD8⁺T cell epitopes. PE31 and Ag85A were cloned into pET-28a and recombinant proteins were expressed in and purified from E. coli. C57BL/6 mice were immunized with purified antigens formulated in adjuvant and the production of antigen-specific Th1 cytokines and antibody were determined. PE31 and Ag85A were also cloned into pcDNA3.1(+) for mammalian cell expression. The resulting DNA vaccines were used to immunize BALB/c mice subcutaneously. The mice were then challenged intravenously by MTB H37Rv. Bacterial burdens in the lungs and spleen were determined 4 weeks post-infection. Results There are similar numbers of predicted CD4⁺ and CD8⁺T cell epitopes in PE31 and Ag85A. Immunization experiments showed that PE31 induced higher level of IFN-γ and TNF-α (~600 pg/ml) than Ag85A and similar levels of antibody response. Mice immunized with the DNA vaccine expressing PE31 had 0.3-0.4log₁₀ fewer MTB counts in the lungs and spleen than those immunized with the empty vector. Conclusions It is demonstrated that PE31 is highly immunogenic and protective, and is an attractive candidate for the development of novel subunit vaccines.

Key words: Tuberculosis, Subunit vaccine, PE31, Latent infection