Immunogenicity and protective efficacy of a subunit vaccine SHP/TMD consisting of multi-stage antigens against Mycobacterium tuberculosis infection

Abstract

Objective To construct a fusion protein SHP of subunit vaccine containing multi-stage antigens, and to confirm the immunogenicity and protective effect of SHP through M. tb infected Chinese population and C57BL/6 mice model. Methods Rv0577(secreted by replicating bacilli), Rv2623(expressed in dormant bacilli) and Rv3478(from PE/PPE family) were selected and to construct fusion protein SHP, WBIA(based on TB-IGRA) was performed to detect the specific concentration of IFN-γ stimulated from peripheral-blood lymphocyte of Chinese M. tb infections and non-infections.C57BL/6 mice were immunized(s.c.) with SHP emulsified in the adjuvant TMD.Nine weeks after immunized, SHP-specific antibody titers(IgG, IgG1, IgG2a), as well as the levels of Th1 cytokines by splenic lymphocytes stimulated with SHP and the mRNA expression levels of molecules in the lung of vaccinated mice were detected.Four weeks after challenge by M. tb H37Rv, the protective efficacy of SHP/TMD was evaluated. Results Recombinant plasmid pET30b-SHP and subgroups were constructed and expressed successfully, which stimulated statistically higher levels of IFN-γ in M. tb infected Chinese subjects than in healthy donors[SHP stimulated IFN-γ levels in infected and healthy groups were (1 420.0±253.9)pg/mL and (236.1±95.1)pg/mL, t=2.063, P<0.01]. SHP/TMD induced higher levels of specific IgG, IgG2a and IgG1 antibodies, and the ratio of IgG2a/IgG1 indicated that SHP/TMD mainly induced the Th1-type cell-mediated immune response.Meanwhile, SHP/TMD induced statistically higher levels of specific IFN-γ, TNF-α and IL-2 from splenic lymphocytes, also the mRNA expression levels of IFN-γ, TNF-α and iNOS from the lung.Moreover, SHP/TMD group resulted in the significant reduction of bacterial load in the lung and spleen organ(the reduction of bacterial load of SHP/TMD in comparison of TMD group was 1.03 log, F=1518, P<0.05), as well as lessened inflammation in alveolar tissue. Conclusion Based on the predominant antigens expressed during multi stages which can be recognized by T cells of M. tb infections from China, a subunit vaccine SHP/TMD was constructed.SHP/TMD can provide significant protective efficacy against acute infection of M. tb, which is mainly attributed to the SHP-specific CD4+ Th1-type cell immune response. Key words: Mycobacterium tuberculosis; Vaccine, subunit; BCG vaccine; Immunity