Induction of cell-mediated immunity against mycobacterium tuberculosis using DNA vaccines encoding cytotoxic and helper T-cell epitopes of the 38-kilodalton protein

Cell-mediated immune responses are crucial in the protection against tuberc ulosis. In this study, we constructed DNA vaccines encoding cytotoxic T lym phocytes (CTL) and T helper cell (Th) epitopes of the 38-kDa lipoglycoprote in of Mycobacterium tuberculosis and analyzed and compared their immunogeni cities with that of pXJ38, a DNA vaccine encoding the entire 38-kDa protein (X. Zhu, N. Venkataprasad, H. S. Thangaraj, M. Hill, M. Singh, J. Ivanyi, and H. M. Vordermeier, J. Immunol. 158:5921-5926, 1997). Plasmid DNAs encod ing a CTL epitope, P3 (pP3), a Th epitope (vTh), or both the Th and the P3 epitopes (pThP3) were prepared and tested in C57BL6/J (H-2(b)) mice. Our re sults confirmed that DNA immunization with pXJ38 induces strong CD8(+) CTL and Th1 responses (high gamma interferon [IFN-gamma], low interleukin-4 [IL -4]). Coadministration of plasmid DNAs encoding a Th epitope with those enc oding a CTL epitope (vTh+pP3) elicited both antigen-specific CD8(+) CTL and Th1 responses. High levels of IFN-gamma were secreted by spleen cells from all plasmid DNA-vaccinated mice after in vitro stimulation with the recomb inant 38-kDa protein. Small or undetectable amounts of IL-4 were observed, which indicates the induction of a Th1-like response. Multiple-epitope vacc ination by vTh+pP3 or pThP3 resulted in a broader Th1 response to peptide o r epitopes than the single-epitope plasmid DNAs. Antigen-specific immunoglo bulin G2a was only detected in sera from mice immunized with the plasmid pX J38, and not in mice immunized with the epitope-based DNA vaccines. Thus, t he absence of an antibody response after immunization with epitope plasmid DNAs and their ability to trigger only a specific cellular immune response may prove to be important advantages for a vaccine against tuberculosis.