Analysis of Mycobacterium tuberculosis genoma and production of a recombinant protein containing specific B and T cell antigenic determinants--new approaches to second generation antituberculosis vaccines.

Tuberculosis is still a major health problem in almost all over the world. Thus, new directions in basic and applied research of tuberculosis are under investigation in several laboratories. In this paper, we provide recent data obtained in our laboratory with the recombinant DNA technology which allow a systematic survey of the microbial genome. Screening of the M. tuberculosis genomic DNA library in the phage lambda gt11 expression vector, using E. coli as surrogate host, has evidenced the possibility of producing recombinant M. tuberculosis proteins recognized by sera from tuberculosis patients and by specific monoclonal antibodies. Using this technology, we have isolated a recombinant protein (molecular weight 130 kilodaltons) which is identified by a murine monoclonal antibody recognizing a mycobacterial cell wall antigenic determinant present on a mycobacterial protein. This protein is only present on the mycobacterial species related to the tuberculosis complex (M. tuberculosis, M. bovis, M. africanum) and does not crossreact with nonpathogenic Mycobacteria. Since the immune response to mycobacterial infections is cell-mediated, the question arises about the use of M. tuberculosis-specific T lymphocytes to screen this gene bank. Thus, the recombinant mycobacterial protein isolated by antibodies has been then used to stimulate the proliferation of T lymphocytes from patients with tubercular pleuritis. This experiment indicates that the recombinant protein contains antigenic determinants recognized by T cells. Moreover, such protein is able to elicit delayed type hypersensitivity skin reaction in mice immunized or infected with M. tuberculosis and M. bovis. Finally, gene mapping and hybridization studies with native M. tuberculosis DNA confirme the mycobacterial nature of the recombinant DNA insert. Thus a good candidate for the prophylaxis and the immunodiagnosis of tuberculosis has been identified. The identification and selection of genes encoding antigenic determinants recognized by mycobacteria-specific T cells with protective functions will allow in the near future the construction by genetic engineering of recombinant vaccines effective in the control of this disease. This paper will briefly discuss the present strategy used in our laboratory to reach this goal.