IDENTIFICATION OF HLA CLASS-II RESTRICTED DETERMINANTS OF MYCOBACTERIUM TUBERCULOSIS-DERIVED PROTEINS BY USING HLA-TRANSGENIC, CLASS-II DEFICIENT MICE

T helper 1 cells play a major role in protective immunity against myco bacterial pathogens. Since the antigen (Ag) specificity of CD4(+) huma n T cells is strongly controlled by HLA class II polymorphism, the imm unogenic potential of candidate Ags needs to be defined in the context of HLA polymorphism. We have taken advantage of class II-deficient (A b(0)) mice, transgenic for either HLA-DRA/B10301 (DR3) or HLA-DQB1*03 02/DQA0301 (DQ8) alleles. In these animals, all CD4+ T cells are rest ricted by the HLA molecule. We reported previously that human DR3-rest ricted T cells frequently recognize heat shock protein (hsp)65 of Myco bacterium tuberculosis, and only a single hsp65 epitope, p1-20. DR3.Ab (0) mice, immunized with bacillus Calmette-Guerin or hsp65, developed T cell responses to M. tuberculosis, and recognized the same hsp65 epi tope, p1-20. Hsp65-immunized DQ8.Ab(0) mice mounted a strong response to bacillus Calmette-Guerin but not to p1-20. Instead, we identified t hree new DQ8-restricted T cell epitopes in the regions 171-200, 311-34 0, and 411-440. DR3.Ab(0) mice immunized with a second major M. tuberc ulosis protein, Ag85 (composed of 85A, 85B, and 85C), also developed T cell responses against only one determinant, 85B p51-70, that was ide ntified in this study. Importantly, subsequent analysis of human T cel l responses revealed that HLA-DR3+, Ag85-reactive individuals recogniz e exactly the same peptide epitope as DR3.Ab(0) mice. Strikingly, both DR3-restricted T cell epitopes represent the best DR3-binding sequenc es in hsp65 and 85B, revealing a strong association between peptide-im munodominance and HLA binding affinity. Immunization of DR3.Ab(0) with the immunodominant peptides p1-20 and p51-70 induced T cell reactivit y to M. tuberculosis. Thus, for two different Ags, T cells from DR3.Ab (0) mice and HLA-DR3+ humans recognize the same immunodominant determi nants. Our data support the use of HLA-transgenic mice in identifying human T cell determinants for the design of new vaccines.