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 mycobacterial pathogens. Since the antigen (Ag) specificity of CD4⁺ human T cells is strongly controlled by HLA class II polymorphism, the immunogenic potential of candidate Ags needs to be defined in the context of HLA polymorphism. We have taken advantage of class II-deficient (Ab⁰) mice, transgenic for either HLA-DRA/B1*0301 (DR3) or HLA-DQB1*0302/DQA*0301 (DQ8) alleles. In these animals, all CD4⁺ T cells are restricted by the HLA molecule. We reported previously that human DR3-restricted T cells frequently recognize heat shock protein (hsp)65 of Mycobacterium tuberculosis, and only a single hsp65 epitope, p1-20. DR3.Ab⁰ mice, immunized with bacillus Calmette-Guerin or hsp65, developed T cell responses to M. tuberculosis, and recognized the same hsp65 epitope, p1-20. Hsp65-immunized DQ8.Ab⁰ mice mounted a strong response to bacillus Calmette-Guerin but not to p1-20. Instead, we identified three new DQ8-restricted T cell epitopes in the regions 171-200, 311-340, and 411-440. DR3.Ab⁰ mice immunized with a second major M. tuberculosis protein, Ag85 (composed of 85A, 85B, and 85C), also developed T cell responses against only one determinant, 85B p51-70, that was identified in this study. Importantly, subsequent analysis of human T cell responses revealed that HLA-DR3+, Ag85-reactive individuals recognize exactly the same peptide epitope as DR3.Ab⁰ mice. Strikingly, both DR3-restricted T cell epitopes represent the best DR3-binding sequences in hsp65 and 85B, revealing a strong association between peptide-immunodominance and HLA binding affinity. Immunization of DR3.Ab⁰ with the immunodominant peptides p1-20 and p51-70 induced T cell reactivity to M. tuberculosis. Thus, for two different Ags, T cells from DR3.Ab⁰ mice and HLA-DR3⁺ humans recognize the same immunodominant determinants. Our data support the use of HLA-transgenic mice in identifying human T cell determinants for the design of new vaccines.