Individuals from different populations identify multiple and diverse T-cell determinants on mycobacterial HSP70

The 70 kDa heat-shock protein (HSP) of Mycobacterium leprae stimulates both cellular and antibody responses in leprosy patients and subclinically infected individuals despite partial homology with host HSP70. Furthermore, mycobacterial HSP70 can act as a carrier protein in unprimed mice, suggesting the presence of widely shared T-cell determinants on this protein. In order to elucidate the frequency and genetic restriction of these T-cell epitopes, we have undertaken a systematic analysis of the proliferative responses to 20mer peptides encompassing the whole protein in different populations. Caucasian BCG vaccinees who responded to recombinant M. leprae HSP70 identified multiple scattered T-cell determinants, four of which were recognized by 60% of subjects in association with a variety of HLA-DR haplotypes. When a group of Nepali leprosy and tuberculosis patients were tested, significant differences in the pattern of peptide recognition were observed. The dominant peptides recognized by Caucasian subjects were infrequently reactive and other peptides were stimulatory, again in association with a variety of HLA-DR phenotypes. The C-terminal 70 residues of the M. leprae HSP70 are specific to M. leprae and sera from lepromatous leprosy patients bind to this region. However, few T-cell determinants were identified in these residues, indicating that this region is unhelpful as a diagnostic tool for detecting M. leprae-specific T-cell responses. When compared with the equivalent regions of the human HSP70, the commonly recognized peptides showed significant differences in amino-acid sequence. When taken in conjunction with the failure of human HSP70 to stimulate M. leprae HSP70-reactive T-cell clones (E. Adams et al., unpublished observations), this finding indicates that the human T-cell response to this protein is largely directed at mycobacterial-specific determinants. The presence of multiple T-cell epitopes on M. leprae HSP70 with varied patterns of HLA-DR association suggests that the whole protein is required for stimulating effective T-cell responses in genetically diverse populations.