IDENTIFICATION OF HUMAN T-CELL EPITOPES IN THE MYCOBACTERIUM-LEPRAE HEAT-SHOCK PROTEIN 70-KD ANTIGEN

In a number of pathogens, heat shock proteins (hsp) stimulate humoral and cellular immune responses despite significant sequence identity wi th host hsp. The 70-kD hsp of Mycobacterium leprae, which shares 47% i dentity with human hsp70 at the protein level, elicited a T cell respo nse in most Myco. bovis (bacille Calmette-Guerin (BCG)) vaccinees as w ell as leprosy and tuberculosis patients and their contacts. In order to locate T cell epitopes, DNA fragments encoding portions of the 70-k D hsp were expressed in the vector pGEX-2T and tested for T cell react ivity in an in vitro proliferative assay. Cultures of peripheral blood mononuclear cells (PBMC) from BCG vaccinees indicated that the C-term inal half of the molecule contained multiple T cell epitopes, as the T cells from a majority of Myco. leprae hsp70-reactive individuals resp onded to C-344. Lower proportions of patients with paucibacillary lepr osy (36%) and tuberculosis patients (16%) responded to C-344. The smal ler C-142 fragment which includes the terminal 70 residues unique to M yco. leprae and is the target for the human antibody response elicited a cellular response in few patients and no vaccinees. In order to map T cell epitopes, two series of synthetic peptides encompassing the re gion 278-502 were prepared. Using overlapping 12mer and 20mer peptides , this region of the molecule was found to contain several potential T cell epitopes. The longer peptides gave a clearer indication of react ive sequences including regions of the molecule which were not identif ied with the 12mer peptides. Fine mapping of reactive peptide pools us ing the 12mer peptides identified two T cell epitopes. Although both w ere located in regions of the molecule shared with Myco. tuberculosis, one appeared to be crossreactive with the equivalent human sequence, and thus has the potential to initiate autoimmune responses.