Long-term persistence of transferred PPD-reactive T cells after allogeneic bone marrow transplantation

T cells play an important role in protective immunity against tuberculosis. As patients are not reimmunized with BCG after BMT, the question arises as to whether PPD-specific memory T cells are transferred from the marrow donor to the recipient and persist in the long-term. We studied long-term survivors of non-T cell-depleted allogeneic bone marrow transplantation for in vitro PPD-induced proliferative responses (n = 14), and delayed-type hypersensitivity after intradermal injection of tuberculin (n = 20). We also studied 7 patients who received T cell-depleted bone marrow. Proliferative responses in the first group were low, but were increased by concentrating CD4+ T cells, the major responding cells in this system. In contrast, PBL from patients who received T cell-depleted marrow remained unresponsive to PPD, although they responded normally to CMV antigens. Of the 15 healthy patients in the first group who underwent tuberculin skin tests, 13 had positive reactions, while only two failed to react. (Five patients of the first group were suffering from chronic GVHD and 3 of them were negative.) All the patients in the second group had negative delayed-hypersensitivity responses. The difference between the two groups of patients was highly significant (P < 0.003). These results show that transferred PPD-specific T cells persist in long-term survivors of non-T cell-depleted BMT, even in the absence of reimmunization.