Characterization of circulating suppressor T lymphocytes in bone marrow transplant recipients

Peripheral blood T lymphocytes from 21 bone marrow transplant (BMT) patients and normal controls were studied for surface expression of HLA-DR, HLA-DQ, and classic T cell markers, including Leu 2, Leu 3, and Leu 4. Although resting T cells from normal subjects did not express HLA-DR or HLA-DQ molecules, up to 86% (range 22-86%) of T cells from BMT recipients expressed HLA-DR. Interestingly, less than or equal to 8% of the cells expressed HLA-DQ, and less than or equal to 3% had receptors for interleukin-2 (IL-2). When T lymphocytes were harvested from BMT recipients one month postransplant, they failed to produce IL-2 constitutively or after stimulation with various mitogens. Further analysis of patient cells revealed that 20-67% of their T lymphocytes were positive for both Leu 2 and Leu 15 (2+, 15+; normal range = 5-8%). Since 2+, 15+ cells from normal subjects have potent suppressor activity, we tested whether the cells from BMT recipients would suppress production of IL-2 from normal cells. In coculture studies, we found that cells from 5/5 BMT patients suppressed normal IL-2 production up to 70%. If patient cells were irradiated (3000 rads) prior to coculture, suppressor activity was abrogated. We propose that the cells described here may play a prominent role in the slow recovery of the immune system in BMT recipients.