Inhibiton of IL 2 production after human allogeneic bone marrow transplantation.

Bone marrow transplantation (BMT) is currently used to treat patients with severe aplastic anemia or leukemia. Despite the use of an HLA identical sibling donor, however, the survival after BMT is reduced by the occurrence of two major immunologic complications: graft-vs-host disease and a long-lasting immune deficiency responsible for late infections. This immune deficiency could be explained by an imbalance of lymphocyte subpopulations reconstituted after transplant. The aim of the present work was to study the helper function by measuring the production of interleukin 2 (IL 2). This lymphokine is responsible for the amplification of the effector phase of immunity. A consecutive series of 34 patients was tested for IL 2 production after BMT. This production was absent or low in 32 of 34 patients for at least 2 yr after BMT. The mechanism of this low IL 2 production was investigated. Irradiation of patients' lymphocytes in vitro with low dose gamma-rays partially restored the IL 2 production after 6 mo of evolution. The IL 2 production was not restored or was slightly affected by irradiation early after BMT. These results suggest that the lack of immune reconstitution after BMT may be caused by the lack of IL 2-producing cells and/or the increased activity of suppressor cells of the helper function. This suppression is radiosensitive.