Forty-four human long-term survivors after marrow transplantation for aplastic anemia or hematologic malignancy were studied for the presence of circulating nonspecific suppressor cells. Twenty-two of the patients were healthy and 22 had mild to moderately severe chronic graft-vs-host disease (GVHD). Patient mononuclear cells (of donor origin) were tested for their ability to suppress the responses of lymphocytes obtained from the respective marrow donors to alloantigens in mixed leukocyte culture (MLC) and/or to concanavalin A (Con A). Tests were carried out between 199 and 2393 (median 376) days after transplantation. Cells from only 1 of 22 patients without chronic GVHD showed suppression of donor cell blastogenesis responses. In contrast, cells from 11 of 22 patients with chronic GVHD showed more than 30% suppression of donor cell responses in MLC and/or to Con A. The finding of suppressor cells was not related to the time of testing after grafting nor to immunosuppressive therapy. Nonspecific suppressor activity was abrogated by irradiation with 1600 rads in vitro in five of six cases tested. Nonspecific suppressor cells may be one explanation for the severe combined immunodeficiency and the recurrent infectious complications characteristic of patients with chronic GVHD.

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This work was supported by Grant Numbers CA 18221, CA 18029, and CA 15704, awarded by the National Cancer Institute, Department of Health, Education, and Welfare.

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