IMMATURE T LYMPHOCYTES IN THE PERIPHERAL BLOOD OF BONE MARROW TRANSPLANT RECIPIENTS1

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Abstract
Recipients of allogeneic bone marrow transplants are characterized by an immunodeficiency of varying intensity and duration. The presence of in vivo activated suppressor T lymphocytes was demonstrated in immunodeficient patients with chronic graft-vs.-host disease. To determine the basis of the immunodeficiency of transplant recipients early after transplantation, the lymphocytes of transplant recipients were analyzed phenotypically by E[erythrocyte]-rosette formation and staiing with monoclonal antibodies (OKT-3, -6, and -8) and functionally by their blastogenic response to mitogens. Only 15% of transplant recipients'' assays 0-3 mo. and 16% of assays 3-12 mo. following transplant were in the normal range. Transplant recipients during the 1st yr after transplantation were characterized by an increased percentage (57%) of patients with a normal percentage of E-rosette-forming cells but reduced PHA [phytohemagglutinin] responsivness. In vitro coculture experiments demonstrated that their lack of PHA responsiveness was not due to the presence of in vivo activated suppressor cells or a decrease in mitogen-presenting cells. Staining with monoclonal antibodies revealed that the T lymphocytes from the majority of recipients at 0-3 mo. following transplantation contained a percentage of OKT8-positive cells greater than or equal to the percentage of OKT3-positive cells. This pattern (OKT8 .gtoreq. OKT3) was not found in the peripheral blood T lymphocytes of normal people but was found in 13 of 15 thymuses. Monoclonal staining with OKT6, a thymocyte-specific antibody, revealed positive staining of > 10% of the peripheral blood leukocytes in the majority of recipients 0-3 mo. following transplantation, compared with only a few normals. The circulating T lymphocytes of transplant recipients are phenotypically and functionally immature. Their relative immaturity contributes to the transplant recipients'' immunodeficiency.