Cell-mediated suppression of human hematopoiesis: evaluation by limiting-dilution analysis of hematopoietic progenitors.

We have used limiting-dilution clonal analysis (LDA) in microwells to study the inhibitory effects of T lymphocytes (T-cells) or natural killer (NK) cells on human marrow progenitor cell growth. In four subjects with normal hematopoiesis, the growth of progenitors showed single-hit kinetics both before and after T-cell removal, indicating that, in the presence of colony-stimulating activity, T-cells have no effect on progenitor growth. In a patient with marrow hypoplasia associated with thymoma, hypogammaglobulinemia, and an increased number of suppressor T-cells (Good's syndrome), the progenitor growth deviated from linearity, demonstrating the presence of cells with suppressor activity. After T-cells were removed from this sample, the progenitor growth showed single-hit kinetics. The suppressive action of E-rosette-positive cells with NK or cytotoxic activities was also suggested in a patient with severe combined immune deficiency and in a patient with T± lymphocytosis. Poor progenitor-cell growth in three other patients with aplastic anemia was not significantly altered by T-cell removal. Thus, LDA of human hematopoietic progenitors is useful for evaluating cell-mediated interactions affecting hematopoiesis. This method may facilitate elucidation of mechanisms of myelosuppression in clinical settings.