Megakaryocytic colony-stimulating activity in patients receiving a marrow transplant during hematopoietic reconstitution.

Megakaryocytic colony formation is dependent upon growth-stimulating activities present in human serum or plasma. Factors with diverse biological activities including megakaryocytic colony-stimulating activity (Mk-CSA) are provided by the medium of mitogen stimulated peripheral mononuclear cells or subsets of peripheral T cells. In this communication we describe the stimulatory activity of plasma collected from allogeneic and autologous bone marrow transplant recipients on the growth of megakaryocytic colonies. Mk-CSA was found to increase after transplantation as bone marrow regenerated. The stimulatory activities for CFU-M were greater in plasma from allogeneic bone marrow transplant patients receiving T cell-depleted donor marrow than in patients receiving unmodified donor marrow. Growth-promoting activities derived from mitogen-stimulated lymphocytes of T4 phenotype, a potent source of Mk-CSA, did not increase the frequency of CFU-M when cultured in plasma collected from transplant patients receiving a T cell-depleted donor marrow. However, a further increase in the number of CFU-M was observed when exogenous Mk-CSA was added to the cultures supplemented with plasma from patients receiving unmodified donor marrow. Plasma of patients who received autologous marrow displayed similar Mk-CSA activity when compared with the activity of plasma obtained from transplant recipients receiving an unmodified allogeneic donor marrow. Stimulatory activities supporting multilineage colonies (CFU-GEMM), erythroid bursts (BFU-E), and granulocytic colonies (CFU-C) derived from plasma of the three different transplant groups revealed no statistical difference with respect to the frequency of CFU-GEMM, BFU-E, or CFU-C colonies when compared with pretransplant plasma. The results suggest that MK-CSA may play an important role in the regulation of megakaryopoiesis in vivo. Moreover the data suggest the presence of humoral regulators that appear to be different with respect to the processing of the donor marrow.