Human stem cell colony-stimulating activity (CFU-GEMMCSA) in medium conditioned by leukemic B-lymphocytes

Media conditioned by B-lymphocytes of patients with chronic lymphocytic leukemia (B-CLL) induced the formation of multilineage colonies (CFU-GEMM) in cultures of human target marrow cells. Maximum levels of stem cell colony-stimulating activity (CFU-GEMMCSA) were detected by day 3 of leukemic B-cell cultures, remaining constant thereafter. Stimulation of leukemic B-lymphocytes with B-cell mitogens such as Cowan strain Staphylococcus aureus (SAC) and anti-mu enhanced the production of CFU-GEMMCSA by these cells. 3H-thymidine uptake in response to these mitogens was detected only in SAC-stimulated cultures, thereby demonstrating that mitogen-induced enhancement of CFU-GEMMCSA production by leukemic B-lymphocytes is independent of DNA synthesis. Conditioned media of leukemic B-lymphocytes stimulated the formation of human marrow granulocyte-macrophage (GM-CFU) and early erythroid (BFU-E) colonies as well. These observations indicate a role for B-lymphocytes in the regulation of hemopoietic stem cell and progenitor cell growth in vitro.