Evidence for the presence in sera from chronic myelogenous leukemia patients of an activity that enhances the number of normal bone marrow-derived granulocyte/monocyte committed stem cell colonies.

In serum from chronic myelogenous leukemia (CML) patients an activity has been demonstrated, which recruits more CFU-GM (cells committed to granulocyte-macrophage lineage) from normal human bone marrow into clonal proliferation as shown by standard agar colony forming assay, in the presence of supramaximal levels of colony stimulating activity. All sera from CML patients at diagnosis (before therapy) were tested and found to be significantly (P less than 0.001) positive for the recruitment activity. This observation led us to believe that younger or more pluripotent CFU-GM which were hitherto non-responsive to colony stimulating activity become responsive in the presence of CML sera. We investigated whether more pluripotent stem cells (CFUs) are stimulated to proliferate in the chronic phase of CML than at diagnosis (before therapy). An activity was detected which recruits more spleen colony forming cells (CFUs) from normal Swiss mouse bone marrow into the cell cycle as shown by a significant increase (P less than 0.001) in the thymidine suicide index. However both these activities were either lowered or undetectable in normal (blood groups AB) serum. These results indicate that CML sera may contain enhanced levels of early growth factors which stimulate proliferation of pluripotent stem cells resulting in an increased CFU-GM pool in CML. It is suggested that this activity may be responsible for the myeloid hyperplasia associated with CML in the chronic phase.