Characteristics of Granulocyte‐Macrophage Colony Formation in Chronic Myelomonocytic Leukemia: A Comparative Study with Other Myelodysplastic and Myeloproliferative Disorders

We studied granulocyte‐macrophage (GM) colony formation in chronic myelomonocytic leukemia (CMML, 6 cases), as compared with that in myelodysplastic syndromes (MDS, 6 cases) and myeloproliferative disorders (MPD, 12 cases). GM colony formation of bone marrow cells by colony‐stimulating factor (CSF) was normal in CMML and MPD patients, but was decreased in MDS patients. Circulating granulocyte‐macrophage progenitors (CFU‐GM) were detected in CMML and MPD patients, but not in MDS patients. GM colony formation without CSF was observed in CMML patients, but not in MDS or MPD patients. These endogenous colonies decreased markedly after adherent cell (AdC) depletion, but AdC did not form endogenous colonies in sufficient numbers to explain their marked decrease after AdC depletion. In CMML patients, the numbers of circulating CFU‐GM and endogenous colonies correlated with leukocyte and monocyte counts, respectively. The cellular composition of GM colonies was normal in MDS and MPD patients, whereas granulocytic colonies predominated in all CMML patients but one. The CSF‐producing capacity of peripheral blood cells was also studied and was found to be increased in CMML patients. This capacity was markedly decreased by AdC depletion; and AdC could produce CSF only in CMML patients. CSF produced by CMML patients supported granulocytic colonies to a greater extent than CSF produced by MDS or MPD patients. These results suggest that enhanced granulopoiesis in CMML patients is closely associated with the possible hyperproduction of granulocytic CSF by their adherent monocytes.