Evidence for a rat granulocyte chalone effect on the proliferation of normal human bone marrow and of myeloid leukemias.

Evidence is presented that rat ascites cell extracts, acting as granulocyte chalone, temporarily inhibit the cell doubling of granulocytopoietic precursors in suspension cultures of human bone marrow. The extracts do not affect the proliferation of erythroblasts and do not show any cytotoxicity. In addition, a relative increase of granulocytic precursors capable of proliferation was found, suggesting an increase in the resting population of the granulocytopoietic proliferation pool due to extract treatment. However, the extract capable of depressing the proliferation of the normal granulocytopoiesis did not affect the granulocytopoiesis of 7 chronic myeloid and 2 chronic myelomonocytic leukemias at the same dose level. In contrast to these chronic leukemias, blast proliferation of 4 acute myeloid and monocytic leukemias was greatly depressed not only for 6 h but for the whole culture period of 48 h.