Different colony stimulating activity by tumoral ascitic fluid and conditioned media.

The effects of intraperitoneal Ehrlich ascites tumor (ET) growth on the kinetics of hemopoietic stem cells in the host bone marrow were studied using the spleen colony and the soft agar culture techniques. There is a decrease in spleen colony forming capacity of bone marrow of ET bearing mice, whereas in vitro assays of the committed macrophage granulocyte precursors, by the soft agar method, show that in the same circumstances a high yield of granulopoietic colonies can still be obtained. A shift of the CFU-c/CFU-s ratio from 15 to 36 thus occurs. Moreover, ascitic fluid from tumoral mice displays strong activity as CSF on normal mouse marrow, twice as strong as the standard mouse embryo CSF. When conditioned medium from cultures of ET cells (ET-CM) is tested, the pattern of agar colonies obtained is different from the previously obtained pattern of growth kinetics; furthermore many colonies are composed of undifferentiated cells. The hypothesis is suggested that among the variety of known CSF's, the ET-CM represents a unique factor, capable of inducing proliferation of marrow CFU-c, but only limited differentiation.