Autocrine function of murine F‐MuLV induced myeloblastic cell lines

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Abstract
Four in vitro permanent suspension cell lines have been established from tumoral organs of myelogenous leukemias developed in mice infected with two biologically cloned Friend helper viruses. Leukemic cells in culture were 100% typical myeloblasts exhibiting a strong myeloperoxidase positivity. A few cells were induced to granulocytic or macrophagic terminal differentiation by post‐endotoxin serum and by various chemical differentiation inducers such as DMSO, N‐butyrate and TPA. We investigated the conditions sustaining the clonal proliferation of these leukemic cells in semi‐solid cultures. Cloning efficiencies were increased by the vicinity of a large number of autologous cells and by the addition of autologous culture supernatant, indicating that the leukemic cells were able to stimulate their own in vitro growth. Cloning efficiencies were also increased by different sources of CSA, such as WEHI‐3B conditioned medium and post‐endotoxin serum. Moreover, the various cell lines stimulated each other through soluble factor(s) secreted in their culture supernatants. Proteins contained in these four culture supernatants were fractionated by successive ammonium sulfate precipitations and ion exchange chromatography. In the four cases the autostimulating activities were eluted in the same fractions as proteins stimulating the normal bone marrow cells colony formation (CSA). These data suggest that the myeloblastic leukemic cell autostimulating factor(s) might be related to the physiological CSA.