ESTABLISHMENT AND CHARACTERIZATION OF AN IMMATURE MYELOID CELL LINE, M-MOK, GROWN IN THE PRESENCE OF FIBROBLAST-FEEDER CELLS

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We have established an human leukemia cell line, M-MOK, with immature myeloid features. M-MOK was grown only in the presence of human embryonic lung derived fibroblast cell line, HEL-O. Histochemical examination revealed that M-MOK was negative for peroxidase and dougle esterase stains. Surface marker profiles were CD34(+),CD33(+),CD41(+),CD42b(+),HLA-DR(-)and glycophorin (-). We investigated the mechanism of growth for M-MOK cells on HEL-O. Nucleopore membrane was used to examine weather direct contact between M-MOK and HEL-O was required for the growth of M-MOK cells. It was demonstrated that M-MOK was able to grow by soluble factor(s) derived from HEL-O without direct contact. Culture supernatant from HEL-O was harvested and used as conditioned medium(CM). RPMI-1640 medium supplemented with 20% fetal calf serum and 20% CM could induce proliferation of M-MOK cells without feeder cells. We maintained M-MOK cells using this CM supplemented medium as long as 1 month. In order to know the nature of the HEL-O derived soluble factors we tried to inhibit the growth of M-MOK cells on HEL-O using various monoclonal antibodies such as anti-VLA4,anti-CD11a, anti-G-CSF, anti-GM-CSF and anti-IL-3 antibodis. Only anti-GM-CSF antibody inhibited the growth of M-MOK cells. Induction of M-MOK proliferation by HEL-O derived conditioned medium was also blocked by the addition of anti-GM-CSF antibody to the culture medium. These data clearly indicated that the soluble factor from HEL-O which support the growth of M-MOK might be GM-CSF. Northern blot hybridization assay of mRNA from HEL-O confirmed the presence of mRNA for GM-CSF in HEL-O cells.