ESTABLISHMENT AND CHARACTERIZATION OF A NOVEL HUMAN IMMATURE MEGAKARYOBLASTIC LEUKEMIA-CELL LINE, M-MOK, DEPENDENT ON FIBROBLASTS FOR ITS VIABILITY

A novel fibroblast-dependent human immature megakaryoblastic leukemia cell line (M-MOK) was established from the bone marrow of a girl with acute megakaryoblastic leukemia, and its growth was determined to be c ompletely dependent on the presence of human embryonic lung-derived fi broblasts, HEL-O. Adhesive interaction between M-MOK and HEL-O was cru cial for viability; once HEL-O was removed from the culture, mortality was total within a few days. On HEL-O cells, M-MOK could be passaged for more than 2 years. With regard to surface marker profile, the esta blished cells were positive for CD11a, CD13, CD18, CD33, CD34, CD41b, CD42b, CD54, and c-kit antigens, but negative for HLA class II antigen and glycophorin. Histochemically, the cells were negative for myelope roxidase, nonspecific esterase, and naphthol ASD chloroacetate esteras e staining. Electron-microscope examination revealed the cells to be n egative for platelet peroxidase (PPO). After induction of differentiat ion by a phorbol ester, however, the cells were demonstrated to be pos itive for PPO with a morphological change to megakaryocytes. From thes e results, M-MOK was considered to represent an immature cell Line of megakaryocyte lineage. Studies of the mechanisms sustaining the HEL-O- dependent continuous in vitro growth of M-MOK cells revealed the follo wing results: (1) M-MOK could grow even when separated from HEL-O by a nucleopore membrane; (2) conditioned medium (CM) from HEL-O supported the growth of M-MOK for more than 1 month without feeder cells; (3) t he growth of M-MOK on HEL-O or CM supplement was nearly entirely inhib ited by anti-GM-CSF (1 mu g/mL); (4) GM-CSF mRNA was detected in HEL-O cells; and (5) HEL-O was found to secrete GM-CSF into the culture med ium. Taken together, the growth of M-MOK might therefore be driven by a soluble factor, that is, GM-CSF secreted from HEL-O cells. The prese nce of HEL-O, however, inhibited anti-GM-CSF-induced M-MOK death. Go-c ulture of M-MOK and HEL-O cells thus offers a useful experimental mode l for analysis of interactions between hematopoietic stem cells and st romal cells.