Ultrastructural studies of spontaneous in vitro transformation of cultured marrow monocyte-macrophage cells from a patient with congenital hypoplastic anemia

The CM-S cell line was established from the bone marrow of a patient suffering from congenital hypoplastic anemia (syndrome of Diamond-Blackfan). The cells grew in suspension in liquid culture and were dependent for their continuous replication in vitro on growth factors produced by the same cells seeded at high density. Initially, undifferentiated blasts, immature myeloid, megakaryocytic and, rarely, erythroid cells were observed. Eventually, a population of cells with characteristics of monocyte-macrophage precursors predominated. These cells could be induced to terminal macrophage differentiation by incubation with the tumor promoter 12-O-tetradecanoylphorbol-13-acetate. During this period (over 150 continuous passages), the cells failed to form colonies in agar and to give rise to tumors when inoculated into athymic mice. On prolonged passages, however, the cells gradually increased their growth capacity in liquid culture and became capable of forming colonies in agar and tumors in animals. Ultrastructural studies revealed that the expression of differentiated traits markedly changed as a function of time: after 277 passages, the transformed cells, although displaying characteristics of monocyte precursors, appeared blocked at this stage and no longer responded to 12-O-tetradecanoylphorbol-13-acetate.