KBM-3, an in vitro model of human acute myelomonocytic leukemia

A human acute myelomonocytic leukemia cell line, KBM-3, was developed to study the pathophysiology of human acute myeloid leukemia. This cell line was characterized by morphology, immunophenotype, Giemsa-banding pattern, in vitro proliferation capacity, and tumorigenicity in nude mice. The KBM-3 cell line was established in the presence of exogenous lymphokines (human placenta-conditioned medium, HPCM), but medium for later passages did not contain HPCM. We found high cellular expression of the mRNA for granulocyte-macrophage colony-stimulating factor (GM-CSF), which we suggest may be important for the immortalization of the cell line. KBM-3 cells have an immature myelomonocytic phenotype. Cytogenetic analysis revealed a pseudodiploid karyotype with five characteristic marker chromosomes and ranging in total number from 45 to 49. In suspension culture, the cells had a doubling time of 23 h and a cloning efficiency of about 30% in soft agar independent of exogenous lymphokines. Two-thirds of nude mice injected with 1 x 10⁴ KBM-3 cells and all animals injected with 1 x 10⁵ cells developed S.C. granulocytic sarcomas within 6-8 weeks. These tumors were locally invasive but did not give rise to distant metastases. When transplanted to a new set of nude mice, all tumors formed secondary sarcomas at the site of implant. We conclude that the KBM-3 cell line may have value for studying the molecular events that underlie the neoplastic transformation in human myeloid leukemia.