KBM-7, A HUMAN MYELOID-LEUKEMIA CELL-LINE WITH DOUBLE PHILADELPHIA CHROMOSOMES LACKING NORMAL C-ABL AND BCR TRANSCRIPTS

A human myeloid leukemia cell line, KBM-7, was developed from a patien t in the blastic phase of chronic myeloid leukemia (CML). We character ized its morphology, immunophenotype, cytogenetics, and proliferative capacity. Developed in the absence of exogenous lymphokines, KBM-7 in vitro cloning capacity actually decreased when colony-stimulating fact ors were added. The cells had an aberrant immature myeloid phenotype, a doubling time of 22 h In suspension cultures and a high cloning effi ciency in a semisolid system (24 +/- 3)%. Early passages contained one near-haploid (predominant) and one hyperdiploid stem line. Gradually the hyperdiploid stem line became predominant, reaching an average of 49 chromosomes per cell. Cells from passage 89 had two Philadelphia ch romosomes [t(9;22)(q34;q11)] and lacked normal copies of chromosomes 9 and 22. Detailed molecular characterization of the breakpoint in the t(9;22)(q34;q11) revealed that KBM-7 had the BCR 2/ABL II splice junct ion. The cells had high protein kinase (p210(BCR-ABL)) activity and ca rried two identified variants of an ABL-BCR message. There was no evid ence that normal BCR or c-ABL messages were expressed, assessed with t he reverse-transcriptase polymerase chain reaction. When KBM-7 cells w ere heterotransplanted into nude mice without immunosuppressive pretre atment, one of three mice injected with 1 x 10(7) cells and all mice i njected with 1 x 10(8) cells developed slowly growing granulocytic sar comas within 6-8 weeks. These tumors were locally invasive but did not metastasize. We conclude that the KBM-7 cell line will be of value fo r investigating molecular events underlying neoplastic transformation in CML, in particular for studying the effects of BCR-ABL and ABL-BCR on the proliferation of CML cells in the absence of normal BCR and c-A BL messages.