ESTABLISHMENT AND CHARACTERIZATION OF A NEW PH1-POSITIVE ALL CELL-LINE (ALL MIK) PRESENTING BCR GENE REARRANGEMENT ON BCR-2 AND ALL-TYPE BCR/ABL TRANSCRIPT - SUGGESTION OF IN-VITRO DIFFERENTIATION TO MONOCYTOID LINEAGE/

A new Ph1-positive acute lymphoblastic leukemia cell line, designated as ALL/MIK, has been developed from a patient with Ph1-positive acute leukemia. The ALL/MIK cells showed an immunophenotype of common ALL wi th rearranged J(H) and J(kappa) genes. The ALL/MIK cells showed no M-b cr rearrangement using Southern blot analysis with either 3' or 5' M-b cr probes, but had the bcr gene rearrangement on bcr-2 within the firs t intron of the bcr gene. Consistent with this result, the reverse tra nscriptase-dependent polymerase chain reaction (RT-PCR) assay revealed that the ALL/MIK cells contained the transcript derived fusion of the first exon of bcr gene and the second exon of abl gene. Although the ALL/MIK cells were defined as early pre-B cells by immunophenotypical and genotypical analyses, they were capable of differentiating into mo nocytoid lineage by when cultured with TPA. Furthermore, another Ph1-p ositive ALL cell line, (TOM-1), was investigated for its ability to di fferentiate to monocytoid lineage. TOM-1 was also induced to monocytoi d lineage by TPA. Thus, the present study suggested that the leukemic transformation in some Ph1-positive ALL may occur at the level of mult ipotential hematopoietic cells capable of differentiating towards lymp hoid and myelo-monocytoid lineage.