Philadelphia Chromosome-positive Acute Lymphoblastic Leukemia Cell Lines without Classical Breakpoint Cluster Region Rearrangement 1

The Philadelphia (Ph) chromosome translocation which is classically observed in chronic myeloid leukemia ((.'Ml,) is sporadically found in acute lymphoblastic leukemia (ALL). In CML the translocation break point on chromosome 22 is within the breakpoint cluster region, while in childhood ALL, no detectable change in breakpoint cluster region is routinely observed. In order to investigate the nature of this difference, we have established and characterized two cell lines from a child with Ph positive ALL. The cell lines have retained the cytochemical staining pattern, enzyme activity, monoclonal antibody profile, and immunoglobulin gene rearrangements of the child's malignant cells. The cell lines had the same Ph translocation t(9;22) (q34;qll) as the child's malignant cells along with additional chromosome changes. Southern blot analysis showed that the Ph translocation did not involve the 5.8-kilobase break point cluster region segment characteristically seen in CML. The cell lines reported here will be a valuable resource in ascertaining the biolog ical significance of the Ph translocation seen in ALL.