Brief Definitive Report CHROMOSOMAL TRANSLOCATION INVOLVING THE a T CELL RECEPTOR GENE IN ACUTE LEUKEMIA

Chromosomal translocations are implicated as important pathogenetic events in many human malignancies (1) . For tumors of B-lymphoid origin, the Ig genes are frequent sites of chromosomal translocations, most commonly resulting in juxtaposition of Ig genes with the c-myc or bcl-2 genes (2) . In rare T cell cancers, the TCR-a gene may be translocated into close proximity of the c-myc protooncogene (3, 4) . Recent cytogenetic observations demonstrating chromosome 783234 abnormalities in a number of T cell malignancies suggest that the TCR-J3 gene may be the frequent target for chromosomal translocations in lymphoid cancers, although the donor chromosomes appear to be much more variable than in human B cell malignancies (5-8) . We report here molecular data showing involvement ofthe TCR-,B gene by a t(7;19)(g34;p13) chromosomal translocation in acute lymphoblastic leukemia. Nucleotide sequence analysis of cloned breakpoint DNA showed that the point of crossover on chromosome 7 occurred adjacent to joining segment J01 .1, suggesting that this translocation resulted from an error in TCR-9 gene rearrangement . On chromosome 19, the translocation occurred near or within a previously uncharacterized transcriptional unit, resulting in the production of aberrant sized RNAs.