CHARACTERIZATION OF TRANSLOCATION T(1 14)(P32 Q11) IN A T-ACUTE AND IN A B-ACUTE LEUKEMIA

The TALI locus on chromosome band 1p32 is rearranged in 15 to 29% of h uman T-cell acute lymphoblastic leukemias (T-ALLs). These alterations consist of either a tal(d) submicroscopic deletion (12-26% of T-ALL)or a t(1;14)(p32;q11) chromosomal translocation (3% of childhood T-ALL). Both types of alterations preferentially affect the 5' part of the TA L1 locus. Their main consequence appears to be transcriptional activat ion of the TAL1 gene. We have characterized two cases of t(1;1 4)(p32; q11) in ALL. Both affect the TCRdelta gene segments at 14q11 and the 5 ' part of the TAL1 locus at 1 p32. The first case represented a 'class ical' t(1;14), associated with T-ALL. Its analysis indicates the use o f a recombination signal-like sequence localized in the third exon of TAL1 in the translocation process. In the other case. the rearrangemen t to the Ddelta region occurred 5' to the TALI transcription start sit es. This case exhibited a B-lymphoid immunophenotype thus suggesting t hat the putative oncogenicity of TAL1 activation is not restricted to T-cell malignancies.