TCR-DELTA GENE REARRANGEMENTS IN ACUTE MYELOID-LEUKEMIA WITH T-LYMPHOID ANTIGEN EXPRESSION

In this review we present our data concerning T-cell receptor (TCR) de lta gene rearrangements in acute myeloid leukemia with coexpression of T-lymphoid features (CD2/CD4/CD7; Ly+ AML). We found a correlation be tween TCR delta gene rearrangements and coexpression of these T-lympho id features. Ten of 66 Ly+ AML and only one of 44 AML cases without th is coexpression exhibited TCR delta gene rearrangements (p = .028). In contrast, no correlation was observed between terminal deoxynucleotid yl transferase (TdT) expression and the occurence of TCR delta gene re arrangements in AML. Rearrangements were found in two of 25 AML with a nd seven of 71 AML cases without TdT expression. Interestingly, nucleo tide sequencing of junctional sites revealed up to 36 N-nucleotides in cases without or with only weak TdT expression indicating downregulat ion of TdT expression after the TCR rearrangement took place. Complete V delta 1J delta 1 and incomplete D delta 2J delta 1 gene rearrangeme nts were observed most frequently in Ly+ AML. These recombination patt erns were similar to patterns observed in acute T-lymphoblastic leukem ia with coexpression of myeloid features (My+ T-ALL) suggesting transf ormation of a common myeloid/T-lymphoid progenitor cell in these cases .