TCRδ Gene Rearrangements in Acute Myeloid Leukemia with T-lymphoid Antigen Expression

In this review we present our data concerning T-cell receptor (TCR) δ gene rearrangements in acute myeloid leukemia with cuexpression of T-lymphoid features (CD2/CD4/CD7; Ly+ AML). We found a correlation between TCRδ gene rearrangements and coexpression of these T-lymphoid features. Ten of 66 Ly+ AML and only one of 44 AML cases without this coexpression exhibited TCRδ gene rearrangements (p = .028). In contrast, no correlation was observed between terminal deoxynucleotidyl transferase (TdT) expression and the occurence of TCRδ gene rearrangements in AML. Rearrangements were found in two of 25 AML with and seven of 71 AML cases without TdT expression. Interestingly, nucleotide sequencing of junctional sites revealed up to 36 N-nucleotides in cases without or with only weak TdT expression indicating downregulation of TdT expression after the TCR rearrangement took place. Complete Vδ1Jδ1 and incomplete Dδ2Jδ1 gene rearrangements were observed most frequently in Ly+ AML. These recombination patterns were similar to patterns observed in acute T-lymphoblastic leukemia with coexpression of myeloid features (My+ T-ALL) suggesting transformation of a common myeloid/T-lymphoid progenitor cell in these cases.