Junctional sequences of T cell receptor V delta 2-D delta 3 or D delta 2-D delta 3 rearrangements in acute lymphoblastic leukemia

T-cell receptor (TCR) delta chain gene rearrangements were studied by polymerase chain reaction (PCR) analysis in 46 patients with acute lymphoblastic leukemia (ALL). Sixteen patients were found to have incomplete rearrangements of the TCR delta genes. Among them, 13 patients displayed V delta 2-D delta 3 rearrangement, while 3 had both V delta 2-D delta 3 and D delta 2-D delta 3 rearrangements. To determine the junctional sequence of TCR delta gene, PCR products from the 16 patients were sequenced directly or after M13 cloning. The results showed the junctional sequences of TCR delta gene are highly specific for each allele. This sequence diversity resulted from several factors including deletion of the 3' end of V delta 2 or D delta 2 segment and 5' end of D delta 3 segment, the presence of D delta 1 or D delta 2 sequences, insertion of N nucleotides and the association of P nucleotides with intact V delta 2 and D delta 3 segments. In addition, analysis of N-nucleotide contents revealed that the amount of GC was much larger than that of AT (70%: 30%), indicating the insertion of N nucleotide was not fully random. Our sequence data confirmed that the imcomplete rearrangement of TCR delta gene is an early event in the lymphoid cell ontogenesis, and its N sequences in V-(D)-J junctional region may be used as a specific marker of clonality to detect the minimal residual disease (MRD) in ALL.