T cell receptor Dδ2Dδ3 rearrangement: a suitable allele-specific marker for the detection of minimal residual disease in childhood acute lymphoblastic leukemia

Abstract

The applicability of T cell receptor (TCR) Dδ 2Dδ 3 junctional regions for the detection of minimal residual disease (MRD) was examined in childhood acute lymphoblastic leukemia (ALL). Southern blot analysis showed a Dδ 2Dδ 3 rearrangement in 22 of 172 (13%) precursor-B ALL. No Dδ 2D δ 3 rearrangement was identified in 29 T-ALL cases. Three patients exhibited D δ 2Dδ 3 recombinations in both alleles. Sequence analysis of D δ2Dδ 3 junctions revealed extensive diversity due to the random insertion and deletion of nucleotides at the joining site. PCR analysis utilizing allele-specific probes or oligonucleotides generated on the basis of Dδ2Dδ 3 junctional sequences reached a sufficient sensitivity of 10⁻⁴ to 10⁻⁵ in the majority of cases. In four of 25 (16%) rearranged alleles, however, the 5′ heptamer–nonamer recombination signal sequence (RSS) of the Dδ2 segment had recombined directly to the 3′ heptamer–nonamer RSS of the Dδ 3 segment thus generating a so-called signal junction. Respective heptamer–heptamer junctions are not suited to design allele-specific oligonucleotides for the detection of MRD because of their limited diversity and hence specificity.