TCRD/A gene rearrangements in precursor-B–ALL. (A) Consecutive rearrangements in the TCRD/A locus involving the Vδ2 gene segment that are characteristic for precursor-B–ALL. The main pathway concerns consecutive Vδ2-Dδ3 → Vδ2-Dδ3-Jα recombinations. Dδ2-Dδ3 and Dδ2-Jα gene rearrangements can also occur, albeit at much lower frequencies. Solid boxes below the gene segments represent the probes used for Southern blot hybridization. (B) Southern blot analysis with TCRDV2 probe in 10 precursor-B–ALL samples. Vδ2-Dδ3 and/or Vδ2-Jα29 gene rearrangements in cases 5602, 5675, 5683, and 5696 are monoclonal. The presence of several rearranged bands of different densities in cases 5515, 5647, 5662, and 5698 is consistent with oligoclonality. Both Vδ2 alleles in case 5670 are deleted, while case 5565 has both Vδ2 alleles in germline (G) configuration.