Developmental process of the T-cell receptor alpha and delta gene assembly in B-cell precursor acute lymphoblastic...

We analysed the organization of V delta genes and delta recombining element (delta Rec) in 27 children with B-cell precursor acute lymphoblastic leukaemia. Twenty-two of 54 alleles showed rearrangements of the T-cell receptor (TCR) delta locus. These rearrangements resulted either from D2D delta 3 (2 alleles) or V delta 2(Dn)D delta 3 (20 alleles) recombinations, and the other V delta and delta Rec were not rearranged. Of 23 alleles with deletion of C delta and rearrangements of J alpha, V delta 2, V delta 4 and V delta 5 appeared to rearrange to J alpha on five alleles. With regard to the relationship between the rearranged V alpha/delta and J alpha genes, gene segments 5' to V delta 2 frequently rearranged to J alpha more proximal to C alpha, whereas V delta 2 and gene segments 3' to V delta 2 showed a tendency to rearrange to J alpha distal to C alpha. Based on these findings, we suggest that the initial recombination event of the TCR-alpha/delta gene may be D2D delta 3 joining, followed by V delta 2 recombination with the D2D delta 3 complex. It was also suggested that use of V alpha/delta and J alpha/delta may depend on the distance between the involved V alpha/delta and J alpha/delta at least in B-lineage cells. These rearrangements in B-precursor cells appear to be aberrant. However, this recombinational process may be one of the normal differentiation pathways in T-lineage cells, because cells with a V delta 2(Dn)D delta 3 rearrangement were detected in 0.1-0.01% of normal peripheral mononuclear cells by the polymerase chain reaction.