HETEROGENEITY OF THE T-CELL RECEPTOR DELTA-GENE INDICATING SUBCLONE FORMATION IN ACUTE PRECURSOR B-CELL LEUKEMIAS

Precursor B-cell acute lymphoblastic leukemias (B-ALLs) have been show n to be oligoclonal at the Ig heavy-chain (IgH) gene level in up to 40 % of cases by Southern blot hybridization. In contrast, oligoclonality as deduced from diversity of T-cell receptor (TcR)-delta gene rearran gements of the immature types (ie, V delta 2-D delta 3, D delta 2-D de lta 3) has not been reported, so far. We detected oligoclonality chara cterized by the coexistence of different junctional regions of identic al V delta 2-D delta 3 rearrangements in four childhood precursor B-AL Ls. No variation was found in the IgH gene status. Therefore, we defin e these populations as subclones. Two leukemias displayed the variants in an unequal proportion. In the other two leukemias, for which simil ar quantities of the coexisting rearrangements were detected, single c ell-nuclei polymerase chain reaction (PCR) showed two separate leukemi c populations. Subclone formation could not be demonstrated by Souther n blot hybridization, but was detectable after PCR amplification of th e V delta 2-D delta 3 rearrangement and separation by polyacrylamide g el electrophoresis. The variants arose independently from each other, as deduced from their individual sequences. Using subclone-specific ol igonucleotides for hybridization to amplified DNA obtained at diagnosi s and during follow-up from bone marrow samples, we demonstrate, (1) s pecificity of all subclone-deduced probes, (2) that one residual leuke mic cell can be detected in 10(4) to 10(5) normal mononuclear cells in a semiquantitative assay, and (3) that none of the subclones persiste d after induction therapy. We propose that in a leukemic cell populati on, TcR-delta gene diversity arises after rearrangements of the IgH ge nes resulting in apparent clonality at the IgH gene level. However, ce lls are oligoclonal, if the TcR-delta gene rearrangements are consider ed. As various subclones may respond differently to chemotherapy, they may hamper the detection of minimal residual disease. Therefore, we u se all subclone-specific oligonucleotides for hybridization to amplifi ed DNA from follow-up samples. (C) 1995 by The American Society of Hem atology.