Cross-lineage T cell receptor gene rearrangements occur in more than ninety percent of childhood precursor-B acute lymphoblastic leukemias: alternative PCR targets for detection of minimal residual disease.

A large series of 202 childhood precursor-B cell acute lymphoblastic leukemia (ALL) patients was analyzed by Southern blotting (SB) for cross-lineage rearrangements and/or deletions in the T cell receptor TCRB, TCRG and TCRD loci. In 93% (187/201) of the precursor-B-ALL patients one or more genes were rearranged and/or deleted. TCRB gene rearrangements were found in 35% (69/196), TCRG gene rearrangements in 59% (113/192), TCRD gene rearrangements in 55% (112/202), and isolated monoallelic or biallelic deletions of TCRD loci in 34% (68/202) of the cases. TCRB gene rearrangements involved exclusively the Jbeta2 locus with complete V(D)Jbeta2 joinings in 53% of gene rearrangements and incomplete Dbeta-Jbeta2 gene rearrangements in 33%. TCRG gene rearrangements frequently occurred on both alleles (65% of cases) and in approximately 70% concerned rearrangements to Jgamma1 gene segments. Most rearranged TCRD alleles (80%) represented incomplete Vdelta2-Ddelta3 or Ddelta2-Ddelta3 gene rearrangements, while the remaining TCRD gene rearrangements remained unidentified. Subsequently, we evaluated, whether heteroduplex PCR analysis of rearranged TCRG and TCRD genes can be used for reliable identification of PCR targets for detection of minimal residual disease (MRD). The concordance between SB and heteroduplex PCR analysis for detection of the various types of clonal TCRG and TCRD gene rearrangements ranged between 78% and 87%. The discrepancies could be assigned to the presence of 'atypical' TCRD gene rearrangements or translocations only detectable by SB, but also to efficient PCR-based detection of rearrangements derived from small subclones, which are difficult to detect with SB. Indications for oligoclonality were observed in 38% and 30% of patients with TCRG and TCRD gene rearrangements, respectively, which is comparable to the frequency of oligoclonality in IGH locus. Based on the combined data it was possible to reduce the broad panel of six TCRD and 12 TCRG primer combinations for MRD studies to two TCRD combinations (Vdelta2-Ddelta3 and Ddelta2-Ddelta3) and six TCRG combinations (VgammaI, VgammaII, VgammaIV family-specific primers with Jgamma1.1/2.1 and Jgamma1.3/2.3 primers) resulting in the detection of 80% and 97% of all TCRD and TCRG gene rearrangements, respectively. Finally, the heteroduplex PCR data indicate that MRD monitoring with TCRG and/or TCRD targets is possible in approximately 80% of childhood precursor-B-ALL patients; approximately 55% of patients even have two TCRG and/or TCRD targets.