Precursor-B-ALL with D sub(H)-J sub(H) gene rearrangements have an immature immunogenotype with a high frequency of oligoclonality and hyperdiploidy of chromosome 14

The IGH gene configuration was investigated in 97 childhood precursor-B-ALL patients at initial diagnosis. Rearrangements were found by Southern blotting in all but three patients (97%) and in 30 cases (31%) we observed oligoclonal IGH gene rearrangements. Heteroduplex PCR analysis revealed at least one clonal PCR product in all Southern blot-positive cases. In 89 patients (92%) complete V(D)J rearrangements were found, while incomplete D sub(H)-J sub(H) rearrangements occurred in only 21 patients (22%). In 5% of cases the D sub(H)-J sub(H) rearrangements were the sole IGH gene rearrangements. Sequence analysis of the 31 identified incomplete rearrangements revealed preferential usage of segments from the D sub(H)2, D sub(H)3 and D sub(H)7 families (78%). While D sub(H)2 and D sub(H)3 gene rearrangements occur frequently in normal B cells and B cell precursors, the relatively frequent usage of D sub(H)7-27 (19%) in precursor-B-ALL patients is suggestive of leukemic transformation during prenatal lymphopoiesis. Among J sub(H) gene segments in the incomplete D sub(H)-J sub(H) rearrangements, the J sub(H)6 segment was significantly overrepresented (61%). This observation together with the predominant usage of the most upstream D sub(H) genes indicates that many of the identified clonal D sub(H)-J sub(H) gene rearrangements in precursor-B-ALL probably represent secondary recombinations, having deleted pre-existing D sub(H)-J sub(H) joinings. The patients with incomplete D sub(H)-J sub(H) gene rearrangements were frequently characterized by hyperdiploid karyotype with additional copies of chromosome 14 and/or by IGH oligoclonality. The presence of incomplete D sub(H)-J sub(H) joinings was also significantly associated with a less mature immunogenotype: overrepresentation of V sub(H)6-1 gene segment usage, absence of biallelic TCRD deletions, and low frequency of TCRG gene rearrangements. This immature immunogenotype of precursor-B-ALL with incomplete IGH gene rearrangements was not associated with more aggressive disease.