Rearranged T-cell receptor beta genes represent powerful targets for quantification of minimal residual disease in childhood and adult T-cell acute lymphoblastic leukemia

Current MRD studies in T-cell acute lymphoblastic leukemia (T-ALL) mainly use T-cell receptor gamma, delta and SIL-TAL1 gene rearrangements as MRD-PCR targets. However, low frequency or limited diversity of these markers restricts the number of evaluable patients, particularly because two markers are recommended for MRD monitoring. Hence, we developed a new strategy implementing the TCR beta (TCRB) locus for MRD quantification. The frequency and characteristics of complete and incomplete TCRB rearrangements were investigated in 53 childhood and 100 adult T-ALL patients using the BIOMED-2 multiplex PCR assay. Clonal rearrangements were identified in 92% both childhood and adult T-ALL (Vβ-Dβ-Jβ rearrangements in 80%, Dβ-Jβ rearrangements in 53%). Comparative sequence analysis of 203 TCRB recombinations revealed preferential usage of the 'end-stage' segment Jβ2.7 in childhood T-ALL (27%), whereas Jβ2.3 was most frequently involved in adult T-ALL (24%). In complete rearrangements, three downstream Vβ segments (19-1/20-1/21-1) were preferentially used. Subsequently, a TCRB real-time quantitative PCR assay to quantify MRD with 13 germline Jβ primer/probe combinations and allele-specific oligonucleotides was developed and applied to 60 clonal TCRB rearrangements. The assay allowed the detection of one leukemic cell within at least 104 polyclonal cells in 93% of cases and will be of high value for future MRD studies.

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