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Hematopoietic stem cell transplantation is becoming an increasingly important approach to treatment of different malignant and non-malignant disorders. There is thus growing demand for diagnostic assays permitting the surveillance of donor/ recipient chimerism posttransplant. Current techniques are heterogeneous, rendering uniform evaluation and comparison of diagnostic results between centers difficult. Leading laboratories from 10 European countries have therefore performed a collaborative study supported by a European grant, the EuroChimerism Concerted Action, with the aim to develop a standardized diagnostic methodology for the detection and monitoring of chimerism in patients undergoing allogeneic stem cell transplantation. Following extensive analysis of a large set of microsatellite/short tandem repeat (STR) loci, the EuroChimerism (EUC) panel comprising 13 STR markers was established with the aim to optimally meet the specific requirements of quantitative chimerism analysis. Based on highly stringent selection criteria, the EUC panel provides multiple informative markers in any transplant setting. The standardized STR-PCR tests permit detection of donor-or recipient-derived cells at a sensitivity ranging between 0.8 and 1.6%. Moreover, the EUC assay facilitates accurate and reproducible quantification of donor and recipient hematopoietic cells. Wide use of the European-harmonized protocol for chimerism analysis presented will provide a basis for optimal diagnostic support and timely treatment decisions.

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SummaryIn this single centre study of childhood acute lymphoblastic leukaemia (ALL) patients treated on the Medical Research Council UKALL 97/99 protocols, it was determined that minimal residual disease (MRD) detected by real time quantitative polymerase chain reaction (RQ-PCR) and 3-colour flow cytometry (FC) displayed high levels of qualitative concordance when evaluated at multiple time-points during treatment (93AE38%), and a combined use of both approaches allowed a multi timepoint evaluation of MRD kinetics for 90% (53/59) of the initial cohort. At diagnosis, MRD markers with sensitivity of at least 0AE01% were identified by RQ-PCR detection of fusion gene transcripts, IGH/TRG rearrangements, and FC. Using a combined RQ-PCR and FC approach, the evaluation of 367 follow-up BM samples revealed that the detection of MRD >1% at Day 15 (P = 0AE04), >0AE01% at the end of induction (P = 0AE02), >0AE01% at the end of consolidation (P = 0AE01), >0AE01% prior to the first delayed intensification (P = 0AE01), and >0AE1% prior to the second delayed intensification and continued maintenance (P = 0AE001) were all associated with relapse and, based on early time-points (end of induction and consolidation) a significant log-rank trend (P = 0AE0091) was noted between survival curves for patients stratified into high, intermediate and low-risk MRD groups.

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The majority of chronic myeloid leukaemia (CML) patients express either e13a2 or e14a2 BCR-ABL1 transcripts. Variant fusion genes can arise, usually due to alternative splicing of either BCR or ABL1 exons, with molecular monitoring by quantitative PCR (qPCR) in response to tyrosine kinase inhibitor therapy rarely reported in such cases. A case of CML is described in which an e13a3 BCR-ABL1 fusion was characterised. A qPCR methodology was developed and applied prospectively to demonstrate a favourable molecular response to imatinib treatment. This case serves to highlight the requirement for molecular monitoring of those CML patients harbouring the e13a3 and other variant BCR-ABL1 transcripts.

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