¹Department of Paediatric Haematology/Oncology, 2nd Medical School, Charles University and University Hospital Motol, Prague, Czech Republic

Correspondence: Dr E Fronkova, Department of Paediatric Haematology/Oncology, 2nd Medical School, Charles University, V Uvalu 84, 15006 Prague 5, Czech Republic. E-mail: eva.fronkova@lfmotol.cuni.cz

²These authors contributed equally to this work.

Received 21 December 2007; Revised 13 March 2008; Accepted 20 March 2008; Published online 19 May 2008.

Abstract

Minimal residual disease (MRD) detection using quantification of clone-specific Ig or TCR rearrangements before and after transplantation in children with high-risk ALL is an important predictor of outcome. The method and guidelines for its interpretation are very precise to avoid both false-negative and -positive results. In a group of 21 patients following transplantation, we observed detectable MRD positivities in Ig/TCR-based real-time quantitative PCR (RQ-PCR) leading to no further progression of the disease (11 of 100 (11%) total samples). We hypothesized that these positivities were mostly the result of nonspecific amplification despite the application of strict internationally agreed-upon measures. We applied two non-self-specific Ig heavy chain assays and received a similar number of positivities (20 and 15%). Nonspecific products amplified in these RQ-PCR systems differed from specific products in length and sequence. Statistical analysis proved that there was an excellent correlation of this phenomenon with B-cell regeneration in BM as measured by flow cytometry and Ig light chain- excision circle quantification. We conclude that although Ig/TCR quantification is a reliable method for post transplant MRD detection, isolated positivities in Ig-based RQ-PCR systems at the time of intense B-cell regeneration must be viewed with caution to avoid the wrong indication of treatment.