OBJECTIVEThe study was aimed to investigate the feasibility and clinical significance of quantitative detection of minimal residual disease (MRD) in childhood acute lymphoblastic leukemia (ALL) by real-time quantitative polymerase chain reaction (RQ-PCR).

METHODSClonal IgH gene rearrangements of samples at diagnosis were identified by standard PCR assay with consensus primers. Monoclonal IgH gene rearrangements were analyzed using DNAPLOT software. Upstream primers were designed with the Primer Express software and allele specific oligonucleotide developed complementary to the V-D or D-J junction. Samples at diagnosis were serially diluted to generate the patient specific standard curves. RQ-PCR method was used to quantify the MRD of the follow up samples collected at five time points during chemotherapy. To check the quantity and quality of DNA, the investigators used RQ-PCR analysis for the albumin gene.

RESULTSTotally 16 monoclonal IgH gene rearrangements were identified from 34 patients with B-ALL. The analysis of the 16 monoclonal rearrangements showed that the most frequently used V segment was from V3 family and J segment from J4 and J6. The RQ-PCR sensitivity of 10(-4) to 10(-5) was mostly reached. Non-specific amplification was seen in 6 patients. The number of inserted and deleted nucleotides did not appear to be related to the sensitivity (P > 0.05). The correlation coefficients of all 16 standard curves were excellent (> or = 0.99). The mean slope of the standard curves was -3.4 +/- 0.37 and the mean intercept was 24.3 +/- 2.95. MRD analysis of follow up samples from the 16 patients showed an association between high degree of MRD and relapse. There was no apparent relationship between MRD degree at the end of induction chemotherapy and other high risk factors of ALL (P > 0.05).

CONCLUSIONThe study showed that the above approach with RQ-PCR was applicable to clinical detection of MRD in childhood ALL. Quantitative and dynamic study of MRD was of prognostic importance.