Minimal Residual Disease Evaluation By Real-Time Quantitative Polymerase Chain Reaction for Wilms Tumor 1 Gene Expression and Multicolour Flow Cytometry, in Pediatric B Lineage Acute Lymphoblastic Leukemia

Introduction: Minimal residual disease (MRD) determination involves the measurement of very low levels of leukemia using sensitive techniques which at present are complex, time consuming and require expertise for performance and interpretation. A ''panleukemic''marker such as Wilm's tumor 1 gene (WT1) which is frequently over expressed in acute leukemia could simplify MRD detection and serve as a useful prognostic marker.

Aim of study: To evaluate the usefulness of WT1 gene expression, as a marker for MRD in B-lineage acute lymphoblastic leukemia (B-ALL).

Method and Material: Flow cytometric immunophenotyping (FCMI) and real time-polymerase chain reaction (RQ-PCR) for WT1 gene expression were performed usingbone marrow at diagnosis and at day 15 (mid-induction). Of the 23 patients recruited, day 15 MRD analyses by both these methods was performed on 11 bone marrow samples of patients who showed WT1 over expression at day 0.

Results:WT1 over expression at diagnosis was found in 69.5% cases (16/23). MRD was detectable in 54.5% cases by WT1 RQ-PCR and by FCM in 72% cases. A statistically significant correlation was seen between WT1 normalized copy number (NCN) at diagnosis with MRD levels detected by FCM.

Conclusion:WT1 represents a candidate MRD and prognostic marker. The significant correlation between WT1 over expression at diagnosis and MRD positivity by flow cytometry at day 15 (mid induction) of chemotherapy suggests that high WT1 expression could correlate with unfavourable outcome in childhood ALL.

However, as not all patients of B-ALL over-express WT1 at diagnosis, quantitative assessment of WT1 transcripts can be used as useful molecular marker for MRD detection, but only in a subset of patients.