OBJECTIVETo probe monitoring Wilms tumor-1（WT1）gene expression level in acute T lymphoblastic leukemia（T- ALL）following allogeneic hematopoietic stem cell transplantation（allo-HSCT）with prognostic significance.

METHODSThis retrospective study analyzed 68 T-ALL cases from January 2009 to March 2012, that monitoring WT1 gene expression level after allo-HSCT. WT1 expression level was measured with real-time quantitative reverse transcription polymerase chain reaction（RQ-PCR） method at + 30, + 60, + 90, + 180, + 270, + 360 days after allo-HSCT, simultaneously monitoring residual leukemia using flow cytometry（FCM）.

RESULTSLow WT1 gene expression level associated with a low risk of recurrence after allo-HSCT in T-ALL. Increased WT1 gene expression levels at +60 and + 90 days after allo- HSCT associated with higher cumulative incidences of relapse（P<0.001, P=0.003）, and low disease- free survival rates（P=0.004, P=0.006）, and low overall survival rates（P=0.004, P=0.007）. The presence of MRD after allo-HSCT was an independent prognostic factor for relapse in T-ALL. Combining WT1 gene and FCM could be used to monitor recurrence after allo-HSCT.

CONCLUSIONIncreased WT1 gene expression level at +60 and + 90 days after allo-HSCT significantly associated with worse prognosis, that should be intervened as early as possible to reduce the risk of recurrence or death. WT1 gene expression level that was less than 0.6% associated with lower risk of recurrence. WT1 gene expression more than 0.6% that needed close follow- up, combined with FCM monitoring MRD, which required intervention to reduce the relapse.