OBJECTIVETo investigate the clinical characteristics of E2A-PBX1（immunoglobulin enhancer binding factor-pre-B leukemia）fusion gene in patients with acute lymphoblastic leukemia（ALL） after allogeneic stem cell transplantation（allo-HSCT）.

METHODSClinical data of 10 patients received allo- HSCT in Peking University Institute of Hematology from December 2010 to January 2015 were retrospectively collected. The E2A-PBX1 gene was examined by real-time quantitative polymerase chain reaction（RQ- PCR）. The correlation between its expression level and the disease status was analyzed.

RESULTSAmong 10 cases of enrolled ALL, the E2A-PBX1 expression of six patients converted to positive after transplant at a median time of 90 days（range, 75-180 days）. The expression level of the first positive sample was 25.200%（range, 0.022%-353.600%）. The duration from E2A-PBX1 positive to hematological relapse was 30 days（range, 0-74 days）. Finally, 4 patients underwent relapse at a median time of 164 days （range, 75- 240 days） after allo- HSCT. The expression of E2A- PBX1 and minimal residual disease （MRD）level examined by flow cytometry were positive correlated（Spearman r=0.743, P=0.002）. Once E2A-PBX1 expression converted to positive after transplant, MRD would increase rapidly. Patients with this type of ALL would have little response to the current intervention towards relapse.

CONCLUSIONMonitoring E2A-PBX1 by RQ-PCR could be used to evaluate MRD status after allo-HSCT. Patients with positive E2A-PBX1 at early stage of transplant will have a poor prognosis.