Monitoring of Wilms' Tumor Gene 1 Levels Predict Early Relapse After Allogeneic Hematopoietic Stem Cells Transplantation in Patients with High Risk Acute Myeloid Leukemia and Myelodysplastic Syndrome,

Abstract 4102 Background: several approaches have been used in AML and MDS patients (pts) in Complete Remission (CR) to detect Minimal Residual Disease (MRD) and predict the risk of relapse. The Wilms' tumor gene 1 (WT1) is over-expressed in > 80% of AML and advanced MDS, making this molecule an ideal marker for MRD monitoring. We analyzed WT1 quantitative expression in pts at high risk of relapse who received an Allogeneic Hematopoietic Stem Cell Transplantation (allo-HSCT) at our Institute. Aim of the study: to analyze WT1 based MRD monitoring as a predictive marker of relapse in AML/MDS pts after allo-HSCT. Materials and methods: in this retrospective study we included 54 pts with high-risk disease (50 AML and 4 MDS) who underwent allo-HSCT (10 MRD, 13 MUD, 28 MMRD, 3 CB), mostly after a myeloablative treosulfan-based (51/54 pts) conditioning between November 2007 and January 2011. In all pts (54/54) WT1 was over-expressed in the presence of active disease. Post-transplant disease evaluations, including WT1 quantification, were performed monthly for the first six months, every three months until one year and then every six months. WT1 transcript levels were quantified in Bone Marrow (BM) by RQ-PCR, with TaqMan technology on RNA from mononucleated cells. The housekeeping gene ABL was used as control gene, with WT1 level being normalized to 10^4 copies of ABL per sample. The cut-off value for WT1 positivity in BM samples was 250 copies/10^4 copies of ABL. Results: at transplant 38 pts (70%) were in CR, 12 pts (22%) had refractory disease, in 4 pts (8%) BM was not evaluable and no leukemic blasts were detectable in the peripheral blood. Median follow up (FU) after allo-HSCT was of 18 months (range: 4–42). At day 30 after transplant hematologic and cytogenetic CR and full donor chimerism (STR) were documented in all 54 pts, with a median BM WT1 value of 118/10e4 ABL (range: 0–10118). 23/54 pts (43%) relapsed at a median time of 180 days after allo-HSCT (range: 60–780). Correlation of post-transplant clinical outcome and WT1 expression levels identified: 1) 24 pts in continuous CR until last FU and BM WT1 levels persistently negative; 2) 13 pts who relapsed and showed an increase of BM WT1 levels above 250 at a median time of 40 days (range: 20–80) before hematological relapse and lose of full donor chimerism; 3) 9 pts who relapsed with WT1 increase concomitant with hematological relapse. These pts missed one or more of planned disease evaluations before relapse; 4) 1 patient who relapsed without documentation of WT1 increase; 5) 7 pts who maintained the CR but showed a transient increase of BM WT1 above 250 at one or two consecutive point of FU with normalization at subsequent evaluations. In 3 of these 7 pts concomitant GvHD was documented and in 4 pts ongoing immunosuppression was discontinued shortly after WT1 data had been obtained. Conclusions: WT1 expression levels in BM are effective in predicting AML/MDS relapse after allo-HSCT thus anticipating the appearance of leukemic blasts and of host chimerism. Our data prompt the use of WT1 based MRD monitoring for tailoring ‘pre-emptive' therapeutic approaches based on exploitation of donor immunity and its putative Graft-versus-Leukemia effect. In several patents the time occurring between WT1 MRD positive results and the clinical recurrence of the disease was relatively short, thus in order to detect disease relapse in time for therapeutic intervention we suggest a monthly monitoring of WT1 levels at least for the first year after allo-HSCT. Disclosures: No relevant conflicts of interest to declare.