Leukemia Relapse after Allogeneic Transplants in AML: Predictive Role of WT1 Expression and Protective Effect of DLI.

Background: relapse remains a significant problem in patients with acute leukemia undergoing an allogeneic hemopoietic transplant (HSCT) and a predictive molecular marker of disease would be useful.

Aim of the study. Assess the role of WT1 expression in AML patients undergoing an allogeneic HSCT, to

• predict relapse and

• drive immune intervention

Methods. We studied 81 patients with AML who received an allogeneic HSCT between 30/1/04 and 11/2/08 in our Unit: 52 patients were in first remission, and 29 patients had more advanced disease. Median age 45 (16–66), prepared with CY-TBI (n=52) or RIC regimen (n=29). WT1 mRNA levels of expression were normalized with respect to the number of ABL transcripts and expressed as WT1 copy numbers every 10⁴ copies of ABL. Patients bone marrow cells were monitored for WT1 expression, and cytology, pretransplant, at day +30 and every month untill day +180, then at scheduled follow up. Patients were considered WT1 positive, when WT1 copy numbers were greater than 180. Escalating doses of donor lymphocyte infusions (DLI) were given, when possible, in WT1+ patients.

WT1 pre-transplant. WT1 pre-HSCT was available in 63 patients, 39 were WT1- and 24 WT1+: their relapse risk was 10% vs 62% (p=0.00002) and their crude survival 79% vs 29% (p=0.0001). When CR1 patients were selected, relapse was 10% vs 50% for WT1- vs WT1+ patients (p=0.02), and survival 81% vs 50% (p=0.9).

WT1 post-transplant. Fifty patients were always WT1- after HSCT, and 31 were found WT1+ at a median interval from HSCT of 80 days (range 24–696): relapse was 8% vs 68% for WT1- vs WT1+ patients (p=<0.0001), and survival 78% vs 26% (p=0.0001).

Cox analysis: in multivariate analysis on relapse WT1 pre-transplant (p<0.0001) and post-transplant (p<0.0001) were independent predictors, whereas disease phase (CR 1/>1) was not (p=0.39). Survival was predicted by all 3 variables, WT1+ pre (p=0.001), WT1+ post (p=0.03) and phase of disease (p=0.002).

Immune intervention. Of the 31 WT1+ patients, 13 had BM blasts on cytology (6– 80%) at the time of first WT1 positivity, and were treated with chemotherapy. 18 patients were WT1+ and had marrow in CR on cytology: 9 of these received DLI and 9 did not; hematologic relapses were seen in 2/9 and 7/9 respectively (p=0.02) and crude survival is 6/9 vs 2/9 (p=0.07). The median interval between WT1+ and relapse was 96 days (39– 246).

Conclusions. This study suggests that WT1 positivity before and after HSCT are independent predictors of relapse and survival in patients with AML. WT1 expression predicts relapse better than disease phase. The interval between WT1 positivity and relapse is approximately 3 months: the use of DLI in this time interval appears to protect against hematologic relapse.