The prognostic value of the WT1 gene expression on relapse and survival AML patients after allogeneic stem cell transplantation
Allogeneic hematopoietic stem cell transplantation (allo-HSCT) is now considered the best treatment of AML with poor prognosis, which is, however, often followed by posttransplant relapses (PTR). Among PTR, molecular and cytological variants (mPTR and cPTR, respectively) are recognized. The WT1 gene is known to be an independent prognostic indicator of the mass of blast cells producing it. The serial measurement of WT1 expression levels provides a real possibility for early diagnosis of mPTR and an evaluation of the overall and event-free survival (OS and EFS, respectively) and the cumulative frequency of relapse (CIR) in patients with AML treated with allo-HSCT.
Patients and methods
The study included 88 AML patients aged 2 to 68 (median, 30 y.o.) who underwent allo-HSCT at our University between 2011 and 2017. WT1 gene expression levels were serially measured by real-time quantitative PCR, and marrow blast counts were performed in marrow samples at the standard control time points: before transplantation (D0) and on days D+30, D+60 and D+100 after transplantation. The WT1 threshold value was selected, as based on the measurement of expression levels of WT1 gene in bone marrow aspirates of healthy donors and determined as 250 WT1 copies/104 copies of ABL gene. At all the time points, groups of patients with elevated and normalized levels of WT1 gene expression (> 250 copies and < 250 copies, respectively) were formed, which allowed for calculating the difference in the 2-year OS, EFS and CIR. Since the increase in the expression of the WT1 gene reflecting the content of the blasts secreting this gene can precede the morphologically identified cPTR, we measured this time interval for all the examined AML patients taking in consideration the posttransplantation
The levels of WT1 gene expression at allo-HSCT ranged from 0 to 56884 WT1/104 ABL copies (median – 253). According to the log-rank criteria, the difference in the 2-year OS, EFS and CIR between the groups of patients with elevated and normalized levels of WT1 gene expression before allo-HSCT was as follows: 79.5%, 69.8%, 28.2% vs. 31.8%, 22.7% and 58.9%, at p<0.001, p<0.001, and p=0.0019, respectively. On D+30, we found no difference in the 2-year OS, EFS and CIR between the groups of patients with elevated and normalized levels of WT1 gene expression. Significant differences in the 2-year OS and CIR in the two groups were found on D+60 (66.2% and 42.3% vs. 35.7% and 61.5% at p=0.012 and р=0.01, respectively), while there was still no significant difference in the EFS (52.3% vs. 38.5%, p=0.084). The greatest differences in the 2-year OS, EFS and CIR between the groups of patients with elevated and normalized levels of WT1 gene expression occurred at the control time point D+100 (28.6%, 19% and 77.8% vs. 75.4% 63.2% and 32.7% at p<0.001, p<0.001, and p<0.001, respectively) (Fig.1). On the basis of proportional Cox risks, the independent positive effect on OS and EFS was preserved only for the normalized level of the WT1 gene expression (p=0.011 and p=0.041) at the time point D+100 after the allo-HSCT and in the presence of chronic GVHD (p=0.038 and p=0.03). In this case, the ratio of the risk of relapse (125) was maximal also on D+100. Concerning mPTR and cPTR, they were documented in 55/88 (62.5%) and 33/88 (37.5%) patients, respectively. In 33.3% of patients (11/33), mPTR and cPTR coincided in time, while in 22 cases cPTR occurred 13-321 (median – 35) days later than mPTR. According to the data obtained, this delay of cPTR from mPTR can be partially ascribed to the therapy performed at the clinic, in particular, donor lymphocyte infusions, and to presence of chronic GVHD in patients, thus being in good agreement with other research data [Pozzi et al, 2013].
Elevated and normalized levels of WT1 gene expression are convenient and clinically useful markers of molecularly controlled mPTR and remission of AML. The optimal point for measuring the level of WT1 gene expression in PTR diagnostics is D+100, followed by D0, D+60 and D+30, as the significance decreases. According to our data, the duration of OS and EFS is also positively affected by the presence of chronic GVHD in AML patients after allo-HSCT, which explains the tendency to use immunotherapy to treat mPTR diagnosed by serial measurements of the WT1 gene expression levels [Di Grazia et al, 2016].
Allogeneic stem cell transplantation, acute myeloid leukemia, WT1, relapse, molecular monitoring.