The PRAME and WT1 Transcripts Constitute a Good Molecular Marker Combination for Monitoring Minimal Residual Disease in Myelodysplastic Syndromes
Authors: Qin Yazhen , Zhu Honghu , Liu Yan-rong , Wang Ya-zhe , Shi Hong-Xia , Lai Yue-yun , Xu Lan-Ping , Liu Daihong , Huang Xiaojun 
Published: October 2019

Abstract
Abstract 3853

Background
With the incorporation of more aggressive therapies such as hematopoietic stem cell transplantation (HSCT), more myelodysplastic syndromes (MDS) patients fall into a status of minimal residual disease (MRD). The sensitive molecular markers are required to monitor MRD and predict relapse. The Wilms' tumor gene (WT1) is now a widely accepted molecular marker of MDS. However, WT1 itself could not fully meet the demands because a subset of MDS patients does not overexpress WT1, and the increase of WT1 expression compared with the normal control of MDS patients was mainly within 2-log. We wondered if the preferentially expressed antigen of melanoma (PRAME) gene could supplement WT1.

Methods
The PRAME and WT1 transcript levels were simultaneously measured in 312 bone marrow samples collected from newly diagnosed MDS patients and 27 samples from non-malignant cytopenia patients. Bone marrow samples from 14 MDS patients after their disease progression were also detected. To evaluate the value of combined detection of WT1 and PRAME transcripts, one hundred and eleven BM samples collected from 17 MDS patients during their treatment were tested them simultaneously (chemotherapy alone: 1 patient; HSCT:16 patients). Bone marrow samples from six MDS patients and five normal controls were sorted into the blasts (CD34+), nucleated erythrocytes (CD71+), immature myeloid cells (CD33+CD34-), and lymphocyte (CD45+high, low SSC) fractions by flow cytometry and measured the PRAME and WT1 transcript levels, respectively. We had previously established that the upper limits of the PRAME and WT1 transcript levels tested in normal bone marrow samples were 0.28% and 0.50%, respectively.

Results
None of the 27 non-malignant cytopenia patients overexpressed PRAME (median 0.085%, range 0.01%-0.28%) and WT1 (median 0.095%, range 0.0089%-0.36%). Both WT1 and PRAME were commonly overexpressed in MDS. Both the overexpression frequency and the >1-log increase expression frequency of PRAME were similar to those of WT1 (74.4 % vs 77.6%; 51.6% vs 49.0%; p>0.05), and 88.1% of the patients overexpressed at least one marker. Moreover, the frequencies of PRAME expression with higher degrees of increase were significantly higher compared with those of WT1 expression (>2-log increase: 30.8% vs 3.8%; >3-log increase: 9.0% vs 0%; all p<0.001). PRAME had a higher log increase than WT1 in 53.3% of the patients with overexpressed WT1. For samples collected from newly diagnosed MDS patients, both the WT1 and PRAME transcript levels were significantly correlated with the percentage of blasts in bone marrow (r=0.35 and 0.22, all p<0.001). After disease progression, both WT1 and PRAME expressions prominently increased in six patients, only WT1 markedly increased in six patients, only PRAME markedly increased in one patient, and neither WT1 nor PRAME increased in one patient. Both PRAME and WT1 transcript levels generally fluctuated within the normal range after HSCT in all 10 patients in continuous complete remission (PRAME: 58/64 samples, WT1: 58/64 samples). Six out of seven patients were predicted relapse by the combined detection: sustained overexpression or significant increase over the normal range of both WT1 and PRAME in three patients, earlier by PRAME than WT1 or by PRAME alone in three patients. The expression patterns of WT1 differed from those of PRAME in the sorted cell fractions: WT1 is overexpressed in blasts and is significantly decreased in relative mature cells. Whereas, PRAME is mainly overexpressed not only by stem cells and blasts but also by the relative mature cells.

Conclusion
The combined detection of WT1 and PRAME transcripts in newly diagnosed MDS patients could find more suitable and sensitive molecular marker for them compared to detecting WT1 alone. The PRAME and WT1 transcripts constitute a good molecular marker combination for monitoring minimal residual disease in MDS.

Disclosures:
No relevant conflicts of interest to declare.