Reduced TET2 expression in Patients with Myelodysplastic Syndromes and Acute Myeloid Leukemia.

Acquired mutations in TET2 and DNMT3A have been found in myelodysplastic syndromes (MDS) and acute myeloid leukemia (AML), and may predict a worse survival in these diseases. TET2 mutations are considered to be a loss-of-function mutation and results in decreased 5-hydroxymethylcitosine (5-hmc) levels. In normal CD34⁺ cells, TET2 silencing skews progenitor differentiation towards the granulomonocytic lineage at the expense of lymphoid and erythroid lineages. Dnmt3a participates in the epigenetic silencing of hematopoietic stem cell regulatory genes, enabling efficient differentiation. Here, we attempted to evaluate the expression of TET2 and DNMT3A in total bone marrow cells from normal donors, patients with MDS and AML, and in CD34⁺ cells from MDS and normal controls during erythroid differentiation.

The study included normal donors (n = 21), patients with MDS (n = 43) and AML (n = 42) at diagnosis. All normal donors and patients provided informed written consent and the study was approved by the ethics committee of the Institution. MDS patients were stratified into low and high-risk according to WHO classification (RCUD/RCMD/RARS=31 and RAEB1/RAEB2=12). TET2 and DNMT3A mRNA expression was assessed by quantitative PCR. CD34⁺ cells from normal donors (n = 9) and low-risk MDS patients (n = 7) were submitted to erythroid differentiation. Cells were collected and submitted to immunophenotyping for GPA and CD71 (days 6 and 12) and q-PCR for TET2 and DNMT3A expression (days 6, 8 and 12). Results of gene expression in normal donors and patients are presented as median, minimum-maximum, and were compared using Mann-Whitney test. Student t test was used for comparison of gene expression during CD34⁺ erythroid diferentiation. Overall survival was defined from the time of sampling to the date of death or last seen. Univariate analysis for overall survival was conducted with the Cox proportional hazards model.

TET2 expression was significantly reduced in both AML (0.62; 0.01–32.69) and MDS (1.46; 0.17–21.30) compared to normal donors (2.72; 0.43–31.49); P<0.0001 and P=0.01, respectively. TET2 expression was also significantly reduced in AML compared to MDS (P=0.0007). MDS patients were stratified into low and high-risk disease, and we still observed a significant reduction in TET2 expression in high-risk (0.73, 0.17–7.25) when compared to low-risk (1.58; 0.48–21.30; P=0.02) patients, but no difference was noted between normal donors vs. low-risk MDS, and high-risk MDS vs. AML. In MDS cohort, the median overall survival was 14 months (range 1–83), increased TET2 expression was associated with a longer survival (HR, 0.44; 95% CI, 0.21–0.91, P=0.03), and, as expected, WHO high-risk disease was associated with a shorter survival (HR, 10.16; 95% CI, 3.06–33.72, P<0.001), even though the confidence interval (CI) was large. TET2 expression did not impact survival in our cohort of AML patients. The erythroid differentiation was effective in cells from normal donors and MDS patients, as demonstrated by the flow cytometry analyses of GPA and CD71. TET2 expression was significantly increased on day 12 of erythroid differentiation, P<0.05. On the other hand, DNMT3A expression was similar between normal donors (0.74; 0.22–1.53), MDS (0.78; 0.26–3.46) and AML (0.95, 0.15–6.46), and during erythroid differentiation, with no impact on survival.

These data suggest that decreased TET2 expression may participate in leukemogenesis, and supports the participation of TET2 in the erythroid differentiation of MDS. DNMT3A was not differentially expressed in AML and MDS, indicating that the presence of mutations in this gene may be the predominant mechanism of changes in protein function. We thus suggest that decreased TET2 expression may explain the reduced levels of 5-hmc found in TET2 wild type patients, and may become a predictive marker for outcomes in MDS and other myeloid diseases. Further studies would be necessary to better elucidate the clinical relevance and biologic significance of our findings, and whether the decreased TET2 expression results in hypermethylation in these diseases.

Maciejewski:NIH: Research Funding; Aplastic Anemia&MDS International Foundation: Research Funding.