Upregulation of HLA-G Gene Expression in Malignant Hematopoietic Cells Treated with 5-Aza-2′- Ddeoxycytidine.

Human leukocyte antigen G (HLA-G) is a nonclassic HLA class I antigen with restricted distribution in normal tissues. It exerts multiple immunregulatory functions that have been suggested to contribute to the immune evasion of tumour cells. Ectopic HLA-G expression observed in some pathological conditions such as malignant transformation may be triggered by epigenetic modifications such as DNA demethylation or histone acetylation.

Mononuclear cells were isolated from peripheral blood of newly diagnosed previously untreated patients with acute myeloblastic leukemia (AML) (n=9) and chronic lymphocytic leukemia (CLL) (n=5) by standard Ficoll-Hypaque density gradient centrifugation. Isolated cells were resuspended in RPMI 1640 medium supplemented with 2mM L-glutamine, 200 μg/ml gentamicin, 0.125 μg/ml amphotericin B and 10% heat-inactivated fetal bovine serum. Demethylating treatment of cells was carried out with100 μM 5-aza-2x- deoxycytidine (AdC) (Sigma) for 3 days. Human choriocarcinoma cell lines JEG3 and JAR (ATCC, Rockville, MD) were used as HLA-G positive and negative controls, respectively. Real time polymerase chain reaction (RT-PCR) and semiquantitative RT-PCR were performed using the ABI Prism 7000 Sequence Detection System and AmpliTaq Gold DNA polymerase to detect HLA-G mRNAs transcriptions. The HLA-G protein expression was examined by western blot analysis using mAb 4H84.

HLA-G transcripts in AdC untreated leukemia samples were demonstrated in 3 out of 5 patients (60%) with B-CLL and in 5 out of 9 patients (56%) with AML. Treatment with demethylating agent AdC resulted in up-regulation of HLA-G transcription and expression of HLA-G protein in 5 out of 8 (63%) examined leukemia cell lines (Table 1).

we conclude that DNA methylation is an important control mechanism of HLA-G gene expression, and treatment of human leukemia with demethylating agent AdC may up-regulate HLA-G gene expression and induce HLA-G protein synthesis in some patients that may allow leukemic cells to escape recognition and destruction by cytotoxic T-cells or NK cells. Therefore patients should be monitored for HLA-G expression in order to follow risk of AdC therapy.

No relevant conflicts of interest to declare.