Human Leukocyte Antigen-G Is Frequently Expressed in Glioblastoma and May Be Induced in Vitro by Combined 5-Aza-2′-Deoxycytidine and Interferon-γ Treatments

Abstract

Human leukocyte antigen-G (HLA-G) is a nonclassical major histocompatibility complex (MHC) class I molecule involved in immune tolerance processes, playing an important role in the maintenance of the semi-allogeneic fetus. Although HLA-G expression is restricted in normal tissues, it is broadly expressed in malignant tumors and may favor tumor immune escape. We analyzed HLA-G protein and mRNA expression in tumor samples from patients with glioblastoma collected in France, Denmark, and Brazil. We found HLA-G protein expression in 65 of 108 samples and mRNA in 20 of 21 samples. The absence of HLA-G protein expression was associated with a better long-term survival rate. The mechanisms underlying HLA-G gene expression were investigated in glioma cell lines U251MG, D247MG, and U138MG. Induction of HLA-G transcriptional activity was dependent of 5-aza-2'-deoxycytidine treatment and enhanced by interferon-γ. HLA-G protein expression was observed in U251MG cells only. These cells exhibited a permissive chromatin state at the HLA-G gene promoter and the highest levels of induced HLA-G transcriptional activity following 5-aza-2'-deoxycytidine treatment. Several antigen-presenting machinery components were up-regulated in U251MG cells after demethylating and IFN-γ treatments, suggesting an effect on the up-regulation of HLA-G cell surface expression. Therefore, because of its role in tumor tolerance, HLA-G found to be expressed in glioblastoma samples should be taken into consideration in clinical studies on the pathology and in the design of therapeutic strategies to prevent its expression in HLA-G-negative tumors.

CD8+ T Cell-Independent Immune-Mediated Mechanisms of Anti-Tumor Activity

“…Subsequent studies confirmed and extended this work to show that HLA-G is frequently expressed by primary GBM biopsies (65 out of 108 in one study). 36,37 These and other studies suggest that HLA-G expression by tumors is a mechanism for immune evasion.…”

Haplotypes of the HLA-G 3’ Untranslated Region Respond to Endogenous Factors of HLA-G+ and HLA-G- Cell Lines Differentially

“…Cell lines expressing HLA-G (JEG-3, FON) or not HLA-G (M8, U251MG) at the cell surface [36, 37] were cultured at 37°C under 5% CO 2 . The JEG-3 choriocarcinoma cell line (ATCC, Manassas, VA, USA) and the U251MG glioma cell line (provided by Dr. Heinz Wiendl, University of Münster) were cultivated in DMEM with Glutamax-I (Invitrogen, Cergy Pontoise, France).…”

Recent advances and future of immunotherapy for glioblastoma

“…Although downregulation of HLA class I reduces the immunogenicity of GBM cells, it could activate NK cell response against the tumor. However, GBM cells overexpress nonclassical HLA class I molecules, such as HLA-G and HLA-E 36, 37 , which are involved in the inhibition of NK and CTL responses to the allogeneic fetus during pregnancy. Changes in HLA class II expression have also been reported in GBM cells and have been associated with epigenetic changes in the class II transactivator (CIITA) promoter 38 .…”