HLA-Ghas a relevant role in immune response regulation. The overall structure of theHLA-Gcoding region has been maintained during the evolution process, in which most of its variable sites are synonymous mutations or coincide with introns, preserving major functionalHLA-Gproperties. TheHLA-Gpromoter region is different from the classical class I promoters, mainly because (i) it lacks regulatory responsive elements for IFN-γand NF-κB, (ii) the proximal promoter region (within 200 bases from the first translated ATG) does not mediate transactivation by the principal HLA class I transactivation mechanisms, and (iii) the presence of identified alternative regulatory elements (heat shock, progesterone and hypoxia-responsive elements) and unidentified responsive elements for IL-10, glucocorticoids, and other transcription factors is evident. At least three variable sites in the 3′ untranslated region have been studied that may influenceHLA-Gexpression by modifying mRNA stability or microRNA binding sites, including the 14-base pair insertion/deletion, +3142C/G and +3187A/G polymorphisms. Other polymorphic sites have been described, but there are no functional studies on them. TheHLA-Gcoding region polymorphisms might influence isoform production and at least two null alleles with premature stop codons have been described. We reviewed the structure of theHLA-Gpromoter region and its implication in transcriptional gene control, the structure of theHLA-G3′UTR and the major actors of the posttranscriptional gene control, and, finally, the presence of regulatory elements in the coding region.

Hypoxia inducible factor-1 mediates the expression of the immune checkpoint HLA-G in glioma cells through hypoxia response element located in exon 2

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.

The immune checkpoint HLA-G prevents maternal rejection of the fetus and contributes in cancer invasion and acceptance of allografts. The 5’ and 3’ regulatory regions of the HLA-G gene are polymorphic and balancing selection probably maintains this variability. It is proposed that nucleotide variations may affect the level of HLA-G expression. To investigate this issue we aimed to analyze how haplotypes of the 3’ untranslated region (3’UTR) with highest worldwide frequencies, namely UTR-1, UTR-2, UTR-3, UTR-4, UTR-5, UTR-18 and UTR-7, impact the expression of a luciferase reporter gene in vitro. Experiments performed with the HLA-G positive cell lines JEG-3 (choricarcinoma) and FON (melanoma), and with the HLA-G negative cell lines M8 (melanoma) and U251MG (glioblastoma) showed that the HLA-G 3’UTR polymorphism influences the response to endogenous cellular factors and may vary according to the cell type. UTR-5 and UTR-7 impact the activity of luciferase the most whereas UTR-2, UTR-3, UTR-4, and UTR-18 have intermediate impact, and UTR-1 has the lowest impact. These results corroborate the previous associations between amounts of plasma sHLA-G levels and 3’UTR haplotypes in healthy individuals and reinforce that 3’UTR typing may be a predictor of the genetic predisposition of an individual to express different levels of HLA-G.

Mesenchymal Stromal/Stem Cells from human Wharton’s jelly (WJ-MSC) are an abundant and interesting source of stem cells for applications in cell and tissue engineering. Their fetal origin confers specific characteristics compared to Mesenchymal Stromal/Stem Cells isolated from human bone marrow (BM-MSC). The aim of this work was to optimize WJ-MSC culture conditions for their subsequent clinical use. We focused on the influence of oxygen concentration during monolayer expansion on several parameters to characterize MSC. Our work distinguished WJ-MSC from BM-MSC in terms of proliferation, telomerase activity and adipogenic differentiation. We also showed that hypoxia had a beneficial effect on proliferation potential, clonogenic capacity and to a lesser extent, on HLA-G expression of WJ-MSC during their expansion. Moreover, we reported for the first time an increase in chondrogenic differentiation when WJ-MSC were expanded under hypoxia. In an allogeneic therapeutic context, production of clinical batches requires generating high numbers of MSC whilst maintaining the cells’ properties. Considering our results, hypoxia will be an important parameter to take into account. In addition, the clinical use of WJ-MSC would provide significant numbers of cells with maintenance of their proliferation and differentiation potential, particularly their chondrogenic potential. Due to their chondrogenic differentiation potential, WJ-MSC promise to be an interesting source of MSC for cell therapy or tissue engineering for cartilage repair and/or regeneration