Cytometry-based analysis of HLA-G functions according to ILT2 expression.

HLA-G was described as a molecule inhibiting NK and T cells functions through its receptor, ILT2. However, most functional studies of HLA-G were so far performed on heterogeneous immune populations and regardless of ILT2 expression. This may lead to an underestimation of the effect of HLA-G. Thus, considering the immune subpopulations sensitive to HLA-G remained an important issue in the field. Here we present a new cytometry assay to evaluate HLA-G effects on both NK and CD8+ T cell cytotoxic functions. Using flow cytometry allows for the comparison of HLA-G function on multiple subsets and multiple functions in the same time. In particular, we sharpen the analysis by specifically studying the immune subpopulations expressing HLA-G receptor ILT2. We focused our work on: IFN-gamma production and cytotoxicity (CD107a expression) by CD8+ T cells and NK cells expressing or not ILT2. We compared the expression of these markers in presence of target cells, expressing or not HLA-G1, and added a blocking antibody to reverse HLA-G inhibition. This new method allows for the discrimination of cell subsets responding and non-responding to HLA-G1 in one tube. We confirm that HLA-G-specifically inhibits the ILT2+ CD8+ T cell and ILT2+ NK cell subsets but not ILT2-negative ones. By blocking HLA-G/ILT2 interaction using an anti-ILT2 antibody we restored the cytotoxicity level, corroborating the specific inhibition of HLA-G1. We believe that our methodology enables to investigate HLA-G immune functions easily and finely towards other immune cell lineages or expressing other receptors, and might be applied in several pathological contexts, such as cancer and transplantation.

Role of HLA-G as a predictive marker of low risk of chronic rejection in lung transplant recipients: a clinical prospective study.

Human leukocyte antigen G (HLA-G) expression is thought to be associated with a tolerance state following solid organ transplantation. In a lung transplant (LTx) recipient cohort, we assessed (1) the role of HLA-G expression as a predictor of graft acceptance, and (2) the relationship between (i) graft and peripheral HLA-G expression, (ii) HLA-G expression and humoral immunity and (iii) HLA-G expression and lung microenvironment. We prospectively enrolled 63 LTx recipients (median follow-up 3.26 years [min: 0.44-max: 5.03]). At 3 and 12 months post-LTx, we analyzed graft HLA-G expression by immunohistochemistry, plasma soluble HLA-G (sHLA-G) level by enzyme-linked immunosorbent assay, bronchoalveolar lavage fluid (BALF) levels of cytokines involved in chronic lung allograft dysfunction (CLAD) and anti-HLA antibodies (Abs) in serum. In a time-dependent Cox model, lung HLA-G expression had a protective effect on CLAD occurrence (hazard ratio: 0.13 [0.03-0.58]; p = 0.008). The same results were found when computing 3-month and 1-year conditional freedom from CLAD (p = 0.03 and 0.04, respectively [log-rank test]). Presence of anti-HLA Abs was inversely associated with graft HLA-G expression (p = 0.02). Increased BALF level of transforming growth factor-ß was associated with high plasma sHLA-G level (p = 0.02). In conclusion, early graft HLA-G expression in LTx recipients with a stable condition was associated with graft acceptance in the long term.

Kidney transplant recipients treated with belatacept exhibit increased naïve and transitional B cells.

Phase III clinical studies have shown that kidney transplant (KT) recipients treated with the costimulation blocker belatacept exhibited a better renal allograft function and lower donor-specific anti-HLA immunization when compared to recipients treated with calcineurin inhibitors (CNI). We analyzed B cell phenotype in KT recipients treated with belatacept and stable renal function (N = 13). Results were compared to those observed in stable patients treated with CNI (N = 12), or with chronic antibody-mediated rejection (N = 5). Both transcriptional profile and phenotypic characterization of peripheral B cells were performed by real-time polymerase chain reaction and flow cytometry, respectively. In belatacept group, the frequency and absolute number of transitional B cells as defined by both phenotypes: CD19(+) CD24(hi) CD38(hi) and CD19(+) IgD(hi) CD38(hi) CD27(-) , as well as naïve B cells were significantly higher compared with CNI group. B cell activating factor (BAFF) and BAFF receptor mRNA levels were significantly lower in belatacept group than in CNI group. These results show for the first time that belatacept influences B cell compartment by favoring the occurrence of transitional B cells with potential regulatory properties, as described in operational tolerant patients. This role may explain the lower alloimmunization rate observed in belatacept-treated patients.

HLA-G 2012 conference: the 15-year milestone update.

The non-classical human leukocyte antigen (HLA) Class I molecule HLA-G is best known for its tolerogenic function at the maternal-fetal interface, where it protects the fetus from destruction by the immune system of its mother. Yet, HLA-G has been the topic of intense investigations and its functions reach much further than originally believed. International conferences on HLA-G have taken place every 3 years since 1998, and the Sixth International Conference on HLA-G, that took place in Paris in July 2012. It counted 180 attendees from 28 countries, 35 speakers in plenary sessions, and 63 presentations of research in symposia and poster sessions, bringing new insight in HLA-G research. Here we summarize the major advances on the function and nature of HLA-G molecule that were reported, with particular interest on the findings in new mechanisms of action through regulatory cells, its relevance in cancer as well as in the molecular structure and functions of HLA-G, which are key for its clinical application.

Soluble HLA-G induces NF-kappaB activation in natural killer cells.

Human leukocyte antigen (HLA)-G is an immunomodulatory molecule discovered for the first time in the maternal-fetal interface. In cancer context, where high number of natural killer (NK) cells is described, the presence of HLA-G in its soluble form is thought to be essential for NK cells signaling. To evaluate intracellular signaling in NK cells upon HLA-G soluble forms stimulation, we investigate the role of soluble HLA-G (HLA-G5- and HLA-G1 shedding form) stimulation on classical nuclear factor (NF)-kappaB pathway activation. We reported that these two forms of soluble HLA-G could activate NF-kappaB in NK cells. NF-kappaB activation in NK cells does implicate neither phosphatidylinositol 3-kinase (PI3K) nor MEK (MAP kinase kinase) as demonstrated after specific inhibition experiments. We demonstrated elsewhere that NF-kappaB activation in NK cells is not implicated in cytotoxicity inhibition by HLA-G. Our findings may suggest the important role played by NF-kappaB activation after soluble HLA-G stimulation in other NK cells function.

Recent advances on the non-classical major histocompatibility complex class I HLA-G molecule.

The human leukocyte antigen (HLA)-G non-classical major histocompatibility complex (MHC) class I molecule was originally described in first-trimester trophoblasts at the fetal-maternal interface in 1990. Eight years later, the First International Conference on this molecule was inaugurated by Prof Jean Dausset, recipient of the Nobel Prize in Medicine. The Fifth International Conference on HLA-G, held in Paris on July 2009, began with a tribute to Prof Jean Dausset who left us recently. This conference was co-chaired by Dr Edgardo D. Carosella and Prof Hans Grosse-Wilde, included 57 oral presentations and was attended by approximately 140 delegates from 16 countries. We summarize here the major advances on the HLA-G molecule that were reported, including findings on its biological activity and characterization of new mechanisms of action, notably through mesenchymal stem cells and regulatory cells, and the previously unexplored role of HLA-G on immune cells such as gammadelta T-cells and B lymphocytes. Furthermore, the role of HLA-G during pregnancy was revisited and its impact in pathologies such as cancer, autoimmune disorders and transplantation was further extended.

The genetic structure of 3'untranslated region of the HLA-G gene: polymorphisms and haplotypes.

The HLA-G gene is predominantly expressed at the maternal-fetal interface. It has been associated with maternal-fetal tolerance and in the inhibition of cytotoxic T lymphocyte and natural killer cytolytic functions. At least two variations in the 3'untranslated region (UTR) of HLA-G locus are associated with HLA-G expression levels, the 14-bp deletion/insertion polymorphism and the +3142 single-nucleotide polymorphism (SNP). However, this region has not been completely characterized yet. The variability of the 3'UTR of HLA-G gene and its haplotype structure were characterized in 155 individuals from Brazil, as well as HLA-G alleles associated with each of the 3'UTR haplotype. The following eight variation sites were detected: the 14-bp polymorphism and SNPs at the positions +3003T/C, +3010C/G, +3027A/C, +3035C/T, +3142G/C, +3187A/G and +3196C/G. Similarly, 11 different 3'UTR haplotypes were identified and several HLA-G alleles presented only one 3'UTR haplotype. In addition, a high linkage disequilibrium among the variation sites was detected, especially among the 14-bp insertion and the alleles +3142G and +3187A, all previously associated with low mRNA availability, demonstrating that their effects are not independent. The detailed analyses of 3'UTR of the HLA-G locus may shed some light into mechanisms underlying the regulation of HLA-G expression.

Immunohistochemical study of HLA-G expression in lung transplant recipients.

Human leukocyte antigen-G (HLA-G), a nonclassical HLA class I protein, promotes immune tolerance of solid-organ allografts, yet its role in lung transplantation (LTx) is unknown. We examined the expression of HLA-G in lung allografts through immunohistochemistry by a cross-sectional study of 64 LTx recipients, classified into four groups (stable patients, acute rejection [AR], bronchiolitis obliterans syndrome [BOS] and symptomatic viral shedders). A marked expression of HLA-G in bronchial epithelial cells (BEC) was frequently observed in stable recipients (n = 18/35 [51%]), but not in patients with AR (n = 14) or with BOS (n = 8). HLA-G was also expressed by 4 of 7 symptomatic viral shedders. In addition, HLA-G-positive patients from the stable group (n = 35) experienced lower incidence of resistant AR and/or BOS during long-term follow-up, as compared with their HLA-G-negative counterparts. Finally, in vitro data showed that interferon-gamma, a cytokine present in lung allograft microenvironment, upregulated HLA-G mRNA and protein expression in primary cultured human BEC. We conclude that HLA-G expression in the bronchial epithelium of lung allograft is elevated in some LTx recipients in association with their functional stability, suggesting a potential role of HLA-G as a tolerance marker.

[HLA-G: from feto-maternal tolerance to organ grafting]. / HLA-G: de la tolérance foeto-maternelle a la greffe d'organe.

E.D. Carosella was the pioneer who demonstrated the protective role of the HLA-G molecule on trophoblasts, which form a shield protecting the fetus from the immune reaction of its mother and subsequent reject. This non-classical HLA class I molecule is first expressed on the fertilized ovocyte, thus enabling a uterine implantation and then on the surface of the placenta trophoblast where the classical class I and II antigens are absent. He brought the first demonstration ex vivo of the protector role of HLA-G molecule present on the surface of fetal cytotrophoblast cells versus the lysis carried out by maternal decidual uterine NK cells, in both semi-allogenic combinations (maternal uterine NK cells and their own fetal cytotropohoblast counterparts) and allogenic combinations (different maternal uterine NK cells and cytotrophoblasts from different fetuses). The blockage of this protein triggers off an important cytotoxicity towards the fetal cells. Furthermore, he showed that HLA-G molecules act as an inhibitor of the T-lymphocytes, NK cells and antigen presenting cells (APC). Through his discovery Carosella also shows for the first time the three major clinical consequences: I) HLA-G molecules are crucial, as an altered expression of these molecules would lead to abortion and failed pregnancies, i.e. recurrent spontaneous abortions and preeclamptic disease. The embryo expression of soluble HLA-G molecules is a mandatory prerequisite to implantation. II) In allogenic transplantation (heart, kidney and liver-kidney graft) the expression of HLA-G protein significantly reduces acute rejection and showed an absence of chronic rejections. III) Finally, this expression on the malignant cells has a negative functional impact in the anti-tumour response. So the expression of HLA-G molecule constitutes an escape mechanism from immunosurveillance, just as the fetal cells protect themselves from the aggression of maternal immune cells.

NK resistance of tumor cells from multiple myeloma and chronic lymphocytic leukemia patients: implication of HLA-G.

Exploiting the antitumor effect of natural killer (NK) cells has regained interest in light of data from preclinical and clinical work on the potential of alloreactive NK cells. Multiple myeloma (MM) and chronic lymphocytic leukemia (CLL) represent the two most prevalent adult hematological malignancies in the western hemisphere. To evaluate the role of NK cells in the immune surveillance and their therapeutic potential for CLL and MM, tumor cell susceptibility to NK-mediated killing was investigated. Results show relative resistance of tumor cells from CLL as well as MM (73 and 70% of the patients, respectively) to NK-mediated killing. To gain insight into molecular mechanisms of this resistance, the expression of the tolerogenic HLA-G molecule in CLL and MM and its relevance to susceptibility to NK-mediated killing were investigated. HLA-G transcript was found in tumor cells from 89% (n=19) of CLL and 100% (n=9) of MM patients examined. HLA-G1 surface expression was observed in CLL and was very low or undetectable in MM. Notably, blocking of HLA-G1 with specific antibody on CLL samples increased their susceptibility to NK-mediated killing, demonstrating that HLA-G participates in protecting CLL cells from NK-mediated killing and may thus contribute to their immune escape in vivo.

HLA-G turns off erythropoietin receptor signaling through JAK2 and JAK2 V617F dephosphorylation: clinical relevance in polycythemia vera.

HLA-G5 is secreted by erythroblasts in all hematopoietic organs, suggesting a role for this protein in erythropoiesis. To examine this, we analyzed whether HLA-G5 affects the proliferation of UT7/EPO and HEL erythroleukemia cells and characterized the mechanism by which HLA-G5 influences erythropoietin receptor (EPOR) signaling. We show that HLA-G5 inhibits the proliferation of UT7/EPO cells, the EPOR signaling of which is similar to that of normal erythroid progenitors. HLA-G5-mediated inhibition was associated with reduced phosphorylation of JAK2 kinase and that of the downstream signaling proteins STAT-5 and STAT-3. Involvement of JAK2 in erythroid cell proliferation has been highlighted by the role of JAK2 V617F mutation in polycythemia vera (PV), a myeloproliferative disorder characterized by erythroid lineage overproduction. We demonstrate that HLA-G5 downregulates EPOR constitutive signaling of JAK2 V617F-expressing HEL cells, leading to inhibition of cell proliferation through G1 cell cycle arrest. Combination of HLA-G5 with JAK inhibitor I further decreases HEL cell growth. Clinical relevance is provided by analysis of PV patients who carry JAK2 V617F mutation, showing that HLA-G5 inhibits the formation of erythropoietin-independent erythroid colonies. Such HLA-G5-mediated inhibition constitutes a new parameter to be considered in the design of future approaches aimed at treating JAK2 V617F-positive myeloproliferative disorders.

Research on HLA-G: an update.

Human leukocyte antigen (HLA)-G is a nonclassical HLA class I molecule from the major histocompatibility complex, which was initially shown to confer protection to the fetus from her mother's immune system. The Third International Conference on HLA-G, held in 2003, showed that beyond its role in fetal-maternal tolerance, HLA-G exerts tolerogenic functions involved in transplant acceptance as well as in tumoral and viral immune escape. The Fourth International Conference, which took place in Paris on July 2006, counted 72 oral presentations and about 200 attendees from 25 countries. The reports presented brought new insight into HLA-G research, and we summarize here the major advances on the HLA-G biology that were reported. Abstracts for all presentations can be found in volume 68 issue number 4 of Tissue Antigens.

Quantification and identification of soluble HLA-G isoforms.

In order to clarify the diagnostic relevance of soluble human leukocyte antigen-G (sHLA-G) molecules, reliable methods for the measurement of sHLA-G in various body fluids are of interest. Therefore, the aims of the 'Wet-Workshop for Quantification of Soluble HLA-G' held in Essen, Germany (at the Institute of Immunology, 18-20 October 2004) were to select and to validate HLA-G-specific enzyme-linked immunosorbent assay (ELISA) formats and purified standard HLA-G proteins, which can be easily generated and used as consensual references. We chose two ELISA formats, one for the simultaneous determination of shed HLA-G1 + sHLA-G5 (sHLA-G1 + G5) and one for the exclusive detection of HLA-G5 molecules. The first ELISA uses the antibody pair monoclonal antibody (mAb) MEM-G/9 + anti-beta2-microglobulin (beta2m), whereas the latter uses mAbs 5A6G7 + W6/32. Purified and well-defined HLA-G5 protein derived from insect SF9 cells transfected with HLA-G5 + human beta2m served as standard reagent. Twenty-five members of 13 international laboratories participated in the 3-day Wet-Workshop. The workshop demonstrated that the HLA-G5 protein was equally detected by both ELISA formats allowing direct comparison of quantitative results obtained by these two ELISA formats, and that sHLA-G1 + G5 and HLA-G5 molecules, respectively, were specifically and reproducibly quantified by the two ELISA formats. The comparison of the two ELISA results obtained allows the conclusion that sHLA-G1 and HLA-G5 molecules can exist in the blood of healthy donors. Moreover, there was evidence for a novel soluble HLA-G structure recognized by the mAbs 5A6G7 + W6/32 antibody combination but not by the one of mAb MEM-G/9 + anti-beta2m.

Functions of HLA-G in the immune system.

Human leukocyte antigen (HLA)-G is a nonclassical HLA class I molecule that has tolerogenic functions and acts on cells of both innate and adaptive immunity. The molecular mechanism leading to tolerance involves the interaction between HLA-G and inhibitory receptors that are expressed at the surface of immune cells. In this review, we will briefly summarize the key advances on the relationships between HLA-G and the immune system and their consequences in pathology.

Increase in HLA-G1 proteolytic shedding by tumor cells: a regulatory pathway controlled by NF-kappaB inducers.

HLA-G is expressed by tumors, in which it contributes to the evasion of immunosurveillance. NF-kappaB appears to be a candidate for regulating HLA-G expression, since it is considered to be a hallmark of cancer. We investigated the role of NF-kappaB in modulating HLA-G expression in HLA-G-positive tumor cells, JEG-3 (choriocarcinoma), FON (melanoma), and M8-HLA-G1 (HLAG1-transfected melanoma). The treatment of tumor cells with two NF-kappaB inducers, tumor necrosis factor-alpha and phorbol 12-myristate 13-acetate, decreased HLA-G1 cell surface expression but increased intracytoplasmic HLA-G proteins. Reduction in HLA-G1 cell surface expression is driven by NF-kappaB and involves a proteolytic shedding process dependent on metalloproteinase activity. In contrast, an increase in intracytoplasmic HLA-G proteins involves post-transcriptional mechanisms that are independent of NF-kappaB. These results, and the fact that soluble HLA-G1 reduces the cytotoxicity of the NKL cell line, lead us to propose a novel regulatory pathway for HLA-G expression by tumor cells that may have particular relevance in tumor escape.

Soluble HLA-G expression and renal graft acceptance.

HLA-G is a potentially interesting molecule associated with immunosuppressive function. We survey here the presence of soluble HLA-G (sHLA-G) in serial serum samples of renal transplants. A total of 330 sera of from 65 patients were tested for sHLA-G with ELISA. IgG/IgM antibodies to HLA, and MICA antibodies were also previously tested. After serial analysis of the 65 patients' 330 sera, 50% of 26 patients in functioning group had consistent sHLA-G expression or became positive, in comparison to 20.5% among 39 patients who rejected their transplants (p=0.013). Thus sHLA-G was associated with functioning transplants. Eighty percent (77 of 96) of the HLA IgG positive sera had no sHLA-G expression, while 81.4% (83 of 102) of the HLA-G(+) sera had no HLA IgG (p=0.005), which showed a negative association between sHLA-G and the presence of HLA IgG antibodies (which was previously been shown to be associated with failure). In this preliminary survey, sHLA-G was found in the serum of about 30% of renal transplant patients. sHLA-G had a negative association with allograft failure from chronic rejection, and a negative relationship with the production of HLA IgG antibodies. The significance of sHLA-G in renal transplants remains to be determined.

Pharmacological inhibition of DNA repair enzymes differentially modulates telomerase activity and apoptosis in two human leukaemia cell lines.

PURPOSE: To investigate the effect of wortmannin and 3-aminobenzamide (3-AB) on telomerase activity and apoptosis in two human leukaemia cells. MATERIALS AND METHODS: MOLT-4 (p53-wild type) and KG1a (p53-null) cells were irradiated with gamma-rays (3 Gy at 1.57 Gy min(-1)) and the effects of wortmannin and 3-AB were evaluated. Telomerase activity was measured by polymerase chain reaction and the expression of human telomerase reverse transcriptase, human telomerase RNA and telomerase-associated protein 1 was assessed by reverse transcriptase-polymerase chain reaction. Apoptosis was evaluated by fluorescence microscopy and flow cytometry. RESULTS: A radiation-induced up-regulation of telomerase activity was observed from 4 h post-irradiation in both cell lines. This up-regulation was abrogated by wortmannin and 3-AB. Telomerase activity was maximal 24 h post-irradiation, coinciding with an accumulation of human telomerase reverse transcriptase mRNA. Apoptosis and G2/M arrest were evident from 4 h post-irradiation in MOLT-4 cells. KG1a cells exhibited a G2/M block at 24 h post-irradiation and apoptosis increased between 24 and 48 h post-irradiation. 3-AB abolished G2/M blockage and enhanced radiation-induced apoptosis in both cell lines, while wortmannin increased apoptosis only in MOLT-4 cells. CONCLUSIONS: 3-AB inhibits the radiation-associated telomerase activity increase and enhances apoptosis in MOLT-4 and KG1a cells. Wortmannin, which also inhibits the radiation-associated telomerase activity increase in both cell lines, does not modify radiation-induced apoptosis in KG1a cells. DNA repair enzymes might be selective targets for enhancing radiosensitivity in certain tumour cells.

Expression of HLA-G in inflammatory bowel disease provides a potential way to distinguish between ulcerative colitis and Crohn's disease.

In addition to being involved in nutrient uptake, the epithelial mucosa constitute the first line of defense against microbial pathogens. A direct consequence of this physiological function is a very complex network of immunological interactions that lead to a strong control of the mucosal immune balance. The dysfunction of immunological tolerance is likely to be a cause of inflammatory bowel disease (IBD), ulcerative colitis (UC) and Crohn's disease (CD). HLA-G is a non-classical major histocompatibility complex (HLA) class I molecule, which is highly expressed by human cytotrophoblast cells. These cells play a role in immune tolerance by protecting trophoblasts from being killed by uterine NK cells. Because of the deregulation of immune system activity in IBD, as well as the immunoregulatory role of HLA-G, we have analyzed the expression of HLA-G in intestinal biopsies of patients with UC and CD. Our study shows that the differential expression of HLA-G provides a potential way to distinguish between UC and CD. Although the reason for this differential expression is unclear, it might involve a different mechanism of immune regulation. In addition, we demonstrate that in the lamina propria of the colon of patients with UC, IL-10 is strongly expressed. In conclusion, the presence of HLA-G on the surface of intestinal epithelial cell in patients with UC lends support to the notion that this molecule may serve as a regulator of mucosal immune responses to antigens of undefined origin. Thus, this different pattern of HLA-G expression may help to differentiate between the immunopathogenesis of CD and UC.

[HLA-G in organ transplantation]. / HLA-G en transplantation d'organes.

The HLA-G molecule plays a crucial role in the protection of the fetus against aggression by the mother's immune system. Recently, it was shown that HLA-G was involved in the protection of the transplanted tissues, via the inhibition of all immune effectors that mediate graft rejection. The inhibitory functions of HLA-G were studied in vitro using allo- and xeno-geneic models, ex vivo on transplanted tissues biopsies, and in an in vivo animal model. In this review, we will summarize recent results which show that HLA-G acts as a regulator of immune function, seems to be directly involved in transplant acceptation, and should be taken into consideration when monitoring transplanted patients' status.