HLA-G suppresses proliferation of CD4(+) T-lymphocytes

Harnessing the potential of HLA-G in cancer therapy: advances, challenges, and prospects

Immune checkpoint blockades have been prized in circumventing and ablating the impediments posed by immunosuppressive receptors, reaching an exciting juncture to be an innovator in anticancer therapy beyond traditional therapeutics. Thus far, approved immune checkpoint blockades have principally targeted PD-1/PD-L1 and CTLA-4 with exciting success in a plethora of tumors and yet are still trapped in dilemmas of limited response rates and adverse effects. Hence, unveiling new immunotherapeutic targets has aroused immense scientific interest in the hope of expanding the clinical application of immune checkpoint blockades to scale new heights. Human leukocyte antigen-G (HLA-G), a non-classical major histocompatibility complex (MHC) class I molecule, is enriched on various malignant cells and is involved in the hindrance of immune effector cells and the facilitation of immunosuppressive cells. HLA-G stands out as a crucial next-generation immune checkpoint showing great promise for the benefit of cancer patients. Here, we provide an overview of the current understanding of the expression pattern and immunological functions of HLA-G, as well as its interaction with well-characterized immune checkpoints. Since HLA-G can be shed from the cell surface or released by various cells as free soluble HLA-G (sHLA-G) or as part of extracellular vesicles (EVs), namely HLA-G-bearing EVs (HLA-GEV), we discuss the potential of sHLA-G and HLA-GEV as predictive biomarkers. This review also addresses the advancement of HLA-G-based therapies in preclinical and clinical settings, with a focus on their clinical application in cancer.

Prognostic significance of HLA-G in patients with colorectal cancer: a meta-analysis and bioinformatics analysis

PURPOSE

Human leukocyte antigen-G (HLA-G) has been reported to be aberrantly expressed in colorectal cancer (CRC); however, its prognostic value remains controversial. Hence, our meta-analysis aims to assess the prognostic value of HLA-G in CRC patients based on published literature and The Cancer Genome Atlas (TCGA) datasets.

METHODS

A systematic search was conducted on relevant studies retrieved from four electronic databases including PubMed, Embase, Web of Science and Cochrane Library. Hazard ratios (HRs) with 95% confidence intervals (CIs) were recorded to be applied as effective values. Fixed-effects models or random-effects models were applied on the basis of the value of heterogeneity (I 2). Publication bias was analyzed by Begg's and Egger's tests. In addition, the results were validated by using TCGA datasets.

RESULTS

Thirteen studies comprising 3896 patients were incorporated into this meta-analysis. The pooled results showed that HLA-G expression was significantly associated with poor overall survival (OS) in both the univariate analysis (HR = 1.44, 95% CI: 1.14-1.83, P = 0.002) and the multivariate analysis (HR = 1.55, 95% CI: 1.23-1.95, P < 0.001). Nevertheless, the expression of HLA-G is not related to age, sex, tumor type, tumor differentiation, TNM stage, or distant metastasis but lymph node metastasis. Notably, the prognosis of colorectal cancer was not consistent with the analysis result from TCGA data.

CONCLUSION

HLA-G expression was significantly related to poor OS in CRC according to the results of our meta-analysis. However, we found that the prognostic significance was inconsistent with our results according to the TCGA data in CRC. Hence, more research is still needed to further illustrate the prognostic role of HLA-G in CRC.

The unique expression pattern of human leukocyte antigen in trophoblasts potentially explains the key mechanism of maternal-fetal tolerance and successful pregnancy

The success of pregnancy mainly depends on immune tolerance of the mother for the semi-allogeneic fetus. The placenta carrying paternal antigens develops in the maternal uterus without suffering immune attack, making the underlying mechanism of maternal tolerance an enduring mystery. As we all know, human leukocyte antigen (HLA) plays an important role in antigen processing and presentation, thus inducing specific immune responses. Therefore, it is reasonable to speculate that the absence of classical HLA class-I（HLA-I) and HLA class-II (HLA-II) molecules in trophoblasts may account for the maternal-fetal tolerance. Here, we review the HLA-involved interactions between trophoblast cells and decidual immune cells, which contribute to the immunotolerance in the development of normal pregnancy. We also compare the similarity between the maternal-fetal interface and tumor-immune microenvironment because the important role of HLA molecules in tumor immune invasion can provide some references to studies of maternal-fetal immune tolerance. Besides, the abnormal HLA expression is likely to be associated with unexplained miscarriage, making HLA molecules potential therapeutic targets. The advances reported by these studies may exert profound influences on other research areas, including tumor immunity, organ transplantation and autoimmune disease in the future.

HLA-G in asthma and its potential as an effective therapeutic agent

OBJECTIVE

Asthma is a heterogeneous disease. Severity of asthma and sensitivity to medications vary across asthma subtypes. Human leukocyte antigen (HLA)-G has a wide range of functions in normal and pathological physiology. Due to its powerful immune function, HLA-G participates in the pathogenesis of different asthma phenotypes by regulating the activity and function of various immune cells. The mechanism of HLA-G in asthma is not fully clear, and there is no consensus on its mechanism in asthma. Further studies are needed to explore the role of HLA-G in different phenotypes of human asthma.

METHODS

Observational study.

RESULTS

HLA-G is an important immunomodulatory factor in asthma. Studies have found different levels of HLA-G in patients with different asthma subtypes and healthy controls, but other studies have come to the opposite conclusion.

CONCLUSION

We speculate that further study on the mechanism of HLA-G in asthma pheno-types may explain some of the contradictions in current studies. Findings should provide information regarding the potential of HLA-G as a novel target for asthma diagnosis and treatment.

Detection of potential functional variants based on systems-biology: the case of feed efficiency in beef cattle

BACKGROUND

Potential functional variants (PFVs) can be defined as genetic variants responsible for a given phenotype. Ultimately, these are the best DNA markers for animal breeding and selection, especially for polygenic and complex phenotypes. Herein, we described the identification of PFVs for complex phenotypes (in this case, Feed Efficiency in beef cattle) using a systems-biology driven approach based on RNA-seq data from physiologically relevant organs.

RESULTS

The systems-biology coupled with deep molecular phenotyping by RNA-seq of liver, muscle, hypothalamus, pituitary, and adrenal glands of animals with high and low feed efficiency (FE) measured by residual feed intake (RFI) identified 2,000,936 uniquely variants. Among them, 9986 variants were significantly associated with FE and only 78 had a high impact on protein expression and were considered as PFVs. A set of 169 significant uniquely variants were expressed in all five organs, however, only 27 variants had a moderate impact and none of them a had high impact on protein expression. These results provide evidence of tissue-specific effects of high-impact PFVs. The PFVs were enriched (FDR < 0.05) for processing and presentation of MHC Class I and II mediated antigens, which are an important part of the adaptive immune response. The experimental validation of these PFVs was demonstrated by the increased prediction accuracy for RFI using the weighted G matrix (ssGBLUP+wG; Acc = 0.10 and b = 0.48) obtained in the ssGWAS in comparison to the unweighted G matrix (ssGBLUP; Acc = 0.29 and b = 1.10).

CONCLUSION

Here we identified PFVs for FE in beef cattle using a strategy based on systems-biology and deep molecular phenotyping. This approach has great potential to be used in genetic prediction programs, especially for polygenic phenotypes.

Biological Characteristics of HLA-G and Its Role in Solid Organ Transplantation

Organ transplantation is a lifesaving option for patients with advanced diseases. Rejection is regarded as one of the most severe risk factors post-transplantation. A molecule that contributes to immune tolerance and resisting rejection is human leukocyte antigen (HLA)-G, which belongs to the non-classical major histocompatibility complex class (MHC) I family. HLA-G was originally found to play a role during pregnancy to maintain immune tolerance between mother and child. It is expressed in the placenta and detected in several body fluids as soluble factor as well as different membrane isoforms on cells. Recent findings on HLA-G show that it can also play multifaceted roles during transplantation. This review will explain the general characteristics and biological function of HLA-G and summarize the views supporting the tolerogenic and other roles of HLA-G to better understand its role in solid organ transplantation (SOT) and its complications. Finally, we will discuss potential future research on the role of HLA-G in prevention, diagnosis, and treatment in SOT.

Suppressor CD4+ T cells expressing HLA-G are expanded in the peripheral blood from patients with acute decompensation of cirrhosis

OBJECTIVE

Identifying components of immuneparesis, a hallmark of chronic liver failure, is crucial for our understanding of complications in cirrhosis. Various suppressor CD4⁺ T cells have been established as potent inhibitors of systemic immune activation. Here, we establish the presence, regulation and mechanism of action of a suppressive CD4⁺ T cell subset expressing human leucocyte antigen G (HLA-G) in patients with acute decompensation of cirrhosis (AD).

DESIGN

Flow cytometry was used to determine the proportion and immunophenotype of CD4⁺HLA-G⁺ T cells from peripheral blood of 20 healthy controls (HCs) and 98 patients with cirrhosis (28 with stable cirrhosis (SC), 20 with chronic decompensated cirrhosis (CD) and 50 with AD). Transcriptional and functional signatures of cell-sorted CD4⁺HLA-G⁺ cells were delineated by NanoString technology and suppression assays, respectively. The role of immunosuppressive cytokine interleukin (IL)-35 in inducing this population was investigated through in vitro blockade experiments. Immunohistochemistry (IHC) and cultures of primary human Kupffer cells (KCs) were performed to assess cellular sources of IL-35. HLA-G-mediated T cell suppression was explored using neutralising antibodies targeting co-inhibitory pathways.

RESULTS

Patients with AD were distinguished by an expansion of a CD4⁺HLA-G⁺CTLA-4⁺IL-35⁺ immunosuppressive population associated with disease severity, clinical course of AD, infectious complications and poor outcome. Transcriptomic analyses excluded the possibility that these were thymic-derived regulatory T cells. IHC analyses and in vitro cultures demonstrate that KCs represent a potent source of IL-35 which can induce the observed HLA-G⁺ phenotype. These exert cytotoxic T lymphocyte antigen-4-mediated impaired responses in T cells paralleled by an HLA-G-driven downregulation of T helper 17-related cytokines.

CONCLUSION

We have identified a cytokine-driven peripherally derived suppressive population that may contribute to immuneparesis in AD.

(Dis)similarities between the Decidual and Tumor Microenvironment

Placenta-specific trophoblast and tumor cells exhibit many common characteristics. Trophoblast cells invade maternal tissues while being tolerated by the maternal immune system. Similarly, tumor cells can invade surrounding tissues and escape the immune system. Importantly, both trophoblast and tumor cells are supported by an abetting microenvironment, which influences invasion, angiogenesis, and immune tolerance/evasion, among others. However, in contrast to tumor cells, the metabolic, proliferative, migrative, and invasive states of trophoblast cells are under tight regulatory control. In this review, we provide an overview of similarities and dissimilarities in regulatory processes that drive trophoblast and tumor cell fate, particularly focusing on the role of the abetting microenvironments.

HLA-G 14bp Ins/Del Polymorphism, Plasma Level of Soluble HLA-G, and Association with IL-6/IL-10 Ratio and Survival of Glioma Patients

HLA-G is an immune checkpoint molecule with immunosuppressive and anti-inflammatory activities, and its expression and level of its soluble form (sHLA-G) may play an important role in tumor prognosis. The HLA-G 14bp ins/del polymorphism and the plasma level of soluble HLA-G (sHLA-G) were investigated by a polymerase chain reaction and ELISA, respectively, in 59 glioma patients. A significantly higher proportion of glioma patients had the 14 nt insert in both homozygous and heterozygous states compared to the control group. Glioma patients also had higher plasma levels of sHLA-G. Patients with methylated MGMT promoters had lower levels of sHLA-G than those with unmethylated MGMT promoters. The level of sHLA-G negatively correlated with the overall survival of patients. Glioblastoma patients who survived more than one year after diagnosis had lower levels of sHLA-G than those surviving less than one year. Patients with sHLA-G levels below the cut-off value of 40 U/mL survived significantly longer than patients with sHLA-G levels above 40 U/mL. The levels of sHLA-G were also negatively correlated with the level of IL-6 (p = 0.0004) and positively with IL-10/IL-6 (p = 0.046). Conclusion: The presence of the 14 nt insert in both homozygous and heterozygous states of the HLA-G 14bp ins/del polymorphism is more frequent in glioma patients and the elevated plasma levels of sHLA-G are negatively associated with their survival.

The Human Leukocyte Antigen G as an Immune Escape Mechanism and Novel Therapeutic Target in Urological Tumors

The non-classical human leukocyte antigen G (HLA-G) is a potent regulatory protein involved in the induction of immunological tolerance. This is based on the binding of membrane-bound as well as soluble HLA-G to inhibitory receptors expressed on various immune effector cells, in particular NK cells and T cells, leading to their attenuated functions. Despite its restricted expression on immune-privileged tissues under physiological conditions, HLA-G expression has been frequently detected in solid and hematopoietic malignancies including urological cancers, such as renal cell and urothelial bladder carcinoma and has been associated with progression of urological cancers and poor outcome of patients: HLA-G expression protects tumor cells from anti-tumor immunity upon interaction with its inhibitory receptors by modulating both the phenotype and function of immune cells leading to immune evasion. This review will discuss the expression, regulation, functional and clinical relevance of HLA-G expression in urological tumors as well as its use as a putative biomarker and/or potential therapeutic target for the treatment of renal cell carcinoma as well as urothelial bladder cancer.

HLA-G: Too Much or Too Little? Role in Cancer and Autoimmune Disease

HLA-G is a non-classical HLA class I molecule with immunomodulatory properties. It was initially described at the maternal-fetal interface, and it was later found that this molecule was constitutively expressed on certain immuneprivileged tissues, such as cornea, endothelial and erythroid precursors, and thymus. The immunosuppressive effect of HLA-G is exerted through the interaction with its cognate receptors, expressed on immunocompetent cells, like ILT2, expressed on NK, B, T cells and APCs; ILT4, on APCs; KIR, found on the surface of NK cells; and finally, the co-receptor CD8. Because of these immunomodulatory functions, HLA-G has been involved in several processes, amongst which organ transplantation, viral infections, cancer progression, and autoimmunity. HLA-G neo-expression on tumors has been recently described in several types of malignancies. In fact, tumor progression is tightly linked to the presence of the molecule, as it exerts its tolerogenic function, inhibiting the cells of the immune system and favoring tumor escape. Several polymorphisms in the 3’UTR region condition changes in HLA-G expression (14bp and +3142C/G, among others), which have been associated with both the development and outcome of patients with different tumor types. Also, in recent years, several studies have shown that HLA-G plays an important role in the control of autoimmune diseases. The ability of HLA-G to limit the progression of these diseases has been confirmed and, in fact, levels of the molecule and several of its polymorphisms have been associated with increased susceptibility to the development of autoimmune diseases, as well as increased disease severity. Thus, modulating HLA-G expression in target tissues of oncology patients or patients with autoimmune diseases may be potential therapeutic approaches to treat these pathological conditions.

HLA-G 3'UTR haplotype frequencies in highland and lowland South Native American populations

Human Leukocyte Antigen (HLA)-G participates in several biological processes, including reproduction, vascular remodeling, immune tolerance, and hypoxia response. HLA-G is a potential candidate gene for high altitude adaptation since its expression is modulated in both micro and macro environment under hypoxia and constant cellular stress. Besides the promoter region, the HLA-G 3'untranslated region (UTR) influences HLA-G expression patterns through several post-transcriptional mechanisms. Currently, the 3'UTR genetic diversity in terms of altitude adaptation of Native American populations is still unexplored, particularly at high altitude ecoregions. Here, we evaluated 288 Native Americans from 9 communities located in the Andes [highland (HL); ≥2,500 m (range = 2,838-4,433 m)] and 8 populations located in lowland (LL) regions [<2,500 m (range = 80-431 m); Amazonian tropical forest, Brazilian central plateau, and Chaco] of South America. In total, nine polymorphic sites and ten haplotypes were observed. The most frequent haplotypes (UTR-1, UTR-2, and UTR-3) accounted for ∼ 77% of haplotypes found in LL, while in the HL, the same haplotypes reach ∼ 93%. Also, a remarkable high frequency of putative ancestral UTR-5 haplotype was observed in LL (21.5%), while in HL UTR-2 reaches up to 47%. Further, UTR-2 frequency positively correlates with altitude-related variables, while a negative correlation for UTR-5 was observed. From an evolutionary perspective, we observed a tendency towards balancing selection in HL and LL populations thus suggesting that haplotypes of ancient and more derived alleles may have been co-opted for relatively recent adaptations such as those experienced by modern humans in the highland and lowland of South America. We also discuss how long-term balancing selection can be a reservoir of genetic variants that can be positively selected. Finally, our study provides some pieces of evidence that HLA-G 3'UTR haplotypes may have contributed to high altitude adaptation in the Andes.

New markers for predictions of acute and chronic rejection and graft outcomes in kidney transplant recipients; HLA-G gene 3'UTR 14 bp polymorphism and sHLA-G

The aim of this study was to evaluate the relation of Human Leukocyte Antigen-G (HLA-G) 14 bp ins/del (insertion/deletion) polymorphism and soluble HLA-G (sHLA-G) level with rejection in kidney transplant recipients. The study was planned as a case-control study involving two hundred fifty kidney transplant recipients. The case group consisted of 125 (female/male: 56/69) kidney transplant recipients diagnosed with acute (n = 52) and chronic rejection (n = 73). The control group consisted of one hundred twenty-five kidney transplant patients with no acute or chronic rejection matched by gender and age in the case group. The sHLA-G level in the recipient's plasma (at the time of rejection for the case, the same time as the case after the transplant for control) was analyzed by Enzyme-Linked Immunosorbent Assay (ELISA). HLA-G 3' untranslated region (3'UTR) polymorphism of recipient and donor was determined using agarose gel electrophoresis and DNA sequencing method. In our study, it was shown that acute rejection rate increased 1.06 times and chronic rejection rate increased 1.14 times in kidney transplant recipients with low serum sHLA-G levels. The rejection patients with the HLA-G 14 bp del/del genotype had higher sHLA-G levels post-transplantation. The frequency of acute rejection was lower in patients with HLA-G 14 bp del/del polymorphism than those with ins/ins and ins/del polymorphisms. This study proposes that HLA-G 3'UTR polymorphism and sHLA-G level might be useful in prediction of rejection in kidney transplant recipients.

Association of HLA-G polymorphisms with systemic lupus erythematosus and correlation between soluble HLA‑G levels and the disease: a meta-analysis

OBJECTIVE

To investigate the association between HLA‑G polymorphisms and systemic lupus erythematosus (SLE) susceptibility as well as the relationship between circulating soluble HLA‑G (sHLA‑G) levels and SLE.

METHODS

A meta-analysis was performed to investigate the relationships between HLA‑G 14-bp insertion (I)/deletion (D), +3142 G/C, +3035 T/C, and +3003 C/T polymorphisms and SLE as well as the relationship between sHLA‑G serum/plasma levels in SLE patients and controls.

RESULTS

Eleven publications fulfilled our inclusion criteria. Meta-analysis under the dominant model showed an association in the overall group between the II+ID genotype of HLA‑G 14-bp I/D polymorphism and SLE (OR = 1.213, 95%CI = 1.077-1.365, P = 0.001). Ethnicity-specific meta-analysis showed an association between II+ID and SLE in Asians but not in South American and European populations. No correlation was observed using the allele contrast between HLA‑G +3142 G/C polymorphisms and SLE. Contrastingly, +3035 T/C and +3003 C/T meta-analysis showed a significant allelic association between SLE and HLA‑G polymorphisms (OR = 1.378, 95%CI = 1.109-1.713, P = 0.004; OR = 1.834, 95%CI = 1.112-3.022, P = 0.017; respectively). sHLA‑G levels were significantly higher in the SLE group than in the controls (SMD = 0.637, 95%CI = 0.382-0.892, P < 0.001).

CONCLUSION

We showed association of HLA‑G 14-bp I/D, +3035 T/C, and +3003 C/T polymorphisms with SLE susceptibility and significantly higher circulating sHLA‑G levels in SLE patients.

Maternal platelets pass interstices of trophoblast columns and are not activated by HLA-G in early human pregnancy

In early human gestation, maternal arterial blood flow into the intervillous space of the developing placenta is obstructed by invaded trophoblasts, which form cellular plugs in uterine spiral arteries. These trophoblast plugs have recently been described to be loosely cohesive with clear capillary-sized channels into the intervillous space by 7 weeks of gestation. Here, we analysed localisation of maternal platelets at the maternal-foetal interface of human first trimester pregnancy, and tested the hypothesis whether HLA-G, which is primarily expressed by extravillous trophoblasts, affects aggregation and adhesion of isolated platelets. Immunohistochemistry of first trimester placental sections localised maternal platelets in vessel-like channels and adjacent intercellular gaps of extravillous trophoblasts in distal parts of columns. Furthermore, this localisation was confirmed by transmission electron microscopy. Neither co-incubation of HLA-G overexpressing JAR cells with isolated platelets, nor incubation with cell-derived soluble HLA-G or recombinant HLA-G affected platelet adhesion and aggregation. Our study suggests that maternal platelets flow through vessel-like channels of distal trophoblast columns and spread into adjacent lateral intercellular gaps, where platelet-derived factors could contribute to trophoblast differentiation into the invasive phenotype.

Inhibition of iNKT Cells by the HLA-G-ILT2 Checkpoint and Poor Stimulation by HLA-G-Expressing Tolerogenic DC

Invariant Natural Killer T (iNKT) cells are a small and distinct population of T cells crucial in immunomodulation. After activation by alpha-GalactosylCeramide (αGC), an exogenic glycolipid antigen, iNKT cells can rapidly release cytokines to enhance specific anti-tumor activity. Several human clinical trials on iNKT cell-based anti-cancer are ongoing, however results are not as striking as in murine models. Given that iNKT-based immunotherapies are dependent mainly on antigen-presenting cells (APC), a human tolerogenic molecule with no murine homolog, such as Human Leucocyte Antigen G (HLA-G), could contribute to this discrepancy. HLA-G is a well-known immune checkpoint molecule involved in fetal-maternal tolerance and in tumor immune escape. HLA-G exerts its immunomodulatory functions through the interaction with immune inhibitory receptors such as ILT2, differentially expressed on immune cell subsets. We hypothesized that HLA-G might inhibit iNKT function directly or by inducing tolerogenic APC leading to iNKT cell anergy, which could impact the results of current clinical trials. Using an ILT2-transduced murine iNKT cell line and human iNKT cells, we demonstrate that iNKT cells are sensitive to HLA-G, which inhibits their cytokine secretion. Furthermore, human HLA-G⁺ dendritic cells, called DC-10, failed at inducing iNKT cell activation compared to their autologous HLA-G^‒ DCs counterparts. Our data show for the first time that the HLA-G/ILT2 ICP is involved in iNKT cell function modulation.

Innate Lymphoid Cells in Human Pregnancy

Innate lymphoid cells (ILCs) are a new set of cells considered to be a part of the innate immune system. ILCs are classified into five subsets (according to their transcription factors and cytokine profile) as natural killer cells (NK cells), group 1 ILCs, group 2 ILCs, group 3 ILCs, and lymphoid tissue inducers (LTi). Functionally, these cells resemble the T helper population but lack the expression of recombinant genes, which is essential for the formation of T cell receptors. In this work, the authors address the distinction between peripheral and decidual NK cells, highlighting their diversity in ILC biology and its relevance to human pregnancy. ILCs are effector cells that are important in promoting immunity, inflammation, and tissue repair. Recent studies have directed their attention to ILC actions in pregnancy. Dysregulation or expansion of pro-inflammatory ILC populations as well as abnormal tolerogenic responses may directly interfere with pregnancy, ultimately resulting in pregnancy loss or adverse outcomes. In this review, we characterize these cells, considering recent findings and addressing knowledge gaps in perinatal medicine in the context of ILC biology. Moreover, we discuss the relevance of these cells not only to the process of immune tolerance, but also in disease.

Roles of HLA-G in the Maternal-Fetal Immune Microenvironment

During pregnancy, the maternal uterus and fetus form a special microenvironment at the maternal-fetal interface to support fetal development. Extravillous trophoblasts (EVTs), differentiated from the fetus, invade into the decidua and interact with maternal cells. Human leukocyte antigen (HLA)-G is a non-classical MHC-I molecule that is expressed abundantly and specifically on EVTs in physiological conditions. Soluble HLA-G (sHLA-G) is also found in maternal blood, amniotic fluid, and cord blood. The abnormal expression and polymorphisms of HLA-G are related to adverse pregnancy outcomes such as preeclampsia (PE) and recurrent spontaneous abortion (RSA). Here we summarize current findings about three main roles of HLA-G during pregnancy, namely its promotion of spiral artery remodeling, immune tolerance, and fetal growth, all resulting from its interaction with immune cells. These findings are not only of great significance for the treatment of pregnancy-related diseases but also provide clues to tumor immunology research since HLA-G functions as a checkpoint in tumors.

Generation of hypoimmunogenic human pluripotent stem cells via expression of membrane-bound and secreted β2m-HLA-G fusion proteins

Allogeneic immune rejection is a major barrier for the application of human pluripotent stem cells (hPSCs) in regenerative medicine. A broad spectrum of immune cells, including T cells, natural killer (NK) cells, and antigen-presenting cells, which either cause direct cell killing or constitute an immunogenic environment, are involved in allograft immune rejection. A strategy to protect donor cells from cytotoxicity while decreasing the secretion of inflammatory cytokines of lymphocytes is still lacking. Here, we engineered hPSCs with no surface expression of classical human leukocyte antigen (HLA) class I proteins via beta-2 microglobulin (B2M) knockout or biallelic knockin of HLA-G1 within the frame of endogenous B2M loci. Elimination of the surface expression of HLA class I proteins protected the engineered hPSCs from cytotoxicity mediated by T cells. However, this lack of surface expression also resulted in missing-self response and NK cell activation, which were largely compromised by expression of β2m-HLA-G1 fusion proteins. We also proved that the engineered β2m-HLA-G5 fusion proteins were soluble, secretable, and capable of safeguarding low immunogenic environments by lowering inflammatory cytokines secretion in allografts. Our current study reveals a novel strategy that may offer unique advantages to construct hypoimmunogenic hPSCs via the expression of membrane-bound and secreted β2m-HLA-G fusion proteins. These engineered hPSCs are expected to serve as an unlimited cell source for generating universally compatible "off-the-shelf" cell grafts in the future.

Extracellular Vesicles Mediate B Cell Immune Response and Are a Potential Target for Cancer Therapy

Extracellular vesicles (EVs) are increasingly understood to participate directly in many essential aspects of host antitumor immune response. Tumor- and immune-cell-derived EVs function in local and systemic contexts with roles in immune processes including cancer antigen conveyance, immune cell priming and activation, as well as immune escape. Current practice of cancer immunotherapy has de facto focused on eliciting T-cell-mediated cytotoxic responses. Humoral immunity is also known to exert antitumor effects, and B cells have been demonstrated to have functions that extend beyond antibody production to include antigen presentation and activation and modulation of T cells and innate immune effectors. Evidence of B cell response against tumor-associated antigens (TAAs) is observed in early stages of tumorigenesis and in most solid tumor types. It is known that EVs convey diverse TAAs, express antigenic-peptide-loaded MHCs, and complex with circulating plasma antitumoral autoantibodies. In this review, we will consider the relationships between EVs, B cells, and other antigen-presenting cells, especially in relation to TAAs. Understanding the intersection of EVs and the cancer immunome will enable opportunities for developing tumor antigen targets, antitumor vaccines and harnessing the full potential of multiple immune system components for next-generation cancer immunotherapies.

TLR3 activation modulates immunomodulatory properties of human periodontal ligament cells

BACKGROUND

Toll-like receptors (TLR) are a group of receptors that play roles in the innate immune system. Human periodontal ligament cells (hPDL cells) express several TLRs, including TLR3, a nucleotide sensing receptor that recognizes double-stranded RNA from viral infection. However, its role in hPDL cells is unclear. The aim of this study was to investigate the responses of hPDL cells in terms of immunomodulation after TLR3 engagement.

METHODS

HPDL cells were treated with various doses of poly I:C, a TLR3 activator. The expression of interferon-gamma (IFNγ), indoleamine 2,3 dioxygenase (IDO), and human leukocyte antigen G (HLA-G) was determined. Chemical inhibitors and small interfering RNA (siRNA) were used to confirm the role of TLR3. Coculture with human peripheral blood mononuclear cells (PBMCs) with poly I:C-activated hPDL cells was performed.

RESULTS

Endosomal TLR3 in hPDL cells was observed by immunocytochemistry. Addition of poly I:C significantly enhanced the expression and secretion of IFNγ, IDO, and HLA-G. Knockdown of TLR3 using siRNA decreased the poly I:C-induced expression of these three molecules. Bafilomycin-A, an inhibitor of auto-phagosome and lysosome fusion, inhibited poly I:C-induced IDO and HLA-G expression, whereas cycloheximide and a TLR3-neutralizing antibody had no effect. In co-culture experiments, poly I:C-activated hPDL cells inhibited PBMCs proliferation and increased mRNA expression of forkhead box P3 (FOXP3), a transcription factor which is a marker of regulatory T cells.

CONCLUSION

Our findings indicated that TLR3 engagement of hPDL cells induced immunosuppressive properties of these cells. Because immunosuppressive properties play an important role in tissue healing and regeneration, activation of TLR3 may help to attenuate tissue destruction by limiting the inflammatory process and perhaps initiate the healing and regeneration process of the periodontium.

The Autoimmune Regulator (Aire) transactivates HLA-G gene expression in thymic epithelial cells

The Autoimmune Regulator (Aire) protein coordinates the negative selection of developing thymocytes by inducing the expression of hundreds of tissue-specific antigens within the thymic medulla, which is also a primary site of the expression of the immune checkpoint HLA-G molecule. Considering the immunomodulatory properties of Aire and HLA-G, and considering that the role of the constitutive thymus expression of HLA-G has not been elucidated, we studied the effect of AIRE cDNA transfection on HLA-G expression in 4D6 thymic cells and in the HLA-G-positive JEG-3 choriocarcinoma cells. Aire promoted the transactivation of HLA-G gene by increasing the overall transcription, inducing the transcription of at least G1 and G2/G4 isoforms, and incrementing the occurrence and distribution of intracellular HLA-G protein solely in 4D6 thymic cells. Luciferase-based assays and chromatin immunoprecipitation experiments performed in 4D6 cells revealed that Aire targeted at least two regions within the 5'-untranslated regulatory region (5'-URR) extending 1·4 kb from the first ATG initiation codon. The interaction occurs independently of three putative Aire-binding sites. These results indicate that the Aire-induced upregulation of HLA-G in thymic cells is likely to act through the interaction of Aire with specific HLA-G 5'-URR DNA-binding factors. Such a multimeric transcriptional complex might operate in the thymus during the process of promiscuous gene expression.

TWIST1, MMP-21, and HLAG-1 co-overexpression is associated with ESCC aggressiveness

Esophageal squamous cell carcinoma (ESCC) is one of the most aggressive types of cancer, requiring reliable biomarkers for prognosis and therapeutic responsiveness. TWIST1, as an important factor responsible for metastasis of several cancers, is involved in tumor invasion and metastasis through indirectly regulation of MMP-21 expression. On the other hand, NF-ĸβ which is a regulator of HLAG-1 has direct interaction with TWIST1 protein. In this retrospective study we investigated the clinical significance of TWIST1, MMP-21, and HLAG-1 expression in ESCC, and the possible correlation between these genes and progression of the disease. The gene expression analyses of TWIST1, MMP-21, and HLA-G1 were performed by relative comparative real-time polymerase chain reaction in 58 ESCCs compared with corresponding margin-normal esophageal tissues. Significant overexpression of HLAG-1, TWIST1, and MMP-21 messenger RNA was observed in 22.4%, 41.4%, and 60.3% of tumor samples, respectively. Concomitant overexpression of TWIST1/MMP-21 and TWIST1/HLAG-1 were significantly correlated to each other in various clinicopathological features, including depth of tumor invasion, stage of tumor progression, lymphatic invasion, and grade of tumor cell differentiation ( P < 0.05). The current study is the first report of coexpression of TWIST1, MMP-21, and HLAG-1 in ESCC. Such findings suggest an oncogenic role for concomitant expression of these genes in ESCC invasion and metastasis.

European Patent in Immunoncology: From Immunological Principles of Implantation to Cancer Treatment

The granted European patent EP 2 561 890 describes a procedure for an immunological treatment of cancer. It is based on the principles of the HLA-supported communication of implantation and pregnancy. These principles ensure that the embryo is not rejected by the mother. In pregnancy, the placenta, more specifically the trophoblast, creates an “interface” between the embryo/fetus and the maternal immune system. Trophoblasts do not express the “original” HLA identification of the embryo/fetus (HLA-A to -DQ), but instead show the non-classical HLA groups E, F, and G. During interaction with specific receptors of NK cells (e.g., killer-immunoglobulin-like receptors (KIR)) and lymphocytes (lymphocyte-immunoglobulin-like receptors (LIL-R)), the non-classical HLA groups inhibit these immunocompetent cells outside pregnancy. However, tumors are known to be able to express these non-classical HLA groups and thus make use of an immuno-communication as in pregnancies. If this occurs, the prognosis usually worsens. This patent describes, in a first step, the profiling of the non-classical HLA groups in primary tumor tissue as well as metastases and recurrent tumors. The second step comprises tailored antibody therapies, which is the subject of this patent. In this review, we analyze the underlying mechanisms and describe the currently known differences between HLA-supported communication of implantation and that of tumors.

HSV-Induced Systemic Inflammation as an Animal Model for Behçet's Disease and Therapeutic Applications

Behçet’s disease (BD) affects multiple organs. It is mainly characterized by recurrent oral, skin, and genital aphthous ulcers, and eye involvement. Successful management of BD is increasing, although its etiology remains unclear. A number of etiologies have been proposed, including environmental, genetic, viral, and immunological factors. To understand its complex etiology and improve its management, animal models of BD have been used to enable more effective therapeutic applications with increased clinical significance. An herpes simplex virus (HSV) type 1-induced BD mouse model has shown disease characteristics similar to those seen in BD patients. An HSV-induced BD animal model has been used to test various therapeutic modalities. The applied modalities are several materials that are derived from natural products, conventional therapeutics, and possible biologics. In this review, we provided how they regulate inflammation in an HSV-induced BD model.

Clinical Significance of Potential Unidentified HLA-G Isoforms Without α1 Domain but Containing Intron 4 in Colorectal Cancer Patients

The ectopic HLA-G expression in malignancies has been extensively explored and clinical significance of the molecule was widely acknowledged. Besides previously well-documented seven isoforms (HLA-G1~-G7), other novel isoforms of HLA-G have been reported but their clinical relavenace remians evaluated. In this study, lesion HLA-G expression in 379 case-matched serial section primary colorectal cancers (CRC) were evaluated with mAb 4H84 (recognizing an epitope in HLA-G α1 domain), and mAb 5A6G7 (recognizing an epitope encoded by intron 4), respectively. Data showed that HLA-G positive staining with mAbs 4H84 and 5A6G7 was 70.7 and 60.4%, respectively. When percentage of HLA-G expression detected with mAb 4H84 subtracted that with mAb 5A6G7, the difference (_ΔHLA-G) with negative (_ΔHLA-G_neg), comparable (_ΔHLA-G_com) and positive (_ΔHLA-G_pos) were observed in 64 (16.9%), 159 (42.0%), and 156 (41.2%) cases, respectively. Noteworthy, unexpected immunostaining was observed in 44 (11.6%) lesions that no staining was detected with mAb 4H84 but positive with mAb 5A6G7 (4H84^neg5A6G7^pos). This staining pattern was unpredictable because all seven known HLA-G isoforms containing the α 1 domain could be recognized by the mAb 4H84. Moreover, patients with _ΔHLA-G_neg had obviously better survival than those with _ΔHLA-G_com and _ΔHLA-G_pos (p = 0.017), and _ΔHLA-G could be an independent prognostic factor for CRC patients (p = 0.008). Our findings provides the first report that potential unidentified HLA-G isoforms is of distinct clinical significance in CRC patients.

10-Year Experience with HLA-G in Heart Transplantation

The Human Leukocyte Antigen-G (HLA-G) is a MHC-class Ib molecule with robust immunomodulatory properties; in transplant, it inhibits cytotoxic activity of immune cells and thus has a pivotal role in protecting the allograft from immune attack. The present review details a 10-year experience investigating the influence of HLA-G on heart transplantation, allograft rejection and cardiac allograft vasculopathy development. Exploration of HLA-G in transplantation began with the initial findings of its increased expression in allograft hearts. Since then, HLA-G has been recognized as an important factor in transplant immunology. We discuss inducers of HLA-G expression, and the importance of HLA-G as a potential biomarker in allograft rejection and heart failure. We also highlight the importance of polymorphisms and how they may influence both HLA-G expression and clinical outcomes. There remains much to be done in this field, however we hope that findings from our group and other groups will ignite interest and facilitate further expansion of HLA-G research in transplantation.

HLA-G peptide preferences change in transformed cells: impact on the binding motif

HLA-G is known for its strictly restricted tissue distribution. HLA-G expression could be detected in immune privileged organs and many tumor entities such as leukemia, multiple myeloma, and non-Hodgkin and Hodgkin’s lymphoma. This functional variability from mediation of immune tolerance to facilitation of tumor immune evasion strategies might translate to a differential NK cell inhibition between immune-privileged organs and tumor cells. The biophysical invariability of the HLA-G heavy chain and its contrary diversity in immunity implicates a strong influence of the bound peptides on the pHLA-G structure. The aim was to determine if HLA-G displays a tissue-specific peptide repertoire. Therefore, using soluble sHLA-G technology, we analyzed the K562 and HDLM-2 peptide repertoires. Although both cell lines possess a comparable proteome and recruit HLA-G-restricted peptides through the same peptide-loading pathway, the peptide features appear to be cell specific. HDLM-2 derived HLA-G peptides are anchored by an Arg at p1 and K562-derived peptides are anchored by a Lys. At p2, no anchor motif could be determined while peptides were anchored at pΩ with a Leu and showed an auxiliary anchor motif Pro at p3. To appreciate if the peptide anchor alterations are due to a cell-specific differential peptidome, we performed analysis of peptide availability within the different cell types. Yet, the comparison of the cell-specific proteome and HLA-G-restricted ligandome clearly demonstrates a tissue-specific peptide selection by HLA-G molecules. This exclusive and unexpected observation suggests an exquisite immune function of HLA-G.

Identification of novel microRNAs regulating HLA-G expression and investigating their clinical relevance in renal cell carcinoma

The non-classical human leukocyte antigen G (HLA-G) is expressed at a high frequency in renal cell carcinoma (RCC) and is associated with a higher tumor grade and a poor clinical outcome. This might be caused by the HLA-G-mediated inhibition of the cytotoxicity of T and NK cells. Therefore a selective targeting of HLA-G might represent a powerful strategy to enhance the immunogenicity of RCC lesions. Recent studies identified a number of HLA-G-regulating microRNAs (miRs) and demonstrated an inverse expression of some of these miRs with HLA-G in RCC in vitro and in vivo. However, it was postulated that further miRs might exist contributing to the tightly controlled selective HLA-G expression.By application of a miR enrichment assay (miTRAP) in combination with in silico profiling two novel HLA-G-regulatory miRs, miR-548q and miR-628-5p, were identified. Direct interactions of both miRs with the 3' untranslated region of HLA-G were confirmed with luciferase reporter gene assays. In addition, qPCR analyses and immunohistochemical staining revealed an inverse, expression of miR-628-5p, but not of miR-548q to the HLA-G protein in primary RCC lesions and cell lines. Stable overexpression of miR-548q and miR-628-5p caused a downregulation of HLA-G mRNA and protein. This leads in case of miR-548q to an enhanced NK cell-mediated HLA-G-dependent cytotoxicity, which could be reverted by ILT2 blockade suggesting a control of the immune effector cell activity at least by this miR. The identification of two novel HLA-G-regulatory miRs extends the number of HLA-G-relevant miRs tuning the HLA-G expression and might serve as future therapeutic targets.

Increased levels of soluble HLA-G molecules in Tunisian patients with chronic hepatitis B infection

Hepatitis B virus (HBV) infection is a global health problem. The mechanisms of immune tolerance in HBV infection are still unclear. The host immune response plays a critical role in determining the outcome of HBV infection. Human leucocyte antigen-G (HLA-G) is involved in immunotolerogenic process and infectious diseases. This study aimed to explore the implication of soluble HLA-G (sHLA-G) and its isoforms in HBV infection. Total sHLA-G (including shedding HLA-G1 and HLA-G5) was analysed by ELISA in 95 chronic HBV patients, 83 spontaneously resolvers and 100 healthy controls (HC). To explore the presence of sHLA-G dimers, we performed an immunoprecipitation and a Western blot analysis on positive samples for sHLA-G in ELISA. The serum levels of sHLA-G were significantly increased in patients with chronic HBV patients compared to spontaneously resolvers and HC (P<.0001). Interestingly, we found an increased level of sHLA-G1 in chronic HBV patients than in spontaneously resolvers and HC (P<.001). In addition, the expression of HLA-G5 seems to be higher in the sera of chronic HBV patients than spontaneously resolvers (P=.026). The analysis of HLA-G dimers showed the presence of homodimers in 93% of chronic HBV patients, 67% in spontaneously resolvers and 60% in HC. These results provide evidence that sHLA-G may have a crucial role in the outcome of HBV infection and could be proposed as a biomarker for infection outcome. Based on its tolerogenic function, HLA-G might be considered as a new promising immunotherapeutic approach to treat the chronic infection with HBV.

HLA-G: At the Interface of Maternal-Fetal Tolerance

During pregnancy, semiallogeneic fetal extravillous trophoblasts (EVT) invade the uterine mucosa without being rejected by the maternal immune system. Several mechanisms were initially proposed by Peter Medawar half a century ago to explain this apparent violation of the laws of transplantation. Then, three decades ago, an unusual human leukocyte antigen (HLA) molecule was identified: HLA-G. Uniquely expressed in EVT, HLA-G has since become the center of the present understanding of fetus-induced immune tolerance. Despite slow progress in the field, the last few years have seen an explosion in our knowledge of HLA-G biology. Here, we critically review new insights into the mechanisms controlling the expression and function of HLA-G at the maternal-fetal interface, and discuss their relevance for fetal tolerance.

"HLA-G 3'UTR gene polymorphisms and rheumatic heart disease: a familial study among South Indian population"

BACKGROUND

Rheumatic heart disease (RHD) is an autoimmune disease where cross reactive CD4⁺ T cells are involved in the pathogenesis of valvular damage. Human Leukocyte Antigen-G (HLA-G), an immunosuppressive molecule playing a crucial role in the inhibition of T cell response is associated with the pathogenesis of various autoimmune and inflammatory diseases. Genetic polymorphisms within the 3'untranslated region (UTR) of HLA-G influences its expression and thus disease pathogenesis. Hence, the present study aims to unravel the association of 14 bp Ins/Del (rs66554220) and +3142 C/G (rs1063320) polymorphisms in 3' UTR of HLA-G with RHD.

METHODS

This familial study consists of 99 RHD families (99 RHD patients, 140 parents and 126 healthy siblings). The 14 bp Ins/Del and +3142 C/G polymorphisms were evaluated by PCR using sequence specific primers and its transmission disequilibrium (TD) was tested by TD test in 70 trio families.

RESULTS

The frequency of +3142 C/C genotype was high in patients with combined valvular lesions (CVL) (OR = 5.88; p_c = 0.012) and pooled RHD patients (P: OR = 2.76; p = 0.043; p_c = 0.076) when compared to healthy siblings. Under the additive (OR = 5.50; p_c = 0.026) and recessive genetic model (OR = 5.88; p_c = 0.012), the +3142 C/C genotype was significantly associated with CVL in patients.

CONCLUSION

The results suggest that the +3142 C/C genotype may be associated with minor risk for the development of RHD and is more likely to influence the severity of the disease.

HLA-G regulatory polymorphisms are associated with susceptibility to HCV infection

BACKGROUND

Hepatitis C virus (HCV) is able to bypass the immune system modulating innate and adaptive immune response and blocking T helper 1 (Th1) cell production. Because the human leukocyte antigen (HLA)-G molecule has immunomodulatory properties inhibiting the function and production of natural killer and cytotoxic lymphocyte T cells, as well as promoting shift from Th1 toward Th2 response, we hypothesized its involvement in susceptibility to HCV infection.

MATERIALS AND METHODS

Considering that HLA-G mRNA expression has been reported to be under genetic control, an association study was conducted analyzing 800 base pairs upstream the ATG at the 5'upstream regulator region (URR) and 850 base pairs from ATG to exon 3 and the 3'untranslated region (UTR) of HLA-G gene in Italian HCV-positive patients and uninfected controls.

RESULTS

Four 5'URR polymorphisms (-725C>G>T, -509C>G, -400G>A and -398G>A), 7 polymorphisms at coding region (+15G>A, +36G>A, +243G>A, insC506, 531G>C, delA615 and 685G>A), the +644G>T polymorphism, and 1 haplotype (TTGTTCCIGAC) showed different frequency distributions between HCV patients and uninfected controls.

CONCLUSION

The results from our study suggest a possible involvement of HLA-G in the risk modulation toward HCV infection.

Expression of bovine non-classical major histocompatibility complex class I proteins in mouse P815 and human K562 cells

Major histocompatibility complex class I (MHC-I) proteins can be expressed as cell surface or secreted proteins. To investigate whether bovine non-classical MHC-I proteins are expressed as cell surface or secreted proteins, and to assess the reactivity pattern of monoclonal antibodies with non-classical MHC-I isoforms, we expressed the MHC proteins in murine P815 and human K562 (MHC-I deficient) cells. Following antibiotic selection, stably transfected cell lines were stained with H1A or W6/32 antibodies to detect expression of the MHC-I proteins by flow cytometry. Two non-classical proteins (BoLA-NC1*00501 and BoLA-NC3*00101) were expressed on the cell surface in both cell lines. Surprisingly, the BoLA-NC4*00201 protein was expressed on the cell membrane of human K562 but not mouse P815 cells. Two non-classical proteins (BoLA-NC1*00401, which lacks a transmembrane domain, and BoLA-NC2*00102) did not exhibit cell surface expression. Nevertheless, Western blot analyses demonstrated expression of the MHC-I heavy chain in all transfected cell lines. Ammonium-sulfate precipitation of proteins from culture supernatants showed that BoLA-NC1*00401 was secreted and that all surface expressed proteins where shed from the cell membrane by the transfected cells. Interestingly, the surface expressed MHC-I proteins were present in culture supernatants at a much higher concentration than BoLA-NC1*00401. This comprehensive study shows that bovine non-classical MHC-I proteins BoLA-NC1*00501, BoLA-NC3*00101, and BoLA-NC4*00201 are expressed as surface isoforms with the latter reaching the cell membrane only in K562 cells. Furthermore, it demonstrated that BoLA-NC1*00401 is a secreted isoform and that significant quantities of membrane associated MHC-I proteins can be shed from the cell membrane.

Soluble monomers, dimers and HLA-G-expressing extracellular vesicles: the three dimensions of structural complexity to use HLA-G as a clinical biomarker

The HLA-G molecule belongs to the family of nonclassical human leukocyte antigen (HLA) class I. At variance to classical HLA class I, HLA-G displays (i) a low number of nucleotide variations within the coding region, (ii) a high structural diversity, (iii) a restricted peptide repertoire, (iv) a limited tissue distribution and (v) strong immune-suppressive properties. The physiological HLA-G surface expression is restricted to the maternal-fetal interface and to immune-privileged adult tissues. Soluble forms of HLA-G (sHLA-G) are detectable in various body fluids. Cellular activation and pathological processes are associated with an aberrant or a neo-expression of HLA-G/sHLA-G. Functionally, HLA-G and its secreted forms are considered to be key players in the induction of short- and long-term tolerance. Thus, its unique expression profile and tolerance-inducing functions render HLA-G/sHLA-G an attractive biomarker to monitor the systemic health/disease status and disease activity/progression for clinical approaches in disease management and treatments. Here, we place emphasis on (i) the current status of the tolerance-inducing functions by HLA-G/sHLA-G, (ii) the current complexity to implement this molecule as a meaningful clinical biomarker regarding the three dimensions of structural diversity (monomers, dimers and HLA-G-expressing extracellular vesicles) with its functional implications, and (iii) novel and future approaches to detect and quantify sHLA-G structures and functions.

The Potential of HLA-G-Bearing Extracellular Vesicles as a Future Element in HLA-G Immune Biology

The HLA-G molecule is a member of the non-classical HLA class I family. Its surface expression is physiologically restricted to the maternal–fetal interface and to immune privileged adult tissues. Despite the restricted tissue expression, HLA-G is detectable in body fluids as secreted soluble molecules. A unique feature of HLA-G is the structural diversity as surface expressed and as secreted molecules. Secreted HLA-G can be found in various body fluids either as free soluble HLA-G or as part of extracellular vesicles (EVs), which are composed of various antigens/ligands/receptors, bioactive lipids, cytokines, growth factors, and genetic information, such as mRNA and microRNA. Functionally, HLA-G and its secreted forms are considered to play a crucial role in the network of immune-regulatory tolerance mechanisms, preferentially interacting with the cognate inhibitory receptors LILRB1 and LILRB2. The HLA-G mediated tolerance is described in processes of pregnancy, inflammation, and cancer. However, almost all functional and clinical implications of HLA-G in vivo and in vitro have been established based on simple single ligand/receptor interactions at the cell surface, whereas HLA-G-bearing EVs were in minor research focus. Indeed, cytotrophoblast cells, mesenchymal stem cells, and cancer cells were recently described to secrete HLA-G-bearing EVs, displaying immunosuppressive effects and modulating the tumor microenvironment. However, numerous functional and clinical open questions persist. Here, we (i) introduce basic aspects of EVs biology, (ii) summarize the functional knowledge, clinical implications and open questions of HLA-G-bearing EVs, and (iii) discuss HLA-G-bearing EVs as a future element in HLA-G biology.

Soluble Human Leukocyte Antigen-G in the Bronchoalveolar Lavage of Lung Cancer Patients

BACKGROUND

The main function of the HLA-G molecule in its membrane-bound and soluble forms is to inhibit the immune response by acting on CD4+ T cells, cytotoxic T cells, NK cells and dendritic cells. Lung cancer is a leading cause of death worldwide, and annual incidence is high in both women and men. Some studies have reported an increase of HLA-G serum levels in lung cancer, probably generated by tumor cells escaping the antitumor immune response. In this study the concentration of soluble HLA-G in bronchoalveolar lavage (BAL) in patients with primary and metastatic lung cancer was measured to determine its relation with tumor histological type and overall patient status according to the Karnofsky scale.

METHODS

Thirty-one lung cancer patients were included. A tumor biopsy was obtained by bronchoscopy and the tumor type was determined by hematoxylin and eosin staining. BAL samples were obtained to measure soluble HLA-G concentrations in an ELISA sandwich assay.

RESULTS

The average value of soluble HLA-G was 49.04ng/mL. No correlation between soluble HLA-G levels and age, gender or smoking was observed. A highly significant difference was observed in the levels of soluble HLA-G in BAL from patients with different histological types of lung cancer, especially in metastatic tumors. The Karnofsky index showed a significant and inverse correlation with soluble HLA-G levels in BAL.

CONCLUSIONS

Soluble HLA-G protein is significantly associated with metastatic tumors and patients with lower Karnofsky index and may be useful as a prognostic marker in lung cancer.

Evaluation of HLA-G 14 bp Ins/Del and +3142G>C Polymorphism with Susceptibility and Early Disease Activity in Rheumatoid Arthritis

Purpose/Background. Mounting evidence designates that HLA-G plays a role in the regulation of inflammatory processes and autoimmune diseases. There are controversial reports concerning the impact of HLA-G gene polymorphism on rheumatoid arthritis (RA). This study was aimed at examining the impact of 14 bp ins/del and +3142G>C polymorphism with susceptibility and early disease activity in RA patients in a sample of the Iranian population. Methods. This case-control study was done on 194 patients with RA and 158 healthy subjects. The HLA-G rs1063320 (+3142G>C) and rs66554220 (14 bp ins/del) variants were genotype by polymerase chain reaction-restriction fragment length polymorphism (PCR-RFP) and PCR method, respectively. Results. The HLA-G +3142G>C polymorphism significantly decreased the risk of RA in codominant (OR = 0.61, 95% CI = 0.38-0.97, p = 0.038, GC versus GG; OR = 0.36, 95% CI = 0.14-0.92, p = 0.034, CC versus GG), dominant (OR = 0.56, 95% CI = 0.36-0.87, p = 0.011, GC + CC versus GG), and allele (OR = 0.58, 95% CI = 0.41-0.84, p = 0.004, C versus G) inheritance models tested. Our finding did not support an association between HLA-G 14 bp ins/del variant and risk/protection of RA. In addition, no significant association was found between the polymorphism and early disease activity. Conclusion. In summary, our results showed that HLA-G +3142G>C gene polymorphism significantly decreased the risk of RA in a sample of the Iranian population.

New Developments in HLA-G in Cardiac Transplantation

Human Leukocyte Antigen-G (HLA-G) is a non-classical class 1b protein, whose gene is located on chromosome 6 (6p21.31). HLA-G inhibits the immune cells' cytotoxic activity by interacting with specific receptors on their membranes. Since it is a naturally occurring immune modulator, HLA-G has been investigated in transplantation. Indeed, a number of investigations reveal that HLA-G expression is influenced by genetic polymorphisms and in turn, those polymorphisms are associated with detrimental or beneficial outcomes in various pathological situations. The present review introduces the HLA-G molecule, the gene and its polymorphisms. It focuses on the expression of HLA-G and the role of polymorphisms primarily in heart transplant outcomes, secondarily in other transplant organs, as well as the role of the allograft and effect of medical therapy. We discuss the limitations in HLA-G transplant investigations and future directions. The immune inhibiting activity of HLA-G has a great deal of potential for its utilization in enhancing diagnostic, preventive and therapeutic strategies against rejection in the setting of transplantation.

Human Leukocyte Antigen-G (HLA-G) Expression in Cancers: Roles in Immune Evasion, Metastasis and Target for Therapy

Aberrant induction of human leukocyte antigen-G (HLA-G) expression has been observed in various malignancies and is strongly associated with tumor immune escape, metastasis and poor prognosis. To date, great achievements have been made in understanding the underlying mechanisms of HLA-G involved in tumor progression. HLA-G could lead to tumor evasion by inhibition of immune cell cytolysis, differentiation and proliferation and inhibition of cytokine production, induction of immune cell apoptosis, generation of regulatory cells and expansion of myeloid-derived suppressive cells and by impairment of chemotaxis. Moreover, HLA-G could arm tumor cells with a higher invasive and metastatic potential with the upregulation of tumor-promoting factor expression such as matrix metalloproteinases (MMPs), indicating that ectopic HLA-G expression could render multiple effects during the progression of malignancies. In this review, we summarized the mechanisms of HLA-G involved in promoting tumor cell immune escaping, metastasis and disease progression. Special attention will be paid to its significance as an attractive therapeutic target in cancers.

Effect of the maternal-fetal interface immunoregulation on the occurrence of intrahepatic cholestasis of pregnancy

Maternal immune tolerance of the fetus is indispensable for a healthy pregnancy. Currently, the study of the immune microenvironment of the maternal-fetal interface has been a heated topic in reproductive immunology research. More and more studies show that the immune imbalance in the maternal-fetal interface plays a very important role in the incidence of intrahepatic cholestasis of pregnancy (ICP). However, the precise etiology and mechanism of immune imbalance in the occurrence of ICP is still unknown. In order to clarify the potential immunologic mechanisms of ICP, this review summarizes the recent studies of the decidual immunology microenvironment and the potential immunologic mechanisms related to the development of ICP.

Analysis of Il-10 gene sequence in patients with sinonasal polyposis

Sinonasal polyposis (SNP) is a chronic inflammatory disease of nasal and paranasal cavities. Human leukocyte antigen-G molecules (HLA-G) are non-classic HLA-I molecules with anti-inflammatory and tolerogenic properties. HLA-G production is mainly induced by interleukin (IL)-10. IL-10 is an anti-inflammatory cytokine that inhibits the production of proinflammatory cytokines and induces HLA-class II down-modulation. Recent studies suggest that HLA-G could play a role in SNP pathogenesis; in SNP patients physiological levels of IL-10 (produced by activated peripheral blood CD14+ monocytes) are not able to induce production of HLA-G. Different mechanisms could justify these findings: genomic or amino-acidic sequence alterations in IL-10 lower IL-10 receptor expression, lower IL-10 receptor affinity, or alterations of the intracellular signal transmission. This study analyzes nucleotidic sequence of IL-10 gene in SNP patients. Sequencing of IL-10 gene shows that the lack of HLA-G production by peripheral blood CD14+ monocytes is not related to alterations in IL-10 gene nucleotidic sequence.