HLA-G, -E, -F preworkshop: tools and protocols for analysis of non-classical class I genes transcription and protein expression

DeepHLAPred: a deep learning-based method for non-classical HLA binder prediction

Human leukocyte antigen (HLA) is closely involved in regulating the human immune system. Despite great advance in detecting classical HLA Class I binders, there are few methods or toolkits for recognizing non-classical HLA Class I binders. To fill in this gap, we have developed a deep learning-based tool called DeepHLAPred. The DeepHLAPred used electron-ion interaction pseudo potential, integer numerical mapping and accumulated amino acid frequency as initial representation of non-classical HLA binder sequence. The deep learning module was used to further refine high-level representations. The deep learning module comprised two parallel convolutional neural networks, each followed by maximum pooling layer, dropout layer, and bi-directional long short-term memory network. The experimental results showed that the DeepHLAPred reached the state-of-the-art performanceson the cross-validation test and the independent test. The extensive test demonstrated the rationality of the DeepHLAPred. We further analyzed sequence pattern of non-classical HLA class I binders by information entropy. The information entropy of non-classical HLA binder sequence implied sequence pattern to a certain extent. In addition, we have developed a user-friendly webserver for convenient use, which is available at http://www.biolscience.cn/DeepHLApred/ . The tool and the analysis is helpful to detect non-classical HLA Class I binder. The source code and data is available at https://github.com/tangxingyu0/DeepHLApred .

B Cells Control Mucosal-Associated Invariant T Cell Responses to Salmonella enterica Serovar Typhi Infection Through the CD85j HLA-G Receptor

Mucosal-associated invariant T (MAIT) cells are an innate-like population of T cells that display a TCR Vα7.2+ CD161+ phenotype and are restricted by the nonclassical MHC-related molecule 1 (MR1). Although B cells control MAIT cell development and function, little is known about the mechanisms underlying their interaction(s). Here, we report, for the first time, that during Salmonella enterica serovar Typhi (S. Typhi) infection, HLA-G expression on B cells downregulates IFN-γ production by MAIT cells. In contrast, blocking HLA-G expression on S. Typhi-infected B cells increases IFN-γ production by MAIT cells. After interacting with MAIT cells, kinetic studies show that B cells upregulate HLA-G expression and downregulate the inhibitory HLA-G receptor CD85j on MAIT cells resulting in their loss. These results provide a new role for HLA-G as a negative feedback loop by which B cells control MAIT cell responses to antigens.

The Molecular and Functional Characteristics of HLA-G and the Interaction with Its Receptors: Where to Intervene for Cancer Immunotherapy?

Human leukocyte antigen G (HLA-G) mediates maternal-fetal immune tolerance. It is also considered an immune checkpoint in cancer since it may mediate immune evasion and thus promote tumor growth. HLA-G is, therefore, a potential target for immunotherapy. However, existing monoclonal antibodies directed against HLA-G lack sufficient specificity and are not suitable for immune checkpoint inhibition in a clinical setting. For this reason, it is essential that alternative approaches are explored to block the interaction between HLA-G and its receptors. In this review, we discuss the structure and peptide presentation of HLA-G, and its interaction with the receptors Ig-like transcript (ILT) 2, ILT4, and Killer cell immunoglobulin-like receptor 2DL4 (KIR2DL4). Based on our findings, we propose three alternative strategies to block the interaction between HLA-G and its receptors in cancer immunotherapy: (1) prevention of HLA-G dimerization, (2) targeting the peptide-binding groove of HLA-G, and (3) targeting the HLA-G receptors. These strategies should be an important focus of future studies that aim to develop immune checkpoint inhibitors to block the interaction between HLA-G and its receptors for the treatment of cancer.

HLA-G Neo-Expression on Tumors

HLA-G is known to modulate the immune system activity in tissues where physiological immune-tolerance is necessary (i.e., maternal-fetal interface, thymus, and cornea). However, the frequent neo-expression of HLA-G in many cancer types has been previously and extensively described and is correlated with a bad prognosis. Despite being an MHC class I molecule, HLA-G is highly present in tumor context and shows unique characteristics of tissue restriction of a Tumor Associated Antigen (TAA), and potent immunosuppressive activity of an Immune CheckPoint (ICP). Consequently, HLA-G appears to be an excellent molecular target for immunotherapy. Although the relevance of HLA-G in cancer incidence and development has been proven in numerous tumors, its neo-expression pattern is still difficult to determine. Indeed, the estimation of HLA-G's actual expression in tumor tissue is limited, particularly concerning the presence and percentage of the new non-canonical isoforms, for which detection antibodies are scarce or inexistent. Here, we summarize the current knowledge about HLA-G neo-expression and implication in various tumor types, pointing out the need for the development of new tools to analyze in-depth the HLA-G neo-expression patterns, opening the way for the generation of new monoclonal antibodies and cell-based immunotherapies.

Carosella E, Benkirane-Jessel N, Moreau P, Rouas-Freiss N, Bensoussan D, Huselstein C. Are the Immune Properties of Mesenchymal Stem Cells from Wharton's Jelly Maintained during Chondrogenic Differentiation?

Background: Umbilical mesenchymal stem/stromal cells (MSCs), and especially those derived from Wharton’s jelly (WJ), are a promising engineering tool for tissue repair in an allogeneic context. This is due to their differentiation capacity and immunological properties, like their immunomodulatory potential and paracrine activity. Hence, these cells may be considered an Advanced Therapy Medicinal Product (ATMP). The purpose of this work was to differentiate MSCs from WJ (WJ-MSCs) into chondrocytes using a scaffold and to evaluate, in vitro, the immunomodulatory capacities of WJ-MSCs in an allogeneic and inflammatory context, mimicked by IFN-γ and TNF-α priming during the chondrogenic differentiation. Methods: Scaffolds were made from hydrogel composed by alginate enriched in hyaluronic acid (Alg/HA). Chondrogenic differentiation, immunological function, phenotype expression, but also secreted soluble factors were the different parameters followed during 28 days of culture. Results: During chondrocyte differentiation, even in an allogeneic context, WJ-MSCs remained unable to establish the immunological synapse or to induce T cell alloproliferation. Moreover, interestingly, paracrine activity and functional immunomodulation were maintained during cell differentiation. Conclusion: These results show that WJ-MSCs remained hypoimmunogenic and retained immunomodulatory properties even when they had undergone chondrocyte differentiation.

The role of HLA-G in parasitic diseases

Little attention has been devoted to the role of HLA-G gene and molecule on parasitic disorders, and the available studies have focused on malaria, African and American trypanosomiasis, leishmaniosis, toxoplasmosis and echinococcosis. After reporting a brief description regarding the role of the cells of innate and adaptive immune system against parasites, we reviewed the major features of the HLA-G gene and molecule and the role of HLA-G on the major cells of immune system. Increased levels of soluble HLA-G (sHLA-G) have been observed in patients presenting toxoplasmosis and in the active phase of echinococcosis. In addition, increased sHLA-G has also been associated with increased susceptibility to malaria and increased susceptibility to develop human African trypanosomiasis (HAT). In contrast, decreased membrane-bound HLA-G has been reported in placenta of patients infected with Plasmodium falciparum and in heart and colon of patients presenting Chagas disease. The 3' untranslated region of the HLA-G gene has been the main focus of studies on malaria, HAT and Chagas disease, exhibiting distinct patterns of associations. Considering that HLA-G is an immune checkpoint molecule, inhibiting the activity of several cells of the immune system, the excessive neoexpression and the increased sHLA-G levels together with the decreased constitutive tissue expression of membrane-bound HLA-G may be detrimental to the host infected with parasite agents.

Novel landscape of HLA-G isoforms expressed in clear cell renal cell carcinoma patients

Immune checkpoints are powerful inhibitory molecules that promote tumor survival. Their blockade is now recognized as providing effective therapeutic benefit against cancer. Human leukocyte antigen G (HLA-G), a recently identified immune checkpoint, has been detected in many types of primary tumors and metastases, in malignant effusions as well as on tumor-infiltrating cells, particularly in patients with clear cell renal cell carcinoma (ccRCC). Here, in order to define a possible anticancer therapy, we used a molecular approach based on an unbiased strategy that combines transcriptome determination and immunohistochemical labeling, to analyze in-depth the HLA-G isoforms expressed in these tumors. We found that the expression of HLA-G is highly variable among tumors and distinct areas of the same tumor, testifying a marked inter- and intratumor heterogeneity. Moreover, our results generate an inventory of novel HLA-G isoforms which includes spliced forms that have an extended 5'-region and lack the transmembrane and alpha-1 domains. So far, these isoforms could not be detected by any method available and their assessment may improve the procedure by which tumors are analyzed. Collectively, our approach provides the first extensive portrait of HLA-G in ccRCC and reveals data that should prove suitable for the tailoring of future clinical applications.

Bronchial Epithelial Cells from Asthmatic Patients Display Less Functional HLA-G Isoform Expression

Not all asthmatic patients adequately respond to current available treatments, such as inhaled corticosteroids or omalizumab^®. New treatments will aim to target the bronchial epithelium-immune response interaction using different pathways. HLA-G is involved in immunomodulation and may promote epithelial cell differentiation and proliferation. HLA-G protein has several isoforms generated by alternative splicing that might have differential functionalities. HLA-G protein expression and genetic polymorphisms have been reported to be associated with asthma. Our hypothesis is that bronchial epithelium from asthmatic patients displays less functional HLA-G isoforms. HLA-G transcriptional isoforms were quantified by real-time PCR in human bronchial epithelium cells (HBEC) grown in air-liquid interface culture obtained from five healthy controls (HC), seven patients with mild asthma (MA), and seven patients with severe asthma (SA). They were re-differentiated, and IL-13 exposure was used as a proxy for a pro-inflammatory cytokine. HLA-G protein expression was assessed by western blot analysis. HLA-G allele was typed by direct sequencing. Our results showed that both MA and SA display less functional HLA-G isoforms than HC (p < 0.05); in vitro HBEC re-differentiation from SA displays a particular isoform expression profile compared to MA and HC (p = 0.03); HLA-G*01:06 frequency in MA and SA was significantly higher than in the healthy population (p = 0.03 and p < 0.001, respectively); and IL-13 exposure had no impact on HLA-G expression. Our results support that an impaired expression of HLA-G isoforms in asthmatic patients could contribute to the loss of inflammation control and epithelium structural remodeling. Therefore, HLA-G might be an interesting alternative target for asthmatic patients not adequately responding to current drugs.

HLA-F coding and regulatory segments variability determined by massively parallel sequencing procedures in a Brazilian population sample

Human Leucocyte Antigen F (HLA-F) is a non-classical HLA class I gene distinguished from its classical counterparts by low allelic polymorphism and distinctive expression patterns. Its exact function remains unknown. It is believed that HLA-F has tolerogenic and immune modulatory properties. Currently, there is little information regarding the HLA-F allelic variation among human populations and the available studies have evaluated only a fraction of the HLA-F gene segment and/or have searched for known alleles only. Here we present a strategy to evaluate the complete HLA-F variability including its 5' upstream, coding and 3' downstream segments by using massively parallel sequencing procedures. HLA-F variability was surveyed on 196 individuals from the Brazilian Southeast. The results indicate that the HLA-F gene is indeed conserved at the protein level, where thirty coding haplotypes or coding alleles were detected, encoding only four different HLA-F full-length protein molecules. Moreover, a same protein molecule is encoded by 82.45% of all coding alleles detected in this Brazilian population sample. However, the HLA-F nucleotide and haplotype variability is much higher than our current knowledge both in Brazilians and considering the 1000 Genomes Project data. This protein conservation is probably a consequence of the key role of HLA-F in the immune system physiology.

Promoter methylation and mRNA expression of HLA-G in relation to HLA-G protein expression in colorectal cancer

Expression of human leukocyte antigen-G (HLA-G) is a suggested mechanism used by tumor cells to escape from host immune recognition and destruction. Advances in the field have made it evident that HLA-G is expressed in different types of malignancies including colorectal cancer (CRC). We analyzed HLA-G expression in 21 low passage CRC cell lines. The level of DNA methylation of the HLA-G gene and the presence of mRNA encoding HLA-G was measured. Moreover, HLA-G protein expression was determined by flow cytometry and immunohistochemistry (IHC). IHC was performed with three different monoclonal antibodies (mAbs) (4H84, MEM-G/1 and MEM-G/2). In addition, HLA-G protein expression was measured in matching primary tumor tissues. RNA analysis using RT-PCR followed by sequencing in 6 samples indicated strong homology of the PCR product with HLA-G3 in 5 samples. In accordance, in none of the cell lines, HLA-G1 expression was detected by flow-cytometry. Furthermore, no association between HLA-G DNA methylation patterns and HLA-G mRNA expression was observed. In addition, different immunohistochemical staining profiles among various anti-HLA-G mAbs were observed. In conclusion, the results of this study show that the HLA-G3 isoform was expressed in some of the CRC cell lines irrespective of the level of DNA methylation of HLA-G.

HLA-G as an Inhibitor of Immune Responses

HLA-G is a nonclassical human leukocyte antigen (HLA) class I molecule which plays important tolerogenic functions in various physiological and pathological situations such as fetus and transplant acceptance, and immune escaping of virus-infected and malignant cells. Here we describe a method, which allows for studying cell surface expression of HLA-G using specific antibodies with flow cytometry analysis.

HLA-G and MHC Class II Protein Expression in Diffuse Large B-Cell Lymphoma

The expression of human leukocyte antigen-G (HLA-G) and HLA class II protein was studied by immunohistochemical staining of lymph nodes from 148 patients with diffuse large B-cell lymphoma (DLBCL) and related to the clinical course of the disease. Negative HLA-G expression was associated with a lower probability of achieving a complete remission (p = 0.04). Patients with negative HLA-G expression tended towards a lower 3-year overall survival (OS) rate compared to those with positive expression of HLA-G (p = 0.08). When restricting the analysis to patients receiving chemotherapy with rituximab, the estimated 3-year OS rate of patients with positive HLA-G expression was 73.3 % compared with 47.5 % (p = 0.03) in those with negative expression. Patients with negative HLA class II expression presented a lower 3-year OS rate compared to subjects with positive expression (p = 0.04). The loss of HLA class II expression (p = 0.05) and belonging to the intermediate high/high IPI risk group (p = 0.001) independently increased the risk of death. HLA class II expression also retained its prognostic value in patients receiving rituximab; the 3-year OS rate was 65.3 % in patients with positive HLA class II expression versus 29.6 % (p = 0.04) in subjects that had loss of HLA class II expression. To our knowledge, for the first time, the expression of HLA-G protein in DLBCL and its association with the clinical course of the disease was demonstrated. Moreover, the link between losing HLA class II protein expression and poor survival of patients treated with immunochemotherapy was confirmed.

Lesion HLA-G5/-G6 isoforms expression in patients with ovarian cancer

HLA-G is an immune tolerant with seven isoforms. HLA-G expression was observed to be associated with tumor cell immune escaping, invasion and metastasis, and with poor prognosis in cancer patients. Different types of HLA-G isoforms could be expressed in clinical settings when meet different cellular and environmental conditions. Lesion total HLA-G expression detected by the monoclonal antibody (mAb) 4H84 was widely investigated in previous studies, while specific HLA-G isoforms such as HLA-G5/-G6 remains to be clarified. In this study, 118 primary ovarian cancer lesions were probed with mAb 5A6G7 which recognizes HLA-G5/-G6 was performed by immunohistochemistry. Data showed that HLA-G5/-G6 was expressed in 79.7% (94/118) of these ovarian cancer lesions, where HLA-G5/-G6 expression was observed in 75.7% (53/70) serous, 63.6% (7/11) mucinous cystadenocarcinoma and in 100% (11/11) endometrioid adenocarcinoma, in 85.7% (6/7) clear cell carcinoma, 100% (10/10) sex cord-stromal tumor and 77.8% (7/9) germ cell tumors. However, lesion HLA-G5/-G6 expression was unrelated to histological type, patient age, FIGO stage and patient survival. Unlike total HLA-G expression, no clinical significance of HLA-G5/-G6 expression in ovarian cancer lesion was observed in this study. Our findings indicated that different HLA-G isoforms might have different biological functions in malignancies.

Significance of tumour cell HLA-G5/-G6 isoform expression in discrimination for adenocarcinoma from squamous cell carcinoma in lung cancer patients

Human leucocyte antigen (HLA)-G has seven isoforms, of which HLA-G1-G4 are membrane-bound and HLA-G5-G7 are soluble. Previous studies reinforced HLA-G expression was strongly related to poor prognosis in different types of cancers. Among these studies, the monoclonal antibody (mAb) 4H84 was used which detects all HLA-G isoform heavy chain; unfortunately, leaves the specific types of isoforms expressed in lesions undistinguished and its clinical significance needs to be clarified. To explore clinical significance of lesion soluble HLA-G (sHLA-G) in non-small-cell lung cancer (NSCLC), mAb 5A6G7 recognizing HLA-G5/-G6 molecules was used. Tumour cell sHLA-G expression in 131 primary NSCLC lesions (66 squamous cell carcinoma, 55 adenocarcinoma and 10 adenosquamous carcinoma) were analysed with immunohistochemistry. Data showed that sHLA-G expression was observed in 34.0% (45/131) of the NSCLC lesions, which was unrelated to patient age, sex, lymph nodal status, tumour-node-metastasis stage and patient survival. However, tumour cell sHLA-G expression in lesions was predominately observed in adenocarcinoma lesions (73.0%, 40/55) which was significantly higher than that in squamous cell carcinoma (6.0%, 4/66) and adenosquamous carcinoma lesions (10.0%, 1/10, P < 0.001). The area under the receiver operating characteristic curve for lesion sHLA-G was 0.833 (95% CI: 0.754-0.912, P < 0.001) for adenocarcinoma versus squamous cell carcinoma. Our findings for the first time showed that tumour cell sHLA-G was predominately expressed in lung adenocarcinoma, which could be a useful biomarker to discriminate adenocarcinoma from squamous cell carcinoma in NSCLC patients.

Increased human leukocyte antigen-G expression at the maternal-fetal interface is associated with preterm birth

Abstract Objective: The maternal-fetal interface must modulate immune function to allow tolerance of fetal cells while still reacting to pathogens to suppress infection. Human leukocyte antigen-G (HLA-G) is a class Ib major histocompatibility complex protein involved in maternal-fetal tolerance. We posited that alterations in placental HLA-G expression predispose women to preterm birth. The aim of this study was to compare HLA-G expression in the maternal-fetal interface of term versus preterm human placentas.

METHODS

We performed a cross-sectional study of specimens from the basal plate of the human placenta from women enrolled in a tissue specimen and clinical data consortium. Immunohistochemistry with digital microscopic analysis was used to quantify HLA-G protein expression in the basal plate from preterm and term placentas.

RESULTS

Preterm birth <37 weeks occurred in 29.5% of 149 singleton pregnancies. HLA-G-positive cells occupied one-third of the basal plates, and the HLA-G-positive area was increased by 14% in placentas from preterm births than in those from term births (32.1% in term placentas versus 36.6% in preterm placentas).

CONCLUSION

Although HLA-G is required for maternal tolerance of the semi-allogeneic fetus, higher levels of HLA-G expression at the maternal-fetal interface is associated with preterm birth.

Role of non-classical MHC class I molecules in cancer immunosuppression

Growing neoplasms employ various mechanisms to evade immunosurveillance. The expression of non-classical MHC class I molecules by both immune and malignant cells in the tumor microenvironment constitute of the strategies used by tumors to circumvent the cytotoxic activity of effector cells of the immune system. The overexpression of HLA-G, -E, and -F is a common finding across a variety of malignancies. However, while the presence of HLA-G and HLA-E has been recently correlated with poor clinical outcome, information on the clinicopathological significance of HLA-F is limited. In the present review, we summarize studies on non-classical MHC class I molecules with special emphasis on their role in the modulation of anticancer immune responses.

Full-length HLA-G1 and truncated HLA-G3 differentially increase HLA-E surface localization

Human leukocyte antigen (HLA)-E plays a role in immune tolerance induction and its transport to the cell surface is limited and dependent on the availability of HLA class I signal peptide. The role of HLA-G in regulating HLA-E surface localization remains controversial. The aim of our study was to clarify whether full-length and truncated HLA-G isoforms regulate HLA-E surface localization. Using a retroviral expression system and flow cytometric analysis, we found that surface HLA-E levels were significantly higher in HLA-G1 (34.1±4.4%, p<0.005) and -G3 (15.3±1.8%, p<0.04) versus empty vector (9.0±1.0%) transductants. Biotinylation and Western blot studies revealed HLA-E surface protein was increased by 4.5- and 1.3-fold in HLA-G1 and -G3 versus empty vector transductants. Although no significant differences in transcript and protein levels were detected between HLA-G1 and -G3 transductants, surface levels of HLA-G1 were 2.5-fold higher than HLA-G3 by flow cytometric analysis and Western blotting. Taken together, our data demonstrate that full-length HLA-G1 and truncated -G3 differentially increase HLA-E surface localization.

HLA-G1 and HLA-G5 active dimers are present in malignant cells and effusions: the influence of the tumor microenvironment

Dimers of the nonclassical HLA-G class I molecule have recently been shown to be active structures that mediate inhibition of NK-cell cytotoxic activity through interaction with the immunoglobulin-like transcript (ILT)-2 inhibitory receptor. However, this has only been proven in trophoblasts and HLA-G transfectants. Here, we document for the first time the existence of HLA-G dimers in cancer. Indeed, we identified both surface and soluble HLA-G dimers in tumor cells and malignant ascites respectively. Interestingly, factors from the tumor microenvironment, such as interferons, enhanced the formation of HLA-G dimers and increased the protection of tumors from NK cell-mediated lysis. These data emphasize the impact of HLA-G conformation on its efficiency at inhibiting the antitumor response and thus favoring tumor progression. In view of these results, the effect of the tumor microenvironment on upregulation of HLA-G function deserves particular attention when designing cancer immunotherapy protocols.

Multimeric structures of HLA-G isoforms function through differential binding to LILRB receptors

The non-classical Human leukocyte antigen G (HLA-G) differs from classical HLA class I molecules by its low genetic diversity, a tissue-restricted expression, the existence of seven isoforms, and immuno-inhibitory functions. Most of the known functions of HLA-G concern the membrane-bound HLA-G1 and soluble HLA-G5 isoforms, which present the typical structure of classical HLA class I molecule: a heavy chain of three globular domains α1-α2-α3 non-covalently bound to β-2-microglobulin (B2M) and a peptide. Very little is known of the structural features and functions of other HLA-G isoforms or structural conformations other than B2M-associated HLA-G1 and HLA-G5. In the present work, we studied the capability of all isoforms to form homomultimers, and investigated whether they could bind to, and function through, the known HLA-G receptors LILRB1 and LILRB2. We report that all HLA-G isoforms may form homodimers, demonstrating for the first time the existence of HLA-G4 dimers. We also report that the HLA-G α1-α3 structure, which constitutes the extracellular part of HLA-G2 and HLA-G6, binds the LILRB2 receptor but not LILRB1. This is the first report of a receptor for a truncated HLA-G isoform. Following up on this finding, we show that the α1-α3-Fc structure coated on agarose beads is tolerogenic and capable of prolonging the survival of skin allografts in B6-mice and in a LILRB2-transgenic mouse model. This study is the first proof of concept that truncated HLA-G isoforms could be used as therapeutic agents.

Enhancement of the immunosuppressive effect of human adipose tissue-derived mesenchymal stromal cells through HLA-G1 expression

BACKGROUND AIMS

Mesenchymal stromal cells (MSC) from several tissues have immunomodulatory properties that involve various immunosuppressive molecules. An example is human leukocyte antigen (HLA)-G, a non-classical major histocompatibility complex (MHC) class I molecule that induces tolerance via interactions with inhibitory receptors present on major immune effector cells. Recently, the molecular mechanisms that regulate MSC-mediated immunosuppression have come under investigation. Our goal was to determine whether HLA-G plays a crucial role in immunosuppression and whether human adipose tissure (hAT) MSC can be used as a tool for biologic immunosuppression with HLA-G in transplantation.

METHODS

MSC were characterized by fluorescence-activated cell sorting (FACS) analysis, reverse transcriptase (RT)-polymerase chain reaction (PCR) and staining for differentiation. The immunogenicity and immunomodulatory effects of MSC were monitored by peripheral blood mononuclear cell (PBMC) proliferation assay with or without phytohemagglutinin (PHA) stimulation. Stable expression of HLA-G1 in MSC was done using a lentiviral system. Results. MSC from different tissues had similar morphology, immunophenotypic characters and differentiation potential. We also found that the immunosuppressive effect of MSC was monitored along with their endogenous HLA-G mRNA and protein levels. Stable expression of HLA-G1 appeared to enhance the immunosuppressive effect of hAT MSC, and the function of HLA-G1 was significantly decreased by HLA-G antagonistic antibody in PBMC proliferation assays.

CONCLUSIONS

Although the HLA-G molecule is not the sole factor for MSC-mediated immunosuppression, our data provide evidence that HLA-G plays an important role in immunosuppression and that hAT MSC can be used as a tool for biologic immunosuppression during transplantation procedures.

Human leukocyte antigen-G expression is associated with a poor prognosis in patients with esophageal squamous cell carcinoma

Human leukocyte antigen (HLA)-G inhibits functions of immune component cells and promotes malignant cells evading from antitumor immunity. We investigated the clinical relevance of HLA-G expression in esophageal squamous cell carcinoma (ESCC). In our study, HLA-G expression in 79 primary ESCC lesions and corresponding adjacent normal tissues were analyzed with immunohistochemistry. Soluble HLA-G (sHLA-G) in plasma was detected with enzyme-linked immunosorbent assay (ELISA) in 41 ESCC patients (including 19 case-matched lesions and plasma samples) and in 153 normal healthy controls. HLA-G expression was observed in 65.8% (52/79) of the ESCC lesions but not in adjacent normal esophageal tissues. HLA-G expression was more frequently observed in patients with advanced disease stage (III/IV vs. I/II, p = 0.01). Patients with HLA-G expression had a significantly worse survival, and HLA-G could be an independent prognostic factor. sHLA-G levels in plasma were significantly increased in patients compared to normal controls (median: 152.4 U/ml vs. 8.9 U/ml, p < 0.001). The area under receiver-operating characteristic (ROC) curve for sHLA-G in plasma was 0.992. However, no significant correlation was found between sHLA-G in plasma and clinical parameters studied. In conclusion, our findings indicated that HLA-G expression in ESCC is associated with poor survival and could be a prognostic indicator. Furthermore, increased levels of sHLA-G in plasma might be a useful preoperative biomarker for diagnosis.

HLA-E and HLA-G expression in classical HLA class I-negative tumors is of prognostic value for clinical outcome of early breast cancer patients

Nonclassical HLAs, HLA-E and HLA-G, are known to affect clinical outcome in various tumor types. We examined the clinical impact of HLA-E and HLA-G expression in early breast cancer patients, and related the results to tumor expression of classical HLA class I. Our study population (n = 677) consisted of all early breast cancer patients primarily treated with surgery in our center between 1985 and 1995. Tissue microarray sections of arrayed tumor and normal control material were immunohistochemically stained for HLA-E and HLA-G. For evaluation of HLA-E and HLA-G and the combined variable, HLA-EG, a binary score was used. Expression of classical HLA class I molecules was determined previously. HLA-E, HLA-G, and HLA-EG on breast tumors were classified as expression in 50, 60, and 23% of patients, respectively. Remarkably, only in patients with loss of classical HLA class I tumor expression, expression of HLA-E (p = 0.027), HLA-G (p = 0.035), or HLA-EG (p = 0.001) resulted in a worse relapse-free period. An interaction was found between classical and nonclassical HLA class I expression (p = 0.002), suggestive for a biological connection. We have demonstrated that, next to expression of classical HLA class I, expression of HLA-E and HLA-G is an important factor in the prediction of outcome of breast cancer patients. These results provide further evidence that breast cancer is immunogenic, but also capable of evading tumor eradication by the host's immune system, by up- or downregulation of HLA class Ia and class Ib loci.

Biology of HLA-G in cancer: a candidate molecule for therapeutic intervention?

Although the expression of the non-classical HLA class I molecule HLA-G was first reported to be restricted to the fetal-maternal interface on the extravillous cytotrophoblasts, the distribution of HLA-G in normal tissues appears broader than originally described. HLA-G expression was found in embryonic tissues, in adult immune privileged organs, and in cells of the hematopoietic lineage. More interestingly, under pathophysiological conditions HLA-G antigens may be expressed on various types of malignant cells suggesting that HLA-G antigen expression is one strategy used by tumor cells to escape immune surveillance. In this article, we will focus on HLA-G expression in cancers of distinct histology and its association with the clinical course of diseases, on the underlying molecular mechanisms of impaired HLA-G expression, on the immune tolerant function of HLA-G in tumors, and on the use of membrane-bound and soluble HLA-G as a diagnostic or prognostic biomarker to identify tumors and to monitor disease stage, as well as on the use of HLA-G as a novel therapeutic target in cancer.

Aberrant human leucocyte antigen-G expression and its clinical relevance in hepatocellular carcinoma

The clinical relevance of human leucocyte antigen-G (HLA-G) has been postulated in malignancies. Hepatocellular carcinoma (HCC) is a major contributor to cancer incidence and mortality worldwide; however, potential roles of HLA-G in HCC remain unknown. In the current study, HLA-G expression in 219 primary HCC lesions and their adjacent non-tumourous samples was analysed with immunohistochemistry. Correlations among HLA-G expression and various clinical parameters were evaluated. Meanwhile, functional analysis of transfected cell surface HLA-G expression on NK cell cytolysis was performed in vitro. HLA-G expression was observed in 50.2% (110/219) of primary HCC lesions, and undetectable in corresponding adjacent normal liver tissues. HLA-G expression was found in 37.8%, 41.9% and 71.4% of stage I, II and III HCC lesions, respectively. Data revealed that HLA-G expression in HCC was strongly correlated to advanced disease stage (I versus II, P= 0.882; I versus III, P= 0.020; II versus III, P= 0.037). HLA-G expression was also more frequently observed in elder patients (≥median 52 years, 57.5%versus 43.4%, P= 0.004). Meanwhile, plasma soluble HLA-G in HCC patients was significantly higher than that in normal controls (median, 92.49U/ml versus 9.29U/ml, P= 0.000). Functional assay showed that HLA-G expression in transfected cells could dramatically decrease the NK cell cytolysis (P= 0.036), which could be markedly restored by the blockade of HLA-G (P= 0.004) and its receptor ILT2 (P= 0.019). Our finding indicated that HLA-G expression was strongly correlated to advanced disease stage, and more frequently observed in elder patients. Its relevance to HCC progression might be result from the inhibition of NK cell cytolysis.

Natural killer cell killing of acute myelogenous leukemia and acute lymphoblastic leukemia blasts by killer cell immunoglobulin-like receptor-negative natural killer cells after NKG2A and LIR-1 blockade

Although the study of natural killer (NK) cell alloreactivity has been dominated by studies of killer cell immunoglobulin-like receptors (KIRs), we hypothesized that NKG2A and LIR-1, present on 53% +/- 13% and 36% +/- 18% of normal NK cells, respectively, play roles in the NK cell killing of primary leukemia targets. KIR(-) cells, which compose nearly half of the circulating NK cell population, exhibit tolerance to primary leukemia targets, suggesting signaling through other inhibitory receptors. Both acute myelogenous leukemia and acute lymphoblastic leukemia targets were rendered susceptible to lysis by fresh resting KIR(-) NK cells when inhibitory receptor-major histocompatibility class I interactions were blocked by pan-HLA antibodies, demonstrating that these cells are functionally competent. Blockade of a single inhibitory receptor resulted in slightly increased killing, whereas combined LIR-1 and NKG2A blockade consistently resulted in increased NK cell cytotoxicity. Dual blockade of NKG2A and LIR-1 led to significant killing of targets by resting KIR(-) NK cells, demonstrating that this population is not hyporesponsive. Together these results suggest that alloreactivity of a significant fraction of KIR(-) NK cells is mediated by NKG2A and LIR-1. Thus strategies to interrupt NKG2A and LIR-1 in combination with anti-KIR blockade hold promise for exploiting NK cell therapy in acute leukemias.

Myocardial HLA-G reliably indicates a low risk of acute cellular rejection in heart transplant recipients

BACKGROUND

Human leukocyte antigen-G (HLA-G), a non-classical MHC I protein with restricted tissue expression, plays an essential role in immune tolerance and has been negatively associated with acute and chronic rejection after heart transplantation. We assessed myocardial HLA-G expression in adult heart transplant patients in an attempt to determine the value of this protein in identifying patients with a low risk of acute cellular rejection.

METHODS

Two groups of patients were included in this study. Group A (non-rejecting) included 29 patients who had no moderate or severe rejection episodes (ISHLT Grade <2R) post-transplant. Group B (rejecting) included 38 patients with at least two moderate or severe rejection episodes (Grade >or=2R) within a 1-year period. Expression of HLA-G in three myocardial biopsies post-transplant from each patient was determined through immunohistochemical staining.

RESULTS

In Group A, 86% of patients had HLA-G(+) biopsies compared with 11% of patients in Group B (p < 0.001; sensitivity 86%, specificity 87%). Whereas 60% of non-rejecting HLA-G(+) patients had at least two positive biopsies, all rejecting HLA-G(+) patients had only one positive biopsy.

CONCLUSIONS

There is a significant negative association between myocardial HLA-G expression and acute cellular rejection after cardiac transplantation. Detection of HLA-G appears to reliably indicate a low risk of developing moderate or severe allograft rejection and may, subsequently, allow for a reduced immunosuppressive regimen.

HLA-G protein expression as a potential immune escape mechanism in classical Hodgkin's lymphoma

Classical Hodgkin's lymphoma (cHL) is characterized by the presence of an abundant reactive infiltrate, lacking effective cytotoxic responses. Especially in Epstein-Barr virus (EBV)-negative cHL, the neoplastic Hodgkin-Reed-Sternberg (HRS) cells have lost protein expression of major histocompatibility complex (MHC) class I, enabling escape from cytotoxic T lymphocyte (CTL) responses. However, downregulation of MHC class I generally induces natural killer (NK) cell activation. The paucity of NK cells in the reactive infiltrate of cHL and the systemic NK cell deficiency observed in cHL patients led us to investigate the expression of human leukocyte antigen (HLA)-G, which is known to inhibit NK-cell- and CTL-mediated cytotoxicity. By immunohistochemistry, HLA-G protein was expressed by HRS cells in 54% (95/175) of cHL cases. This expression was associated with absence of MHC class I on the cell surface of HRS cells (P < 0.001) and EBV-negative status (P < 0.001). Previously, genetic markers located in the proximity of the HLA-A and HLA-G genes had been shown to be associated with susceptibility to EBV-positive cHL. In the present study, these markers associated with MHC class I protein expression but not with presence of HLA-G. Our results suggest that induction of HLA-G protein expression in HRS cells contributes to the modulation of immune responses observed in cHL.

HLA-G: from biology to clinical benefits

The relevance of the nonclassical human leukocyte antigen (HLA) class I molecule HLA-G in human physiological and pathological contexts has been the center of intense investigation. In light of the recent advances, we report here the clinical implications of HLA-G as a tolerogenic molecule promoting uterine implantation of the embryo or acceptance of solid allografts while allowing the evasion of tumors or viruses from the immune response. These recent findings are important in terms of clinical benefits at both diagnostic and therapeutic levels.

Role of HLA-G in innate immunity through direct activation of NF-κB in natural killer cells

HLA-G is a non-classical HLA class I molecule involved in immunotolerance. HLA-G protects the fetus from maternal immune recognition and promotes allograft acceptance and tumor escape. Its low polymorphism and primary function, which is not peptide presentation to T lymphocytes, led us to compare the signal transduced after interaction between HLA-G and its receptor to those of innate immunity receptors with their ligands. We investigated the role of HLA-G in the classical NF-kappaB pathway in natural killer (NK) cells, which is the major pathway activated by innate immunity receptors. In NK cells stimulated with HLA-G1-expressed cells, we demonstrate that HLA-G induces the phosphorylation and the degradation of IkappaBalpha leading to nuclear translocation of NF-kappaB. This effect is independent of the presence of ILT-2 receptors and is still observed using a peptide corresponding to the alpha-1 domain of HLA-G. All these data support an unsuspected role for HLA-G in innate immunity by activating classical NF-kappaB pathway in NK cells.

Soluble human leukocyte antigen-G5 in septic shock: marked and persisting elevation as a predictor of survival

OBJECTIVE

Although it is established that septic shock induces immunosuppression, the mechanisms for this phenomenon remain poorly understood. Human leukocyte antigen-G exerts strong inhibitory effects that are directed at different arms of the immune system. The main objective of the current study was to measure human leukocyte antigen-G (soluble and membrane proteins) in septic shock.

DESIGN

Observational study.

SETTING

Adult intensive care units in a university hospital.

PATIENTS

Sixty-four consecutive patients with septic shock (7 days of follow-up).

INTERVENTIONS

None.

MEASUREMENTS AND MAIN RESULTS

We measured plasma human leukocyte antigen-G5 (with enzyme linked immunosorbent assay) and human leukocyte antigen-G1 (with flow cytometry) expression on circulating leukocytes. As early as days 1-2 after the onset of shock, we observed a marked elevation of soluble human leukocyte antigen-G5 in patients: 60 ng/mL (34-146) as median (Q1-Q3) (reference values <5 ng/mL). This increase was stable over time. Most important, we also found at days 1-2 a significant difference between survivors and nonsurvivors: 109 ng/mL (43-183) vs. 37 ng/mL (19-61), respectively (p = .003). This difference remained significant until day 7. Receiver operating characteristic curve analysis showed that human leukocyte antigen-G5 was a good predictor of outcome (areas under curves: 0.76 and 0.84 at days 1-2 and days 3-4, respectively, p < .001). Adjusted logistic regression analysis suggested that human leukocyte antigen-G5 at days 3-5 was a better prognostic marker than decreased monocyte human leukocyte antigen-DR and/or severity score.

CONCLUSIONS

The present results show a marked elevation of soluble human leukocyte antigen-G5 protein during septic shock. We may hypothesize that given its potent inhibitory properties and its association with survival, human leukocyte antigen-G5 has an important role in the numerous negative feedback signals that limit the process of inflammation during septic shock.

Cellular co-localization of intron-4 containing mRNA and HLA-G soluble protein in melanoma analyzed by fluorescence in situ hybridization

HLA-G5, -G6, and -G7 soluble isoforms of the immunosuppressive HLA-G molecule are produced from the splice variants of the primary HLA-G mRNA transcript containing intron-4 that encodes a specific 21 amino acids tail. In particular, HLA-G5 interacts with the inhibitory ILT2/4 and KIR2DL4 receptors that are expressed on immune cells. Acquisition of soluble HLA-G in the microenvironment may turn a HLA-G non-expressing cell into a HLA-G-bearing one. To address the question of how to distinguish cells that express soluble HLA-G generated by alternative splicing from those that have acquired HLA-G, we have developed a method capable of detecting intron-4 containing mRNA and protein in situ simultaneously. M8 melanoma cell line either transfected or not with HLA-G5 cDNA was analyzed by indirect immunofluorescence confocal microscopy using double staining with a HLA-G intron-4 digoxygenin labeled probe along with a monoclonal antibody directed against the 21 amino acid tail. The combined fluorescence in situ hybridization was also used on the HLA-G-positive choricarcinoma cell line JEG-3. This method would be helpful to follow-up bona fide HLA-G expression in a heterogeneous cell population and to elucidate the mechanisms underlying soluble HLA-G mediated immune modulation in physiological conditions such as pregnancy and pathophysiological situations such as cancer.

Modulation of HLA-G and HLA-E expression in human neuronal cells after rabies virus or herpes virus simplex type 1 infections

Human Leukocyte Antigen (HLA)-G and E are nonclassical human MHC class I molecules. They may promote tolerance leading to virus and tumor immune escape. We recently described that the herpes simplex virus type 1 (HSV-1), a neurotropic virus inducing chronic infection and neuron latency, and rabies virus (RABV), a neuronotropic virus triggering acute neuron infection, up-regulate HLA-G expression in human neurons (NT2-N). Surface expression was only detected after RABV infection. We investigated here whether RABV and HSV-1 up-regulate HLA-E expression in human neuronal precursors (Ntera-2D/1). We found that RABV, not HSV-1, up-regulates HLA-E expression, nevertheless HLA-E could not be detected on the surface of RABV-infected Ntera-2D/1. Altogether these data suggest that HLA-G and not HLA-E could contribute to the immune escape of RABV. In contrast, there was no evidence that these molecules are used by latent HSV-1 infection. Thus, neurotropic viruses that escape the host immune response totally (RABV) or partially (HSV-1) regulate HLA-G expression on human neuronal cells differentially.

HLA-G, -E and -F: allelism, function and evolution

The major histocompatibility complex class I genes comprise a bunch of classical genes (A, B, C), non-classical genes (E, F and G), pseudogenes and truncated genes. MHC-E, -F and -G are now considered immune "tolerization" molecules, which not only interact with NK cells but with T lymphocyte subsets and other cells and have a role in fetus acceptation. A strong positive directional selection is acting for maintaining the observed low polymorphism on E, F and G loci in human and apes. Invariance must be important for this non-classical class I proteins function.

Expression and release of HLA-E by melanoma cells and melanocytes: potential impact on the response of cytotoxic effector cells

HLA-E are nonclassical MHC molecules with poorly characterized tissue distribution and functions. Because of their capacity to bind the inhibitory receptor, CD94/NKG2A, expressed by NK cells and CTL, HLA-E molecules might play an important role in immunomodulation. In particular, expression of HLA-E might favor tumor cell escape from CTL and NK immunosurveillance. To address the potential role of HLA-E in melanoma immunobiology, we assessed the expression of these molecules ex vivo in human melanoma biopsies and in melanoma and melanocyte cell lines. Melanoma cell lines expressed no or low surface, but significant intracellular levels of HLA-E. We also report for the first time that some of them produced a soluble form of this molecule. IFN-gamma significantly increased the surface expression of HLA-E and the shedding of soluble HLA-E by these cells, in a metalloproteinase-dependent fashion. In contrast, melanocyte cell lines constitutively expressed HLA-E molecules that were detectable both at the cell surface and in the soluble form, at levels that were poorly affected by IFN-gamma treatment. On tumor sections, a majority of tumor cells of primary, but a low proportion of metastatic melanomas (30-70 and 10-20%, respectively), expressed HLA-E. Finally, HLA-E expression at the cell surface of melanoma cells decreased their susceptibility to CTL lysis. These data demonstrate that HLA-E expression and shedding are normal features of melanocytes, which are conserved in melanoma cells of primary tumors, but become dependent on IFN-gamma induction after metastasis. The biological significance of these findings warrants further investigation.

Expression of HLA-G in malignant mesothelioma and clinically aggressive breast carcinoma

The aim of the present study was to evaluate HLA-G expression in breast carcinoma and malignant mesothelioma (MM). Malignant breast carcinoma effusions (46) and corresponding solid tumors (39) and 104 MM (26 effusions, 78 solid tumors) were analyzed using immunohistochemistry (IHC). HLA-G protein and mRNA expression were further studied using immunoblotting (IB) and RT-PCR. HLA-ABC expression was analyzed using flow cytometry (FCM). IHC showed predominantly focal HLA-G expression in 12 of 46 (26%) breast carcinoma effusions and 16 of 39 (41%) solid lesions. In MM, 20 of 78 (26%) solid lesions and 14 of 26 (54%) effusions were focally HLA-G positive. Expression in MM was higher in effusions (p=0.008). IB showed more frequent HLA-G expression in MM compared with breast carcinoma effusions, while RT-PCR showed HLA-G mRNA expression in both tumors. FCM showed conserved HLA-ABC expression in 15 of 15 effusions. Breast cancer patients with HLA-G-positive tumor cells had shorter disease-free survival (mean 37 vs 85, median 25 vs 31 months), though not significantly (p=0.14). In conclusion, HLA-G is focally expressed in MM and breast carcinoma, while HLA-ABC expression is conserved. However, the up-regulated expression of HLA-G in MM effusions and its possible association with shorter disease-free survival in advanced stage of breast carcinoma suggest a possible role in immune response evasion in some tumors.

Evidence to Support the Role of HLA-G5 in Allograft Acceptance through Induction of Immunosuppressive/ Regulatory T Cells

The soluble HLA-G5 isoform encoded by intron-4 retaining spliced transcript has been previously detected in vivo in sera and grafts from transplanted patients who had significantly better graft acceptance. These findings led us to investigate the role of HLA-G5 in tolerance induction in vitro and its biological relevance in allograft acceptance in vivo. We demonstrated that engagement of Ig-like transcript-2 and Ig-like transcript-4 receptors by HLA-G5 is involved in inhibition of T cell alloproliferative responses. Naive T cells sensitized in vitro with HLA-G5, for as little as 18 h, 1) lost their ability to respond to subsequent allogeneic stimulus, and 2) acquired regulatory properties because they inhibited the reactivity of other T cells. These HLA-G5-induced T cells act in an Ag-nonspecific fashion and through soluble factors. Biological relevance was provided by ex vivo analyzes of samples from liver-kidney cotransplanted patients who had high HLA-G5 serum levels and no graft rejection. We showed that addition of HLA-G5-containing sera from these patients inhibited T cell alloresponses and that serum HLA-G5 was responsible for this inhibition. Notably, PBMC from transplanted patients exposed to high levels of circulating HLA-G5 did not respond to allostimulation and inhibited alloreactivity of other T cells. These results demonstrate that HLA-G5-mediated tolerance involves the induction of immunosuppressive T cells. These findings provide evidence supporting the tolerogenic properties of HLA-G and emphasize its potential application as a relevant therapeutic candidate capable of limiting allograft rejection.