Characterization of monoclonal antibodies recognizing HLA-G or HLA-E: new tools to analyze the expression of nonclassical HLA class I molecules

Conformational Alterations of the Cell Surface of Monomeric and Dimeric β2m-Free HLA-I (Proto-HLA) May Enable Novel Immune Functions in Health and Disease

Human leukocyte antigens (HLAs) are polymorphic glycoproteins expressed on the cell surface of nucleated cells and consist of two classes, HLA class I and HLA class II. In contrast, in mice, these molecules, known as H-2, are expressed on both nucleated cells and erythrocytes. HLA-I molecules (Face-1) are heterodimers consisting of a polypeptide heavy chain (HC) and a light chain, B2-microglobulin (B2m). The heterodimers bind to antigenic peptides and present them to the T-cell receptors of CD8+ cytotoxic T lymphocytes. The HCs can also independently emerge on the cell surface as B2m-free HC monomers without peptides (Face-2). Early investigators suggested that the occurrence of B2m-free HCs on the cell surface resulted from the dissociation of B2m from Face-1. However, others documented the independent emergence of B2m-free HCs (Face-2) from the endoplasmic reticulum (ER) to the cell surface. The clustering of such HC molecules on either the cell surface or on exosomes resulted in the dimerization of B2m-free HCs to form homodimers (if the same allele, designated as Face-3) or heterodimers (if different alleles, designated as Face-4). Face-2 occurs at low levels on the cell surface of several normal cells but is upregulated on immune cells upon activation by proinflammatory cytokines and other agents such as anti-CD3 antibodies, phytohemagglutinin, and phorbol myristate acetate. Their density on the cell surface remains high as long as the cells remain activated. After activation-induced upregulation, Face-2 molecules undergo homo- and heterodimerization (Face-3 and Face-4). Observations made on the structural patterns of HCs and their dimerization in sharks, fishes, and tetrapod species suggest that the formation of B2m-free HC monomers and dimers is a recapitalization of a phylogenetically conserved event, befitting the term Proto-HLA for the B2m-free HCs. Spontaneous arthritis occurs in HLA-B27+ mice lacking B2m (HLA-B27+ B2m-/-) but not in HLA-B27+ B2m+/+ mice. Anti-HC-specific monoclonal antibodies (mAbs) delay disease development. Some HLA-I polyreactive mAbs (MEM series) used for immunostaining confirm the existence of B2m-free variants in several cancer cells. The conformational alterations that occur in the B2m-free HCs enable them to interact with several inhibitory and activating receptors of cellular components of the innate (natural killer (NK) cells) and adaptive (T and B cells) immune systems. The NK cells express killer immunoglobulin-like receptors (KIRs), whereas leukocytes (T and B lymphocytes, monocytes/macrophages, and dendritic cells) express leukocyte immunoglobulin-like receptors (LILRs). The KIRs and LILRs include activating and inhibitory members within their respective groups. This review focuses on the interaction of KIRs and LILRs with B2m-free HC monomers and dimers in patients with spondylarthritis. Several investigations reveal that the conformational alterations occurring in the alpha-1 and alpha-2 domains of B2m-free HCs may facilitate immunomodulation by their interaction with KIR and LILR receptors. This opens new avenues to immunotherapy of autoimmune diseases and even human cancers that express B2m-free HCs.

Diversity in the HLA-I Recognition of HLA-F Monoclonal Antibodies: HLA-F or HLA-Ib Monospecific, HLA-E or HLA-G Bispecific Antibodies with or without HLA-Ia Reactivity

Previous investigators have used various anti-HLA-F monoclonal antibodies (mAbs) to demonstrate that the tissue distribution of HLA-F is highly restricted. Notably, these mAbs differed in their immunodiagnostic capabilities. Specifically, mAbs Fpep1.1 and FG1 detected HLA-F intracellularly in B cells but not on the cell surface, whereas mAb 3D11 detected HLA-F on the cell surface. The presence of HLA-F on T cells was recognized by mAb FG1 but not by mAb Fpep1.1. mAb 3D11 detected HLA-F on the cell surface of activated B cells and on peripheral blood lymphocytes, but not on the normal cells. Importantly, mAb 3D11 revealed that HLA-F exists as a heavy chain (HC) monomer, rather than as an HC associated with B2m. Although these mAbs are believed to be specific to HLA-F, their monospecificity has not been formally established, which is critical for immunodiagnostic and therapeutic purposes. Previously, we investigated the diversity of HLA class I reactivities of anti-HLA-E mAbs using HLA-I coated multiplex bead assays on a Luminex platform. We reported that more than 80% of the HLA-E mAbs were cross-reactive with other HLA-I molecules, with exceptionally few truly HLA-E-monospecific mAbs. In the present investigation, we generated IgG mAbs against HCs of HLA-F in Balb/C mice and examined the cross-reactivity of anti-HLA-F mAbs with other HLA-I alleles using a multiplex bead assay on the Luminex platform. Beads coated with an array of HLA homo- and heterodimers of different HLA-Ia (HLA-A, HLA-B, and HLA-C) and Ib (HLA-E, HLA-F, and HLA-G) alleles were used to examine the binding of the anti-HLA-F mAbs. Only two mAbs were HLA-F monospecific, and five were HLA-Ib restricted. Several anti-HLA-F mAbs cross-reacted with HLA-E (n = 4), HLA-G (n = 3), HLA-Ia alleles (n = 9), HLA-G and HLA-Ia (n = 2), and HLA-Ib and HLA-Ia (n = 6). This monospecificity and polyreactivity were corroborated by the presence of HLA-F monospecific and HLA-I-shared sequences. This study emphasizes the need to monitor the mono-specificity of HLA-F for reliable immunodiagnostics and passive immunotherapy.

Cell Surface B2m-Free Human Leukocyte Antigen (HLA) Monomers and Dimers: Are They Neo-HLA Class and Proto-HLA?

Cell surface HLA-I molecules (Face-1) consist of a polypeptide heavy chain (HC) with two groove domains (G domain) and one constant domain (C-domain) as well as a light chain, B2-microglobulin (B2m). However, HCs can also independently emerge unfolded on the cell surface without peptides as B2m-free HC monomers (Face-2), B2m-free HC homodimers (Face 3), and B2m-free HC heterodimers (Face-4). The transport of these HLA variants from ER to the cell surface was confirmed by antiviral antibiotics that arrest the release of newly synthesized proteins from the ER. Face-2 occurs at low levels on the normal cell surface of the lung, bronchi, epidermis, esophagus, breast, stomach, ilium, colorectum, gall bladder, urinary bladder, seminal vesicles ovarian epithelia, endometrium, thymus, spleen, and lymphocytes. They are upregulated on immune cells upon activation by proinflammatory cytokines, anti-CD3 antibodies, antibiotics (e.g., ionomycin), phytohemagglutinin, retinoic acid, and phorbol myristate acetate. Their density on the cell surface remains high as long as the cells remain in an activated state. After activation-induced upregulation, the Face-2 molecules undergo homo- and hetero-dimerization (Face-3 and Face-4). Alterations in the redox environment promote dimerization. Heterodimerization can occur among and between the alleles of different haplotypes. The glycosylation of these variants differ from that of Face-1, and they may occur with bound exogenous peptides. Spontaneous arthritis occurs in HLA-B27+ mice lacking B2m (HLA-B27+ B2m-/-) but not in HLA-B27+ B2m+/- mice. The mice with HLA-B27 in Face-2 spontaneous configuration develop symptoms such as changes in nails and joints, hair loss, and swelling in paws, leading to ankyloses. Anti-HC-specific mAbs delay disease development. Some HLA-I polyreactive mAbs (MEM series) used for immunostaining confirm the existence of B2m-free variants in several cancer cells. The upregulation of Face-2 in human cancers occurs concomitantly with the downregulation of intact HLAs (Face-1). The HLA monomeric and dimeric variants interact with inhibitory and activating ligands (e.g., KIR), growth factors, cytokines, and neurotransmitters. Similarities in the amino acid sequences of the HLA-I variants and HLA-II β-chain suggest that Face-2 could be the progenitor of both HLA classes. These findings may support the recognition of these variants as a neo-HLA class and proto-HLA.

Antibodies for β2-Microglobulin and the Heavy Chains of HLA-E, HLA-F, and HLA-G Reflect the HLA-Variants on Activated Immune Cells and Phases of Disease Progression in Rheumatoid Arthritis Patients under Treatment

Rheumatoid arthritis (RA) is a progressive, inflammatory, autoimmune, symmetrical polyarticular arthritis. It is characterized by synovial infiltration and activation of several types of immune cells, culminating in their apoptosis and antibody generation against “altered” autoantigens. β2-microglobulin (β2m)-associated heavy chains (HCs) of HLA antigens, also known as closed conformers (Face-1), undergo “alteration” during activation of immune cells, resulting in β2m-free structural variants, including monomeric open conformers (Face-2) that are capable of dimerizing as either homodimers (Face-3) or as heterodimers (Face-4). β2m-free HCs uncover the cryptic epitopes that can elicit antibodies (Abs). We report here the levels of IgM and IgG Abs against both β2m and HCs of HLA-E, HLA-F, and HLA-G in 74 RA patients receiving immunosuppressive drugs. Anti-β2m IgM was present in 20 of 74 patients, whereas anti-β2m IgG was found in only 8 patients. Abs against β2m would be expected if Abs were generated against β2m-associated HLA HCs. The majority of patients were devoid of either anti-β2m IgM or IgG but had Abs against HCs of different HLA-Ib molecules. The paucity of anti-β2m Abs in this cohort of patients suggests that Abs were developed against β2m-free HLA HCs, such as Face-2, Face-3, and Face-4. While 63 of 68 patients had IgG Abs against anti-HLA-F HCs, 36 and 50 patients showed IgG Ab reactivity against HLA-E and anti-HLA-G HCs, respectively. Evidently, anti-HLA-F HC Abs are the most predominant anti-HLA-Ib HC IgG Abs in RA patients. The incidence and intensity of Abs against HLA-E, HLA-F, and HLA-G in the normal control group were much higher than those observed in RA patients. Evidently, the lower level of Abs in RA patients points to the impact of the immunosuppressive drugs on these patients. These results underscore the need for further studies to unravel the nature of HLA-F variants on activated immune cells and synoviocytes of RA patients.

Peripheral HLA-G/ILT-2 immune checkpoint axis in acute and convalescent COVID-19 patients

The immunosuppressive non-classical human leukocyte antigen-G (HLA-G) can elicits pro-viral activities by down-modulating immune responses. We analysed soluble forms of HLA-G, IL-6 and IL-10 as well as on immune effector cell expression of HLA-G and its cognate ILT-2 receptor in peripheral blood obtained from hospitalised and convalescent COVID-19 patients. Compared with convalescents (N = 202), circulating soluble HLA-G levels (total and vesicular-bound molecules) were significantly increased in hospitalised patients (N = 93) irrespective of the disease severity. During COVID-19, IL-6 and IL-10 levels were also elevated. Regarding the immune checkpoint expression of HLA-G/ILT-2 on peripheral immune effector cells, the frequencies of membrane-bound HLA-G on CD3+ and CD14+ cells were almost identical in patients during and post COVID-19, while the frequency of ILT-2 receptor on CD3+ and CD14+ cells was increased during acute infection. A multi-parametric correlation analysis of soluble HLA-G forms with IL-6, IL-10, activation markers CD25 and CD154, HLA-G, and ILT-2 expression on immune cells revealed a strong positive correlation of soluble HLA-G forms with membrane-bound HLA-G molecules on CD3+/CD14+ cells only in convalescents. During COVID-19, only vesicular-bound HLA-G were positively correlated with the activation marker CD25 on T cells. Thus, our data suggest that the elevated levels of soluble HLA-G in COVID-19 are due to increased expression in organ tissues other than circulating immune effector cells. The concomitant increased expression of soluble HLA-G and ILT-2 receptor frequencies supports the concept that the immune checkpoint HLA-G/ILT-2 plays a role in the immune-pathogenesis of COVID-19.

HLA sharing and maternal HLA expression in couples with recurrent pregnancy loss in Taiwan

OBJECTIVE

The aim of this study is to investigate the frequency and distribution of human HLA sharing and maternal HLA allele expression in couples with recurrent pregnancy loss in Taiwan.

MATERIALS AND METHODS

We retrospectively reviewed couples experienced two or more pregnancy loss before 20th weeks of gestation from March 2014 to November 2020 having HLA determination. Fertile individuals with one or more live-birth offspring receiving HLA allele determination during the same period were included as the control group. The distribution and frequency of HLA sharing were analyzed and presented by descriptive statistics. Fisher Exact Test were used to analyze specific maternal and paternal HLA allele comparing individuals with RPL to fertile group. P-value < 0.05 was thought to be statistically significant.

RESULTS

72 couples were enrolled from March 2014 to November 2020. Regarding the distribution of HLA sharing, HLA sharing between females and their male partners less and equal to 2 pairs were found in 40.3% of the couples. HLA sharing greater and equal to 3 pairs are found in 59.8% couples. HLA sharing was most frequently found in alleles HLA-A02, A11, DQ07, C07 and B60 in descending order. There was a significant lower expression of HLA-B13 in women with RPL compared to women who had successful pregnancy (p = 0.0234). Compared infertile men with fertile men cohort, the frequency of HLA-DR04 (p = 0.0438, OR 2.444, 95% CI 1.0251-5.8287), HLA-DR12 (p = 0.001, OR 30.85, 95% CI 4.0296-236.19) and HLA-15 (p = 0.0357, OR 9.354, 95% CI 1.1610-75.37) were found to be significantly higher in men with RPL. On the contrary, HLA-DR07 (p = 0.0085, OR 0.124, 95% CI 0.0264-0.587) and HLA-DR10 (p = 0.0395, OR 0.048, 95% CI 0.0027-0.8641) were found to be significantly lower in men with RPL.

CONCLUSION

We found a tendency to recurrent pregnancy loss in couples with more than 2 pairs of HLA sharing. The similarity of HLA sharing, the expression of maternal HLA-B13 allele and paternal HLA-DR alleles in Taiwanese couples might play a role in recurrent pregnancy loss.

Homotypic and heterotypic in cis associations of MHC class I molecules at the cell surface

Through the presentation of peptide antigens to cytotoxic T lymphocytes, major histocompatibility complex (MHC) class I molecules mediate the adaptive immune response against tumors and viruses. Additional non-immunological functions include the heterotypic association of class I molecules with cell surface receptors, regulating their activities by unknown mechanisms. Also, homotypic associations resulting in class I dimers and oligomers - of unknown function - have been related to pathological outcomes. In this review, we provide an overview of the current knowledge about the occurrence, biochemical nature, and dynamics of homotypic and heterotypic associations of class I molecules at the cell surface with special focus on the molecular species that take part in the complexes and on the evidence that supports novel biological roles for class I molecules. We show that both heterotypic and homotypic class I associations reported in the literature describe not one but several kinds of oligomers with distinctive stoichiometry and biochemical properties.

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Major histocompatibility complex class I molecules form homotypic and heterotypic associations at the cell surface.

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Associations show distinctive stoichiometry and biochemical properties.

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Associations might regulate immunological and non-immunological processes.

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Heterotypic association with cell surface receptors might regulate receptor's activity.

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Homotypic associations have been related to pathological outcomes.

Isolation of HLA-G+ cells using MEM-G/9 antibody-conjugated magnetic nanoparticles for prenatal screening: a reliable, fast and efficient method

The development of an effective and noninvasive early method for obtaining fetal cells is crucial to prenatal screening. Despite proving the presence of fetal cells in the reproductive tract, their use is limited due to their inability to properly isolate them from maternal cells. Magnetic-activated cell sorting (MACS) is a simple technique to separate cells. The present study aimed to develop a MACS-based platform for the isolation of the HLA-G expressing trophoblast cells. For this purpose, first, the triazine functionalized MNPs were synthesized and characterized. Then, MNPs were directly and indirectly conjugated by the MEM-G/9 antibodies targeting HLA-G+ cells. The antibody amount on the surface of the nanoparticles was determined with the Bradford assay. The cell capture efficiency was also investigated. Various characterization methods confirmed the successful nanoparticle synthesis and antibody conjugation. The optimal initial antibody amount for the immobilization was about 20 μg and the optimal time was 3 h. The antibody-nanoparticles by the indirect method had better targeting and capture efficiency than the direct method. The MNPs indirectly conjugated with antibodies are an efficient tool for cell isolation and present considerable potential to be applied in biomedical fields.

Increased HLA-G Expression in Tissue-Infiltrating Cells in Inflammatory Bowel Diseases

BACKGROUND

Since HLA-G is an immune checkpoint molecule and since Crohn's disease (CD) and ulcerative colitis (UC) exhibit deregulated immune-mediated mechanisms, we aimed to evaluate intestinal HLA-G expression and soluble HLA-G (sHLA-G) levels in CD/UC patients stratified according to the CD phenotype/localization and UC extension.

METHODS

HLA-G tissue expression was assessed by immunohistochemistry in biopsies collected from 151 patients (90 CD, 61 UC) and in surgical resection specimens (28 CD, 12 UC). Surgical material from 24 healthy controls was also assessed. Plasma sHLA-G levels (97 CD, 81 UC, and 120 controls) were evaluated using ELISA.

RESULTS

HLA-G expression was similarly observed in the intestinal epithelial cells of control and CD/UC specimens. However, in biopsies, the plasma cells/lymphocytes infiltrating the lamina propria in CD/UC presented (1) increased HLA-G expression compared to controls (P < 0.0001), (2) greater cell staining in UC cells than in CD cells irrespective of disease extent (P = 0.0011), and (3) an increased number of infiltrating cells in the inflammatory CD phenotype compared to that in the stenosing and fistulizing phenotypes (P = 0.0407). In surgical specimens, CD/UC patients exhibited higher infiltrating cell HLA-G expression in lesion areas than in margins. sHLA-G levels were higher in UC/CD patients (P < 0.0001) than in controls, but no difference was observed between diseases.

CONCLUSIONS

Increased infiltrating cell HLA-G expression associated with increased sHLA-G levels in CD/UC patients may reflect ongoing host strategies to suppress chronic inflammation.

HLA-G expression correlates with histological grade but not with prognosis in colorectal carcinoma

Trophoblast-specific expression of HLA-G induces immune tolerance for the developing fetus. Pathological HLA-G expression later in life might contribute to immune escape of various cancers. We studied the still controversial role of HLA-G in colorectal carcinoma (CRC) using the MEM-G/1 antibody and a tissue microarray series of CRC tumors (n = 317). HLA-G expression appeared in 20% of the tumors and showed high intratumoral heterogeneity. HLA-G positivity was associated with better differentiation (p = 0.002) and non-mucinous histology (p = 0.008). However, HLA-G expression alone showed no prognostic value: 5-years disease-specific survival among patients with HLA-G expression was 68.9% (95% CI: 62.7%-75.0%) compared to 74.8% (95% CI: 63.2%-86.3%) among those without expression. These results support a modulatory role of HLA-G in CRC.

Appropriate fixative for MEM-G/9 staining of cultured human HLA-G-positive JEG-3 trophoblast tumor cells

Human leukocyte antigen (HLA-G) participates in immunosuppression and is useful for prenatal diagnostics. Isolation of fetal cells positive for HLA-G by HLA-G antibody conjugated nanoparticles from the cervix of pregnant women is the basis for non-invasive prenatal testing. Endocervical specimens are fixed in transport medium before isolation using antibody conjugated nanoparticles. Staining of HLA-G using MEM-G/9 antibody, however, is restricted to unfixed cells. We investigated the effect of several fixatives on the interaction of HLA-G with MEM-G/9 in the HLA-G-positive cell line, JEG-3. We investigated absolute methanol, 1:1 acetate buffer:methanol, Pap solution and paraformaldehyde. The effects of these fixatives were evaluated using immunofluorescence. We found no MEM-G/9 surface staining of methanol fixed cells. Approximately 40% of JEG-3 cells fixed with paraformaldehyde failed to stain. Nearly all cells were stained with MEM-G/9 following fixation with acetate buffer:methanol or Pap solution. Our findings indicate the importance of using an appropriate fixative for preserving HLA-G cell surface antigen for studies using the MEM-G/9 antibody.

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.

The NKG2A-HLA-E Axis as a Novel Checkpoint in the Tumor Microenvironment

The success of checkpoint blockade therapy revolutionized cancer treatment. However, we need to increase the fraction of responding patients and overcome acquired resistance to these therapies. Recently, the inhibitory receptor NKG2A received attention as a new kid on the block of immune checkpoints. This receptor is selectively expressed on cytotoxic lymphocytes, including natural killer cells and CD8 T cells, and NKG2A+ T cells are preferentially residing in tissues, like the tumor microenvironment. Its ligand, histocompatibility leucocyte antigen E (HLA-E), is a conserved nonclassical HLA class I molecule that binds a limited peptide repertoire and its expression is commonly detected in human cancer. NKG2A blockade as a standalone therapy appears poorly effective in mouse tumor models, however, in the presence of activated T cells, for example, induced by PD-1/PD-L1 blockade or cancer vaccines, exerts strongly enhanced efficacy. Clinical trials demonstrated safety of the humanized NKG2A-blocking antibody, monalizumab, and first results of phase II trials demonstrate encouraging durable response rates. Further development of this axis is clearly warranted.

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.

HLA-G Expression in Human Mesenchymal Stem Cells (MSCs) Is Related to Unique Methylation Pattern in the Proximal Promoter as well as Gene Body DNA

Multipotent human mesenchymal stem cells (MSCs) harbor clinically relevant immunomodulation, and HLA-G, a non-classical MHC class I molecule with highly restricted tissue expression, is one important molecule involved in these processes. Understanding of the natural regulatory mechanisms involved in expression of this elusive molecule has been difficult, with near exclusive reliance on cancer cell lines. We therefore studied the transcriptional control of HLA-G in primary isolated human bone marrow- (BM), human embryonic stem cell-derived (hE-), as well as placenta-derived MSCs (P-MSCs), and found that all 3 types of MSCs express 3 of the 7 HLA-G isoforms at the gene level; however, fibroblasts did not express HLA-G. Protein validation using BM- and P-MSCs demonstrated expression of 2 isoforms including a larger HLA-G-like protein. Interferon-γ (IFN-γ) stimulation upregulated both gene and protein expression in MSCs but not the constitutively expressing JEG-3 cell line. Most interestingly in human MSCs and placental tissue, hypomethylation of CpG islands not only occurs on the HLA-G proximal promoter but also on the gene body as well, a pattern not seen in either of the 2 commonly used choriocarcinoma cell lines which may contribute to the unique HLA-G expression patterns and IFN-γ-responsiveness in MSCs. Our study implicates the importance of using normal cells and tissues for physiologic understanding of tissue-specific transcriptional regulation, and highlight the utility of human MSCs in unraveling the transcriptional regulation of HLA-G for better therapeutic application.

Expression analysis of immune-regulatory molecules HLA-G, HLA-E and IDO in endometrial cancer

HLA-G has been widely implicated in advanced cancers through different pathways of immunosuppression allowing tumor escape. Contrarily, HLA-E has a controversial role in the tumor escape from the immune system. IDO catabolic enzyme is known to be up-regulated in many tumors types allowing their immune escape. Based on these considerations, we investigated the expression of HLA-G, HLA-E and IDO molecules in endometrial cancer (EC) and their association with prognostic clinicopathologic parameters. Their expression were checked in tumoral and adjacent endometrial tissues. Both HLA-G and IDO immunostaining were significantly increased in EC tissues compared to normal residual endometrial glands (Mann Whitney U-test, p = 0.0001 and p = 0,020 respectively). However, HLA-E was highly expressed in tumoral tissues as well as in normal residual endometrial glands (respectively, 100% and 81.8%). Increased HLA-G expression levels were observed in high histological grade (grade 3), and in the non-endometrioid type 2 EC. Unexpectedly, patients with IDO Low expression had significantly impaired overall survival compared to patients with IDO High (log-rank p = 0.021). Conversely, HLA-E low expression was associated to an improved overall survival EC (log-rank p = 0.004). We concluded that, HLA-G and IDO are highly expressed in EC compared to adjacent normal endometrial tissues, that might be interesting for the EC outcome.

HLA-G 14 bp In/Del and +3142 C/G genotypes are differentially expressed between patients with grade IV gliomas and controls

Aim: Human Leukocyte Antigen-G (HLA-G) is a non-classical class I molecule that is involved in maternal-fetal immunotolerance. In cancer, this molecule contributes to the tumor escape. The aim of this study was to evaluate the 14 bp In/Del and +3142 C > G polymorphisms of the HLA-G 3' UTR and its relation with plasma and tissue HLA-G expression in patients with grade IV (high-grade) and grade I/II (low-grade) gliomas and controls.Patients and methods: Peripheral blood and tumor biopsies were collected from 85 patients with gliomas and blood samples from 94 controls. Polymorphisms were analyzed from blood DNA. Soluble HLA-G (sHLA-G) was measured by ELISA in plasma of the subjects and the tissue expression by immunohistochemistry on patient's tissue.Results: Higher levels of sHLA-G were observed in grade IV gliomas patients than in controls (p < 0.0001). In grade IV patients, the heterozygous 14pb In/Del, +3142 C/G genotypes and Del/C*In/G haplotype were associated with higher sHLA-G levels (p < 0.0001) when compared with controls. GBM patients were stratified into high and low sHLA-G expression and an association was found between +3142 C allele and high sHLA-G plasmatic levels (p = 0.0095). Tissue HLA-G immunolabel was higher in high-grade than low-grade gliomas (p = 0.0033).Conclusion: This was the first study evaluating HLA-G 3' UTR polymorphisms and expression in patients with gliomas. The 14 bp In/Del and +3142 C/G genotypes and haplotypes showed high influence over sHLA-G expression, suggesting a heterozygous advantage in the tumor context and may contribute to a worse prognosis in glioma patients.

Evaluation of the Reactivity and Receptor Competition of HLA-G Isoforms toward Available Antibodies: Implications of Structural Characteristics of HLA-G Isoforms

The human leucocyte antigen (HLA)-G, which consists of seven splice variants, is a tolerogenic immune checkpoint molecule. It plays an important role in the protection of the fetus from the maternal immune response by binding to inhibitory receptors, including leukocyte Ig-like receptors (LILRs). Recent studies have also revealed that HLA-G is involved in the progression of cancer cells and the protection from autoimmune diseases. In contrast to its well characterized isoform, HLA-G1, the binding activities of other major HLA-G isoforms, such as HLA-G2, toward available anti-HLA-G antibodies are only partially understood. Here, we investigate the binding specificities of anti-HLA-G antibodies by using surface plasmon resonance. MEM-G9 and G233 showed strong affinities to HLA-G1, with a nM range for their dissociation constants, but did not show affinities to HLA-G2. The disulfide-linker HLA-G1 dimer further exhibited significant avidity effects. On the other hand, 4H84 and MEM-G1, which can be used for the Western blotting of HLA-G isoforms, can bind to native HLA-G2, while MEM-G9 and G233 cannot. These results reveal that HLA-G2 has a partially intrinsically disordered structure. Furthermore, MEM-G1, but not 4H84, competes with the LILRB2 binding of HLA-G2. These results provide novel insight into the functional characterization of HLA-G isoforms and their detection systems.

HLA-G expression during hookworm infection in pregnant women

INTRODUCTION

HLA-G plays a key role on immune tolerance. Pathogens can induce soluble HLA-G (sHLA-G) production to down-regulate the host immune response, creating a tolerogenic environment favorable for their dissemination. To our knowledge, no study has yet been conducted to assess the relationship between sHLA-G and geohelminth infections.

METHODS

The study was conducted in Allada, Southeastern Benin, from 2011-2014. The study population encompassed 400 pregnant women, included before the end of the 28th week of gestation and followed-up until delivery. At two antenatal care visits and at delivery, stool and blood samples were collected. Helminths were diagnosed by means of the Kato-Katz concentration technique. We used quantile regression to analyze the association between helminth infections and sHLA-G levels during pregnancy.

RESULTS

sHLA-G levels gradually increased during pregnancy and reached maximal levels at delivery. Prevalence of helminth infections was low, with a majority of hookworm infections. We found significantly more hookworm-infected women above the 80th quantile (Q80) of the distribution of the mean sHLA-G level (p < 0.03, multivariate quantile regression). Considering only women above the Q80 percentile, the mean sHLA-G level was significantly higher in hookworm-infected compared to uninfected women (p = 0.04).

CONCLUSION

High levels of sHLA-G were associated with hookworm infection in pregnant women. This result is consistent with the potential involvement of sHLA-G in immune tolerance induced by helminths during pregnancy.

High level of soluble human leukocyte antigen (HLA)-G at beginning of pregnancy as predictor of risk of malaria during infancy

Placental malaria has been associated with an immune tolerance phenomenon and a higher susceptibility to malaria infection during infancy. HLA-G is involved in fetal maternal immune tolerance by inhibiting maternal immunity. During infections HLA-G can be involved in immune escape of pathogens by creating a tolerogenic environment. Recent studies have shown an association between the risk of malaria and HLA-G at both genetic and protein levels. Moreover, women with placental malaria have a higher probability of giving birth to children exhibiting high sHLA-G, independently of their own level during pregnancy. Our aim was to explore the association between the level of maternal soluble HLA-G and the risk of malaria infection in their newborns. Here, 400 pregnant women and their children were actively followed-up during 24 months. The results show a significant association between the level of sHLA-G at the first antenatal visit and the time to first malaria infection during infancy adjusted to the risk of exposure to vector bites (aHR = 1.02, 95%CI [1.01–1.03], p = 0.014). The level of sHLA-G is a significant predictor of the occurrence of malaria infection during infancy consistent with the hypothesis that mother sHLA-G could be a biomarker of malaria susceptibility in children.

Senescent cells evade immune clearance via HLA-E-mediated NK and CD8+ T cell inhibition

Senescent cells accumulate in human tissues during ageing and contribute to age-related pathologies. The mechanisms responsible for their accumulation are unclear. Here we show that senescent dermal fibroblasts express the non-classical MHC molecule HLA-E, which interacts with the inhibitory receptor NKG2A expressed by NK and highly differentiated CD8+ T cells to inhibit immune responses against senescent cells. HLA-E expression is induced by senescence-associated secretary phenotype-related pro-inflammatory cytokines, and is regulated by p38 MAP kinase signalling in vitro. Consistently, HLA-E expression is increased on senescent cells in human skin sections from old individuals, when compared with those from young, and in human melanocytic nevi relative to normal skin. Lastly, blocking the interaction between HLA-E and NKG2A boosts immune responses against senescent cells in vitro. We thus propose that increased HLA-E expression contributes to persistence of senescent cells in tissues, thereby suggesting a new strategy for eliminating senescent cells during ageing.

Enhancing Natural Killer and CD8+ T Cell-Mediated Anticancer Cytotoxicity and Proliferation of CD8+ T Cells with HLA-E Monospecific Monoclonal Antibodies

Cytotoxic NK/CD8+ T cells interact with MHC-I ligands on tumor cells through either activating or inhibiting receptors. One of the inhibitory receptors is CD94/NKG2A. The NK/CD8+ T cell cytotoxic capability is lost when tumor-associated human leukocyte antigen, HLA-E, binds the CD94/NKG2A receptor, resulting in tumor progression and reduced survival. Failure of cancer patients to respond to natural killer (NK) cell therapies could be due to HLA-E overexpression in tumor tissues. Preventing the inhibitory receptor-ligand interaction by either receptor- or ligand-specific monoclonal antibodies (mAbs) is an innovative passive immunotherapeutic strategy for cancer. Since receptors and ligands can be monomeric or homo- or heterodimeric proteins, the efficacy of mAbs may rely on their ability to distinguish monospecific (private) functional epitopes from nonfunctional common (public) epitopes. We developed monospecific anti-HLA-E mAbs (e.g., TFL-033) that recognize only HLA-E-specific epitopes, but not epitopes shared with other HLA class-I loci as occurs with currently available polyreactive anti-HLA-E mAbs. Interestingly the amino acid sequences in the α1 and α2 helices of HLA-E, critical for the recognition of the mAb TFL-033, are strikingly the same sequences recognized by the CD94/NKG2A inhibitory receptors on NK/CD8+ cells. Such monospecific mAbs can block the CD94/NKG2A interaction with HLA-E to restore NK cell and CD8+ anticancer cell cytotoxicity. Furthermore, the HLA-E monospecific mAbs significantly promoted the proliferation of the CD4-/CD8+ T cells. These monospecific mAbs are also invaluable for the specific demonstration of HLA-E on tumor biopsies, potentially indicating those tumors most likely to respond to such therapy. Thus, they can be used to enhance passive immunotherapy once phased preclinical studies and clinical trials are completed. On principle, we postulate that NK cell passive immunotherapy should capitalize on both of these features of monospecific HLA-E mAbs, that is, the specific determination HLA-E expression on a particular tumor and the enhancement of NK cell/CD8+ cytotoxicity if HLA-E positive.

The association of HLA-G polymorphisms and the synergistic effect of sMICA and sHLA-G with chronic kidney disease and allograft acceptance

The HLA-G and MICA genes are stimulated under inflammatory conditions and code for soluble (sMICA and sHLA-G) or membrane-bound molecules that exhibit immunomodulatory properties. It is still unclear whether they would have a synergistic or antagonistic effect on the immunomodulation of the inflammatory response, such as in chronic kidney disease (CKD), contributing to a better prognosis after the kidney transplantation. In this study, we went from genetic to plasma analysis, first evaluating the polymorphism of MICA, NKG2D and HLA-G in a cohort from Southern Brazil, subdivided in a control group of individuals (n = 75), patients with CKD (n = 94), and kidney-transplant (KT) patients (n = 64). MICA, NKG2D and HLA-G genotyping was performed by polymerase chain reaction with specific oligonucleotide probes, Taqman and Sanger sequencing, respectively. Levels of soluble forms of MICA and HLA-G were measured in plasma with ELISA. Case-control analysis showed that the individuals with haplotype HLA-G*01:01/UTR-4 have a lower susceptibility to develop chronic kidney disease (OR = 0.480; p = 0.032). Concerning the group of kidney-transplant patients, the HLA-G genotypes +3010 GC (rs1710) and +3142 GC (rs1063320) were associated with higher risk for allograft rejection (OR = 5.357; p = 0.013 and OR = 5.357, p = 0.013, respectively). Nevertheless, the genotype +3010 GG (OR = 0.136; p = 0.041) was associated with kidney allograft acceptance, suggesting that it is a protection factor for rejection. In addition, the phenotypic analysis revealed higher levels of sHLA-G (p = 0.003) and sMICA (p < 0.001) in plasma were associated with the development of CKD. For patients who were already under chronic pathological stress and underwent a kidney transplant, a high sMICA (p = 0.001) in pre-transplant proved to favor immunomodulation and allograft acceptance. Even so, the association of genetic factors with differential levels of soluble molecules were not evidenced, we displayed a synergistic effect of sMICA and sHLA-G in response to inflammation. This increase was observed in CKD patients, that when undergo transplantation, had this previous amount of immunoregulatory molecules as a positive factor for the allograft acceptance.

Prediction of non-muscle-invasive bladder cancer recurrence by measurement of checkpoint HLAG's receptor ILT2 on peripheral CD8+ T cells

Background and Objective

Recurrence of non-muscle invasive bladder cancer (NMIBC) after initial management occurs in 60–70% of patients. Predictive criteria for recurrence remain only clinical and pathological. The aim of this study was to investigate the prognostic significance of the proportion of checkpoint HLA-G’s receptor ILT2-expressing peripheral CD8⁺ T cells.

Results

The proportion of CD4⁺ILT2⁺and CD8⁺ILT2⁺ T cells was not increased in NMIBC compared to controls. However, a strong association was found between recurrence and CD8⁺ILT2⁺ T cell population levels (p = 0.0006). Two-year recurrence-free survival was 83% in patients with less than 18% CD8⁺ILT2⁺ T cells, 39% in the intermediary group, and 12% in patients with more than 46% CD8⁺ILT2⁺ T cells. Multivariate analyses demonstrated that the proportion of CD8⁺ILT2⁺ T cells was an independent predictive factor for recurrence. Adding CD8⁺ILT2⁺ T cells population level to clinical variables increased the predictive accuracy of the model by 4.5%.

Materials and Methods

All patients treated for NMIBC between 2012 and 2014 were included prospectively. Blood samples, tumor and clinico-pathological characteristics were collected. HLA-G expression was measured using IHC, and CD8⁺ILT2⁺ T cell levels using flow cytometry. Association between HLA-G and CD8⁺ILT2⁺ T cell population levels with NMIBC risk of recurrence was investigated using Cox regression analyses. Prediction was measured using the concordance index statistic.

Conclusions

We demonstrated a strong association between the proportion of circulating CD8⁺ILT2⁺ T cells and NMIBC risk of recurrence. Gain in prediction was substantial. If externally validated, such immunological marker could be integrated to predict NMIBC recurrence.

Regeneration of cervical reserve cell-like cells from human induced pluripotent stem cells (iPSCs): A new approach to finding targets for cervical cancer stem cell treatment

Cervical reserve cells are epithelial progenitor cells that are pathologically evident as the origin of cervical cancer. Thus, investigating the characteristics of cervical reserve cells could yield insight into the features of cervical cancer stem cells (CSCs). In this study, we established a method for the regeneration of cervical reserve cell-like properties from human induced pluripotent stem cells (iPSCs) and named these cells induced reserve cell-like cells (iRCs). Approximately 70% of iRCs were positive for the reserve cell markers p63, CK5 and CK8. iRCs also expressed the SC junction markers CK7, AGR2, CD63, MMP7 and GDA. While iRCs expressed neither ERα nor ERβ, they expressed CA125. These data indicated that iRCs possessed characteristics of cervical epithelial progenitor cells. iRCs secreted higher levels of several inflammatory cytokines such as macrophage migration inhibitory factor (MIF), soluble intercellular adhesion molecule 1 (sICAM-1) and C-X-C motif ligand 10 (CXCL-10) compared with normal cervical epithelial cells. iRCs also expressed human leukocyte antigen-G (HLA-G), which is an important cell-surface antigen for immune tolerance and carcinogenesis. Together with the fact that cervical CSCs can originate from reserve cells, our data suggested that iRCs were potent immune modulators that might favor cervical cancer cell survival. In conclusion, by generating reserve cell-like properties from iPSCs, we provide a new approach that may yield new insight into cervical cancer stem cells and help find new oncogenic targets.

Immunohistochemical investigations on the expression of programmed cell death ligand 1, human leukocyte antigens G and E, and granzyme B in intraoral mucoepidermoid carcinoma

OBJECTIVE

To identify the expression of nonclassical human leukocyte antigen G and E (HLA-G and -E), programmed cell death ligand-1 (PD-L1) and granzyme B (GB) in intraoral mucoepidermoid carcinomas (MECs), and to assess whether such expressions are related to metastasis, survival, staging, tumor grade and number of GB-positive cells.

DESIGN

For this cross-sectional study, samples of MEC (n=30) were selected and classified as low-grade (LG), intermediate-grade (IG) or high-grade (HG), according to the WHO grading system. HLA-G, -E and PD-L1 were identified by immunohistochemistry and quantified as the proportion of positive neoplastic cells. The density of GB+ cells was also evaluated. The Kruskal-Wallis test was used with a 5% significance level.

RESULTS

Expressions of HLA-G, -E and PD-L1 were identified in the majority of epidermoid, intermediate and clear cells, but not in the mucous cells of the MECs. The quantitative analysis of the total percentage of positive neoplastic cells showed overexpression of this set of proteins in all MEC samples. The expression of these proteins and histological grading were positively correlated [HLA-G (LG=79% positive cells, IG=96%, HG=99%; p=0.0004), HLA-E (LG=70%, IG=96%, HG=99%; p<0.0001) and PD-L1 (LG=34%, IG=79%, HG=80%; p=0.01)]. No relationship was observed between the immunosuppressive proteins and other clinicopathological parameters. Low GB density was found in all MEC samples.

CONCLUSIONS

The augmented expression of HLA-G, -E and PD-L1 in the intraoral MEC might suggest a role of these molecules in the scape of neoplastic cells from immunosurveillance.

The Influence of Cytomegalovirus on Expression of HLA-G and its Ligand KIR2DL4 by Human Peripheral Blood Leucocyte Subsets

HLA-G is a non-classical class I HLA antigen, normally expressed in high levels only on extravillous cytotrophoblast. It has immunosuppressive properties in pregnancy and has also been found to be upregulated on leucocytes in viral infection. In this study, proportions of all leucocyte subsets expressing HLA-G were found to be low in healthy subjects positive or negative for cytomegalovirus (CMV). Significantly greater proportions of CD4+ CD69+ and CD56+ T cells expressed HLA-G compared to other T cells. However, following stimulation with CMV antigens or intact CMV, proportions of CD4+, CD8+, CD69+ and CD56+ T cells, and also B cells expressing HLA-G, were significantly increased in CMV+ subjects. Despite some subjects having alleles of HLA-G associated with high levels of expression, no relationship was found between HLA-G genotype and expression levels. Purified B cells from CMV+ subjects stimulated in mixed culture with CMV antigens showed significantly increased HLA-G mRNA expression by real-time polymerase chain reaction. Serum levels of soluble HLA-G were similar in CMV- and CMV+ subjects but levels in culture supernatants were significantly higher in cells from CMV+ than from CMV- subjects stimulated with CMV antigens. The HLA-G ligand KIR2DL4 was mainly expressed on NK cells and CD56+ T cells with no differences between CMV+ and CMV- subjects. Following stimulation with IL-2, an increase in the proportion of CD56+ T cells positive for KIR2DL4 was found, together with a significant decrease in CD56dimCD16+ NK cells. The results show that CMV influences HLA-G expression in healthy subjects and may contribute to viral immune evasion.

HLA class Ia and Ib molecules and FOXP3+ TILs in relation to the prognosis of malignant melanoma patients

HLA class Ia (HLA-ABC) and HLA class Ib (HLA-E, -F and -G) molecules and FOXP3+ tumor-infiltrating lymphocytes (TILs) are often reported as relevant factors of tumor immune regulation. We investigated their expression as prognostic factors in 200 patients with primary cutaneous melanoma (PCM). In our cohort, patients with tumors showing upregulation of HLA-ABC molecules had significantly thicker tumors (32% vs 7%, P<0.001), frequent ulceration (20% vs 6%, P=0.007) and frequent nodular melanomas (20% vs 4%, P=0.001). Additionally, high expression of HLA-G in the tumor was a sign of bad prognosis for the patients, being associated with thick tumors (30% vs 12%, P=0.017), ulceration (24% vs 5%, P<0.001) and positive sentinel node (13% vs 6%, P=0.015). HLA-E, HLA-F and FOXP3+ TILs were not indicative of the prognosis in PCM. High HLA-ABC and HLA-G were associated with tumor aggressiveness and could be relevant predictive markers for effective immunotherapy of melanoma tumors.

Evaluation of HLA-G, HLA-E, and PD-L1 proteins in oral osteosarcomas

OBJECTIVE

The aim of this study was to investigate the expression of human leukocyte antigens (HLAs) G and E and programmed death-ligand 1 (PD-L1) in oral osteosarcoma (OO) (n = 13). The relationship between the expression of these molecules and histologic grading and metastasis was also evaluated.

STUDY DESIGN

HLA-G, HLA-E, and PD-L1 were identified by immunohistochemistry. Samples of normal bone tissue (n = 6) were used as controls. The sections were evaluated using a semiquantitative scoring system with an immunoreactive score, where a score of 0 was considered absent, ≤2 was low, and >2 was high expression.

RESULTS

We identified high expression of HLA-G, HLA-E, and PD-L1 by malignant osteoblastic cells in 69.2% of OO cases, which was statistically higher than that in controls (P < .05). Overexpression of these proteins was identified in 8 of 11 samples of high-grade and 1 of 2 samples of low-grade OO. Additionally, 66.6% of patients with metastases (n = 4) and 71.4% of patients without metastases (n = 5) had high expression of HLA-G, HLA-E, and PD-L1 in tumor samples (P > .05).

CONCLUSION

OO had high expression of HLA-G, HLA-E, and PD-L1 irrespective of clinicopathologic parameters, including histologic grading and metastasis.

A soluble recombinant form of human leucocyte antigen-G 6 (srHLA-G6)

Human Leucocyte Antigen-G (HLA-G) is a non classical major histocompatibility complex (MHC) molecule that through RNA splicing can encode seven isoforms which are membrane bound (-G1, -G2, -G3 and -G4) and soluble (-G5, -G6 and -G7). HLA-G is described as important immune suppressor endogenous molecule to favor maternal-fetal tolerance, transplant survival and tumor immune scape. HLA-G shows low protein variability and a unique structural complexity that is related with the expression of different isoforms followed by biochemical processes, such as, proteolytic cleavage, molecular interactions, and protein ubiquitination. Studies with HLA-G have shown difficult to assess the role of the individual isoforms. Thus, the aim of this work was to obtain a HLA-G6 recombinant form. The results indicated the production of high homogeneous preparations of soluble recombinant HLA-G6 (srHLA-G6) with molecular mass 23,603.76 Da, determined by MALD-TOF/TOF. In addition, native and denatured srHLA-G6 were detected by ELISA, using commercial monoclonal antibodies. Finally, we developed a suitable methodology to express srHLA-G6 that could contribute in structural and functional studies involving specific isoforms.

Soluble human leukocyte antigen -G during pregnancy and infancy in Benin: Mother/child resemblance and association with the risk of malaria infection and low birth weight

Human leukocyte antigen (HLA) G is a tolerogenic molecule involved in the maternal-fetal immune tolerance phenomenon. Its expression during some infectious diseases leading to immune evasion has been established. A first study conducted in Benin has shown that the production of soluble HLA-G (sHLA-G) during the first months of life is strongly correlated with the maternal level at delivery and associated with low birth weight and malaria. However sHLA-G measurements during pregnancy were not available for mothers and furthermore, to date the evolution of sHLA-G in pregnancy is not documented in African populations. To extend these previous findings, between January 2010 and June 2013, 400 pregnant women of a malaria preventive trial and their newborns were followed up in Benin until the age of 2 years. Soluble HLA-G was measured 3 times during pregnancy and repeatedly during the 2 years follow-up to explore how sHLA-G evolved and the factors associated. During pregnancy, plasma levels of sHLA-G remained stable and increased significantly at delivery (p<0.001). Multigravid women seemed to have the highest levels (p = 0.039). In infants, the level was highest in cord blood and decreased before stabilizing after 18 months (p<0.001). For children, a high level of sHLA-G was associated with malaria infection during the follow-up (p = 0.02) and low birth weight (p = 0.06). The mean level of sHLA-G during infancy was strongly correlated with the mother’s level during pregnancy (<0.001), and not only at delivery. Moreover, mothers with placental malaria infection had a higher probability of giving birth to a child with a high level of sHLA-g (p = 0.006). High sHLA-G levels during pregnancy might be associated with immune tolerance related to placental malaria. Further studies are needed but this study provides a first insight concerning the potential role of sHLA-G as a biomarker of weakness for newborns and infants.

Expression of HLA-E molecules in the placental tissue of women infected with HIV-1 and uninfected women

INTRODUCTION

Expression of HLA-E molecule in the placental extravillous trophoblast is associated with immune system cell inhibition, resulting in immune tolerance to fetus during pregnancy. HIV-1 can infect trophoblast cells and modify the expression of HLA-E, which may inhibit the cytotoxic activity of the immune system.

AIM

The aim of this study was to evaluate HLA-E expression in third trimester placental tissue of women infected with HIV-1 and uninfected women.

METHODS

We performed an immunohistochemistry assay to evaluate HLA-E staining in the placental tissue of 99 HIV-1 infected and 85 uninfected women. A pathologist analyzed and classified the HLA-E expression in the placental cells.

RESULTS

Irrespective of the HIV status, HLA-E staining was observed in the extravillous trophoblast cells, endothelial cells and Hofbauer cells, but not in the syncytiotrophoblast. HLA-E staining showed no significant difference between the placental tissue of women infected with HIV-1 and uninfected women (P = 0.76). Considering HIV-1 infected women, HLA-E staining was not influenced by HIV-1 viral load (P = 0.48), CD4+ T-cell count (P = 0.10) and antiretroviral therapy used during pregnancy (P = 0.54).

DISCUSSION

Despite the presence of HIV-1 infection, the expression of HLA-E molecules in the placental tissue was not modified when the infection was under antiretroviral therapy control.

HIV-1 Vpu Mediates HLA-C Downregulation

Many pathogens evade cytotoxic T lymphocytes (CTLs) by downregulating HLA molecules on infected cells, but the loss of HLA can trigger NK cell-mediated lysis. HIV-1 is thought to subvert CTLs while preserving NK cell inhibition by Nef-mediated downregulation of HLA-A and -B but not HLA-C molecules. We find that HLA-C is downregulated by most primary HIV-1 clones, including transmitted founder viruses, in contrast to the laboratory-adapted NL4-3 virus. HLA-C reduction is mediated by viral Vpu and reduces the ability of HLA-C restricted CTLs to suppress viral replication in CD4+ cells in vitro. HLA-A/B are unaffected by Vpu, and primary HIV-1 clones vary in their ability to downregulate HLA-C, possibly in response to whether CTLs or NK cells dominate immune pressure through HLA-C. HIV-2 also suppresses HLA-C expression through distinct mechanisms, underscoring the immune pressure HLA-C exerts on HIV. This viral immune evasion casts new light on the roles of CTLs and NK cells in immune responses against HIV.

Immunomodulation of classical and non-classical HLA molecules by ionizing radiation

Radiotherapy has been employed for the treatment of oncological patients for nearly a century, and together with surgery and chemotherapy, radiation oncology constitutes one of the three pillars of cancer therapy. Ionizing radiation has complex effects on neoplastic cells and on tumor microenvironment: beyond its action as a direct cytotoxic agent, tumor irradiation triggers a series of alterations in tumoral cells, which includes the de novo synthesis of particular proteins and the up/down-regulation of cell surface molecules. Additionally, ionizing radiation may induce the release of "danger signals" which may, in turn lead to cellular and molecular responses by the immune system. This immunomodulatory action of ionizing radiation highlights the importance of the combined use (radiotherapy plus immunotherapy) for cancer healing. Major histocompatibility complex antigens (also called Human Leukocyte Antigens, HLA in humans) are one of those molecules whose expression is modulated after irradiation. This review summarizes the modulatory properties of ionizing radiation on the expression of HLA class I (classical and non-classical) and class II molecules, with special emphasis in non-classical HLA-I molecules.

Non-classical HLA-class I expression in serous ovarian carcinoma: Correlation with the HLA-genotype, tumor infiltrating immune cells and prognosis

In our previous studies, we have shown that patients with serous ovarian carcinoma in advanced surgical stage disease have a particularly poor prognosis if they carry the HLA-A*02 genotype. This represent a stronger prognostic factor than loss or downregulation of the MHC class I heavy chain (HC) on tumor cells. In this study, we investigated the expression of the non-classical, immune tolerogenic HLA -G and -E on the tumor cells along with the infiltration of immune cells in the tumor microenvironment. FFPE primary tumors from 72 patients with advanced stages of serous adenocarcinoma and metastatic cells present in ascites fluid from 8 additional patients were included in this study. Both expression of HLA-G and aberrant expression of HLA-E were correlated to a significant worse prognosis in patients with HLA-A*02, but not with different HLA genotypes. Focal cell expression of HLA-G correlated to a site-specific downregulation of classical MHC class I HC products and aberrant HLA-E expression, showing a poor survival. HLA-G was more frequently expressed in metastatic cells than in primary tumor lesions and the expression of HLA-G inversely correlated with the frequency of tumor infiltrating immune cells. All these parameters can contribute together to identify and discriminate subpopulations of patients with extremely poor prognosis and can give them the opportunity to receive, and benefit of individually tailored treatments.

Inhibition of ERK and proliferation in NK cell lines by soluble HLA-E released from Japanese encephalitis virus infected cells

Productive infection of human endothelial cells with Japanese encephalitis virus (JEV), a single stranded RNA virus induces shedding of sHLA-E. We show here that sHLA-E that is released upon infection with this flavivirus can inhibit IL-2 and PMA mediated ERK 1/2 phosphorylation in two NK cell lines, Nishi and NKL. Virus infected or IFN-γ treated cell culture supernatants containing sHLA-E were found to partially inhibit IL-2 mediated induction of CD25 molecules on NKL cells. It was also found that sHLA-E could inhibit IL-2 induced [(3)H]-thymidine incorporation suggesting that, similar to cell surface expressed HLA-E, sHLA-E could also inhibit NK cell responses. Hence JEV-induced shedding of sHLA-E needs further investigation to better understand immune responses in JEV infections since it may have a role in viral evasion of NK cell responses.

Heterologous expression of mutated HLA-G1 reduces alloreactivity of human dermal fibroblasts

Aim: To engineer a stable HLA-G molecule and evaluate its immunomodulatory properties in transgenic human dermal fibroblasts (HDFs). Materials & methods: A mutated HLA-G1 (mHLA-G1) molecule was generated by modifying the endoplasmic reticulum retrieval motif and 3′-untranslated region miRNA-binding sites of HLA-G1. Immunomodulatory properties of transgenic HDF-mHLA-G1 were evaluated in vitro. Results: Stable mHLA-G1 expressing HDF cells were successfully generated and flow cytometry analysis revealed that mHLA-G1 efficiently localized to the cell surface. Natural killer cell-mediated cytolysis of HDF-mHLA-G1/green fluorescent protein (GFP) was reduced by 73% compared with HDF-GDP. HDF-mHLA-G1/GFP decreased phytohemagglutinin-activated peripheral blood mononuclear cell proliferation by 30% versus HDF-GFP. Conclusion: We are the first to successfully create a human fibroblast source with reduced alloreactivity using a novel mHLA-G1 construct. This approach may be extended to other cell types including human embryonic stem cells for use in allogeneic transplantation for cell-based regenerative medicine applications.

Sera from early-onset, severely preeclamptic women directly modulate HLA-E expression in the EA.hy296 endothelial cell line

The expression of endothelial HLA-E in the context of the systemic inflammatory response observed in preeclampsia has not been established. An experimental study was designed to determine the effect of the sera of pregnant women on the expression of HLA-E in EA.hy296 endothelial cells. First, measurements of protein fractions were performed in sera from early-onset, severely preeclamptic women without HELLP syndrome, in which there was no significant difference in total proteins between the groups, but a reduced level of plasma albumin and an increase in α1-globulin were observed in both groups of pregnant women compared with non-pregnant women. Measurements of colloid osmotic pressure (COP) using a recalculated albumin/globulin ratio formula determined only a significant decrease in COP in all pregnant groups compared with non-pregnant women. The expression of membrane HLA-E was increased in EA.hy296 endothelial cells stimulated with sera of early-onset, severely preeclamptic women, while recombinant interferon-γ (IFN-γ) significantly reduced the expression of membrane HLA-E. Pro-inflammatory cytokines were measured by Luminex in the serum samples, and increased levels of tumor necrosis factor (TNF) and decreased levels of IFN-γ were observed in early-onset, severe preeclampsia compared with normal pregnancy. Moreover, soluble HLA-E was detected in these serum samples by Western blot and ELISA, but no significant difference was found. This raises the possibility that a systemic inflammatory response promotes a compensatory mechanism of COP balance in severe preeclampsia by release of inflammation-induced factors, including endothelial HLA-E. Evidence is now provided regarding HLA-E expression by EA.hy296 cells.

High plasma levels of HLA-G are associated with low birth weight and with an increased risk of malaria in infancy

Background

The immunosuppressive properties of HLA-G protein can create a tolerogenic environment that may allow Plasmodium falciparum to avoid host immune responses. There are known associations between high levels of circulating soluble HLA-G (sHLA-G) and either parasite or viral infections and it has been suggested that the induction of sHLA-G expression could be a mechanism via which infectious agents subvert host immune defence. The study presented here is the first to investigate the possible association between sHLA-G and malaria or malaria related risk factors in Benin.

Methods

A parasitological and clinical follow-up of 165 mothers and their newborns from delivery through to one year of age was conducted in the Tori Bossito area of southern Benin. Plasma levels of sHLA-G were determined by ELISA in maternal peripheral and cord blood and again in infants' peripheral blood at 3, 6, 9 and 12 months of age. The associations between the levels of sHLA-G and malaria risk factors were investigated through multivariate mixed models.

Results

Strong correlations were observed between the maternal and cord plasma concentrations of sHLA-G. In multivariate analyses, high cord plasma levels of sHLA-G were independently associated with (i) low birth weight and (ii) an increased risk of P. falciparum infection in infancy.

Conclusion

These results show for the first time the possible involvement of sHLA-G in generating immune tolerance during pregnancy-associated malaria. Soluble HLA-G may represent a useful marker of susceptibility to malaria in infants and be associated with the higher susceptibility to infection observed for LBW children.

Prognostic value of HLA class I, HLA-E, HLA-G and Tregs in rectal cancer: a retrospective cohort study

BACKGROUND

Evasion of immune surveillance and suppression of the immune system are important hallmarks of tumorigenesis. The goal of this study was to establish distinct patterns that reflect a rectal tumors' immune-phenotype and to determine their relation to patient outcome.

METHODS

The study population consisted of 495 Stage I-IV non-preoperatively treated rectal cancer patients of which a tissue micro array (TMA) was available. Sections of this TMA were immunohistochemically stained and quantified for presence of Foxp3+ cells (Tregs) and tumor expression of HLA Class I and non-classical HLA-E and HLA-G. All markers were, separate and combined, analyzed for clinical prognostic value.

RESULTS

Expression of HLA class I (DFS HR 0.637 (0.458-0.886), p = 0.013), Foxp3+ infiltration above median (OS HR 0.637 (0.500-0.813), p < 0.001 and DFS HR 0.624 (0.491-0.793), p < 0.001) and expression of HLA-G (DFS HR 0.753 (0.574-0.989), p = 0.042) were related to a better clinical prognosis. When these markers were combined, patients with 2 or 3 markers associated with poor prognosis (loss of HLA Class I, Foxp3+ below median, and weak HLA-G expression), showed a significantly worse survival (OS and DFS p < 0.001). This immune-phenotype was an independent predictor for DFS (HR 1.56 (1.14-2.14), p = 0.019).

CONCLUSIONS

In conclusion, rectal tumors showing loss of HLA class I expression, Foxp3+ infiltration below median and weak HLA-G expression were related to a worse OS and DFS. Combining these immune markers lead to the creation of tumor immune-phenotypes , which related to patient outcome and were significant independent clinical prognostic markers in rectal cancer.

Human leukocyte antigen G is associated with esophageal squamous cell carcinoma progression and poor prognosis

Human leukocyte antigen G (HLA-G) is a non-classical HLA class I molecule thought to play a key role in maternal-fetal tolerance and cancer immune evasion. This study aimed to investigate the HLA-G expression in lesion sections and plasma sHLA-G levels of primary esophageal squamous cell carcinoma (ESCC) patients and its clinical significance in diagnosis and prognosis of ESCC. 60 ESCC patients and 28 healthy controls were recruited, and the positive expression of HLA-G in ESCC lesions and adjacent normal tissues were 70% (42/60) and 8.6% (5/60) (P<0.05), respectively, while no expression was found in normal controls. HLA-G1 and HLA-G5 were determined to be dominating isoforms measured by RT-PCR. There was a significant difference in plasma sHLA-G levels between patients with ESCC (15.04 U/ml, range 4.33-250.00 U/ml) and healthy controls (6.81 U/ml, range 0-29.27 U/ml) (P<0.01). The plasma IL-10 level was higher in ESCC patients than the controls (23.86 pg/ml vs. 12.81 pg/ml, P<0.01). HLA-G expression in lesion tissues was correlated with cancer cell differentiation (P=0.033), lymph node metastasis (P=0.035) of ESCC. However, no obvious correlations were demonstrated between the plasma sHLA-G levels and the clinicopathological parameters. There was a significant correlation between sHLA-G and IL-10 expression (r=0.353, P=0.006) in patients with Esophageal squamous cell carcinoma. HLA-G positive expression showed poorer prognosis of ESCC. HLA-G positive expression might serve as a potential marker in the diagnosis or prediction of ESCC.

Combined analysis of HLA class I, HLA-E and HLA-G predicts prognosis in colon cancer patients

BACKGROUND

Evasion of immune surveillance and suppression of the immune system are important hallmarks of tumour development in colon cancer. The goal of this study was to establish a tumour profile based on biomarkers that reflect a tumour's immune susceptibility status and to determine their relation to patient outcome.

METHODS

The study population consisted of 285 stage I-IV colon cancer patients of which a tissue micro array (TMA) was available. Sections were immunohistochemically stained for the presence of Foxp3+ cells and tumour expression of HLA Class I (HLA-A, -B, -C) and non-classical HLA-E and HLA-G. All markers were combined for further analyses, resulting in three tumour immune phenotypes: strong immune system tumour recognition, intermediate immune system tumour recognition and poor immune system tumour recognition.

RESULTS

Loss of HLA class I expression was significantly related to a better OS (P-value 0.005) and DFS (P-value 0.008). Patients with tumours who showed neither HLA class I nor HLA-E or -G expression (phenotype a) had a significant better OS and DFS (P-value <0.001 and 0.001, respectively) compared with phenotype b (OS HR: 4.7, 95% CI: 1.2-19.0, P=0.001) or c (OS HR: 8.2, 95% CI: 2.0-34.2, P=0.0001). Further, the tumour immune phenotype was an independent predictor for OS and DFS (P-value 0.009 and 0.013, respectively).

CONCLUSION

Tumours showing absence of HLA class I, HLA-E and HLA-G expressions were related to a better OS and DFS. By combining the expression status of several immune-related biomarkers, three tumour immune phenotypes were created that related to patient outcome. These immune phenotypes represented significant, independent, clinical prognostic profiles in colon cancer.

Mutated HLA-G3 localizes to the cell surface but does not inhibit cytotoxicity of natural killer cells

HLA-G plays an important role in the induction of immune tolerance. Various attempts to produce good manufacturing practice levels of HLA-G as a therapeutic molecule have failed to date partly due to the complicated structure of full-length HLA-G1. Truncated HLA-G3 is simpler and easier to produce than HLA-G1 and contains the expected functional epitope in its only α1 monomorphic domain. In this study, we engineered the ER retrieval and retention signal on HLA-G3's cytoplasmic tail by replacing its RKKSSD motif with RAASSD. We observed that mutated HLA-G3 was highly expressed on the cell surface of transduced K562 cells but did not inhibit cytotoxicity of natural killer cells.

Quantified colocalization reveals heterotypic histocompatibility class I antigen associations on trophoblast cell membranes: relevance for human pregnancy

Human placental syncytiotrophoblasts lack expression of most types of human leukocyte antigen (HLA) class I and class II molecules; this is thought to contribute to a successful pregnancy. However, the HLA class Ib antigens HLA-G, -E, and -F and the HLA class Ia antigen HLA-C are selectively expressed on extravillous trophoblast cells, and they are thought to play a major role in controlling feto-maternal tolerance. We have hypothesized that selective expression, coupled with the preferential physical association of pairs of HLA molecules, contribute to the function of HLA at the feto-maternal interface and the maternal recognition of the fetus. We have developed a unique analytical model that allows detection and quantification of the heterotypic physical associations of HLA class I molecules expressed on the membrane of human trophoblast choriocarcinoma cells, ACH-3P and JEG-3. Automated image analysis was used to estimate the degree of overlap of HLA molecules labeled with different fluorochromes. This approach yields an accurate measurement of the degree of colocalization. In both JEG-3 and ACH-3P cells, HLA-C, -E, and -G were detected on the cell membrane, while the expression of HLA-F was restricted to the cytoplasm. Progesterone treatment alone induced a significant increase in the expression level of the HLA-G/HLA-E association, suggesting that this heterotypic association is modulated by this hormone. Our data shows that the cell-surface HLA class I molecules HLA-G, -E, and -C colocalize with each other and have the potential to form preferential heterotypic associations.

In vivo identification of an HLA-G complex as ubiquitinated protein circulating in exosomes

The nonclassical human leukocyte antigen-G (HLA-G) is a tolerogenic molecule that can be released to the circulation by expressing cells. This molecule can form dimers but some other complexed HLA-G forms have been proposed to be present in vivo. Here, we further characterized these other complexed HLA-G forms in vivo. Ascitic and pleural exudates from patients were selected based on positivity for HLA-G by ELISA. Complexed HLA-G was detected in exosomes, which indicates an intracellular origin of these forms. 2D-PAGE analysis of exudates and isolated exosomes showed that these high molecular weight complexes were more heterogeneous than the HLA-G1 expressed by cell cultures. Treatment with deglycosylating enzymes did not change the molecular weight of HLA-G complexes. Immunoblot analysis of exudates and exosomes with an anti-ubiquitin antibody showed that at least some of these structures correspond to ubiquitinated HLA-G. HLA-G ubiquitination could be reproduced in vitro in HLA-G1-transfected cell lines, although with a lower modified/nonmodified protein proportion than in exudates. In summary, we demonstrate new circulating HLA-G forms in vivo that open a new perspective in the study of HLA-G function and analysis.