Expression and regulation of HLA-G in human glioma cell lines

Recurrence/Regrowth in Grade I Meningioma: How to Predict?

The HLA-G and HLA-E molecules, Ki67, progesterone (PR), estrogen (ER) and androgen receptors (AR), p53, COX-2, and HER2 were studied to assess whether the biological behavior of grade I meningiomas is related to their expression. Tissue samples from 96 patients with grade I intracranial meningiomas were analyzed by immunohistochemistry on tissue microarray blocks (TMA) using antibodies specific for HLA-G, HLA-E, Ki67, PR, ER, AR, p53, COX-2, and HER2. Meningiomas were classified as small (≤2 cm, 1.0%), medium (>2 and ≤4 cm, 32.3%), and large (>4 cm, 66.7%). Tumor size was not related to recurrence/regrowth (p = 0.486), but was significantly correlated with peritumoral edema (p = 0.031) and intratumoral calcifications (p = 0.018). Recurrent meningiomas were observed in 14.6% of cases. Immunostaining for each marker was: HLA-G 100%; HLA-E 95.6%; PR 62%; ER 2.1%; AR 6.5%; p53 92.6%; COX-2 100%; HER2 0%; Ki67, mean 2.61 ± 2.29%, median 2.1%. Primary and recurrent meningiomas showed no significant relation with HLA-E and hormone receptors (p > 0.05), except for Ki67, where a higher median was observed in recurrent tumors than in primary (p = 0.014). The larger the tumor, the more severe the peritumoral edema, and the greater the presence of calcifications. Ki67 appears to be a good biomarker of recurrence/regrowth in grade I meningiomas.

Human Parthenogenetic Embryonic Stem Cell-Derived Neural Stem Cells Express HLA-G and Show Unique Resistance to NK Cell-Mediated Killing

Parent-of-origin imprints have been implicated in the regulation of neural differentiation and brain development. Previously we have shown that, despite the lack of a paternal genome, human parthenogenetic (PG) embryonic stem cells (hESCs) can form proliferating neural stem cells (NSCs) that are capable of differentiation into physiologically functional neurons while maintaining allele-specific expression of imprinted genes. Since biparental ("normal") hESC-derived NSCs (N NSCs) are targeted by immune cells, we characterized the immunogenicity of PG NSCs. Flow cytometry and immunocytochemistry revealed that both N NSCs and PG NSCs exhibited surface expression of human leukocyte antigen (HLA) class I but not HLA-DR molecules. Functional analyses using an in vitro mixed lymphocyte reaction assay resulted in less proliferation of peripheral blood mononuclear cells (PBMC) with PG compared with N NSCs. In addition, natural killer (NK) cells cytolyzed PG less than N NSCs. At a molecular level, expression analyses of immune regulatory factors revealed higher HLA-G levels in PG compared with N NSCs. In line with this finding, MIR152, which represses HLA-G expression, is less transcribed in PG compared with N cells. Blockage of HLA-G receptors ILT2 and KIR2DL4 on natural killer cell leukemia (NKL) cells increased cytolysis of PG NSCs. Together this indicates that PG NSCs have unique immunological properties due to elevated HLA-G expression.

Expression of human leucocyte antigen-G primarily targets affected skin of patients with psoriasis

BACKGROUND

The nonclassical human leucocyte antigen (HLA)-G molecule has been well recognized as a tolerogenic molecule and few studies have evaluated the role of the molecule in inflammatory cutaneous autoimmune diseases.

OBJECTIVES

To evaluate the expression of HLA-G in skin specimens of patients with psoriasis and to analyse its correlation with epidemiological and clinical variables.

METHODS

Thirty untreated patients with psoriasis and 32 healthy individuals were enrolled. Immunohistochemistry was applied to identify HLA-G expression in formalin-fixed paraffin-embedded cutaneous skin biopsies.

RESULTS

Soluble and membrane-bound HLA-G expression was detected in 30 (90%) of the skin specimens from patients presenting clinical and histopathological features of psoriasis. Although infiltrating lymphomononuclear cells of the dermis exhibited HLA-G expression, the epidermis was primarily targeted. HLA-G expression was also observed in 27% (three of 11) of the specimens that exhibited no clinical and histopathological features of psoriasis (nonaffected areas). In contrast, skin specimens obtained from healthy individuals exhibited no HLA-G expression (P < 0·0001). The intensity of HLA-G expression was not associated with type I/II psoriasis, Psoriasis Area and Severity Index score or clinical forms.

CONCLUSIONS

As the HLA-G molecule was consistently expressed in affected and, to a lesser extent, in nonaffected areas of untreated patients with psoriasis, irrespective of the severity of the clinical variants, one may hypothesize that the presence of HLA-G may be responsible, at least in part, for the regulation of autoimmune effector cells.

Production of immune-modulatory nonclassical molecules HLA-G and HLA-E by tumor infiltrating ameboid microglia/macrophages in glioblastomas: a role in innate immunity?

The possible role of immune-modulatory nonclassical molecules HLA-G and HLA-E in an anti-tumoral response and development of glioblastoma is not well characterized. In this study, we evaluated an expression of HLA-G and HLA-E by activated tumor infiltrating microglia/macrophages. We found production of HLA-G and HLA-E by tumor infiltrating activated microglia/macrophages in a majority of glioblastomas. We speculate that the expression of these molecules by activated microglia/CNS macrophages plays a role in the anti-tumoral immunity in the development of glioblastoma. Mechanisms of microglia-glioblastoma cell interactions with respect to the expression of these molecules deserves further study.

Neurons under viral attack: victims or warriors?

When the central nervous system (CNS) is under viral attack, defensive antiviral responses must necessarily arise from the CNS itself to rapidly and efficiently curb infections with minimal collateral damage to the sensitive, specialized and non-regenerating neural tissue. This presents a unique challenge because an intact blood-brain barrier (BBB) and lack of proper lymphatic drainage keeps the CNS virtually outside the radar of circulating immune cells that are at constant vigilance for antigens in peripheral tissues. Limited antigen presentation skills of CNS cells in comparison to peripheral tissues is because of a total lack of dendritic cells and feeble expression of major histocompatibility complex (MHC) proteins in neurons and glia. However, research over the past two decades has identified immune effector mechanisms intrinsic to the CNS for immediate tackling, attenuating and clearing of viral infections, with assistance pouring in from peripheral circulation in the form of neutralizing antibodies and cytotoxic T cells at a later stage. Specialized CNS cells, microglia and astrocytes, were regarded as sole sentinels of the brain for containing a viral onslaught but neurons held little recognition as a potential candidate for protecting itself from the proliferation and pathogenesis of neurotropic viruses. Accumulating evidence however indicates that extracellular insult causes neurons to express immune factors characteristic of lymphoid tissues. This article aims to comprehensively analyze current research on this conditional alteration in the protein expression repertoire of neurons and the role it plays in CNS innate immune response to counter viral infections.

Immune-refractory cancers and their little helpers--an extended role for immunetolerogenic MHC molecules HLA-G and HLA-E?

There is strong evidence to support a role for non-classical MHC class I (class Ib) molecules, most notably HLA-E and HLA-G in tumour immune escape. In this article, we summarize the current knowledge on their expression, regulation and functional relevance in various malignancies, particularly brain tumours. Special emphasis is devoted to the phenomenon that these tolerogenic molecules are expressed by non-transformed cells that are found in close neighborhood to tumour cells representing either parenchymal cells or immune cells attracted to the tumour microenvironment. Here they may act as "natural" or "inducible" suppressors of anti-tumoural immune responses. We thus speculate about the role of HLA-G expressing T cells, a novel population of natural regulatory cells that was identified recently. It is suggested that various cell types within a tumour cooperate in order to inhibit anti-tumour immunity-and that immunetolerogenic HLA-G may play a major role in this context.

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.

The innate immune facet of brain: human neurons express TLR-3 and sense viral dsRNA

Inflammation is an important factor in the pathogenesis of neurodegenerative diseases, such as Alzheimer's disease or multiple sclerosis, and during microbial infections of the nervous system. Glial cells were thought to be the main contributor for cytokine and chemokine production and Toll-like receptor (TLR) expression in the brain. Here, we report that human neurons express TLR-3, a major receptor in virus-mediated innate immune response. We established that these cells can mount a strong inflammatory response characterized by the expression of inflammatory cytokines (TNF-alpha, IL-6), chemokines (CCL-5 and CXCL-10), and antiviral molecules (2'5'OAS and IFN-beta) after treatment with dsRNA - a by-product of viral infection and ligand of TLR-3. This work firmly establishes that human neurons, in absence of glia, have the intrinsic machinery to trigger robust inflammatory, chemoattractive, and antiviral responses.

Expression of Toll-like receptor 3 in the human cerebellar cortex in rabies, herpes simplex encephalitis, and other neurological diseases

There is recent in vitro evidence that human neurons express the innate immune response receptor, Toll-like receptor-3 (TLR-3), and that expression is enhanced in viral infections. The authors examined the immunohistochemical expression of TLR-3 in the cerebellar cortex of postmortem human brains. Purkinje cells were found to express TLR-3 in all cases of rabies (4 of 4) and herpes simplex encephalitis (2 of 2) as well as in cases of amyotrophic lateral sclerosis (1 of 2), stroke (1 of 2), and Alzheimer's disease (3 of 3). In cases of viral infection, direct viral infection was not necessary for enhanced neuronal TLR-3 expression, suggesting that soluble factors likely play an important role in inducing TLR-3 expression. In addition to neurons, occasional Bergmann glia expressed TLR-3 in some cases. This study has provided evidence that human brain neurons can express TLR-3 in vivo and suggests that neurons may play an important role in initiating an inflammatory reaction in a variety of neurological diseases.

Non-classical HLA-G antigen and its role in the cancer progression

Various changes take place during the progression of cancer, some of which are favorable for tumor development and may help to escape the immunosurvillance. These include changes in the microenvironment around the developing tumor, which could be produced in response to phenotypic alterations or could modulate the expression of certain markers of tumor development. One such newly discovered molecule is HLA-G, which has been found to have immunosuppressive and immunomodulatory roles in the cancer development. The regulatory sequences, as seen, may be induced by various factors that may be present in tumor microenvironment. A recent study has investigated the antigen -G as a marker of susceptibility to chemotherapy. Further, its expression on tumors and how it can be exploited for diagnosis and therapy is discussed in this article.

Modulation of HLA-G expression in human neural cells after neurotropic viral infections

HLA-G is a nonclassical human major histocompatibility complex class I molecule. It may promote tolerance, leading to acceptance of the semiallogeneic fetus and tumor immune escape. We show here that two viruses-herpes simplex virus type 1 (HSV-1), a neuronotropic virus inducing acute infection and neuron latency; and rabies virus (RABV), a neuronotropic virus triggering acute neuron infection-upregulate the neuronal expression of several HLA-G isoforms, including HLA-G1 and HLA-G5, the two main biologically active isoforms. RABV induces mostly HLA-G1, and HSV-1 induces mostly HLA-G3 and HLA-G5. HLA-G expression is upregulated in infected cells and neighboring uninfected cells. Soluble mediators, such as beta interferon (IFN-beta) and IFN-gamma, upregulate HLA-G expression in uninfected cells. The membrane-bound HLA-G1 isoform was detected on the surface of cultured RABV-infected neurons but not on the surface of HSV-1-infected cells. Thus, neuronotropic viruses that escape the host immune response totally (RABV) or partially (HSV-1) regulate HLA-G expression on human neuronal cells differentially. HLA-G may therefore be involved in the escape of certain viruses from the immune response in the nervous system.

Mechanisms of resistance to natural killer cell-mediated cytotoxicity in acute lymphoblastic leukemia

OBJECTIVE

Natural killer (NK) cell-mediated cytotoxicity contributes to the innate immune response against numerous malignancies, including leukemias. Acute lymphoblastic leukemias (ALL) often display a high degree of resistance, the mechanisms of which have not been elucidated.

METHODS

We used the well-characterized NK cell line NK-92 as a model to investigate whether mechanisms commonly implicated in tumor escape from NK cell killing are relevant for ALL.

RESULTS

We demonstrate selective resistance of B-precursor ALL to NK-92 cytotoxicity even in the absence of inhibitory killer cell immunoglobulin-like receptors (KIR), except for KIR2DL4. We also show that human leukocyte antigen-G, a ligand of KIR2DL4, expressed on a subset of ALL, does not mediate resistance of NK-cell mediated lysis. Similarly, intracellular adhesion molecule/lymphocyte function-associated antigen-1 interaction did not contribute significantly to resistance. In contrast the NK-sensitive T-ALL (MOLT-4) expressed moderate amounts of MHC class I chain-related gene AB (MICA/B) a ligand for the NK cell activating receptor NKG2D, while expression of MICA/B was absent in resistant B-ALL cell lines.

CONCLUSIONS

The NK cell-resistance of B-lineage ALLs does not appear to involve inhibitory mechanisms, but suggests deficient NK cell activation. Thus, immunostrategies designed to enhance ALL sensitivity toward NK cell-mediated cytotoxicity should focus on mechanisms of NK cell activation.

Switch ofHLA-G alternative splicing in a melanoma cell line causes loss of HLA-G1 expression and sensitivity to NK lysis

Considerable information has been accumulated on HLA-G expression in tumor lesions in which HLA-G is viewed as a way to turn off anti-tumoral immunity. Nevertheless, there is little data concerning the mechanisms by which expression and function of HLA-G are regulated in malignant cells. Here, we have addressed these points by studying a melanoma cell line derived from a surgically-removed HLA-G-positive melanoma lesion. We show that HLA-G expression in melanoma cells can be regulated at the mRNA splicing level. Indeed, melanoma cells rapidly switched from cell-surface HLA-G1 to intra-cellular HLA-G2 expression. This mechanism restored tumor sensitivity to NK lysis. Moreover, switch from HLA-G1 to HLA-G2 was strong enough to prevent re-expression of immunoprotective HLA-G1 even following treatments with cytokines and DNA demethylating agent. Modulating HLA-G at the mRNA splicing level would be an efficient way of lifting in vivo HLA-G-mediated tumor immune escape.

Differential in vivo and in vitro HLA-G expression in melanoma cells: potential mechanisms

The potential role of human leukocyte antigen G (HLA-G) in tumor immune escape has stimulated interest in the analysis of the expression of this molecule in malignant cells. In melanoma approximately 30% and less than 1% of surgically-removed lesions and cultured cell lines, respectively, have been found to express HLA-G protein. The reason for the marked difference in HLA-G expression frequency is unknown. Here we discuss the potential role of HLA-G detection methodology, stress factors in the tumor microenvironment, and epigenetic changes during tumor progression in the differential in vivo and in vitro HLA-G expression in melanoma cells. We propose a model that may account for the preferential in vivo HLA-G expression in melanoma cells. If proven correct, this model represents a useful background to investigate the mechanisms regulating HLA-G expression in melanoma cells and to devise strategies to counteract HLA-G expression in patients with melanoma.

HLA-G in melanoma: can the current controversies be solved?

The potential role of HLA-G in tumor immune escape has stimulated interest in the analysis of HLA-G antigens in malignant cells. Malignant melanoma is the tumor which has been mostly analyzed for HLA-G expression. Results obtained by seven groups of investigators about HLA-G expression in 108 melanoma cell lines have been concordant. HLA-G mRNA has been found in about 50% of the cell lines tested, whereas HLA-G protein has been found in less than 1% of the cell lines analyzed. In contrast, results obtained from six groups of investigators about HLA-G protein expression in 133 melanoma lesions have been conflicting. The possible causes of these conflicting results as well as the reasons for the discrepancy in HLA-G expression between cultured melanoma cell lines and surgically removed lesions have been discussed. Lastly, data about the potential clinical relevance of HLA-G expression in melanoma has been reviewed. The available data in the literature strongly suggest that progress in this exciting research area would greatly benefit from experiments to solve the current controversies in the field.

Hide-and-seek in the brain: a role for HLA-G mediating immune privilege for glioma cells

This review summarizes the current knowledge on the expression and functional role of HLA-G in normal CNS cells and brain tumor cells in vitro and in vivo. The CNS has classically been viewed as an immune-privileged organ. Here we discuss some of the particularities of anti-tumoral responses within this compartment. Special emphasis is dedicated to the possible role of the non-classical MHC molecule HLA-G as an alternative mechanism of immune escape. We review the mechanisms how glioma cell-derived HLA-G may paralyze the immune system and which cellular subsets of the immune system are affected. Possible therapeutic implications derived from these observations include the targeting of HLA-G expression within the framework of inducing glioma-specific immunity.

HLA-G in cancer: a way to turn off the immune system

The expression of HLA-G in cancer represents a strategy employed by tumors to avoid immune destruction. Indeed, this non-classical HLA class I molecule suppresses various immune cell functions through binding to inhibitory receptors. We here review the studies done by our group that described for the first time (i) HLA-G expression in malignancies such as melanomas, renal and breast carcinomas. (ii) the up-regulation of HLA-G gene transcription by tumor environmental factors such as cytokines and stress and by agents used in chemotherapy such as demethylating molecules, and (iii) the biological relevance of such HLA-G expression in the evasion of malignant cells from antitumor immune response.

HLA-G in transplantation: a relevant molecule for inhibition of graft rejection?

The human MHC class I molecule HLA-G has long been known as a molecule selectively expressed by cytotrophoblastic cells. By inhibiting the cytolytic function of decidual NK cells, HLA-G protects the HLA-A and -B negative semiallogeneic embryonic tissue against the mother's immune system. In the light of this immuno-suppressive function, the role of HLA-G in transplantation was investigated. We will review here recently published data on this topic, showing that expression of HLA-G affects the responsive capacity of the immune system, might directly participate in graft acceptation, and should be taken into account for the monitoring of transplantation patients.

HLA-G Molecules: from Maternal–Fetal Tolerance to Tissue Acceptance

Over the past few years, HLA-G, the non-classical HLA class I molecule, has been the center of investigations that have led to the description of its specific structural and functional properties. Although located in the HLA class I region of chromosome six, the HLA-G gene may be distinguished from other HLA class I genes by its low polymorphism and alternative splicing that generates seven HLA-G proteins, whose tissue-distribution is restricted to normal fetal and adult tissues that display a tolerogeneic function toward both innate and acquired immune cells. We review these points, with special emphasis on the role of HLA-G in human pathologies, such as cancer, viral infection, and inflammatory diseases, as well as in organ transplantation.

A functional role of HLA-G expression in human gliomas: an alternative strategy of immune escape

HLA-G is a nonclassical MHC molecule with highly limited tissue distribution that has been attributed chiefly immune regulatory functions. Glioblastoma is paradigmatic for the capability of human cancers to paralyze the immune system. To delineate the potential role of HLA-G in glioblastoma immunobiology, expression patterns and functional relevance of this MHC class Ib molecule were investigated in glioma cells and brain tissues. HLA-G mRNA expression was detected in six of 12 glioma cell lines in the absence of IFN-gamma and in 10 of 12 cell lines in the presence of IFN-gamma. HLA-G protein was detected in four of 12 cell lines in the absence of IFN-gamma and in eight of 12 cell lines in the presence of IFN-gamma. Immunohistochemical analysis of human brain tumors revealed expression of HLA-G in four of five tissue samples. Functional studies on the role of HLA-G in glioma cells were conducted with alloreactive PBMCs, NK cells, and T cell subpopulations. Expression of membrane-bound HLA-G1 and soluble HLA-G5 inhibited alloreactive and Ag-specific immune responses. Gene transfer of HLA-G1 or HLA-G5 into HLA-G-negative glioma cells (U87MG) rendered cells highly resistant to direct alloreactive lysis, inhibited the alloproliferative response, and prevented efficient priming of cytotoxic T cells. The inhibitory effects of HLA-G were directed against CD8 and CD4 T cells, but appeared to be NK cell independent. Interestingly, few HLA-G-positive cells within a population of HLA-G-negative tumor cells exerted significant immune inhibitory effects. We conclude that the aberrant expression of HLA-G may contribute to immune escape in human glioblastoma.

Specific activation of the non-classical class I histocompatibility HLA-G antigen and expression of the ILT2 inhibitory receptor in human breast cancer

The HLA-G molecule is a non-classical HLA class I antigen selectively expressed by trophoblastic cells that invade the maternal decidua during human pregnancy. HLA-G is believed to contribute to tolerance of the semi-allogeneic fetus by inhibiting maternal immune responses. Similarly, HLA-G expression in tumour cells may favour their escape from host immune surveillance. This study investigated HLA-G expression in human mammary tumours. Immunohistochemical analysis of cryo-preserved and paraffin-embedded breast tissue biopsies, using two HLA-G-specific antibodies, revealed that unlike non-cancerous breast tissue in the vicinity of the tumour, 14 out of 36 breast cancer lesions selectively expressed HLA-G. HLA-G expression was significantly more frequent in lesions that were highly infiltrated by host immune cells, thus correlating HLA-G activation with inflammation. Further histological and double-staining immunofluorescence analysis attributed HLA-G expression mainly to tumour epithelial cells and to subsets of infiltrating CD68+ and CD8+ cells. RT-PCR analysis suggested that HLA-G was activated at the transcriptional level in breast tumours. The presence of ILT2 (Ig-like transcript 2) killing inhibitory receptors known to interact with HLA-G was also demonstrated in host immune cells that infiltrate breast cancer lesions. These results indicate that HLA-G is up-regulated at high frequencies in human breast cancer, where it may impair efficient anti-tumour immunity.

Modulation of HLA-G antigens expression by human cytomegalovirus: specific induction in activated macrophages harboring human cytomegalovirus infection

After infection, human CMV (HCMV) establishes a latent and persistent infection in immature myeloid progenitors and peripheral blood monocytes. Completion of the HCMV life cycle is possible upon maturation of monocytes to tissue macrophages and under permissive circumstances, e.g., immunosuppression. We investigated the hypothesis that HLA-G molecules could be induced during HCMV reactivation in activated macrophages to favor virus dissemination. In this study, we provide evidence that HLA-G Ags are produced during viral reactivation in macrophages generated after allogeneic stimulation of HCMV latently infected monocytes. While HLA-G surface expression is up-regulated, classical MHC-I molecules are partially down-regulated by HCMV. In vivo, bronchoalveolar macrophages collected from patients suffering from acute HCMV pneumonitis also express HLA-G molecules. The direct correlation between HLA-G Ag induction and HCMV infection was confirmed in U-373 MG astrocytoma cells. Soluble HLA-G expression is stimulated upon HCMV infection, and this modulation depends on the cooperative action of the two immediate-early-1 pp72 and immediate-early-2 pp86 products. Because HLA-G transcription is active in macrophages and U-373 MG astrocytoma cells, it is likely that the modulation of HLA-G protein expression during HCMV replication occurs at a post-transcriptional level. Our data suggest that induction of HLA-G molecules could be an additional mechanism that helps HCMV to subvert host defenses.