Up-regulation of HLA-G expression in cervical premalignant and malignant lesions

Analogies between HPV Behavior in Oral and Vaginal Cavity: Narrative Review on the Current Evidence in the Literature

Human genital papilloma virus infection is the most prevalent sexually transmitted infection in the world. It is estimated that more than 75% of sexually active women contract this infection in their lifetime. In 80% of young women, there is the clearance of the virus within 18-24 months. In developed countries, oral squamous cell carcinoma (OSCC) is now the most frequent human papilloma virus (HPV)-related cancer, having surpassed cervical cancer, and it is predicted that by 2030 most squamous cell carcinomas will be the HPV-related rather than non-HPV-related form. However, there are currently no screening programs for oral cavity infection. While the natural history of HPV infection in the cervix is well known, in the oropharynx, it is not entirely clear. Furthermore, the prevalence of HPV in the oropharynx is unknown. Published studies have found wide-ranging prevalence estimates of 2.6% to 50%. There are also conflicting results regarding the percentage of women presenting the same type of HPV at two mucosal sites, ranging from 0 to 60%. Additionally, the question arises as to whether oral infection can develop from genital HPV infection, through oral and genital contact or by self-inoculation, or whether it should be considered an independent event. However, there is still no consensus on these topics, nor on the relationship between genital and oral HPV infections. Therefore, this literature review aims to evaluate whether there is evidence of a connection between oral and cervical HPV, while also endorsing the usefulness of the screening of oral infection in patients with high-risk cervical HPV as a means of facilitating the diagnosis and early management of HPV-related oral lesions. Finally, this review emphasizes the recommendation for the use of the HPV vaccines in primary prevention in the male and female population as the most effective means of successfully counteracting the increasing incidence of OSCC to date.

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

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

HLA-G 3'UTR polymorphism diplotypes and soluble HLA-G plasma levels impact cervical cancer susceptibility and prognosis

Background

Human leukocyte antigen G (HLA-G) is an immune checkpoint molecule with relevance in several cancers. The aim of this study was to evaluate the potential role of soluble HLA-G (sHLA-G), its genetic polymorphisms and its haplotype structure in the susceptibility and prognosis of primary cervical cancer in a Chinese Han population.

Methods

We investigated sHLA-G plasma levels and 3' untranslated region (3'UTR) polymorphisms through ELISA and direct DNA sequencing, respectively, in cervical cancer patients (120 cases) and healthy control women (96 cases). The data were analyzed for associations using PowerMarker, Haploview, and GraphPad Prism.

Results

In this study, 8 polymorphic sites, 16 haplotypes and 23 diplotypes in the HLA-G 3'UTR were identified in our study population. We observed that each pair of 8 polymorphic sites exhibited linkage disequilibrium. The heterozygote CT genotype at position +3422 (rs17875408) was more common in cervical cancer patients than in healthy women (OR=5.285, P<0.05). Haplotypes UTR-1, UTR-3, and UTR-7 accounted for more than 85% of both groups, but no significant difference was found. The frequency of the UTR-1/UTR-3 diplotype in patients was significantly higher than that in controls (P<0.05). In addition, we further observed that HLA-G 3'UTR polymorphisms may influence the sHLA-G plasma level in patients' peripheral blood, especially 14 bp Ins/Del (rs371194629) and +3142 C/G (rs1063320). A receiver operating characteristic (ROC) curve analysis showed that the sHLA-G level had good diagnostic performance in differentiating patients with cervical cancer from healthy women (AUC>0.7). Among patients, mean sHLA-G levels increased with increasing FIGO stages but were not related to the overall survival time.

Conclusions

The results of the present study enhance our understanding of how HLA-G 3'UTR polymorphisms can influence the peripheral sHLA-G plasma level and play a key role in cervical carcinogenesis. This study further confirmed that sHLA-G may represent a novel plasma biomarker for the prognosis and potential therapeutic target of cervical cancer.

Dynamic changes of soluble HLA-G and cytokine plasma levels in cervical cancer patients: potential role in cancer progression and immunotherapy

PURPOSE

Chronic inflammation has been proven to be an important factor in carcinogenesis. Cytokines are the central mediators in the inflammatory microenvironment, and their release may be influenced by soluble HLA-G (sHLA-G). The aim of this study was to monitor the dynamic process of these soluble factors in patients with cervical cancer at Taizhou Hospital of Zhejiang Province, trying to understand their relationship with diagnosis, treatment, and prognosis.

METHODS

We quantified plasma levels of sHLA-G and 12 cytokines using ELISA and flow cytometry, respectively, in the peripheral blood of patients with cervical cancer divided into three groups: preoperation, postoperation and clinical relapse. Healthy women were used as the control group. Data were analysed by non-parametric tests, receiver-operating characteristic (ROC) curves, and Kaplan-Meier plotter (log-rank test).

RESULTS

In this study, our findings showed that preoperation plasma levels of sHLA-G and the cytokines IL-6, IL-10, and IFN-γ in cervical cancer patients had a good discriminatory effect between cervical cancer patients and healthy women. It should be noted that plasma levels of sHLA-G, IL-6, and IL-10 were significantly decreased within 30 days after radical hysterectomy (P < 0.05). A positive correlation was observed between IL-6 and IL-10, IL-8 and IL-17 levels preoperatively. In contrast, sHLA-G levels were negatively correlated with IL-10 but not with other cytokines. An increased survival rate in patients with cervical cancer was associated with IL-5 < 1.70 pg/mL, IL-17 < 2.30 pg/mL, and IFN-α < 2.26 pg/mL preoperatively. In addition, our findings showed that the levels of cytokines IL-6, IL-8, IL-12p70, IL-17, and IFN-γ may be related to 5-year relapse rates and/or the metastasis of cervical cancer.

CONCLUSION

The current findings enhance our understanding of the dynamic process (preoperation, postoperation and clinical relapse) of sHLA-G and these cytokines in the plasma of patients with cervical cancer from diagnosis to prognosis. These biomarkers may play a potential therapeutic target role of such dynamic changes in the immunotherapy for cervical cancer.

The Creation of the Suppressive Cancer Microenvironment in Patients with HPV-Positive Cervical Cancer

The development of malignancy is closely connected with the process of cancer microenvironment remodeling. As a malignancy develops, it stimulates the creation of the suppressive microenvironment of the tumor through the presence of cells that express membrane proteins. These proteins are secreted into the cancer microenvironment, where they enable tumor growth. In patients with cancer of the cervix, the development of the disease is also linked to high-risk HPV (hr-HPV) infection. Such infections are common, and most clear spontaneously; however, a small percentage of these infections can persist and progress into precancerous cervical intraepithelial neoplasia and invasive cervical carcinoma. Consequently, it is assumed that the presence of hr-HPV infection alone is not sufficient for the development of cancer. However, chronic HPV infection is associated with the induction of the remodeling of the microenvironment of the epithelium. Furthermore, the local microenvironment is recognized as a cofactor that participates in the persistence of the HPV infection and disease progression. This review presents the selected immune evasion mechanisms responsible for the persistence of HPV infection, beginning with the delay in the virus replication process prior to the maturation of keratinocytes, the shift to the suppressive microenvironment by a change in keratinocyte immunomodulating properties, the alteration of the Th1/Th2 polarization of the immune response in the microenvironment, and, finally, the role of HLA-G antigen expression.

A Novel Prognostic Risk Model for Cervical Cancer Based on Immune Checkpoint HLA-G-Driven Differentially Expressed Genes

Human leukocyte antigen G (HLA-G) is a potential checkpoint molecule that plays a key role in cervical carcinogenesis. The purpose of this study was to construct and validate a prognostic risk model to predict the overall survival (OS) of cervical cancer patients, providing a reference for individualized clinical treatment that may lead to better clinical outcomes. HLA-G-driven differentially expressed genes (DEGs) were obtained from two cervical carcinoma cell lines, namely, SiHa and HeLa, with stable overexpression of HLA-G by RNA sequencing (RNA-seq). The biological functions of these HLA-G-driven DEGs were analysed by GO enrichment and KEGG pathway using the “clusterProfiler” package. The protein-protein interactions (PPIs) were assessed using the STRING database. The prognostic relevance of each DEG was evaluated by univariate Cox regression using the TCGA-CESC dataset. After the TCGA-CESC cohort was randomly divided into training set and testing set, and a prognostic risk model was constructed by LASSO and stepwise multivariate Cox regression analysis in training set and validated in testing set or in different types of cervical cancer set. The predictive ability of the prognostic risk model or nomogram was evaluated by a series of bioinformatics methods. A total of 1108 candidate HLA-G-driven DEGs, including 391 upregulated and 717 downregulated genes, were obtained and were enriched mostly in the ErbB pathway, steroid biosynthesis, and MAPK pathway. Then, an HLA-G-driven DEG signature consisting of the eight most important prognostic genes CD46, LGALS9, PGM1, SPRY4, CACNB3, PLIN2, MSMO1, and DAGLB was identified as a key predictor of cervical cancer. Multivariate Cox regression analysis showed that this signature is an independent risk factor for the overall survival of CESC patients. Kaplan-Meier survival analysis showed that the 5-year overall survival rate is 23.0% and 84.6% for the high-risk and low-risk patients, respectively (P<0.001). The receiver operating characteristic (ROC) curve of this prognostic model with an area under the curve (AUC) was 0.896 for 5 years, which was better than that of other clinical traits. This prognostic risk model was also successfully validated in different subtypes of cervical cancer, including the keratinizing squamous cell carcinoma, non-keratinizing squamous cell carcinoma, squamous cell neoplasms, non-squamous cell neoplasms set. Single-sample gene set enrichment (ssGSEA) algorithm and Tumor Immune Dysfunction and Exclusion (TIDE) analysis confirmed that this signature influence tumour microenvironment and immune checkpoint blockade. A nomogram that integrated risk score, age, clinical stage, histological grade, and pathological type was then built to predict the overall survival of CESC patients and evaluated by calibration curves, AUC, concordance index (C-index) and decision curve analysis (DCA). To summarize, we developed and validated a novel prognostic risk model for cervical cancer based on HLA-G-driven DEGs, and the prognostic signature showed great ability in predicting the overall survival of patients with cervical cancer.

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

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

Evaluating the HLA-G (rs1063320) genetic variant and risk of human papillomavirus infection: a meta-analysis of 953 cases and 877 controls

Human leukocyte antigen-G (HLA-G) has immune-modulatory functions. Although the role of genetic variant HLA-G (rs1063320) in susceptibility to human papillomavirus (HPV) infection has been widely considered, it is still a matter of discussion. In order to shed light on the issue, we, therefore, conducted a meta-analysis to evaluate the common impact of the HLA-G (rs1063320) variant on susceptibility to HPV infection. Subsequently, the distribution of genotypes, genotyping techniques and ethnicity groups was collected, and general analyses were performed. A total number of five studies with 953 cases and 877 controls were found to meet our criteria. The polymorphism of HLA-G (rs1063320) was evaluated. This is the first meta-analysis to explore the connection between the HLA-G 3' UTR + 3142C/G (rs1063320) genetic variant and the risk of HPV infection. Our results showed no association between the variant of HLA-G 3' UTR + 3142C/G (rs1063320) and susceptibility to HPV infection in studied target populations.Impact StatementWhat is already known on this subject? Human papillomavirus (HPV) is the most widespread sexually transmitted infection in both men and women all over the world. It is correlated with prominent load of diseases and malignancies, including anogenital warts and anogenital and oropharyngeal cancers. In recent years, several studies manifested that different SNPs located on special genes seems to influence HPV infection risk.What the results of this study add? Our findings disclosed no relation between the variant of HLA-G 3' UTR + 3142C/G (rs1063320) and vulnerability to HPV infection in the target individuals.What are the implications of these findings for clinical practice and/or further research? The findings in current survey may offer a basis for further study on HLA-G variant in future investigation.

Comprehensive Transcriptomic Analysis Reveals the Role of the Immune Checkpoint HLA-G Molecule in Cancers

Human leukocyte antigen G (HLA-G) is known as a novel immune checkpoint molecule in cancer; thus, HLA-G and its receptors might be targets for immune checkpoint blockade in cancer immunotherapy. The aim of this study was to systematically identify the roles of checkpoint HLA-G molecules across various types of cancer. ONCOMINE, GEPIA, CCLE, TRRUST, HAP, PrognoScan, Kaplan-Meier Plotter, cBioPortal, LinkedOmics, STRING, GeneMANIA, DAVID, TIMER, and CIBERSORT were utilized. Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment analyses were performed. In this study, we comprehensively analysed the heterogeneous expression of HLA-G molecules in various types of cancer and focused on genetic alterations, coexpression patterns, gene interaction networks, HLA-G interactors, and the relationships between HLA-G and pathological stage, prognosis, and tumor-infiltrating immune cells. We first identified that the mRNA expression levels of HLA-G were significantly upregulated in both most tumor tissues and tumor cell lines on the basis of in-depth analysis of RNAseq data. The expression levels of HLA-G were positively associated with those of the other immune checkpoints PD-1 and CTLA-4. Abnormal expression of HLA-G was significantly correlated with the pathological stage of some but not all tumor types. There was a significant difference between the high and low HLA-G expression groups in terms of overall survival (OS) or disease-free survival (DFS). The results showed that HLA-G highly expressed have positive associations with tumor-infiltrating immune cells in the microenvironment in most types of tumors (P<0.05). Additionally, we identified the key transcription factor (TF) targets in the regulation of HLA-G expression, including HIVEP2, MYCN, CIITA, MYC, and IRF1. Multiple mutations (missense, truncating, etc.) and the methylation status of the HLA-G gene may explain the differential expression of HLA-G across different tumors. Functional enrichment analysis showed that HLA-G was primarily related to T cell activation, T cell regulation, and lymphocyte-mediated immunity. The data may provide novel insights for blockade of the HLA-G/ILT axis, which holds potential for the development of more effective antitumour treatments.

HLA-G and single nucleotide polymorphism (SNP) associations with cancer in African populations: Implications in personal medicine

The immune system plays an important role in protecting the body against malignancy. During cancer immunoediting, the immune system can recognize and keep checking the tumor cells by down-expression of some self-molecules or by increasing expression of some novel molecules. However, the microenvironment created in the course of cancer development hampers the immune ability to recognize and destroy the transforming cells. Human Leukocyte Antigen G (HLA-G) is emerging as immune checkpoint molecule produced more by cancer cells to weaken the immune response against them. HLA-G is a non-classical HLA class I molecule which is normally expressed in immune privileged tissues as a soluble or membrane-bound protein. HLA-G locus is highly polymorphic in the non-coding 3′ untranslated region (UTR) and in the 5′ upstream regulatory region (5′ URR). HLA-G expression is controlled by polymorphisms located in these regions, and several association studies between these polymorphic sites and disease predisposition, response to therapy, and/or HLA-G protein expression have been reported. Various polymorphisms are demonstrated to modulate its expression and this is increasingly finding more significance in cancer biology. This review focuses on the relevance of the HLA-G gene and its polymorphisms in cancer development. We highlight population genetics of HLA-G as evidence to espouse the need and importance of exploring potential utility of HLA-G in cancer diagnosis, prognosis and immunotherapy in the currently understudied African population.

HLA-G polymorphism impacts the outcome of oral HPV infections in women

BACKROUND

Human leukocyte antigen (HLA)-G may have an important role in the natural history of human papillomavirus (HPV) infection. Our aim was to evaluate the role of HLA-G in the outcome of genital and oral HPV infections in women.

METHODS

Analyses included 306 women from the Finnish Family HPV-study and were followed-up for six years. Genital and oral samples were tested for 24 different HPV types with multiplex HPV genotyping. HLA-G alleles were determined through direct DNA-sequencing. Unconditional logistic regression was used to determine the associations between HLA-G genotypes and HPV infection outcomes.

RESULTS

Ten HLA-G alleles were identified. Most common HLA-G genotypes were the wild type G*01:01:01/01:01:01 (31.3%) followed by G*01:01:01/01:01:02 (26.8%). G*01:01:01/01:01:01 genotype was associated with increased risk of oral HPV infections by any HPV type or single-type with OR = 1.86 (95% CI 1.14-3.04, P = 0.01) and 2.22 (95% CI 1.14-3.71, P = 0.02), respectively. G*04:01+ allele and the G*01:01:01/01:04:01 genotype both protected from any and single oral HPV infections; OR = 0.46 (95% CI 0.23-0.89, P = 0.02) and 0.53 (95% CI 0.23-0.97, P = 0.03), respectively. G*01:01:02/01:04:01 genotype increased significantly the risk of infertility and its treatments, with respective OR = 5.06 (95% CI 1.22-21.02, P = 0.03) and OR = 9.07 (95% CI 1.22-39.50, P = 0.03). Both HLA-G alleles and genotypes showed several significant associations with the outcomes of oral HPV infections, but none of them had any impact on the outcomes of genital HPV infections in these women.

CONCLUSIONS

The host HLA-G genotypes appear to impact the outcomes of oral HPV infections in women but have little if any effect on genital HPV status or infection outcomes.

The Role of HLA-G in Tumor Escape: Manipulating the Phenotype and Function of Immune Cells

Human leukocyte antigen-G (HLA-G) is a non-classical major histocompatibility complex class I (MHC I) molecule, and under physiological conditions, its expression is strictly restricted to the maternal–fetal interface and immune-privileged organs where HLA-G is expected to contribute to establishment and maintenance of immune tolerance. However, the expression of HLA-G has been found in various types of tumors, and the level of its expression frequently correlates with high-grade histology and poor prognosis, raising the possibility that it may play a negative role in tumor immunity. ILT2 and ILT4, present on a broad of immune cells, have been identified as the main receptors engaging HLA-G, and their interactions have been found to allow the conversion of effectors like NK cells and T cells to anergic or unresponsive state, activated DCs to tolerogenic state, and to drive the differentiation of T cells toward suppressive phenotype. Therefore, tumors can employ HLA-G to modulate the phenotype and function of immune cells, allowing them to escape immune attack. In this review, we discuss the mechanism underlying HLA-G expression and function, its role played in each step of the tumor-immunity cycle, as well as the potential to target it for therapeutic benefit.

Understanding HLA-G driven journey from HPV infection to cancer cervix: Adding missing pieces to the jigsaw puzzle

Human Papillomavirus (HPV) is a vital risk-factor for cancer cervix. However, persistent HPV infection results in cervical cancer in only a minority. Probably, HPV subdues the host immune response for persistence, which includes augmentation of HLA-G and plausibly aids in progression to cervical cancer. HLA-G, which comprises of membrane and soluble form, downregulates the host's immune response and generate tolerance. The current study aimed to analyze both forms of HLA-G in fresh tissue and plasma of women with HPV-infected and uninfected cervix and cancer cervix using Western blot and ELISA. The study cohort included 30 women with cervical carcinoma and equal number with normal cervix and 6 with HPV infected cervix. We observed a significant upregulation of membranous HLA-G expression in HPV infected cervix and cervical carcinoma (P < 0.001). Interestingly, the pairwise comparison of HLA-G tissue protein expression of the normal cervix and cervical carcinoma, as well as the normal cervix with HPV infected cervix, was significant (P < 0.001). Levels of soluble HLA-G were significantly raised in carcinoma cervix. We observed a progressive increase in HLA-G protein expression in HPV infected cervix and cervical carcinoma. These findings compel us to hypothesize that the upregulation of HLA-G expression favors the persistence of HPV in a microenvironment of a submissive host response. This progressive upregulation further leads to cervical cancer. Thus elimination of HPV infection seems to be a desirable proposition to prevent cervical cancer. In the absence of antiviral therapy for HPV, exploration of HLA-G antibody-based therapeutic strategies appear promising.

The Role of HLA-G in Human Papillomavirus Infections and Cervical Carcinogenesis

Human leukocyte antigen (HLA)-G, a non-classical HLA-class I molecule, has a low polymorphism frequency, restricted tissue distribution and immunoinhibitory property. HLA-G expression in tumor cells and cells chronically infected with virus may enable them to escape from host immune surveillance. It is well-known that the HLA-G molecule is a novel biomarker and potential therapeutic target that is relevant in various types of cancers, but its role in cervical cancer has not been fully explored. In this review, we aim to summarize and discuss the immunologic role of the HLA-G molecule in the context of HPV infections and the process of cervical cancer carcinogenesis. A better understanding of the potential impact of HLA-G on the clinical course of persistent HPV infections, cervical epithelial cell transformation, tumor growth, recurrence and metastasis is needed to identify a novel diagnostic/prognostic biomarker for cervical cancer, which is critical for cervical cancer risk screening. In addition, it is also necessary to identify HLA-G-driven immune mechanisms involved in the interactions between host and virus to explore novel immunotherapy strategies that target HLA-G/immunoglobulin-like transcript (ILT) immune checkpoints.

Soluble HLA-G expression levels and HLA-G/irinotecan association in metastatic colorectal cancer treated with irinotecan-based strategy

We here explore the soluble Human Leukocyte Antigen-G (sHLA-G) expression level as clinical biomarker in metastatic colorectal cancer (mCRC). To this aim the sHLA-G protein was measured in plasma samples of 40 patients with mCRC treated with the FOLFIRI (irinotecan (CPT-11) plus 5-fluorouracil (5-FU) and leucovorin (LV)) regimen. The results suggest a link between HLA-G levels and irinotecan (CPT-11) pharmacokinetic, leading to hypothesize a molecular interaction between sHLA-G and CPT-11. This interaction was confirmed experimentally by fluorescence spectroscopy. HLA-G is known to exist in a number of polymorphs that affect both the protein expression levels and its peptide-binding cleft. The interaction between HLA-G polymorphs and CPT-11 was explored by means of computational modelling, confirming the hypothesis that CPT-11 could actually target the peptide binding cleft of the most common HLA-G polymorphs.

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

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

Association of HLA-G 3' UTR polymorphism and expression with the progression of cervical lesions in human papillomavirus 18 infections

Background

Human leukocyte antigen (HLA)-G is an immune checkpoint molecule, which expression in cervical cancer cells enables them to escape immunosurveillance. To date, limited information has been published on the association of HLA-G genetic background in malignant cells with levels of HLA-G expression and the clinical outcome of patients.

Methods

We investigated the influence of the HLA-G 14 bp In/Del (rs66554220) and + 3142C/G (rs1063320) polymorphisms in 130 cases of HPV16 infection, 130 cases of HPV18 infection and 185 age-matched, unrelated, HPV-negative, and cytologically normal Chinese Han women. Case-matched cervical biopsy tissues were evaluated by immunohistochemistry.

Results

Our findings show that the frequency of alleles, 14 bp In (38.5% vs 29.2%, OR = 1.52, P < 0.05) and + 3142G (72.7% vs 57.0%, OR = 2.01, P < 0.05), were significantly increased in the HPV18-infected group compared with the control group. The HLA-G polymorphisms (alleles 14 bp In and + 3142G) are also associated with the progression of HPV18-related cervical lesions. Moreover, HLA-G expression increased from CIN1 to CIN2/3 lesions and was highest in patients with adenocarcinoma; however, a significant association between these characteristics and the HLA-G polymorphisms was not observed.

Conclusion

Our results support that the HLA-G 14 bp In and + 3142G alleles are risk factors for HPV18 infections and influence the progression of HPV18-related cervical lesions. This suggests that HLA-G-driven immune mechanisms play an important role in cervical carcinogenesis.

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.

Importance of the plasma soluble HLA-G levels for prognostic stratification with traditional prognosticators in colorectal cancer

An increased peripheral soluble HLA-G (sHLA-G) expression has been observed in various malignancies while its prognostic significance was rather limited. In this study, the prognostic value of plasma sHLA-G in 178 colorectal cancer (CRC) patients was investigated. sHLA-G levels were analyzed by specific enzyme-linked immunosorbent assay. Data showed sHLA-G levels were significantly increased in CRC patients compared with normal controls (36.8 U/ml vs 25.4 U/ml, p = 0.009). sHLA-G in the died were obviously higher than that of alive CRC patients (46.8 U/ml vs 27.4 U/ml, p = 0.012). Patients with sHLA-G above median levels (≥ 36.8 U/ml, sHLA-Ghigh) had a significantly shorter survival time than those with sHLA-Glow (< 36.8 U/ml, p < 0.001), and sHLA-G could be an independent prognostic factor for CRC patients. With stratification of clinical parameters in survival by sHLA-Glow and sHLA-Ghigh, sHLA-G exhibited a significant predictive value for CRC patients of the female (p = 0.036), the elder (p = 0.009), advanced tumor burden (T3 + 4, p = 0.038), regional lymph node status (N0, p = 0.041), both metastasis status (M0, p = 0.014) and (M1, p=0.018), and clinical stage (I + II, p = 0.018), respectively. Summary, our data demonstrated for the first time that sHLA-G levels is an independent prognosis factor and improves the prognostic stratification offered by traditional prognosticators in CRC patients.

Evaluation of ascitic soluble human leukocyte antigen-G for distinguishing malignant ascites from benign ascites

The overexpression of soluble human leukocyte antigen-G is associated with malignant tumours. The purpose of our study was to detect soluble human leukocyte antigen-G concentrations in ascites and to evaluate the value of ascitic soluble human leukocyte antigen-G for the diagnosis of malignant ascites. Enzyme-linked immunosorbent assay was used to detect soluble human leukocyte antigen-G levels in 64 patients with malignant ascites and 30 patients with benign ascites. Receiver operating characteristic curves were used to evaluate the diagnostic efficacy of ascitic soluble human leukocyte antigen-G for the detection of malignant ascites. Ascitic soluble human leukocyte antigen-G levels were significantly higher in the malignant ascites group than in the benign ascites group (20.718 ± 3.215 versus 12.467 ± 3.678 µg/L, t = 7.425, p < 0.001). The area under the receiver operating characteristic curve for ascitic soluble human leukocyte antigen-G was 0.957 (95% confidence interval, 0.872-0.992). At a cut-off value of 19.60 µg/L, the sensitivity and specificity of ascitic soluble human leukocyte antigen-G were 87.5% (95% confidence interval, 71.0%-96.5%) and 100% (95% confidence interval, 88.4%-100%), respectively. With respect to area under the receiver operating characteristic curve, sensitivity and specificity, ascitic carcinoembryonic antigen (0.810, 68.75% and 83.33%, respectively) and carbohydrate antigen 19-9 (0.710, 65.63% and 70%, respectively) significantly differed (all p < 0.05). In malignant ascites that were cytology-negative and biopsy-positive, the rate of positivity for ascitic soluble human leukocyte antigen-G was 75%, which was higher than the corresponding rates for ascitic carcinoembryonic antigen (31.25%) and carbohydrate antigen 19-9 (6.25%; both p < 0.05). In conclusion, The detection of ascitic soluble human leukocyte antigen-G exhibited good performance for diagnosing malignant ascites, and particularly those that were cytology-negative and biopsy-positive.

Greater expression of the human leukocyte antigen-G (HLA-G) and interleukin-17 (IL-17) in cervical intraepithelial neoplasia: analytical cross-sectional study

CONTEXT AND OBJECTIVE

Impaired local cell immunity seems to contribute towards the pathogenesis and progression of cervical intraepithelial neoplasia (CIN), but the underlying molecular mechanisms promoting its progression remain unclear. Identification of new molecular markers for prognosis and diagnosis of early-stage CIN may aid in decreasing the numbers of CIN cases. Several novel immunoregulatory molecules have been discovered over the past few years, including the human leukocyte antigen G (HLA-G), which through interaction with its receptors exerts important tolerogenic functions. Several lines of evidence suggest that T-helper interleukin-17 (IL-17)-producing cells (Th17 cells) may play a role in antitumor immunity. However, recent reports have implicated Th17 cells and their cytokines in both pro and anti-tumorigenic processes. The aim of the study was to evaluate the roles of HLA-G and Th17 in the immunopathogenesis of CIN I.

DESIGN AND SETTING

Analytical cross-sectional study with a control group using 58 cervical specimens from the files of a public university hospital providing tertiary-level care.

METHODS

We examined HLA-G and IL-17 expression in the cervical microenvironment by means of immunohistochemistry, and correlated these findings with clinical and pathological features.

RESULTS

There was a greater tendency towards HLA-G and IL-17 expression in specimens that showed CIN I, thus suggesting that these molecules have a contribution towards cervical progression.

CONCLUSION

These findings suggest that HLA-G and IL-17 expression may be an early marker for assessing the progression of cervical lesions.

High levels of soluble MICA are significantly related to increased disease-free and disease-specific survival in patients with cervical adenocarcinoma

Downregulation of major histocompatibility complex class I chain-related molecule A (MICA) and upregulation of human leukocyte antigen G (HLA-G) on the tumor cells are important immune escape mechanisms for different epithelial tumors. In addition, upregulation of the soluble forms of the latter molecules in serum leads to peripheral T-cell and natural killer (NK)-cell tolerance. As for cervical cancer, it remains unknown whether soluble MICA (sMICA) and soluble HLA-G (sHLA-G) concentrations are related to tumor characteristics or patient survival rates. We measured sMICA and sHLA-G in pre-treatment sera of a large cohort of cervical cancer patients (n = 366) by enzyme-linked immunosorbent assay (ELISA). We detected a median sMICA of 174.73 pg/ml and a median sHLA-G of 5.35 U/ml. We did not find an association between sHLA-G levels and clinicopathological characteristics. In adenocarcinoma, low sMICA concentration was positively related to recurrent disease, a higher International Federation of Gynecology and Obstetrics (FIGO) stage and vaginal involvement (Mann-Whitney U-test; P = 0.018, P = 0.042 and P = 0.013, respectively). In the latter patient group, high sMICA levels were associated with better disease-free survival (DFS) and disease-specific survival (DSS) (P = 0.011 and P = 0.047). After adjusting for confounding factors, high sMICA proved to be an independent predictor for a better DFS and DSS [HR 0.16; 95% confidence interval (CI) 0.04-0.64; P = 0.009 and HR 0.12; 95% CI 0.03-0.50; P = 0.004]. sHLA-G did not influence survival in cervical cancer patients, regardless of histology. We conclude that cervical adenocarcinoma patients with high sMICA levels have an increased DFS and DSS. This data warrants a prospective trial to study the functional role of sMICA in cervical adenocarcinoma.

Human leukocyte antigen (HLA)-G and cervical cancer immunoediting: a candidate molecule for therapeutic intervention and prognostic biomarker?

While persistent infection with oncogenic types of human Papillomavirus (HPV) is required for cervical epithelial cell transformation and cervical carcinogenesis, HPV infection alone is not sufficient to induce tumorigenesis. Only a minor fraction of HPV infections produce high-grade lesions and cervical cancer, suggesting complex host-virus interactions. Based on its pronounced immunoinhibitory properties, human leukocyte antigen (HLA)-G has been proposed as a possible prognostic biomarker and therapeutic target relevant in a wide variety of cancers and viral infections, but to date remains underexplored in cervical cancer. Given the possible influence of HLA-G on the clinical course of HPV infection, cervical lesions and cancer progression, a better understanding of HLA-G involvement in cervical carcinogenesis might contribute to two aspects of fundamental importance: 1. Characterization of a novel diagnostic/prognostic biomarker to identify cervical cancer and to monitor disease stage, critical for patient screening; 2. Identification of HLA-G-driven immune mechanisms involved in lesion development and cancer progression, leading to the development of strategies for modulating HLA-G expression for treatment purposes. Thus, this systematic review explores the potential involvement of HLA-G protein expression and polymorphisms in cervical carcinogenesis.

Non-classical MHC-I human leukocyte antigen (HLA-G) in hepatotropic viral infections and in hepatocellular carcinoma

The human leukocyte antigen (HLA)-G is a "nonclassical" major histocompatibility complex (MHC) class Ib gene, located at chromosome 6, in the 6p21.3 region. The HLA-G presents immunomodulatory functions essential in pregnancy for the tolerance of the semi-allogenic fetus, but an abnormal expression of HLA-G has been observed in numerous pathological conditions, such as tumors, autoimmune diseases and viral infections. In recent years, numerous studies have assessed the clinical relevance of HLA-G expression in different types of cancer: in general, a higher HLA-G expression correlates with a lower survival rate or a shorter disease-free survival. Altered expression of HLA-G has been found in both HCV and HBV infection, and some genetic polymorphisms have been associated with altered susceptibility/disease development for these infections, however, whether the biologic role of HLA-G in HCV and HBV infection is beneficial or hazardous, it is not completely clear. In the context of hepatocellular carcinoma, HLA-G has shown a potential diagnostic role, moreover a prognostic value in HCC patients has been also attributed to HLA-G molecules. We revise here the role of HLA-G in hepatotropic HBV/HCV infections and in hepatocellular carcinoma (HCC).

Human leukocyte antigen-G (HLA-G) polymorphism and expression in breast cancer patients

Human leukocyte antigen-G (HLA-G) is known to be implicated in a tumor-driven immune escape mechanism in malignancies. The purpose of this study was to investigate HLA-G polymorphism and expression in breast cancer. HLA-G alleles were determined by direct DNA sequencing procedures from blood samples of 80 breast cancer patients and 80 healthy controls. Soluble HLA-G (sHLA-G) was measured by enzyme-linked immunosorbent assay (ELISA) from serum specimens. HLA-G expression in breast cancer lesions was also analyzed by immunohistochemistry staining. The presence of HLA-G 3' untranslated region (UTR) 14-bp sequence was analyzed and found to be associated with reduced risk of breast cancer susceptibility based on HLA-G expression in tissues (P = 0.0407). Levels of sHLA-G were higher in the breast cancer group (median 117.2 U/mL) compared to the control group (median 10.1 U/mL, P<0.001). The area under the receiver operating characteristic curve (AU-ROC) values of sHLA-G for differentiating breast cancer from normal controls and for detecting metastasis from other stages of breast cancer were 0.89 and 0.79, respectively. HLA-G polymorphism and expression may be involved in breast carcinogenesis and sHLA-G concentrations could be used as a diagnostic marker for detecting breast cancer.

HLA-G 3' untranslated region polymorphisms influence the susceptibility for human papillomavirus infection

Human leukocyte antigen (HLA)-G molecule acts as a potential factor for the regulation of immune responses and its expression in virus-infected cells may enable them to escape immunosurveillance. Besides its polymorphic promoter region, the 3' untranslated region (UTR) seems to play an important role in regulating HLA-G expression. In this study, we investigated the influence of HLA-G 14 bp (rs66554220) and +3142 (rs1063320) polymorphisms in 179 women with active human papillomavirus (HPV) infection and 143 age-matched, unrelated, HPV-negative, normal Chinese Han population. Our findings showed that frequency of the allele +3142 C [31.3% vs 44.4%, odds ratio (OR) = 0.57, Pc < 0.01] and the genotype +3142 CC (10.6% vs 21.7%, OR = 0.43, Pc = 0.012) was significantly decreased in HPV infected patients compared with normal controls. Furthermore, the haplotype -14 bp/C was associated with a reduced risk for HPV infection (OR = 0.57, Pc = 0.001). Our findings also showed that HLA-G homozygous +14 bp/+14 bp genotype was significantly associated with an increased risk for HPV18 infection (OR = 12.95, P < 0.01), whereas HLA-G heterozygous +14 bp/-14 bp genotype increased risk for HPV58 (OR = 5.55, P < 0.05). Furthermore, frequency of the haplotype +14 bp/G was significantly increased in HPV18 infected patients (60.0% vs 27.3%, OR = 4.00, Pc < 0.05). Taken together, our results supported a role of the HLA-G 3' UTR polymorphisms as a susceptible factor for the active HPV infection, and suggested a possible interference of the HLA-G molecule in the response to virus infection.

Molecular pathways: human leukocyte antigen G (HLA-G)

Human leukocyte antigen G (HLA-G) is a nonclassical MHC class I molecule that exerts important tolerogenic functions. Its main physiologic expression occurs in the placenta, where it participates in the maternal tolerance toward the fetus. HLA-G expression was found in embryonic tissues, in adult immune privileged organs, and in cells of the hematopoietic lineage. It is expressed in various types of primary solid (melanoma, head and neck, lung, urogenital, gastrointestinal, and breast cancers) and hematologic malignancies (acute leukemia, lymphomas) and metastases. HLA-G ectopic expression is observed in cancer, suggesting that its expression is one strategy used by tumor cells to escape immune surveillance. In this review, we will focus on HLA-G expression in cancers and its association with the prognosis. We will highlight the underlying molecular mechanisms of impaired HLA-G expression, the immune tolerant function of HLA-G in tumors, and the potential diagnostic use of membrane-bound and soluble HLA-G as a biomarker to identify tumors and to monitor disease stage. As HLA-G is a potent immunoinhibitory molecule, its blockade remains an attractive therapeutic strategy against cancer. Elimination of HLA-G-expressing cancer cells would be important in the efficacy of anticancer therapies.

Case-control study of HLA-G promoter methylation status, HPV infection and cervical neoplasia in Curitiba, Brazil: a pilot analysis

Background

The causal association between persistent human papillomavirus (HPV) infection and cervical cancer has been established, but the mechanisms that favor HPV persistence in cervical cells are still unknown. The diminished capability of the immune system to control and resolve HPV infection is one of several hypotheses. The tolerogenic protein HLA-G has shown aberrant expression in a variety of cancers, which has been suggested as a mechanism for tumor escape from immunosurveillance. In the present study we evaluate the role of epigenetic modification (promoter de-methylation) of the HLA-G gene on susceptibility to HPV infection and development of high-grade cervical lesions.

Methods

A case–control study was carried out in Curitiba, Brazil, between February and June 2010. A total of 789 women aged 15–47 years were recruited: 510 controls with normal cervical cytology, and 279 cases with histologically confirmed cervical intraepithelial neoplasia grade 2 (CIN2, N = 150) or grade 3 (CIN3, N = 129). All women were administered a questionnaire by interview, which collected information on demographic and lifestyle factors, and a cervical sample was collected. HPV DNA detection was performed by GP5+/GP6+ primer-mediated PCR. HPV-positive samples were genotyped by multiplex PCR. A pilot analysis of HLA-G promoter methylation was carried out in a subset of the study population (96 cases and 76 controls) by pyrosequencing. HLA-G methylation and HPV infection status of cases and controls were compared, and confounding factors were computed by t Student and non-parametric Wilcoxon tests. Comparison of HLA-G methylation between cases and controls was assessed by the Bonferroni correction. The association of HLA-G methylation with CIN2/3 was evaluated by logistic regression.

Results

HPV prevalence was 19.6% in controls and 94.3% in CIN2/3 cases. HPV16, 31, 33, 35 and 18 were the most prevalent types. Methylation analysis of seven CpGs in the HLA-G promoter did not reveal any spontaneous de-methylation events in CIN2/3 cases (mean proportion of methylation: 75.8%) with respect to controls (mean 73.7%; odds ratio 1.01, 95% confidence interval 0.96, 1.07).

Conclusions

This study did not support the hypothesis that spontaneous de-methylation events in the HLA-G promoter play a primary role in promoting escape from immunosurveillance in the development of precancerous cervical lesions.

Human papillomavirus immunization is associated with increased expression of different innate immune regulatory receptors

Human papillomavirus (HPV) is able to inhibit the secretion of gamma interferon (IFN-γ) and the expression of some immune innate cell receptors. Immunoglobulin-like transcript 2 (ILT2) is a regulatory receptor that seems to participate in the pathogenesis of viral infections. We have studied the expression and function of ILT2 and the expression of other NK cell receptors in 23 healthy women before and after immunization with the quadrivalent HPV (type 6/11/16/18) vaccine (Gardasil). Receptor expression was analyzed by flow cytometry in freshly isolated peripheral blood mononuclear cells as well as after in vitro stimulation with the quadrivalent HPV (type 6/11/16/18) vaccine. In addition, the regulatory function of ILT2 on cell proliferation and IFN-γ production was analyzed. We found a significant increase in the expression of ILT2 by NK and CD3(+) CD56(+) lymphocytes and monocytes after quadrivalent HPV (type 6/11/16/18) vaccine immunization. In addition, the in vitro stimulation with the quadrivalent HPV (type 6/11/16/18) vaccine also increased the proportion of CD3(-) CD56(+) ILT2(+) NK cells. Although the inhibitory function of ILT2 on cell proliferation was enhanced after HPV immunization, the in vitro engagement of this receptor did not affect the synthesis of IFN-γ induced by HPV. Finally, a significant increase in the expression of NKG2D, NKp30, and NKp46 by NK and CD3(+) CD56(+) lymphocytes was detected after quadrivalent HPV (type 6/11/16/18) vaccine immunization. Our data indicate that HPV immunization is associated with significant changes in the expression and function of different innate immune receptors, including ILT2, which may participate in the protective effect of HPV vaccines.

The immunosuppressive molecule HLA-G and its clinical implications

Human leukocyte antigen G (HLA-G) is a non-classical major histocompatibility complex (MHC) class I molecule that, through interaction with its receptors, exerts important tolerogenic functions. Its main physiological expression occurs in placenta where it seems to participate in the maternal tolerance toward the fetus. HLA-G has been studied as a marker of pregnancy complications such as abortion or pre-eclapmsia. Although HLA-G is not expressed in most adult tissues, its ectopic expression has been observed in some diseases such as viral infections, autoimmune disorders, and especially cancer. HLA-G neo-expression in cancer is associated with the capability of tumor cells to evade the immune control. In this review, we will summarize HLA-G biology and how it participates in these physiopathological processes. Special attention will be paid to its role as a diagnostic tool and also as a therapeutic target.

The role of classical and non-classical HLA class I antigens in human tumors

In human tumors alterations in the surface expression and/or function of the major histocompatibility complex (MHC) class I antigens are frequently found and equip neoplastic cells with mechanisms to escape immune control. The aberrant expression of HLA class I molecules can be caused by structural alterations or dysregulations of genes encoding the classical HLA class I antigens and/or components of the HLA class I antigen processing machinery (APM). The dysregulation of APM components could occur at the epigenetic, transcriptional or post-transcriptional level. In some malignancies these abnormalities are significantly associated with a higher tumor staging, grading, disease progression and a reduced survival of patients as well as a failure to CD8(+) T cell-based immunotherapies. In addition to HLA class I abnormalities, expression of the non-classical HLA-G antigen is often induced in tumors, which could be mediated by various microenvironmental factors. Interestingly, soluble HLA-G serum and plasma levels have been useful markers for the prediction of some malignancies. The biological consequence of HLA-G expression or sHLA-G is an escape from T and NK cell-mediated recognition. Thus, alterations of non-classical and classical HLA class I antigens and components of the antigen processing pathway provide tumor cells with different mechanisms to inactivate immune responses resulting in tumor growth and evasion from host immune surveillance.

Human leukocyte antigen G polymorphism is associated with an increased risk of invasive cancer of the uterine cervix

Human leukocyte antigen (HLA)-G acts as negative regulator of the immune responses and its expression in tumor cells may enable them to escape immunosurveillance. The purpose of this study was to investigate the influence of HLA-G polymorphism on risk of high-grade cervical intraepithelial neoplasia (HG-CIN) and cervical cancer in a Canadian population. The authors have analyzed 1,372 women from participants recruited between 2001 and 2009 in the ongoing Biomarkers of Cervical Cancer Risk case-control study. A total of 539 women with histologically confirmed HG-CIN and invasive cancer formed the case series, and 833 women with normal cytology served as controls. Cervical specimens were tested for human papillomavirus (HPV) DNA using the MY09/11 PCR protocol and HLA-G alleles where determined using a direct DNA sequencing procedures. HLA-G polymorphisms were not associated with HG-CIN or HPV infection. However, the risk for invasive cancer was significantly increased with the homozygous genotypes HLA-G*01:01:02 [odds ratio (OR) = 3.52, 95% confidence interval (CI): 1.43-8.61, p = 0.006], -G*01:06 (OR = 19.1, 95% CI: 2.29-159, p = 0.005) and -G* 3'UTR 14-bp insertion (OR = 2.17, 95% CI: 1.10-4.27, p = 0.020), whereas, the heterozygotic form of the G*01:01:01 wild-type allele was significantly associated with a reduced risk of invasive cancer (OR = 0.31, 95% CI: 0.16-0.59, p < 0.0001) after adjusting for age, HPV infection and ethnicity. These associations were also observed with progression of disease from HG-CIN to invasive cancer among HPV-positive women. These results suggest that HLA-G polymorphism is an independent risk factor for the development of invasive cervical cancer.

Human leukocyte antigen-G in cancer: are they clinically relevant?

The immunotolerant human leukocyte antigen (HLA)-G has direct inhibitory effects on natural killer cells (NK), dendritic cells (DC), T cells and can induce tolerant regulatory cells. The expression of HLA-G has been correlated with the tolerance of the fetus, the acceptance of organ transplants, and the immune escape of tumor cells and virus-infected cells. In the context of malignancies, aberrant induction of HLA-G expression has been extensively investigated and its clinical relevance has been postulated. We here focus on the HLA-G expression in malignancies and its relevance to tumor cell immune escaping and disease progression.