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

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

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

Prognostic value of human leukocyte antigen G expression in solid tumors: a systematic review and meta-analysis

Introduction

Identification of modulators of the immune response with inhibitory properties that could be susceptible for therapeutic intervention is a key goal in cancer research. An example is the human leukocyte antigen G (HLA-G), a nonclassical major histocompatibility complex (MHC) class I molecule, involved in cancer progression.

Methods

In this article we performed a systematic review and meta-analysis on the association between HLA-G expression and outcome in solid tumors. This study was performed in accordance with PRISMA guidelines and registered in PROSPERO.

Results

A total of 25 studies met the inclusion criteria. These studies comprised data from 4871 patients reporting overall survival (OS), and 961 patients, reporting disease free survival (DFS). HLA-G expression was associated with worse OS (HR 2.09, 95% CI = 1.67 to 2.63; P < .001), that was higher in gastric (HR = 3.40; 95% CI = 1.64 to 7.03), pancreatic (HR = 1.72; 95% CI = 0.79 to 3.74) and colorectal (HR = 1.55; 95% CI = 1.16 to 2.07) cancer. No significant differences were observed between the most commonly utilized antibody (4H84) and other methods of detection. HLA-G expression was associated with DFS which approached but did not meet statistical significance.

Discussion

In summary, we describe the first meta-analysis associating HLA-G expression and worse survival in a variety of solid tumors.

Systematic Review Registration

https://www.crd.york.ac.uk/PROSPERO/, identifier CRD42022311973.

Meta-analysis of HLA-G 14bp insertion/deletion polymorphism and soluble HLA-G revealed an association with digestive cancers initiation and prognosis

Background/Objective

Conflicting results on the association between HLA-G and digestive cancers were reported. We conducted a meta-analysis to further investigate the true relationship between HLA-G and digestive cancers (DC).

Methods

Following PRISMA guidelines, we performed a meta-analysis including 7 case-control studies on HLA-G 14-bp Insertion/deletion (I/D) polymorphism, and 15 studies on soluble HLA-G (sHLA-G). Odds ratios (OR) and their corresponding 95% confidence intervals (CI) for genetic polymorphisms were calculated. The pooled OR was calculated under three genetic models: allelic, recessive, and dominant models. Concerning sHLA-G meta-analysis, standardized mean differences (SMDs) were calculated.

Results

The HLA-G 14-bp I/D was not associated with the risk of DC. However, in the subset of HBV/HCV positive hepato-cellular cancer (HCC) patients, we reported a significant association of HLA-G 14-bp I/D with the disease initiation under allelic (D vs. I; OR = 1.698, 95% CI = 1.263–2.282, p = 0.000), dominant (DD + ID vs. II; OR = 2.321, 95% CI = 1.277–4.218, p = 0.006)and recessive (DD vs. DI + II; OR = 1.739, 95% CI = 1.173–2.577, p = 0.006) genetic models. Interestingly, HLA-G 14-bp I/D was not associated with the disease initiation in HBV/HCV negative HCC patients. However, the infection by HBV/HCV seems to be implicated in the HCC development when we compared HBV/HCV positive patients to HBV/HCV negative patients under allelic (D vs. I; OR = 1.429, 95% CI = 1.029–1.983, p = 0.033, and dominant (DD + ID vs.II; OR = 1.981, 95% CI = 1.002–3.916, p = 0.049) genetic models.

Overall analysis of DC showed significant increased sHLA-G in patients compared to healthy controls (SMD = 3.341, 95% CI = 2.415–4.267, p = 0.000). In Asian patients with gastric cancer, sHLA-G was significantly increased in grade 3 compared to low grades (SMD = 0.448, 95% CI = 0.109–0.787, p = 0.000). Further analysis showed that sHLA-G was significantly increased in positive DC vascular invasion (SMD = 0.743, 95% CI = 0.385–1.100, p = 0.000). Accordingly, sHLA-G was associated with a poor prognosis for DC.

Conclusion

The current meta-analysis supports the significant role of HLA-G in DC. The HLA-G 14-bp I/D polymorphism was associated with HCC patients with concomitant HBV/HCV viral infections. Increased sHLA-G indicated a poor prognosis for DC cancer patients.

HLA-G/sHLA-G and HLA-G-Bearing Extracellular Vesicles in Cancers: Potential Role as Biomarkers

As a non-classic major histocompatibility complex (MHC) class I molecule, human leukocyte antigen G (HLA-G) is expressed in fetal-maternal interface and immunoprivileged site only in healthy condition, and in pathological conditions such as cancer, it can be de novo expressed. It is now widely accepted that HLA-G is a key molecule in the process of immune escape of cancer cells, which is ubiquitously expressed in the tumor environment. This raises the possibility that it may play an adverse role in tumor immunity. The expression level of HLA-G has been demonstrated to be highly correlated with clinical parameters in many tumors, and its potential significance in the diagnosis and prognosis of cancer has been postulated. However, because HLA-G itself has up to seven different subtypes, and for some subtypes, detected antibodies are few or absent, it is hard to evaluate the actual expression of HLA-G in tumors. In the present work, we described (a) the structure and three main forms of HLA-G, (b) summarized the mechanism of HLA-G in the immune escape of tumor cells, (c) discussed the potential role of HLA-G as a tumor marker, and reviewed (d) the methods for detecting and quantifying HLA-G.

Lesion human leukocyte antigen-E is associated with favourable prognosis for patients with oesophageal squamous cell carcinoma

Objective

To investigate the clinical significance of human leukocyte antigen (HLA)-E levels in oesophageal squamous cell carcinoma (ESCC).

Methods

The levels of HLA-E immunostaining in ESCC lesions and 47 corresponding adjacent normal tissues were measured using immunohistochemistry. The correlation between the levels of immunostaining and clinical parameters was analysed.

Results

This study analysed 110 paraffin-embedded primary tumour lesions and 47 case–controlled paracancerous tissues that were surgically resected from 110 patients with ESCC. Positive immunostaining for HLA-E was observed in 88.2% (97 of 110) of ESCC lesions and 29.8% (14 of 47) of normal oesophageal tissues. There was no correlation between HLA-E immunostaining in ESCC lesions and clinicopathological characteristics such as lymph node metastasis, tumour–node–metastasis stage and differentiation grade. Kaplan–Meier survival analysis revealed a significantly better prognosis in patients with higher levels of HLA-E immunostaining than in those with lower levels of HLA-E immunostaining; overall survival was 28.6 months (95% confidence interval [CI], 23.2, 34.0) versus 15.3 months (95% CI, 11.5, 19.1), respectively. Furthermore, multivariate analysis showed that the HLA-E level was an independent prognostic factor in patients with ESCC.

Conclusion

A higher level of HLA-E immunostaining was associated with favourable survival in patients with ESCC.

A Critical Assessment of the Association between HLA-G Expression by Carcinomas and Clinical Outcome

Human leukocyte antigen-G (HLA-G) conveys immunological tolerance at the maternal-foetal interface. HLA-G expression by tumour cells may also play such a role, resulting in tumour immune evasion, making HLA-G a potential target for immunotherapies. The aim of this review was to determine to what extent it is justified that HLA-G expression is considered as a target for immune checkpoint inhibiting therapy by critically assessing the association between HLA-G expression by carcinomas and clinical outcome of patients. The used HLA-G-detecting mAb, HLA-G quantification methods and statistically significant HLA-G-associated clinicopathological parameters are discussed. Tumour HLA-G expression correlated with poor clinical outcome in breast, esophageal, gastric and hepatocellular carcinoma patients. Tumour HLA-G expression was not associated with clinical outcome in ovarian and oral carcinoma patients. Cervical, colorectal, lung, and pancreatic carcinoma patients presented discrepant and therefore inconclusive results regarding the association between tumour HLA-G expression and clinical outcome. These disparities might partly be the result of differences in the methodological approach to quantify HLA-G expression between studies. Therefore, implementation of universal methodological procedures is strongly advised. Overall, HLA-G expression did not univocally result in poor clinical outcome of carcinoma patients. This implies that tumour HLA-G expression is not necessarily part of an inhibited tumour-immune response and tumour progression. Consequently, it remains elusive whether HLA-G expression by carcinomas functions as an immune checkpoint molecule affecting a tumour-immune response. It may also reflect derailed control of gene expression in tumours, with no real functional consequences.

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/ILTs Targeted Solid Cancer Immunotherapy: Opportunities and Challenges

Immune checkpoint inhibitors (ICIs) have become a promising immunotherapy for cancers. Human leukocyte antigen-G (HLA-G), a neoantigen, its biological functions and clinical relevance have been extensively investigated in malignancies, and early clinical trials with “anti-HLA-G strategy” are being launched for advance solid cancer immunotherapy. The mechanism of HLA-G as a new ICI is that HLA-G can bind immune cell bearing inhibitory receptors, the immunoglobulin-like transcript (ILT)-2 and ILT-4. HLA-G/ILT-2/-4 (HLA-G/ILTs) signaling can drive comprehensive immune suppression, promote tumor growth and disease progression. Though clinical benefits could be expected with application of HLA-G antibodies to blockade the HLA-G/ILTs signaling in solid cancer immunotherapy, major challenges with the diversity of HLA-G isoforms, HLA-G/ILTs binding specificity, intra- and inter-tumor heterogeneity of HLA-G, lack of isoform-specific antibodies and validated assay protocols, which could dramatically affect the clinical efficacy. Clinical benefits of HLA-G-targeted solid cancer immunotherapy may be fluctuated or even premature unless major challenges are addressed.

Prognostic and Clinicopathological Value of Human Leukocyte Antigen G in Gastrointestinal Cancers: A Meta-Analysis

BACKGROUND

The prognostic value of human leukocyte antigen G (HLA-G) expression in gastrointestinal (GI) cancers remains controversial. Thus, this meta-analysis aimed to summarize available evidence from case-control or cohort studies that evaluated this association.

METHODS

The PubMed, EMBASE, Cochrane Library, and Web of Science databases were searched to identify relevant studies written in English published up to April 1, 2021, and with no initial date. Furthermore, the Google Scholar and Google databases were also searched manually for gray literature. The protocol for this meta-analysis was registered at PROSPERO (CRD42020213411). Pooled hazard ratios (HRs) or odds ratios (ORs) and 95% confidence intervals (CIs) were estimated for end points using fixed- and random-effects statistical models to account for heterogeneity. Publication bias was evaluated using a funnel plot, Begg's and Egger's tests, and the "trim and fill" method.

RESULTS

A total of 30 eligible articles with 5737 unique patients, including 12 studies on colorectal cancer (CRC), 6 on gastric cancer (GC), 5 on esophageal cancer (ESCC), 5 on hepatocellular carcinoma (HCC), and 2 on pancreatic adenocarcinoma (PC), were retrieved. Both univariate (HR = 2.01, 95% CI: 1.48 ~ 2.72) and multivariate (HR = 2.69, 95% CI: 2.03 ~ 3.55) analyses revealed that HLA-G expression was significantly correlated with poor overall survival (OS), regardless of the cancer type or antibody used. Subgroup analysis stratified by antibody showed that the 4H84 (I2 = 45.8%, P = 0.101) antibodies could be trustworthy and reliable for detecting HLA-G expression in GI cancers. In addition, HLA-G expression was found to be correlated with adverse clinicopathological parameters such as clinical stage, nodal status, metastasis, and histological grade but not tumor status.

CONCLUSION

Elevated HLA-G expression indicates a poor prognosis for GI cancer patients, and screening for this marker could allow for the early diagnosis and treatment of GI cancers to improve survival rates.

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.

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.

The role of Human leukocyte antigen class I on patient survival in Gastrointestinal cancers: a systematic review and meta- analysis

The prognostic role of Human leukocyte antigen class I (HLA- I) in gastrointestinal cancers has been remained controversial. We performed a meta-analysis to determine the role of classical HLA-I in predicting survival of patients. In addition, the relationship between HLA- I and some clinicopathological factors was evaluated. Published studies investigated HLA-I expression effect on gastrointestinal cancers were evaluated to determine association between HLA- I and overall survival (OS) and recurrence-free survival (RFS) in patients. The used effect sizes were hazard ratio (HR) and Odds ratio (OR) with 95% confidence interval (CI). A total of ten studies included 1307 patients were analyzed. The pooled results revealed that HLA- I overexpression was positively related to OS (HR: 0.72; 95% CI: 0.53–0.96) and demonstrated little association for RFS (HR: 0.70; 95% CI: 0.46–1.08). HLA-I overexpression is negative associated with poorer differentiation of tumor (OR: 0.53; 95% CI (0.43–0.81) and also higher stages of cancer (OR: 0.29; 95% CI (0.13–0.64). HLA- I overexpression was related to a better prognosis on OS and probably had little impact on RFS.

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.

MHC/HLA Class I Loss in Cancer Cells

In this chapter I describe Tumour Immune Escape mechanisms associated with MHC/HLA class I loss in human and experimental tumours. Different altered HLA class-I phenotypes can be observed that are produced by different molecular mechanisms. Experimental and histological evidences are summarized indicating that at the early stages of tumour development there is an enormous variety of tumour clones with different MHC class I expression patterns. This phase is followed by a strong T cell mediated immune-selection of MHC/HLA class-I negative tumour cells in the primary tumour lesion. This transition period results in a formation of a tumour composed only of HLA-class I negative cells. An updated description of this process observed in a large variety of human tumors is included. In the second section I focus on MHC/HLA class I alterations observed in mouse and human metastases, and describe the generation of different tumor cell clones with altered MHC class I phenotypes, which could be similar or different from the original tumor clone. The biological and immunological relevance of these observations is discussed. Finally, the interesting phenomenon of metastatic dormancy is analyzed in association with a particular MHC class I negative tumor phenotype.

Heterogeneity of HLA-G Expression in Cancers: Facing the Challenges

Phenotypic heterogeneity has been observed in most malignancies, which represents a considerable challenge for tumor therapy. In recent decades, the biological function and clinical significance of the human leukocyte antigen (HLA)-G have been intensively explored. It is now widely accepted that HLA-G is a critical marker of immunotolerance in cancer cell immune evasion and is strongly associated with disease progress and prognosis for cancer patients. Moreover, it has recently been emphasized that the signaling pathway linking HLA-G and immunoglobulin-like transcripts (ILTs) is considered an immune checkpoint. In addition, HLA-G itself can generate at least seven distinct isoforms, and intertumor and intratumor heterogeneity of HLA-G expression is common across different tumor types. Furthermore, HLA-G heterogeneity in cancers has been related to disease stage and outcomes, metastatic status and response to different therapies. This review focuses on the heterogeneity of HLA-G expression in malignant lesions, and clinical implications of this heterogeneity that might be relevant to personalized treatments are also discussed.

Human leukocyte antigen-G expression and polymorphisms promote cancer development and guide cancer diagnosis/treatment

Human leukocyte antigen-G (HLA-G) is a non-classical HLA molecule, predominantly expressed in cytotrophoblast cells to protect the fetus during pregnancy. Notably, a high frequency of HLA-G expression has been observed in a wide variety of cancer types in previous studies. Furthermore, HLA-G expression in cancer has been considered to be detrimental, since it can protect cancer cells from natural killer cell cytotoxic T lymphocyte-mediated destruction, promote tumor spreading and shorten the survival time of patients by facilitating tumor immune evasion. In addition, HLA-G polymorphisms have been investigated in numerous types of cancer and are considered as risk factors and predictive markers of cancer. This review focuses on HLA-G expression and its polymorphisms in cancer, analyzing the mechanisms of HLA-G in promoting cancer development, and evaluating the potential and value of its clinical application as a diagnostic and prognostic biomarker, or even as a prospective therapeutic target in certain types of tumors.

Soluble HLA-G is a differential prognostic marker in sequential colorectal cancer disease stages

The expression of HLA-G by tumour cells is an established mechanism to escape recognition and immune mediated destruction, allowing tumour survival, growth and metastasis. However, the prognostic value of soluble HLA-G (sHLA-G) remains unknown. Mucinous carcinoma (MC) is a distinct form of colorectal cancer (CRC) found in 10 to 15% of patients, which has long been associated with poor response to treatment. To investigate the prognostic value of plasma sHLA-G levels in CRC patients, preoperative plasma sHLA-G levels were determined by ELISA in CRC patients (n = 133). In addition, the local expression of HLA-G in tumour biopsies was assessed using tissue microarray analysis (n = 255). Within the high 33rd percentile of sHLA-G levels (265-890 U/mL; n = 44) we observed higher frequency of MC patients (p = 0.012; Chi-square), and higher sHLA-G levels in patients with vascular invasion (p = 0.035; two-tailed t-test). Moreover, MC patients had significantly higher sHLA-G levels compared to those with adenocarcinoma not otherwise specified (p = 0.036; two-tailed t-test). Surprisingly, while stage II patients showed negative correlation between sHLA-G levels and liver metastasis free survival (LMFS) (p = 0.041; R = -0.321), in stage III patients high sHLA-G levels were associated with significantly longer LMFS (p = 0.002), and sHLA-G levels displayed positive correlation with LMFS (p = 0.006; R = 0.409). High HLA-G expression in tumours was associated with poor cancer specific overall survival in stage II to III (p = 0.01), and with shorter LMFS in stage II patients (p = 0.004). Our findings reveal that sHLA-G levels are associated with distinct progression patterns in consecutive disease stages, indicating a potential value as surrogate marker in the differential prognosis of CRC.

Cancer treatment and the KIR-HLA system: an overview

Accumulating evidence indicates that the success of cancer therapy depends not only on a combination of adequate procedures (surgery, chemotherapy and radiotherapy) that aim to eliminate all tumor cells, but also on the functional state of the host immune system. HLA and KIR molecules, in particular, are critical to the interactions between tumor cells and both innate and adaptive immune cells such as NK cells and T cells. Different KIR-HLA gene combinations as well as different HLA expression levels on tumor cells associate with variable tumor prognosis and response to treatment. On the other hand, different therapies have different effects on HLA molecules and immune cell functions regulated by these molecules. Here, we provide an overview of the KIR-HLA system, a description of its alterations with clinical relevance in diverse tumor types, and an analysis of the consequences that conventional cancer therapies may have on it. We also discuss how this knowledge can be exploited to identify potential immunological biomarkers that can help to select patients for tailored therapy.

The Pathophysiological Impact of HLA Class Ia and HLA-G Expression and Regulatory T Cells in Malignant Melanoma: A Review

Malignant melanoma, a very common type of cancer, is a rapidly growing cancer of the skin with an increase in incidence among the Caucasian population. The disease is seen through all age groups and is very common in the younger age groups. Several studies have examined the risk factors and pathophysiological mechanisms of malignant melanoma, which have enlightened our understanding of the development of the disease, but we have still to fully understand the complex immunological interactions. The examination of the interaction between the human leucocyte antigen (HLA) system and prognostic outcome has shown interesting results, and a correlation between the down- or upregulation of these antigens and prognosis has been seen through many different types of cancer. In malignant melanoma, HLA class Ia has been seen to influence the effects of pharmaceutical drug treatment as well as the overall prognosis, and the HLA class Ib and regulatory T cells have been correlated with tumor progression. Although there is still no standardized immunological treatment worldwide, the interaction between the human leucocyte antigen (HLA) system and tumor progression seems to be a promising focus in the way of optimizing the treatment of malignant melanoma.

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.

Human leukocyte antigen-G overexpression predicts poor clinical outcomes in low-grade gliomas

Overexpression of human leukocyte antigen-G (HLA-G), a non-classical major histocompatibility complex class-I molecule associated with immunosuppression, has been reported in various human malignancies. In the present study, we examined the role of HLA-G in gliomas. Clinical characteristics, mRNA expression microarrays and follow-up data pertaining to 293 patients with histologically confirmed gliomas were analyzed. The expression levels of HLA-G were compared between different grades of gliomas and correlated with progression-free survival (PFS) and overall survival (OS) to evaluate its prognostic value. We found that HLA-G was overexpressed in gliomas as compared to that in normal brain tissue samples (-1.288±0.265). The highest expression levels were in glioblastomas (GBMs), anaplastic gliomas (AGs) and low-grade gliomas (LGGs), in that order (0.328±0.778, 0.176±0.881, -0.388±0.686, respectively). Significant inter-group differences were observed between low-grade and high-grade glioma tissues (p<0.001 and p<0.001, t-test, AGs and GBMs, respectively). More astrocytoma patients exhibited increased HLA-G expression as compared to other LGG patients (p=0.004, Chi-square test). Significant differences were observed with respect to PFS and OS (p=0.009 and 0.032, log-rank test, for PFS and OS, respectively) between the high- and low-expression subgroups in patients with LGGs. On Cox regression analysis, overexpression of HLA-G appeared to be an independent predictor of clinical outcomes (p=0.007 and 0.026, for PFS and OS, respectively). Our results suggest that HLA-G expression may serve as a potential biomarker for predicting aggressive tumor grades of gliomas and for histological subtype of LGGs. Elevated HLA-G expression could serve as an independent predictor of poor clinical outcomes in patients with low-grade gliomas.

The prognostic impact of soluble and vesicular HLA-G and its relationship to circulating tumor cells in neoadjuvant treated breast cancer patients

The non-classical human leukocyte antigen G (HLA-G) molecule and its soluble forms exert multiple immune suppressive regulatory functions in malignancy and in stem cells contributing to immune escape mechanisms. HLA-G can be secreted as free soluble HLA-G molecules or via extracellular vesicles (EVs). Here we evaluated these soluble HLA-G forms as prognostic marker for prediction of the clinical outcome of neoadjuvant chemotherapy (NACT) treated breast cancer (BC) patients. Plasma samples of BC patients procured before (n=142) and after (n=154) NACT were quantified for total soluble HLA-G (sHLA-Gtot) and HLA-G levels in ExoQuick™ derived EV fractions (sHLA-GEV) by ELISA. The corresponding increments were specified as free sHLA-G (sHLA-Gfree). Total and free sHLA-G were significantly increased in NACT treated BC patients compared to healthy controls (n=16). High sHLA-Gfree levels were exclusively associated to estrogen receptor expression before NACT. Importantly, high sHLA-GEV levels before NACT were related to disease progression and the detection of stem cell-like circulating tumor cells, but high sHLA-Gfree levels indicated an improved clinical outcome. Thus, this study demonstrates for the first time that the different sHLA-G subcomponents represent dissimilar qualitative prognostic impacts on the clinical outcome of NACT treated BC patients, whereas the total sHLA-G levels without separating into subcomponents are not related to clinical outcome.

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

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

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.

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

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

The Role of HLA-G Molecule and HLA-G Gene Polymorphisms in Tumors, Viral Hepatitis, and Parasitic Diseases

Considering that the non-classical HLA-G molecule has well-recognized tolerogenic properties, HLA-G expression is expected to be deleterious when present in tumor cells and in cells chronically infected by viruses, whereas HLA-G expression is expected to be advantageous in autoimmune disorders. The expression of HLA-G on tissue or peripheral blood cells, the levels of soluble HLA-G and polymorphic sites along the gene have been studied in several disorders. In this study, we revised the role of the molecule and polymorphic sites along the HLA-G gene in tumors, viral hepatitis, and parasitic disorders. Overall, several lines of evidence clearly show that the induction of HLA-G expression in tumors has been associated with worse disease outcome and disease spread. In addition, the few studies conducted on hepatitis and parasitic disorders indicate that HLA-G may contribute to disease pathogenesis. Few isolated polymorphic sites, primarily located at the coding or 3′ untranslated HLA-G region, have been evaluated in these disorders, and a complete HLA-G typing together with the study of gene regulatory elements may further help on the understanding of the influence of the genetic background on disease susceptibility.

The Utility of Immunohistochemistry in the Differential Diagnosis of Gynecologic Disorders

Context

Immunohistochemistry has assumed an increasing role in the identification and characterization of gynecologic disorders including lesions with deceptively bland morphology, uncommon and underdiagnosed neoplasms, and neoplasms with specific genetic alterations associated with overexpression or loss of expression of specific proteins. The diagnostic accuracy has been significantly improved owing to the discovery and increasing experience with the tumor-associated biomarkers, and the increasing demand for precise tumor classification to assess suitability for the expanding therapeutic modalities including clinical trials.

Objective

To differentiate lesions of the gynecologic tract through the use of effective immunohistochemical panels.

Data Sources

Literature review and authors' personal practice experience.

Conclusions

The application of diagnostic and prognostic immunohistochemical panels has enabled pathologists to better guide therapeutic decisions and to better predict the clinical outcome. It is now well established that the use of ancillary testing, including immunohistochemistry, has a significant power in the identification, differentiation, and classification of reactive, premalignant, and malignant gynecologic disorders. This article discusses the utilities and pitfalls of the commonly used immunohistochemical markers in the context of overlapping morphologic features encountered in the uterus, ovaries, and fallopian tubes.

HLA-G expression is an independent predictor for improved survival in high grade ovarian carcinomas

Aberrant expression of human leukocyte antigens (HLA) class I has prognostic importance in various cancers. Here, we evaluated the prognostic value of classical (A/B/C) and nonclassical (G/E) HLA expression in 169 high grade epithelial ovarian cancer samples and linked that to clinicopathological characteristics and survival. Expression of HLA-A, -B/C, or -E was not correlated with survival. Survival was prolonged when tumours expressed HLA-G (P = 0.008) and HLA-G was an independent predictor for better survival (P = 0.011). In addition, HLA-G expression was associated with longer progression-free survival (P = 0.036) and response to chemotherapy (P = 0.014). Accordingly, high expression of HLA-G mRNA was associated with prolonged disease-free survival (P = 0.037) in 65 corresponding samples. Elevated serum-soluble HLA-G levels as measured by enzyme-linked immunosorbent assay in 50 matched patients were not correlated to HLA-G protein expression or gene expression nor with survival. During treatment, sHLA-G levels declined (P = 0.038). In conclusion, expression of HLA-G is an independent prognostic factor for improved survival in high grade epithelial ovarian cancer and a predictor for platinum sensitivity.

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.

In vivo evidence that secretion of HLA-G by immunogenic tumor cells allows their evasion from immunosurveillance

Human leukocyte antigen-G (HLA-G) expression by tumors has been evidenced in numerous malignancies in association with poor prognosis and resistance to immunotherapy in humans. Particularly, soluble form of HLA-G was measured at high concentrations in malignant effusions and plasma from cancer patients, and inhibits antitumor immune cells in vitro through interaction with immunoglobulin-like transcript (ILT) receptors. Nevertheless, in vivo study demonstrating that HLA-G secretion by tumor cells allows their escape from immunosurveillance remained to be established. Despite nondescribed murine homolog, direct functional interaction of HLA-G with murine paired immunoglobulin-like receptor (PIR)-B, ortholog of human ILT receptors, enables to investigate its role in vivo. Immunocompetent mice were injected either with syngeneic tumor cells co-expressing HLA-G5, the main soluble HLA-G isoform, and the conformation stabilizer human β2-microglubulin (hβ2m), or with hβ2m+ HLA-G5- tumor cells. hβ2m expressed at both tumor cell surface acted as a tumor antigen triggering a specific humoral response. Interestingly, although hβ2m+ HLA-G5- tumors were rejected, secreted HLA-G5 provided hβ2m+ HLA-G5+ tumors a protection against hβ2m-elicited immune rejection, enabling such immunogenic tumors to grow similarly to a poorly immunogenic tumor. HLA-G5 tumor expression was associated with local and peripheral immunosuppression, characterized by dampened anti-hβ2m B-cell response, quantitative and functional T-and B-cell defects, accumulation of myeloid-derived suppressor cells able to inhibit T-cell proliferation and reduced T- and B-cell tumor infiltrate. Our study provides the first in vivo proof that soluble HLA-G counteracts tumor rejection and reinforces the importance to consider HLA-G as a promising target to optimize current cancer immunotherapies.

The clinicopathologic significance of the expression of HLA-G in oral squamous cell carcinoma

OBJECTIVE

This study aimed to evaluate HLA-G expression in primary oral cavity squamous cell carcinoma (OCSCC) and potentially malignant lesions and to evaluate its relationship with clinicopathologic parameters.

STUDY DESIGN

HLA-G expression in samples from patients with metastatic and nonmetastatic OCSCC (n = 60), potentially malignant lesions (n = 15), and clinically and histologically normal oral mucosa (n = 10) was characterized by immunohistochemistry. The density of CD8, CD83, and CD68 cells and Ki-67(+) and bcl-2(+) neoplastic cells were analyzed.

RESULTS

HLA-G expression by neoplastic cells was significantly higher in metastatic OCSCC compared with nonmetastatic OCSCC (P = .01). Higher HLA-G expression was observed in OCSCC than in potentially malignant lesions (P = .006). Moreover, patients with lower HLA-G expression exhibited a tendency toward longer survival (22 months) compared with those with higher HLA-G expression (16 months).

CONCLUSIONS

Our findings suggest that increased HLA-G expression in metastatic OCSCC may represent a tumor escape mechanism, which portends an unfavorable clinical prognosis.

Molecular alterations and clinical relevance in esophageal squamous cell carcinoma

Esophageal squamous cell carcinoma (ESCC) is one of the most common types of gastrointestinal cancers, and the fourth leading cause of cancer-related deaths in China. Early detection and intervention in time may dramatically increase the survival of the patients by initiating treatment regimens during earlier stages of ESCC or even during precancerous stages. Molecular classification will be useful for subtyping esophageal tumors or precancerous lesions to improve current therapeutics or early intervention of the disease. In this review, we summarize the findings in investigating the molecular alterations and clinical relevance of ESCC.

Immunity of human epithelial ovarian carcinoma: the paradigm of immune suppression in cancer

Epithelial ovarian cancer (EOC) is a significant cause of cancer-related mortality in women, and there has been no substantial decrease in the death rates due to EOC in the last three decades. Thus, basic knowledge regarding ovarian tumor cell biology is urgently needed to allow the development of innovative treatments for EOC. Traditionally, EOC has not been considered an immunogenic tumor, but there is evidence of an immune response to EOC in patients. Clinical data demonstrate that an antitumor immune response and immune evasion mechanisms are correlated with a better and lower survival, respectively, providing evidence for the immunoediting hypothesis in EOC. This review focuses on the immune response and immune suppression in EOC. The immunological roles of chemotherapy and surgery in EOC are also described. Finally, we detail pilot data supporting the efficiency of immunotherapy in the treatment of EOC and the emerging concept that immunomodulation aimed at counteracting the immunosuppressive microenvironment must be associated with immunotherapy strategies.

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 leukocyte antigen-G is frequently expressed in glioblastoma and may be induced in vitro by combined 5-aza-2'-deoxycytidine and interferon-γ treatments: results from a multicentric study

Human leukocyte antigen-G (HLA-G) is a nonclassical major histocompatibility complex (MHC) class I molecule involved in immune tolerance processes, playing an important role in the maintenance of the semi-allogeneic fetus. Although HLA-G expression is restricted in normal tissues, it is broadly expressed in malignant tumors and may favor tumor immune escape. We analyzed HLA-G protein and mRNA expression in tumor samples from patients with glioblastoma collected in France, Denmark, and Brazil. We found HLA-G protein expression in 65 of 108 samples and mRNA in 20 of 21 samples. The absence of HLA-G protein expression was associated with a better long-term survival rate. The mechanisms underlying HLA-G gene expression were investigated in glioma cell lines U251MG, D247MG, and U138MG. Induction of HLA-G transcriptional activity was dependent of 5-aza-2'-deoxycytidine treatment and enhanced by interferon-γ. HLA-G protein expression was observed in U251MG cells only. These cells exhibited a permissive chromatin state at the HLA-G gene promoter and the highest levels of induced HLA-G transcriptional activity following 5-aza-2'-deoxycytidine treatment. Several antigen-presenting machinery components were up-regulated in U251MG cells after demethylating and IFN-γ treatments, suggesting an effect on the up-regulation of HLA-G cell surface expression. Therefore, because of its role in tumor tolerance, HLA-G found to be expressed in glioblastoma samples should be taken into consideration in clinical studies on the pathology and in the design of therapeutic strategies to prevent its expression in HLA-G-negative tumors.

Importance of HLA-G expression and tumor infiltrating lymphocytes in molecular subtypes of breast cancer

This study is aimed at investigating whether or not human leukocyte antigen-G (HLA-G) expression is associated with breast cancer molecular subtypes. HLA-G expression was immunohistochemically investigated in 104 patients with invasive ductal breast carcinoma, in which 56 were luminal A, 17 were luminal B, 19 were HER-2, and 12 were basal-like/normal breast-like subtype classified according to immunohistochemical staining results of ER, HER-2, CK5/6, and EGFR. Host immune response status was assessed by estimating the density of tumor infiltrating lymphocytes (TIL). For comparison, other biomarkers such as Ki67, p53 and VEGF were also investigated. Associations of these biomarkers and TIL with molecular subtypes were statistically analyzed. We found that there were more cases with high expressions of HLA-G in non-luminal than in luminal subtypes (P=0.035). In contrast, more cases with high density of TIL was found in luminal than in non-luminal subtypes (P=0.023). Compared to all the biomarkers studied, only HLA-G expression was found to be inversely associated with the density of TIL (P=0.004). Furthermore, patients with HLA-G(high)/TIL(low) status had a higher risk of recurrence than those with HLA-G(low)/TIL(high) status, regardless of the molecular subtypes. Therefore, a combination of the status of HLA-G and TIL could improve the prognostic prediction for patients with various molecular subtypes of breast cancer.

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 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.