Soluble HLA-G molecules increase during acute leukemia, especially in subtypes affecting monocytic and lymphoid lineages

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.

Differentially Expressed Bone Marrow microRNAs Are Associated With Soluble HLA-G Bone Marrow Levels in Childhood Leukemia

HLA-G is a nonclassical histocompatibility class I molecule that plays a role in immune vigilance in cancer and infectious diseases. We previously reported that highly soluble HLA-G (sHLA-G) levels in the bone marrow were associated with a high blood cell count in T-acute lymphoblastic leukemia, a marker associated with a poor prognosis. To understand the posttranscriptional HLA-G gene regulation in leukemia, we evaluated the bone marrow microRNA profile associated with the HLA-G bone marrow mRNA expression and sHLA-G bone marrow levels in children exhibiting acute leukemia (B-ALL, T-ALL, and AML) using massively parallel sequencing. Ten differentially expressed miRNAs were associated with high sHLA-G bone marrow levels, and four of them (hsa-miR-4516, hsa-miR-486-5p, hsa-miR-4488, and hsa-miR-5096) targeted HLA-G, acting at distinct HLA-G gene segments. For qPCR validation, these miRNA expression levels (ΔCt) were correlated with HLA-G5 and RREB1 mRNA expressions and sHLA-G bone marrow levels according to the leukemia subtype. The hsa-miR-4488 and hsa-miR-5096 expression levels were lower in B-ALL than in AML, while that of hsa-miR-486-5p was lower in T-ALL than in AML. In T-ALL, hsa-miR-5096 correlated positively with HLA-G5 and negatively with sHLA-G. In addition, hsa-miR-4516 correlated negatively with sHLA-G levels. In AML, hsa-miR-4516 and hsa-miR-4488 correlated positively with HLA-G5 mRNA, but the HLA-G5 negatively correlated with sHLA-G. Our findings highlight the need to validate the findings of massively parallel sequencing since the experiment generally uses few individuals, and the same type of leukemia can be molecularly quite variable. We showed that miRNA’s milieu in leukemia’s bone marrow environment varies according to the type of leukemia and that the regulation of sHLA-G expression exerted by the same miRNA may act by a distinct mechanism in different types of leukemia.

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.

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.

Redirecting the Immune Microenvironment in Acute Myeloid Leukemia

Simple Summary

Despite remarkable progress in the outcome of childhood acute myeloid leukemia (AML), risk of relapse and refractory diseases remains high. Treatment of the chemo-refractory disease is restricted by dose-limiting therapy-related toxicities which necessitate alternative tolerable efficient therapeutic modalities. By disrupting its immune environment, leukemic blasts are known to gain the ability to evade immune surveillance and promote disease progression; therefore, many efforts have been made to redirect the immune system against malignant blasts. Deeper knowledge about immunologic alterations has paved the way to the discovery and development of novel targeted therapeutic concepts, which specifically override the immune evasion mechanisms to eradicate leukemic blasts. Herein, we review innovative immunotherapeutic strategies and their mechanisms of action in pediatric AML.

Abstract

Acute myeloid leukemia is a life-threatening malignant disorder arising in a complex and dysregulated microenvironment that, in part, promotes the leukemogenesis. Treatment of relapsed and refractory AML, despite the current overall success rates in management of pediatric AML, remains a challenge with limited options considering the heavy but unsuccessful pretreatments in these patients. For relapsed/refractory (R/R) patients, hematopoietic stem cell transplantation (HSCT) following ablative chemotherapy presents the only opportunity to cure AML. Even though in some cases immune-mediated graft-versus-leukemia (GvL) effect has been proven to efficiently eradicate leukemic blasts, the immune- and chemotherapy-related toxicities and adverse effects considerably restrict the feasibility and therapeutic power. Thus, immunotherapy presents a potent tool against acute leukemia but needs to be engineered to function more specifically and with decreased toxicity. To identify innovative immunotherapeutic approaches, sound knowledge concerning immune-evasive strategies of AML blasts and the clinical impact of an immune-privileged microenvironment is indispensable. Based on our knowledge to date, several promising immunotherapies are under clinical evaluation and further innovative approaches are on their way. In this review, we first focus on immunological dysregulations contributing to leukemogenesis and progression in AML. Second, we highlight the most promising therapeutic targets for redirecting the leukemic immunosuppressive microenvironment into a highly immunogenic environment again capable of anti-leukemic immune surveillance.

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.

The Potential of Soluble Human Leukocyte Antigen Molecules for Early Cancer Detection and Therapeutic Vaccine Design

Human leukocyte antigen (HLA) molecules are essential for anti-tumor immunity, as they display tumor-derived peptides to drive tumor eradication by cytotoxic T lymphocytes. HLA molecules are primarily studied as peptide-loaded complexes on cell membranes (mHLA) and much less attention is given to their secretion as soluble HLA–peptide complexes (sHLA) into bodily fluids. Yet sHLA levels are altered in various pathologies including cancer, and are thus of high interest as biomarkers. Disconcordance in results across studies, however, hampers interpretation and generalization of the relationship between sHLA levels and cancer presence, thereby impairing its use as a biomarker. Furthermore, the question remains to what extent sHLA complexes exert immunomodulatory effects and whether shifts in sHLA levels contribute to disease or are only a consequence of disease. sHLA complexes can also bear tumor-derived peptides and recent advancements in mass spectrometry now permit closer sHLA peptide cargo analysis. sHLA peptide cargo may represent a “liquid biopsy” that could facilitate the use of sHLA for cancer diagnosis and target identification for therapeutic vaccination. This review aims to outline the contradictory and unexplored aspects of sHLA and to provide direction on how the full potential of sHLA as a quantitative and qualitative biomarker can be exploited.

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.

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.

NKG2A/CD94 Is a New Immune Receptor for HLA-G and Distinguishes Amino Acid Differences in the HLA-G Heavy Chain

Natural killer (NK) cell therapies are a tool to antagonize a dysfunctional immune system. NK cells recognize malignant cells, traffic to a tumor location, and infiltrate the solid tumor. The immune checkpoint molecule human leukocyte antigen (HLA)-G is upregulated on malignant cells but not on healthy surrounding cells, the requirement of understanding the basis of receptor mediated events at the HLA-G/NK cell interface becomes obvious. The NK cell receptors ILT2 and KIR2DL4 have been described to bind to HLA-G; however, their differential function and expression levels on NK cell subsets suggest the existence of an unreported receptor. Here, we performed a ligand-based receptor capture on living cells utilizing sHLA-G*01:01 molecules coupled to TriCEPS and bound to NK cells followed by mass spectrometric analyses. We could define NKG2A/CD94 as a cognate receptor of HLA-G. To verify the results, we used the reciprocal method by expressing recombinant soluble heterodimeric NKG2A/CD94 molecules and used them to target HLA-G*01:01 expressing cells. NKG2A/CD94 could be confirmed as an immune receptor of HLA-G*01:01. Despite HLA-G is marginal polymorphic, we could previously demonstrate that the most common allelic subtypes HLA-G*01:01/01:03 and 01:04 differ in peptide repertoire, their engagement to NK cells, their catalyzation of dNK cell proliferation and their impact on NK cell development. Continuing these studies with regard to NKG2A/CD94 engagement we engineered recombinant single antigen presenting K562 cells and targeted the surface expressed HLA-G*01:01, 01:03 or 01:04 molecules with NKG2A/CD94. Specificity and sensitivity of HLA-G*01:04/NKG2A/CD94 engagement could be significantly verified. The binding affinity decreases when using K562-G*01:03 or K562-G*01:01 cells as targets. These results demonstrate that the ligand-receptor assignment between HLA-G and NKG2A/CD94 is dependent of the amino acid composition in the HLA-G heavy chain. Understanding the biophysical basis of receptor-mediated events that lead to NK cell inhibition would help to remove non-tumor reactive cells and support personalized mild autologous NK cell therapies.

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.

Serum and peritoneal fluid concentrations of soluble human leukocyte antigen, tumor necrosis factor alpha and interleukin 10 in patients with selected ovarian pathologies

Background

Although immune system plays a key role in the pathogenesis of both endometriosis and ovarian cancer, its function is different. Therefore, we hypothesized, that selected immune parameters can serve as diagnostic markers of these two conditions. The aim of this study was to compare serum and peritoneal fluid concentrations of sHLA-G, IL-10 and TNF-alpha in women with selected ovarian pathologies: benign serous cysts, endometrioma and malignant tumors. Clinical significance of using them for diagnostic purposes in women with serous ovarian cysts, endometriosis, and ovarian cancer, which in the future may improve the early diagnosis of ovarian diseases.

Case Presentation

The study included women treated surgically for benign serous ovarian cysts, ovarian endometrioma and serous ovarian adenocarcinomas. Peripheral blood and peritoneal fluid samples were obtained intraoperatively.

Patients with benign serous cysts, endometrioma and ovarian malignancies did not differ significantly in terms of their serum and peritoneal fluid concentrations of sHLA-G. Ovarian cancer patients presented with significantly higher median serum concentrations of IL-10 and TNF-alpha than other study subjects. Median concentrations of IL-10 and TNF-alpha in peritoneal fluid turned out to be the highest in ovarian cancer patients, followed by women with endometrioma and subjects with benign serous cysts. All these intergroup differences were statistically significant. Irrespective of the group, median concentrations of sHLA-G, IL-10 and TNF-alpha in peritoneal fluid were higher than serum levels of these markers.

Conclusions

Elevated serum and peritoneal fluid concentrations of IL-10 and TNF-alpha distinguish ovarian malignancies and endometriomas from benign serous ovarian cysts. In contrast to endometriosis, ovarian malignancies are characterized by elevated peritoneal fluid concentrations of IL-10 and TNF-alpha, elevated serum concentrations of IL-10 and low serum levels of TNF-alpha. Serum and peritoneal fluid concentrations of sHLA-G have no diagnostic value in differentiating between ovarian malignancies and endometriomas.

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.

Outcomes of Interferon/Ribavirin Therapy in Patients with HCV Defined by Expression of Plasma Soluble Human Leukocyte Antigen-G but Not IL-37

Background

Chronic hepatitis C virus (HCV) infection leads to life-threatening complications worldwide. Immunomodulation signals the response to virus clearance. The immune-suppressive molecule human leukocyte antigen-G (HLA-G) has been shown to function in inhibiting both innate and adaptive immune responses. The objective of this study was to investigate the expression of HLA-G and IL-37 in sustained virological response (SVR) and non-SVR HCV-positive patients before and after complete treatment with a combination of pegylated interferon (IFN) and ribavirin (RBV).

Material/Methods

Our study included 132 chronic hepatitis C patents who received combined therapy with IFN-α and RBV. Both SVR and non-SVR patients were included. The end-of-treatment response was defined as undetectable HCV RNA at week 48. Patients with end-of-treatment response were detected by HCV RNA at 24 weeks after therapy. The expression levels of HLA-G and IL-37 at the end and 24 weeks after treatment were detected by ELISA.

Results

Plasma HLA-G and IL-37 were significantly increased in HCV-infected patients compared with healthy individuals before treatment. Furthermore, HLA-G in SVR patients was noticeably decreased after treatment, while HLA-G in non-SVR patients had no changes after treatment. Additionally, both in SVR and non-SVR patients, the expression of IL-37 was remarkably reduced compared with baseline after treatment.

Conclusions

These findings suggest that elevation of HLA-G and IL-37 in HCV may play an important role in response to combined therapy with IFN-α and RBV. Monitoring the expression of HLA-G during therapy could contribute to adjusting the treatment program of HCV-infected patients.

Biology of the immunomodulatory molecule HLA-G in human liver diseases

The non-classical human leukocyte antigen-G (HLA-G), plays an important role in inducing tolerance, through its immunosuppressive effects on all types of immune cells. Immune tolerance is a key issue in the liver, both in liver homeostasis and in the response to liver injury or cancer. It would therefore appear likely that HLA-G plays an important role in liver diseases. Indeed, this molecule was recently shown to be produced by mast cells in the livers of patients infected with hepatitis C virus (HCV). Furthermore, the number of HLA-G-positive mast cells was significantly associated with fibrosis progression. The generation of immune tolerance is a role common to both HLA-G, as a molecule, and the liver, as an organ. This review provides a summary of the evidence implicating HLA-G in liver diseases. In the normal liver, HLA-G transcripts can be detected, but there is no HLA-G protein. However, HLA-G protein is detectable in the liver tissues and/or plasma of patients suffering from hepatocellular carcinoma, hepatitis B or C, or visceral leishmaniasis and in liver transplant recipients. The cells responsible for producing HLA-G differ between diseases. HLA-G expression is probably induced by microenvironmental factors, such as cytokines. The expression of HLA-G receptors, such as ILT2, ILT4, and KIRD2L4, on liver cells has yet to be investigated, but these receptors have been detected on all types of immune cells, and such cells are present in liver. The tolerogenic properties of HLA-G explain its deleterious effects in cancers and its beneficial effects in transplantation. Given the key role of HLA-G in immune tolerance, new therapeutic agents targeting HLA-G could be tested for the treatment of these diseases in the future.

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.

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.

The emerging role of soluble HLA-G in the control of chemotaxis

HLA-G is an immunosuppressive molecule, that impairs the function of different immune cell populations, both in physiological and pathological conditions. Here, we have analyzed data obtained by our group and others regarding sHLA-G concentration in plasma from patients with different diseases. Next, we have summarized novel data regarding the impairment of chemotaxis of different immune effector cells mediated by sHLA-G. Finally, we have discussed the impact of this function on the immune response during cancer, viral infection, autoimmunity, and on B cell differentiation in secondary lymphoid organs. In conclusion, we have delineated a role of sHLA-G in the control of chemotaxis of immune effector cells, that may be relevant to modulate immune responses in different settings.

The dual role of HLA-G in cancer

We here review the current data on the role of HLA-G in cancer based on recent findings of an unexpected antitumor activity of HLA-G in hematological malignancies. For the past decade, HLA-G has been described as a tumor-escape mechanism favoring cancer progression, and blocking strategies have been proposed to counteract it. Aside from these numerous studies on solid tumors, recent data showed that HLA-G inhibits the proliferation of malignant B cells due to the interaction between HLA-G and its receptor ILT2, which mediates negative signaling on B cell proliferation. These results led to the conjecture that, according to the malignant cell type, HLA-G should be blocked or conversely induced to counteract tumor progression. In this context, we will here present (i) the dual role of HLA-G in solid and liquid tumors with special emphasis on (ii) the HLA-G active structures and their related ILT2 and ILT4 receptors and (iii) the current knowledge on regulatory mechanisms of HLA-G expression in tumors.

HLA-G expression on blasts and tolerogenic cells in patients affected by acute myeloid leukemia

Human Leukocyte Antigen-G (HLA-G) contributes to cancer cell immune escape from host antitumor responses. The clinical relevance of HLA-G in several malignancies has been reported. However, the role of HLA-G expression and functions in Acute Myeloid Leukemia (AML) is still controversial. Our group identified a subset of tolerogenic dendritic cells, DC-10 that express HLA-G and secrete IL-10. DC-10 are present in the peripheral blood and are essential in promoting and maintaining tolerance via the induction of adaptive T regulatory (Treg) cells. We investigated HLA-G expression on blasts and the presence of HLA-G-expressing DC-10 and CD4⁺ T cells in the peripheral blood of AML patients at diagnosis. Moreover, we explored the possible influence of the 3′ untranslated region (3′UTR) of HLA-G, which has been associated with HLA-G expression, on AML susceptibility. Results showed that HLA-G-expressing DC-10 and CD4⁺ T cells are highly represented in AML patients with HLA-G positive blasts. None of the HLA-G variation sites evaluated was associated with AML susceptibility. This is the first report describing HLA-G-expressing DC-10 and CD4⁺ T cells in AML patients, suggesting that they may represent a strategy by which leukemic cells escape the host's immune system. Further studies on larger populations are required to verify our findings.

High proportions of CD4⁺ T cells among residual bone marrow T cells in childhood acute lymphoblastic leukemia are associated with favorable early responses

Residual nonmalignant T cells in the bone marrow of patients with acute leukemias may be involved in active immune responses to leukemic cells. Here, we investigated the phenotypic signature of T cells present at diagnosis in 39 pediatric patients with acute lymphoblastic leukemia (ALL) treated within standardized ALL-BFM study protocols. Previously described age associations of lymphocyte subpopulations in the peripheral blood of healthy children were reproduced in leukemic bone marrow. Analysis of individual lymphocyte parameters and risk-associated variables using univariate linear regression models revealed a correlation of higher CD4/CD8 ratios at diagnosis with a favorable bone marrow response on day 15. Separate analysis of CD4⁺ cells with the CD4⁺CD25(hi)FoxP3⁺ T(reg) cell phenotype showed that the association was caused by non-T(reg) CD4⁺ cells. The association of higher CD4/CD8 ratios with a favorable bone marrow response on day 15 of treatment persisted in a cohort extended to 69 patients. We conclude that CD4⁺ non-T(reg) cells in leukemic bone marrow at diagnosis may have a role in early response to treatment. Prospective analysis of the CD4/CD8 ratio in a large cohort of pediatric patients is now needed. Moreover, future experiments will establish the functional role of the individual T cell subsets in immune control in pediatric ALL.

Promoter sequences confirm the three different evolutionary lineages described for HLA-G

HLA-G alleles follow a different pattern of polymorphism generation that those of the HLA classical I alleles. However, this polymorphism maintenance could have an evolutionary specific pathways based on non coding regions as introns, 14 bp deletion/insertion (exon 8) or promoter regions. For this reason, a systematic sequencing study of HLA-G promoter region was done in 36 individuals with a total of 15 different alleles. From the 12 sequences obtained, 7 were new sequences and not previously described. Results show that the sequences have three different patterns of evolution confirming the results obtained in the rest of the sequence regions (exons, introns and 3'UTR) where three different lineages were established. Only one of these lineages includes the non-human primate promoter sequences suggesting the possibility of this lineage could come directly from non-human primates while the other two could be generated after the speciation. More non-human primates MHC-G promoter sequences must be obtained to confirm this hypothesis. Expression and functional assays could be done considering the differences obtained in the promoter regions involving the HLA-G function (mRNA expression, isoforms).

Polymorphic variants in exon 8 at the 3' UTR of the HLA-G gene are associated with septic shock in critically ill patients

Introduction

Critically ill patients are characterized as individuals hospitalized in the Intensive Care Unit (ICU) and can evolve to sepsis, septic shock or even death. Among others, genetic factors can influence the outcome of critically ill patients. HLA-G is a non-classical class Ib molecule that has limited protein variability, presenting seven isoforms generated by alternative splicing, and presents immunomodulatory properties. Polymorphisms at the 3'UTR are thought to influence HLA-G gene expression. It was previously observed that increased sHLA-G5 levels were predictive of survival among septic shock patients. We assessed the frequencies of 7 polymorphisms in exon 8 at the 3' UTR of HLA-G and associated these variants with different clinical outcomes in critically ill patients.

Methods

Exon 8 at the 3' UTR of the HLA-G gene from 638 critically ill subjects was amplified by PCR and sequenced. Genotypes were identified using FinchTV software v.1.4.0 and the most probable haplotype constitution of each sample was determined by PHASE software v.2.1. Haplotype frequencies, linkage disequilibrium, heterozygosity test and Hardy-Weinberg Equilibrium were estimated using ARLEQUIN software v.3.5.

Results

Among all critically ill patients, an association between carriers of the +2960IN_+3142 G_+3187A haplotype and septic shock (P = 0.047) was observed. Septic patients who carried the +2960IN_+3142G_+3187A haplotype presented an increased risk for septic shock (P = 0.031).

Conclusions

The present study showed, for the first time, an association between polymorphisms in exon 8 at the 3 'UTR of HLA-G gene and outcomes of critically ill patients. These results may be important for understanding the mechanisms involved in evolution to septic shock in critically ill patients.

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.

Plasma soluble HLA-G is a potential biomarker for diagnosis of colorectal, gastric, esophageal and lung cancer

Human leukocyte antigen-G (HLA-G) is a novel tumor marker and its soluble isoforms produce secretory proteins. Increased soluble HLA-G (sHLA-G) levels have been reported in patients with melanoma, neuroblastoma, lymphoproliferative disorders, breast, ovarian and colorectal carcinoma when compared to healthy controls or subjects with benign neoplasms. The aim of this study is to investigate whether or not plasma sHLA-G can be used as a potential biomarker for cancer diagnosis. We measured plasma sHLA-G levels in 166 patients with early stages of colorectal cancer (CRC, n = 37), gastric cancer (GC, n = 28), esophageal squamous cell carcinoma (ESCC, n = 58) and non-small cell lung cancer (NSCLC, n = 43), and compared them to healthy controls (n = 260) by using a specific HLA-G enzyme-linked immunosorbent assay (ELISA). We found that plasma sHLA-G levels were significantly higher in cancer patients than in healthy controls (all P < 0.0001). The areas under the receiver-operating characteristic (ROC) curves for sHLA-G were 0.97, 0.91, 0.98 and 0.80 for healthy controls vs CRC, GC, ESCC and NSCLC, respectively. At 100% specificity, the highest sensitivity achieved to detect CRC, GC, ESCC and NSCLC was 94% [95% confidence interval (CI), 89-99], 85% (95% CI, 76-94), 91% (95% CI, 88-94) and 51% (95% CI, 43-59) at a cutoff value of 49 U/ml, respectively. These findings suggest that plasma sHLA-G may be a useful molecule in the differential diagnosis of these malignancies against healthy controls.

Clinical relevance and functional implications for human leucocyte antigen-g expression in non-small-cell lung cancer

HLA-G has been documented both in establishment of anti-tumour immune responses and in tumour evasion. To investigate the clinical relevance of HLA-G in non-small-cell lung cancer (NSCLC), expression status and potential significance of HLA-G in NSCLC were analysed. In this study, HLA-G expression in 101 NSCLC primary lesions and plasma soluble HLA-G (sHLA-G) from 91 patients were analysed with immunohistochemistry and ELISA, respectively. Correlations between HLA-G status and various clinical parameters including survival time were evaluated. Meanwhile, functional analysis of transfected cell surface HLA-G expression and plasma sHLA-G form NSCLC patients on natural killer (NK) cell cytolysis were performed. Data revealed that HLA-G was expressed in 41.6% (42/101) NSCLC primary lesions, while undetectable in adjacent normal lung tissues. HLA-G expression in NSCLC lesions was strongly correlated to disease stages (P= 0.002). Plasma sHLA-G from NSCLC patients was markedly higher than that in normal controls (P= 0.004), which was significantly associated with the disease stages (I versus IV, P= 0.025; II versus IV, P= 0.029). Patient plasma sHLA-G level (≥median, 32.0 U/ml) had a significantly shorter survival time (P= 0.044); however, no similar significance was observed for the lesion HLA-G expression. In vitro data showed that both cell surface HLA-G and patient plasma sHLA-G could dramatically decrease the NK cell cytolysis. Our findings indicated that both lesion HLA-G expression and plasma sHLA-G in NSCLC is related to the disease stage and can exert immunosuppression to the NK cell cytolysis, indicating that HLA-G could be a potential therapeutic target. Moreover, plasma sHLA-G in NSCLC patients could be used as a prognosis factor for NSCLC.

Implications of the polymorphism of HLA-G on its function, regulation, evolution and disease association

The HLA-G gene displays several peculiarities that are distinct from those of classical HLA class I genes. The unique structure of the HLA-G molecule permits a restricted peptide presentation and allows the modulation of the cells of the immune system. Although polymorphic sites may potentially influence all biological functions of HLA-G, those present at the promoter and 3′ untranslated regions have been particularly studied in experimental and pathological conditions. The relatively low polymorphism observed in the MHC-G coding region both in humans and apes may represent a strong selective pressure for invariance, whereas, in regulatory regions several lines of evidence support the role of balancing selection. Since HLA-G has immunomodulatory properties, the understanding of gene regulation and the role of polymorphic sites on gene function may permit an individualized approach for the future use of HLA-G for therapeutic purposes.

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

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

HLA-G and immune evasion in cancer cells

Acquisition of novel gene products or new antigens in cancer cells elicits a host immune response that results in selection pressure for tumor clones to evade immunosurveillance. Similar to maternal-fetal tolerance and allotransplantation acceptance, upregulation of HLA-G expression has been found as one of the mechanisms that are programmed in cancer cells. HLA-G expression is frequently detected in a wide variety of human cancers and its protein levels negatively correlate with poor clinical outcome. The immune inhibitory effect can be achieved by binding of HLA-G molecules to the immunoglobulin-like inhibitory receptors that are expressed on the immunocompetent cells at all stages of the immune response. This review summarizes recent studies of HLA-G expression in human cancer, with a special focus on the molecular mechanisms that underlie how HLA-G molecules facilitate tumor cell evasion of the host immune response, and presents new directions for developing HLA-G-based diagnosis/therapeutics.

Prognostic relevance of soluble human leukocyte antigen-G and total human leukocyte antigen class I molecules in lung cancer patients

The aim of this study was to determine the prognostic significance of soluble human leukocyte antigen (HLA) class I (sHLA-I) and HLA-G molecules in lung cancer patients. A total of 23 small-cell lung cancer (SCLC) and 114 non-small-cell lung cancer (NSCLC) patients, including 55 adenocarcinoma, 46 squamous cell carcinoma (SCC), and 13 patients with undifferentiated carcinoma, were prospectively enrolled. Levels of sHLA-G and sHLA-I were analyzed by specific enzyme-linked immunosorbent assay. Median levels of sHLA-G and sHLA-I were significantly increased in patients compared with controls (34 ng/ml [3.6-160] vs 14 ng/ml [0-98], p < 0.0001; 2580 ng/ml [749-5770] vs 1370 ng/ml [274-2670], p < 0.0001, respectively). Regarding the different subgroups, patients with NSCLC or SCLC showed increased sHLA-I levels, whereas sHLA-G was exclusively elevated in NSCLC, especially in patients with SCC. Patients with sHLA-I<2800 ng/ml (p = 0.008) or sHLA-G<40 ng/ml (p = 0.073) showed prolonged overall survival (OS). Using these cut-offs in patients with SCC, a pronounced prognostic significance for sHLA-G (p = 0.003) and sHLA-I (p = 0.004) was observed for the prediction of OS. Here, multivariate analysis confirmed sHLA-G and sHLA-I in addition to disease stage as independent prognostic factors. The prognostic power was further enhanced by combining the two factors and comparing the OS of patients with low sHLA-I and low sHLA-G against the remaining ones. In conclusion, plasma levels of sHLA-G and sHLA-I are potent predictors for OS in lung cancer patients.

HLA-G expression in human breast cancer: implications for diagnosis and prognosis, and effect on allocytotoxic lymphocyte response after hormone treatment in vitro

OBJECTIVE

The aim of this study is to investigate clinical implications of human leukocyte antigen-G (HLA-G) expression in breast cancer.

METHODS

HLA-G expression in 235 primary breast cancer tissues was investigated using immunohistochemistry, and plasma soluble HLA-G (sHLA-G) was measured in 44 breast cancer patients using a specific HLA-G enzyme-linked immunosorbent assay (ELISA). Effects of estradiol/progesterone and their antagonists tamoxifen/RU486 on HLA-G expression in cultured breast cancer MCF-7 cells were determined by real-time polymerase chain reaction (PCR) and the ELISA. Alterations of HLA-G expression by the hormone treatments on subsequent allocytotoxic lymphocyte (allo-CTL) response were also examined.

RESULTS

In the study, approximately 66% of neoplasm lesions were identified to have positive HLA-G expression. This expression was significantly correlated with tumor size, nodal status, and clinical disease stage (P = 0.0001, 0.012, and 0.0001, respectively). Patients with positive HLA-G expression had a lower survival rate than those with negative expression (P < 0.028). Plasma sHLA-G levels were significantly higher in breast cancer patients than in healthy controls (P < 0.001), with the area under the receiver-operating characteristic (ROC) curve being 0.95. HLA-G expression in breast cancer MCF-7 cells was enhanced by estradiol/progesterone but reduced by their antagonists. Cytotoxicity studies showed that allo-CTL response in MCF-7 cells was inhibited by prior treatment with estradiol/progesterone, but was amplified by their antagonists. The effects could be restored or further strengthened by the addition of anti-HLA-G antibodies.

CONCLUSION

Our findings suggest that HLA-G may have potential clinical implications in diagnosis, prognosis, and immunotherapy of patients with breast cancer.

Cancer and pregnancy: parallels in growth, invasion, and immune modulation and implications for cancer therapeutic agents

Many proliferative, invasive, and immune tolerance mechanisms that support normal human pregnancy are also exploited by malignancies to establish a nutrient supply and evade or edit the host immune response. In addition to the shared capacity for invading through normal tissues, both cancer cells and cells of the developing placenta create a microenvironment supportive of both immunologic privilege and angiogenesis. Systemic alterations in immunity are also detectable, particularly with respect to a helper T cell type 2 polarization evident in advanced cancers and midtrimester pregnancy. This review summarizes the similarities between growth and immune privilege in cancer and pregnancy and identifies areas for further investigation. Our PubMed search strategy included combinations of terms such as immune tolerance, pregnancy, cancer, cytokines, angiogenesis, and invasion. We did not place any restrictions on publication dates. The knowledge gained from analyzing similarities and differences between the physiologic state of pregnancy and the pathologic state of cancer could lead to identification of new potential targets for cancer therapeutic agents.

Low expression of human histocompatibility soluble leukocyte antigen-G (HLA-G5) in invasive cervical cancer with and without metastasis, associated with papilloma virus (HPV)

Human leukocyte antigen-G (HLA-G) is a non-classical major histocompatibility complex class Ib molecule that acts as a specific immunosuppressor. Some studies have demonstrated that human papillomavirus (HPV) seems to be involved in lower or absent HLA-G expression, particularly in cervical cancer. In this study, we performed a cross-sectional study, systematically comparing the qualitative expression of the HLA-G5 isoform in invasive cervical carcinoma (ICC), stratifying patients according to the presence [ICC with metastasis (ICC(W))] and absence [ICC without metastasis (ICC(WT))] of metastasis, correlating these findings with interference of HPV and demographic and clinical variables. Seventy-nine patients with a diagnosis of ICC were stratified into two groups: ICC(WT) (n=52 patients) and ICC(W) (n=27). Two biopsies were collected from each patient (one from the tumor lesion and one from a lymph node). Immunohistochemistry analyses were performed for the HLA-G5 isoform, for HPV detection, and virus typing. HLA-G5 isoform molecules were detected in 25 cases (31.6%), 17 (32.7%) without metastasis and 8 (29.6%) with metastasis. HPV was detected in the cervical lesions of 74 patients (93.7%), but low expression of the HLA-G5 isoform was observed in all HPV-related cases. These findings are important; however, additional studies are necessary to identify the influence of HPV with HLA-G5 isoform expression on invasive cervical malignancies.

Non-classical transcriptional regulation of HLA-G: an update

Human leucocyte antigen-G (HLA-G) plays a key role in maternal–foetal tolerance and allotransplantation acceptance and is also implicated in tumour escape from the immune system. The modulation of HLA-G expression can prove to be very important to therapeutic goals in some pregnancy complications, transplantation, cancer and possibly autoimmune diseases. In spite of substantial similarities with classical HLA-class I genes, HLA-G is characterized by a restricted tissue-specific expression in non-pathological situations. HLA-G expression is mainly controlled at the transcriptional level by a unique gene promoter when compared with classical HLA-class I genes, and at the post-transcriptional level including alternative splicing, mRNA stability, translation and protein transport to the cell surface. We focus on the characteristics of the HLA-G gene promoter and the factors which are involved in HLA-G transcriptional modulation. They take part in epigenetic mechanisms that control key functions of the HLA-G gene in the regulation of immune tolerance.

Neoplasia: the second decade

This issue marks the end of the 10-year anniversary of Neoplasia where we have seen exciting growth in both number of submitted and published articles in Neoplasia. Neoplasia was first published in 1999. During the past 10 years, Neoplasia has dynamically adapted to the needs of the cancer research community as technologies have advanced. Neoplasia is currently providing access to articles through PubMed Central to continue to facilitate rapid broad-based dissemination of published findings to the scientific community through an Open Access model. This has in part helped Neoplasia to achieve an improved impact factor this past year, demonstrating that the manuscripts published by Neoplasia are of great interest to the overall cancer research community. This past year, Neoplasia received a record number of articles for review and has had a 21% increase in the number of published articles.