Ionizing radiation modulates the surface expression of human leukocyte antigen-G in a human melanoma cell line

Effects of radiation therapy on tumor microenvironment: an updated review

ABSTRACT

Cancer is a major threat to human health and causes death worldwide. Research on the role of radiotherapy (RT) in the treatment of cancer is progressing; however, RT not only causes fatal DNA damage to tumor cells, but also affects the interactions between tumor cells and different components of the tumor microenvironment (TME), including immune cells, fibroblasts, macrophages, extracellular matrix, and some soluble products. Some cancer cells can survive radiation and have shown strong resistance to radiation through interaction with the TME. Currently, the complex relationships between the tumor cells and cellular components that play major roles in various TMEs are poorly understood. This review explores the relationship between RT and cell-cell communication in the TME from the perspective of immunity and hypoxia and aims to identify new RT biomarkers and treatment methods in lung cancer to improve the current status of unstable RT effect and provide a theoretical basis for further lung cancer RT sensitization research in the future.

Combining radiotherapy and NK cell-based therapies: The time has come

Natural killer (NK) cells are innate lymphoid cells that play an essential role in the anti-tumor response through immunosurveillance, multiple mechanisms of cytotoxicity and the synthesis of cytokines modulating the immune tumor microenvironment (TME). After the dramatic advances in immunotherapy targeting T cells including the success of checkpoint inhibitors or autologous chimeric antigen receptor (CAR) expressing T cells in clinical practice, NK cells have gained growing interest for the development of new therapies. Although NK cells have shown promising responses in leukemia patients, the effects of NK-targeted therapies are currently limited in the treatment of solid tumors. Thus, radiotherapy could provide a valuable solution to improve treatments targeting NK cells. Indeed, ionizing radiations represent a powerful immuno-modulator that can either induce a pro-inflammatory and anti-tumor TME, or conversely lead to immunosuppression of effector immune cells in favor of tumor growth and therapeutic escape, depending on how it is delivered and tumor models. However, the effects of ionizing radiation on NK cells are only partially understood. Therefore, we review the effects of radiotherapy on the NK cell-mediated anti-tumor response, and propose potential strategies to reinvigorate NK cells by combining radiotherapy with NK cell-targeted therapies.

Disruption of the NKG2A:HLA-E Immune Checkpoint Axis to Enhance NK Cell Activation against Cancer

Ligation of the inhibitory receptor NKG2A by its ligand HLA-E negatively regulates the activation of natural killer (NK) cells, as well as subsets of CD8+ T cells and innate T cell populations. NKG2A has recently become a novel immune checkpoint target for the treatment of cancer and direct antibody mediated blockade of NKG2A function is currently under assessment in two phase 3 clinical trials. In addition to direct targeting, the NKG2A:HLA-E axis can also be disrupted indirectly via multiple different targeted cancer agents that were not previously recognised to possess immunomodulatory properties. Increased understanding of immune cell modulation by targeted cancer therapies will allow for the design of rational and more efficacious drug combination strategies to improve cancer patient outcomes. In this review, we summarise and discuss the various strategies currently in development which either directly or indirectly disrupt the NKG2A:HLA-E interaction to enhance NK cell activation against cancer.

HLA-E and HLA-F Are Overexpressed in Glioblastoma and HLA-E Increased After Exposure to Ionizing Radiation

BACKGROUND/AIM

Glioblastoma (GBM) is one of the deadliest human cancers responding very poorly to therapy. Although the central nervous system has been traditionally considered an immunologically privileged site with an enhanced immune response, GBM appears to benefit from this immunosuppressive milieu. Immunomodulatory molecules play an important role in immune tumor-host interactions. Non-classical human leukocyte antigens (HLA) class Ib molecules HLA-E, HLA-F, and HLA-G have been previously described to be involved in protecting semi-allogeneic fetal allografts from the maternal immune response and in transplant tolerance as well as tumoral immune escape. Unfortunately, their role in GBM remains poorly understood. Our study, therefore, aimed to characterize the relationship between the expression of these molecules in GBM on the transcriptional level and clinicopathological and molecular features of GBM as well as the effect of ionizing radiation.

MATERIALS AND METHODS

We performed the analysis of HLA-E, HLA-F, and HLA-G mRNA expression in 69 GBM tissue samples and 21 non-tumor brain tissue samples (controls) by reverse transcription polymerase chain reaction. Furthermore, two primary GBM cell cultures had been irradiated to identify the effect of ionizing radiation on the expression of non-classical HLA molecules.

RESULTS

Analyses revealed that both HLA-E and HLA-F are significantly up-regulated in GBM samples. Subsequent survival analysis showed a significant association between low expression of HLA-E and shorter survival of GBM patients. The dysregulated expression of both molecules was also observed between patients with methylated and unmethylated O-6-methylguanine-DNA methyltransferase (MGMT) promoter. Finally, we showed that ionizing radiation increased HLA-E expression level in GBM cells in vitro.

CONCLUSION

HLA-E and HLA-F play an important role in GBM biology and could be used as diagnostic biomarkers, and in the case of HLA-E also as a prognostic biomarker.

Natural Killer Cells and Anti-Cancer Therapies: Reciprocal Effects on Immune Function and Therapeutic Response

Simple Summary

Natural Killer (NK) cells are innate lymphocytes that play an important role in the immune response against cancer. Their activity is controlled by a balance of inhibitory and activating receptors, which in cancer can be skewed to favor their suppression in support of immune escape. It is therefore imperative to find ways to optimize their antitumor functionality. In this review, we explore and discuss how their activity influences, or even mediates, the efficacy of various anti-cancer therapies and, vice versa, how their activity can be affected by these therapies. Knowledge of the mechanisms underlying these observations could provide rationales for combining anti-cancer treatments with strategies enhancing NK cell function in order to improve their therapeutic efficacy.

Abstract

Natural Killer (NK) cells are innate immune cells with the unique ability to recognize and kill virus-infected and cancer cells without prior immune sensitization. Due to their expression of the Fc receptor CD16, effector NK cells can kill tumor cells through antibody-dependent cytotoxicity, making them relevant players in antibody-based cancer therapies. The role of NK cells in other approved and experimental anti-cancer therapies is more elusive. Here, we review the possible role of NK cells in the efficacy of various anti-tumor therapies, including radiotherapy, chemotherapy, and immunotherapy, as well as the impact of these therapies on NK cell function.

Radiotherapy in combination with systemic therapies for brain metastases: current status and progress

Brain metastases (BMs) are the most common cause of intracranial neoplasms in adults with poor prognosis. Most BMs originate from lung cancer, breast cancer, or melanoma. Radiotherapy (RT), including whole brain radiotherapy (WBRT) and stereotactic radiation surgery (SRS), has been widely explored and is considered a mainstay anticancer treatment for BMs. Over the past decade, the advent of novel systemic therapies has revolutionized the treatment of BMs. In this context, there is a strong rationale for using a combination of treatments based on RT, with the aim of achieving both local disease control and extracranial disease control. This review focuses on describing the latest progress in RT as well as the synergistic effects of the optimal combinations of RT and systemic treatment modalities for BMs, to provide perspectives on current treatments.

Immunomodulation of NK Cells by Ionizing Radiation

Natural killer (NK) cells play a critical role in the antitumor immunity. Ionizing radiation (IR) has a pronounced effect on modifying NK cell biology, while the molecular mechanisms remain elusive. In this review, we briefly introduce the anti-tumor activity of NK cells and summarize the impact of IR on NK cells both directly and indirectly. On one hand, low-dose ionizing radiation (LDIR) activates NK functions while high-dose ionizing radiation (HDIR) is likely to partially impair NK functions, which can be reversed by interleukin (IL)-2 pretreatment. On the other hand, NK functions may be adjusted by other immune cells and the alternated malignant cell immunogenicity under the settings of IR. Various immune cells, such as the tumor-associated macrophage (TAM), dendritic cell (DC), regulatory T cell (Treg), myeloid-derived suppressor cell (MDSC), and tumor exhibited ligands, such as the natural killer group 2 member D ligand (NKG2DL), natural cytotoxicity receptors (NCR) ligand, TNF-related apoptosis-inducing ligand-receptor (TRAIL-R), and FAS, have been involved in this process. Better understanding the molecular basis is a promising way in which to augment NK-cell-based antitumor immunity in combination with IR.

Immune targets in the tumor microenvironment treated by radiotherapy

Radiotherapy (RT), the major anti-cancer modality for more than half of cancer patients after diagnosis, has the advantage of local tumor control with relatively less systematic side effects comparing to chemotherapy. However, the efficacy of RT is limited by acquired tumor resistance leading to the risks of relapse and metastasis. To further enhance the efficacy of RT, with the renaissances of targeted immunotherapy (TIT), increasing interests are raised on RT combined with TIT including cancer vaccines, T-cell therapy, and antibody-based immune checkpoint blockers (ICB) such as anti-CTLA-4 and anti-PD1/PD-L1. In achieving a significant synergy between RT and TIT, the dynamics of radiation-induced response in tumor cells and stromal cells, especially the cross-talk between tumor cells and immune cells in the irradiated tumor microenvironment (ITME) as highlighted in recent literature are to be elucidated. The abscopal effect refereeing the RT-induced priming function outside of ITME could be compromised by the immune-suppressive factors such as CD47 and PD-L1 on tumor cells and Treg induced or enhanced in the ITME. Cell surface receptors temporally or permanently induced and bioactive elements released from dead cells could serve antigenic source (radiation-associated antigenic proteins, RAAPs) to the host and have functions in immune regulation on the tumor. This review is attempted to summarize a cluster of factors that are inducible by radiation and targetable by antibodies, or have potential to be immune regulators to synergize tumor control with RT. Further characterization of immune regulators in ITME will deepen our understanding of the interplay among immune regulators in ITME and discover new effective targets for the combined modality with RT and TIT.

HLA-G Expression in Tumor Tissues and Soluble HLA-G Plasma Levels in Patients with Gastrointestinal Cancer

Background:

Overexpression of human leukocyte antigen G (HLA-G) and increased plasma levels of soluble HLA-G (sHLA-G) have been reported in different human malignancies, and are believed to be involved in tumor immune evasion.

Objectives:

This study was designed to evaluate the expression of HLA-G in tumor tissues and the plasma levels of sHLA-G in patients with gastrointestinal cancer, and to determine their associations with clinicopathological factors. The link between Helicobacter pylori infection and increased HLA-G expression or sHLA-G levels was also investigated in patients with gastric cancer.

Methods:

HLA-G expression was investigated in tumor tissues from 100 patients with gastric and colorectal adenocarcinoma using immunohistochemistry test, and plasma levels of sHLA-G were measured in 82 patients with ELISA method. The presence of H. pylori genome was investigated in tumor tissues from 25 patients with gastric cancer by PCR method.

Results:

HLA-G expression was observed in 43% of colorectal cancers and 34.6% of gastric cancers, and was not related with any of the clinicopathological factors. There was a significant correlation between increased sHLA-G level and stage I tumors. Eight of 25 (32%) gastric cancer specimens were positive for H. pylori, of which 3 samples were positive for HLA-G. Soluble HLA-G levels were above the cut-off value in all H. pylori-positive patients.

Conclusion:

Plasma levels of sHLA-G were significantly increased in our patients with a sensitivity of 89% and a specificity of 62%. Soluble HLA-G level can be considered a useful indicator for the early diagnosis of gastric and colorectal adenocarcinoma.

HLA-G+3027 polymorphism is associated with tumor relapse in pediatric Hodgkin's lymphoma

In this study, we tested whether polymorphisms in human leukocyte antigen G (HLA-G) were associated with event-free survival (EFS) in pediatric Hodgkin's lymphoma (HL). We evaluated the association of HLA-G 3′-UTR polymorphisms with EFS in 113 pediatric HL patients treated using the AIEOP LH-2004 protocol. Patients with the +3027-C/A genotype (rs17179101, UTR-7 haplotype) showed lower EFS than those with the +3027-C/C genotype (HR= 3.23, 95%CI: 0.99-10.54, P=0.012). Female patients and systemic B symptomatic patients with the HLA-G +3027 polymorphism showed lower EFS. Multivariate analysis showed that the +3027-A polymorphism (HR 3.17, 95%CI 1.16-8.66, P=0.025) was an independent prognostic factor. Immunohistochemical analysis showed that HL cells from patients with the +3027-C/A genotype did not express HLA-G. Moreover, HLA-G +3027 polymorphism improved EFS prediction when added to the algorithm for therapeutic group classification of pediatric HL patients. Our findings suggest HLA-G +3027 polymorphism is a prognostic marker in pediatric HL patients undergoing treatment according to LH-2004 protocol.

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.

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.

HLA-G1 increases the radiosensitivity of human tumoral cells

Different molecules regulate the response of tumoral tissues to ionizing radiation. The objective of this work was to determine if HLA-G1 expression modulates the radiosensitivity of human tumoral cell lines. To this end, human melanoma M8 and human erythroleukemia K562 cell lines, with their correspondent HLA-G1 negative and positive variants, were gamma irradiated and the survival frequency was determined by clonogenic assay. The survival fraction of HLA-G1 expressing cells was around 60% of HLA-G1 negative cells. The generation of acidic vesicular organelles was higher in HLA-G1 positive cells. Apoptosis levels showed statistically significant differences only in K562 cells, whereas the variation in G2/M cycle progression was only significant in M8 cells. In addition, irradiation diminished cell-surface HLA-G1 and increased soluble HLA-G1 levels. Soluble HLA-G1 has no influence on cell survival in any cell line. In summary, we could demonstrate that HLA-G1 confers higher radiosensitivity to HLA-G1 expressing cells.

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

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

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.

Serum soluble HLA-E in melanoma: a new potential immune-related marker in cancer

BACKGROUND

Tumor-derived soluble factors, including soluble HLA molecules, can contribute to cancer immune escape and therefore impact on clinical course of malignant diseases. We previously reported that melanoma cells produce, in vitro, soluble forms of the non-classical MHC class I molecule HLA-E (sHLA-E). In order to investigate sHLA-E production by various tumors and to address its potential value as a tumor-associated marker, we developed a specific ELISA for the quantification of sHLA-E in biological fluids.

METHODOLOGY/PRINCIPAL FINDINGS

We developed a sHLA-E specific and sensitive ELISA and we showed that serum sHLA-E levels were significantly elevated (P<0.01) in melanoma patients (n = 127), compared with healthy donors (n = 94). sHLA-E was also detected in the culture supernatants of a wide variety of tumor cell lines (n = 98) including melanomas, kidney, colorectal and breast cancers. Cytokines regulation of sHLA-E production by tumor cells was also carried out. IFN-γ, IFN-α and TNF-α were found to upregulate sHLA-E production by tumor cells.

CONCLUSIONS/SIGNIFICANCE

In view of the broad tumor tissue release of HLA-E and its up-regulation by inflammatory cytokines, sHLA-E should be studied for its involvement in immune responses against tumors. Interestingly, our results demonstrated a positive association between the presence of serum sHLA-E and melanoma. Therefore, the determination of sHLA-E levels, using ELISA approach, may be investigated as a clinical marker in cancer patients.

Expression of immune-modulatory molecules HLA-G and HLA-E by tumor cells in glioblastomas: an unexpected prognostic significance?

The role of nonclassical human leukocyte antigens G and E (HLA-G and HLA-E) was originally thought to be restricted to the protection of the fetus from a maternal allorecognition. Now it is known that HLA-G and HLA-E exert multiple immunoregulatory functions. A prognostic significance of the expression of HLA-G and HLA-E by neoplastic cells in glioblastoma is not well characterized. In this study, we evaluated the expression of HLA-G and HLA-E by neoplastic cells in 39 cases of glioblastoma. We found the production of HLA-G and HLA in a majority of cases. There was an unexpected positive correlation between the expression of HLA-E and length of survival. We speculate that the expression of this molecule by neoplastic cells may represent a coincidental selective pro-host advantage related to better response to subsequent therapeutic modalities. Mechanisms of glioblastoma cell pathophysiology and mechanisms of responses to therapeutic interventions in respect to the expression of these molecules deserves further study.