Natural killer cell dysfunction in hepatocellular carcinoma and NK cell-based immunotherapy

The mechanisms linking hepatitis B virus (HBV) and hepatitis C virus (HCV) infection to hepatocellular carcinoma (HCC) remain largely unknown. Natural killer (NK) cells account for 25%–50% of the total number of liver lymphocytes, suggesting that NK cells play an important role in liver immunity. The number of NK cells in the blood and tumor tissues of HCC patients is positively correlated with their survival and prognosis. Furthermore, a group of NK cell-associated genes in HCC tissues is positively associated with the prolonged survival. These facts suggest that NK cells and HCC progression are strongly associated. In this review, we describe the abnormal NK cells and their functional impairment in patients with chronic HBV and HCV infection, which contribute to the progression of HCC. Then, we summarize the association of NK cells with HCC based on the abnormalities in the numbers and phenotypes of blood and liver NK cells in HCC patients. In particular, the exhaustion of NK cells that represents lower cytotoxicity and impaired cytokine production may serve as a predictor for the occurrence of HCC. Finally, we present the current achievements in NK cell immunotherapy conducted in mouse models of liver cancer and in clinical trials, highlighting how chemoimmunotherapy, NK cell transfer, gene therapy, cytokine therapy and mAb therapy improve NK cell function in HCC treatment. It is conceivable that NK cell-based anti-HCC therapeutic strategies alone or in combination with other therapies will be great promise for HCC treatment.     

Novel strategies of regenerative medicine using chemical compounds

Many diseases and/or physical defects due to injury result in the loss of specialized cells within organ systems and lead to organ system dysfunction. The ultimate goal of cell-based therapies is to regenerate and restore normal function. Populations of embryonic, fetal, adult stem cells and inducible pluripotent stem cells generated by reprogramming of adult cells show promise for the treatment of a variety of diseases. In addition, the recent advancements in adult stem cell biology in both normal and pathological conditions have led to the identification of some intrinsic and extrinsic factors that govern the decision between self renewal versus differentiation of tissue-resident adult stem cells. This is of primary importance for the design of an approach of stem cell-based therapy focused on their in vivo modulation by conventional chemical and biological therapeutics capable to stimulate endogenous cell regeneration. Such therapeutics can act in vivo to promote cell survival, proliferation, differentiation, reprogramming and homing of stem cells or can modulate their niches. In this review, we will highlight the burst of recent literature on novel perspectives of regenerative medicine and their possible clinical applications.     

The interaction of NK cells and dendritic cells in the tumor environment: how to enforce NK cell & DC action under immunosuppressive conditions?

The crosstalk of natural killer (NK) and dendritic cells (DCs) plays an important role in the induction of the tumor-specific immune response against cancer. During the last decade, our advanced understanding of the immune system led to the development of new therapeutic strategies in the field of immunotherapy and cellular immunology. However, these immunotherapeutic concepts have not been as successful as initially expected because of their inability to counteract cancer-induced immunosuppressive pathways. Some of the major difficulties of effective cellular immunotherapy are the highly immunosuppressive factors induced by tumor cells themselves or by their microenvironment. Therefore, one major challenge in immunotherapy is the question: "How to enforce NK cell & DC action under immunosuppressive conditions?" This review focuses on the current knowledge on the tumor microenvironment, the crosstalk of NK cells and DCs, as well as their deregulation in the complex interplay with the immunosuppressive tumor microenvironment. We further discuss possible strategies to minimize the negative impact of the tumor microenvironment on the immune system.     

The effect of chemotherapy/radiotherapy on cancerous pattern recognition by NK cells

In recent years, the effects of cancer chemotherapy and radiotherapy (CT/RT) regimens as they apply to the immune system have been explored. NK cells represent the main cytotoxic arm of the innate immune system, and their functionality is vital to establishing an effective anti tumor immune response. This review examines current CT/RT interventions in light of their effects on NK cell functionality. The effects of CT/RT on the expression of the various ligands for activating and inhibitory NK cell receptors are discussed. Expression of ligands for the activating NKG2D receptor is enhanced by cell stress; accordingly there are numerous reports of their higher expression in cells exposed to various CT/RT agents. In contrast, some agents have been reported to cause ligand shedding, which can serve to inhibit NK cell activity. Reported effects of CT/RT on tumor expression of ligands for the activating Natural Cytotoxicity Receptors, and of HLA class I ligands for NK cell inhibitory receptors are also noted. Additionally, we describe reports concerning the direct effects of CT/RT on NK cell function. Many treatments adversely affect NK cell function directly, but observations made through in vitro systems may differ from those obtained utilizing clinical samples. The effects of CT/RT on both direct NK cell cytotoxicity and on NK cell-mediated Antibody Dependent Cellular Cytotoxicity are explored. Taken together, CT/RT affects NK cell anti-tumor immunity from multiple angles. The interplay is complex, and future work is needed to achieve the optimal synergy between CT/RT and innate as well as adaptive immunity in the treatment of cancer.     

Role of natural killer cells in the pathogenesis and progression of multiple sclerosis.

Natural killer (NK) cells are a subset of lymphocytes which have long been alleged to play an immunoregulatory role in the prevention of autoimmune diseases. Here, we briefly review NK cell features and the major findings from studies on NK cells in human and animals susceptible to multiple sclerosis (MS). Although most studies in human seem to suggest an association between disease and deficiencies in NK cells, it is also clear that NK cells can be both protective and pathogenic in MS models. These contrasting observations could result from differences in experimental procedures as well as from differences in NK cell subset targeted. Whatever the case, the functional features of these cells and their potential role in regulation of autoimmunity suggest that NK cell-based therapies might be an interesting approach for the treatment of multiple sclerosis.     

Natural killer cells preferentially target cancer stem cells; role of monocytes in protection against NK cell mediated lysis of cancer stem cells

Mounting effective anti-tumor immune responses by cytotoxic effectors is important for the clearance of tumors. However, accumulated evidence suggests that the cytotoxic function of immune effectors is largely suppressed in the tumor microenvironment by a number of distinct effectors and their secreted factors. The aims of this review are to provide a rationale and potential mechanism for immunosuppression in cancer, and to demonstrate the significance of such immunosuppression in cellular differentiation and tissue regeneration in pathological conditions, and progression of cancer. We have recently shown that increased NK cell function was seen when they were cultured with primary oral squamous carcinoma stem cells (OSCSCs) as compared to their more differentiated oral squamous carcinoma cells (OSCCs). In addition, human embryonic stem cells (hESCs), Mesenchymal Stem Cells (hMSCs), dental pulp stem cells (hDPSCs) and induced pluripotent stem cells (hiPSCs) were significantly more susceptible to NK cell mediated cytotoxicity than their differentiated counterparts or parental cells from which they were derived. We have also reported that inhibition of differentiation or reversion of cells to a less-differentiated phenotype by blocking NFκB or targeted knock down of COX2 augmented NK cell function significantly. Total population of monocytes and those depleted of CD16(+) subsets were able to substantially prevent NK cell mediated lysis of OSCSCs, MSCs and DPSCs. Taken together, our results suggest that stem cells are significant targets of the NK cell cytotoxicity. The concept of split anergy in NK cells and its contribution to tissue repair and regeneration and in tumor resistance and progression will be discussed in this review. Therefore, patients with cancer may benefit from repeated allogeneic NK cell transplantation at the site of the tumor for specific elimination of cancer stem cells.     

Mesenchymal stem cells engineered for cancer therapy

Recent pre-clinical and clinical studies have shown that stem cell-based therapies hold tremendous promise for the treatment of human disease. Mesenchymal stem cells (MSC) are emerging as promising anti-cancer agents which have an enormous potential to be utilized to treat a number of different cancer types. MSC have inherent tumor-trophic migratory properties, which allows them to serve as vehicles for delivering effective, targeted therapy to isolated tumors and metastatic disease. MSC have been readily engineered to express anti-proliferative, pro-apoptotic, anti-angiogenic agents that specifically target different cancer types. Many of these strategies have been validated in a wide range of studies evaluating treatment feasibility or efficacy, as well as establishing methods for real-time monitoring of stem cell migration in vivo for optimal therapy surveillance and accelerated development. This review aims to provide an in depth status of current MSC-based cancer therapies, as well as the prospects for their clinical translation.     

Imbalance of NKG2D and its inhibitory counterparts: how does tumor escape from innate immunity?

NK cells form a first line of defence against pathogens or host cells that are stressed or cancerous. NK cells express surface receptors that receive signals from the environment and determine their response to foreign or malignant cells. The effector functions of NK cells are regulated by integrated signals across the array of stimulatory and inhibitory receptors engaged upon interaction with target cell surface ligands. NKG2D is a peculiar activating receptor that is expressed as a disulphide-linked homodimer by all NK cells, alphabeta CD8(+) T cells, gammadeltaT cells and murine macrophages. It not only activates NK cells but also delivers co-stimulatory signals to CD8(+) T cells and gammadeltaT cells. The ligands of NKG2D are induced by cellular stress and are specifically expressed by some tumor cells. Recent studies reveal that the expression of MIC and ULBP on human tumor cells is sufficient to overcome the inhibitory effects of MHC class I expression on NK cell killing and indicate that NKG2D provides first line surveillance against stressed or abnormal cells that have been induced to express one of its ligands. However, malignant tumors develop means to control the expression of activating versus inhibitory receptors on immune cells and their ligands on tumor cell themselves in favor of tolerance. Modulating the balance between activating and inhibitory signals through NK cell receptors on NK cells may open a new approach to NK cell-based biotherapy for cancer and infectious diseases.     

Immune Cell Recruitment and Cell-Based System for Cancer Therapy

Immune cells, such as cytotoxic T lymphocytes, natural killer cells, B cells, and dendritic cells, have a central role in cancer immunotherapy. Conventional studies of cancer immunotherapy have focused mainly on the search for an efficient means to prime/activate tumor-associated antigen-specific immunity. A systematic understanding of the molecular basis of the trafficking and biodistribution of immune cells, however, is important for the development of more efficacious cancer immunotherapies. It is well established that the basis and premise of immunotherapy is the accumulation of effective immune cells in tumor tissues. Therefore, it is crucial to control the distribution of immune cells to optimize cancer immunotherapy. Recent characterization of various chemokines and chemokine receptors in the immune system has increased our knowledge of the regulatory mechanisms of the immune response and tolerance based on immune cell localization. Here, we review the immune cell recruitment and cell-based systems that can potentially control the systemic pharmacokinetics of immune cells and, in particular, focus on cell migrating molecules, i.e., chemokines, and their receptors, and their use in cancer immunotherapy.     

Targeting tumours by adoptive transfer of immune cells

1. Surgery, radiotherapy and chemotherapy are the most widely used and well-established modalities for treating malignant diseases. Surgery is used to excise solid tumours and radiotherapy/chemotherapy are used for the treatment of liquid tumours and for solid tumours where there is a risk of micrometastases. A major drawback for both radiotherapy and chemotherapy is their lack of specificity for tumour cells. Both these treatments can destroy normal bone marrow cells and result in severe side-effects. 2. The impairment of haemapoiesis due to bone marrow destruction combined with the use of toxins in chemotherapy that inhibit the proliferation of immune cells leaves many patients immunocompromised. This complicates the development of prophylactic (vaccine) strategies for tumours where patients are undergoing conventional therapy. 3. An alternative approach is to expand and activate tumour-specific immune cells in vitro that can then be adoptively transferred back in large numbers. This is defined as adoptive immunotherapy and has the advantage of potentially bypassing the immuno-inhibitory effects of conventional therapies. 4. Transferred immune cells have been shown to mediate tumour regression in patients by both direct and indirect mechanisms. The immune cells used include tumour reactive T lymphocytes and dendritic cells, which elicit tumour specific responses. 5. Many novel cell-based immunotherapeutic strategies developed in murine tumour models are now being applied in human clinical trials. The malignancies targeted include melanoma, chronic myelogenous leukaemia and breast, ovarian, colon and kidney cancers. In the present review, we discuss these novel cell-based strategies and the implications they have for the future treatment of human malignancies.     

Advancements in immune tolerance

In recent years, considerable attention has been given to immune tolerance and its potential clinical applications for the treatment of cancers and autoimmune diseases, and the prevention of allo-graft rejection and graft-versus-host diseases. Advances in our understanding of the underlying mechanisms of establishment and maintenance of immune tolerance in various experimental settings and animal models, and in our ability to manipulate the development of various immune tolerogenic cells in vitro and in vivo, have generated significant momentum for the field of cell-based tolerogenic therapy. This review briefly summarizes the major tolerogenic cell populations and their mechanisms of action, while focusing mainly on potential exploitation of their tolerogenic mechanisms for clinical applications.     

Abscopal effect in radioimmunotherapy

Abscopal effect is an interesting phenomenon in radiobiology that causes activation of immune system against cancer cells. Traditionally, this phenomenon was known as a suppressor of non-irradiated tumors or metastasis. However, it can be used as a stimulator of the immune system against primary tumor during radiotherapy. Immunotherapy, a novel tumor therapy modality, also triggers immune system against cancer. To date, some immunotherapy types have been developed. However, immune checkpoint blockade is a more common modality and some drugs have been approved by the FDA. Studies have shown that radiotherapy or immunotherapy administered alone have low efficiency for tumor control. However, their combination has a more potent anti-tumor immunity. For this aim, it is important to induce abscopal effect in primary tumors, and also use appropriate drugs to target the mechanisms involved in the exhaustion of cytotoxic CD8+T lymphocytes (CTLs) and natural killer (NK) cells. Among the different radiotherapy techniques, stereotactic body radiation therapy (SBRT) with some few fractionations is the best choice for inducing abscopal effect. On the other hand, programmed cell death 1 (PD-1) is known as one of the best targets for triggering anti-tumor immunity. This combination is known as the best choice among various strategies for radioimmunotherapy. However, there is the need for other strategies to improve the duration of immune system’s activity within tumor microenvironment (TME). In this review, we explain the cellular and molecular mechanisms behind abscopal effect by radiotherapy and evaluate the molecular targets which induce potent anti-tumor immunity.     

Reprogramming cell fates towards novel cancer immunotherapies

Recent advances in our understanding of host immune and cancer cells interactions have made immunotherapy a prominent choice in cancer treatment. Despite such promise, cell-based immunotherapies remain inapplicable to many patients due to severe limitations in the availability and quality of immune cells isolated from donors. Reprogramming technologies that facilitate the engineering of cell types of interest, are emerging as a putative solution to such challenges. Here we focus on the recent progress being made in reprogramming technologies with respect to the immune system and their potential for clinical applications.     

Non-steroidal anti-inflammatory drugs, tumour immunity and immunotherapy

Non-steroidal anti-inflammatory drugs (NSAIDs) have received considerable importance in cancer chemoprevention over the last few years. They are now being considered as prospective candidates in cancer immunotherapy because of their striking immune-enhancing impact on various effector elements of anti-tumour immunity on one hand, and to augment the efficacy of different anti-cancer immunotherapeutic strategies on the other. This review specifically discusses the role of NSAIDs in anti-tumour immunity by describing their immunomodulatory effects on different immune cells including tumour-associated macrophages (TAM), dendritic cells (DC), natural killer (NK) cells, T effector cells, and T regulatory cells (Treg). Secondly, the therapeutic perspective of NSAIDs in combination with different anti-cancer immunotherapeutic approaches, in particular the cancer vaccines, tumour-specific monoclonal antibodies, and cytokine-based therapy, has been outlined. At the end, the impact of anti-inflammatories other than NSAIDs on tumour immunity and immunotherapy, and the immunopharmacological potential of selective E-prostanoid (EP) receptor antagonists with respect to cancer immunity have also been discussed briefly.     

Drug delivery to tumours: recent strategies

Despite several advancements in chemotherapy, the real therapy of cancer still remains a challenge. The development of new anti-cancer drugs for the treatment of cancer has not kept pace with the progress in cancer therapy, because of the nonspecific drug distribution resulting in low tumour concentrations and systemic toxicity. The main hindrance for the distribution of anti-cancer agents to the tumour site is the highly disorganized tumour vasculature, high blood viscosity in the tumour, and high interstitial pressure within the tumour tissue. Recently, several approaches such as drug modifications and development of new carrier systems for anti-cancer agents have been attempted to enhance their tumour reach. Approaches such as drug delivery through enhanced permeability and retention (EPR) effect have resulted in a significant improvement in concentration in tumours, while approaches such as drug-carrier implants and microparticles have resulted in improvement in local chemotherapy of cancer. This review discusses different strategies employed for the delivery of anti-cancer agents to tumours, such as through EPR effect, local chemotherapeutic approaches using drug delivery systems, and special strategies such as receptor-mediated delivery, pH-based carriers, application of ultrasound and delivery to resistant tumour cells and brain using nanoparticles.     

Advances in systemic delivery of anti-cancer agents for the treatment of metastatic cancer

ABSTRACT

Introduction: The successful treatment of metastatic cancer is refractory to strategies employed to treat confined, primary lesions, such as surgical resection and radiation therapy, and thus must be addressed by systemic delivery of anti-cancer agents. Conventional systemically administered chemotherapeutics are often ineffective and come with severe dose-limiting toxicities.

Areas covered: This review focuses on the recent developments in systemic therapy for metastatic cancer. Firstly, the strategies employed to improve the efficacy of conventional chemotherapeutics by ‘passively’ and ‘actively’ targeting them to tumors are discussed. Secondly, recent advances in the use of biologics to better target cancer and to instigate anti-tumor immunity are reviewed. Under the label of ‘biologics’, antibody-therapies, T cell engaging therapies, oncolytic virotherapies and cell-based therapies are examined and evaluated.

Expert opinion: Improving specificity of action, and engaging the immune system appear to be key goals in the development of novel or reformulated anti-cancer agents for the treatment of metastatic cancer. One of the largest areas of opportunity in this field will be the identification of robust predictive biomarkers for use in conjunction with these agents. Treatment regimens that combine an agent to elicit an immune response (such as an oncolytic virus), and an agent to potentiate/mediate that immune response (such as immune checkpoint inhibitors) are predicted to be more effective than treatment with either agent alone.     

Research progress and clinical prospect of immunocytotherapy for the treatment of hepatocellular carcinoma

As a common malignant tumor, hepatocellular carcinoma (HCC) has high fatality rate due to its strong metastasis and high degree of malignancy. Current treatment strategies adopted in clinical practice were still conventional surgery, assisted with interventional therapy, radiotherapy and chemotherapy. However these treatments have limited effects with high recurrence rate. Current research progress of immunocytotherapy has shown that tumor cells can be directly identified and killed by stimulating the immune function and enhancing the anti-tumor immunity in tumor microenvironment. Targeted immunotherapeutics have therefore become the hope of conquering cancer in the future. It can kill tumor cells without damaging the body's immune system and function, restore and strengthen the body's natural anti-tumor immune system. It can reduce the toxic side effects of radiotherapy and chemotherapy, reduce the recurrence rate and prolong the survival period of patients with HCC. Currently, the immune cells widely studied are mainly as follows: Dendritic cells (DC), Cytokine-induced killer (CIK), DC-CIK, Chimeric antigen receptor T cells (CAR-T), Tumor infiltrating lymphocyte (TIL) and Natural killer cell (NK). Immunocytotherapy is a long-term treatment method, some studies have combined traditional therapy with immunocytotherapy and achieved significant effects, providing experimental basis for the application of immunocytotherapy. However, there are still some difficulties in the clinical application of immune cells. In this article, we discuss the application of immunocytotherapy in the clinical treatment of HCC, their effectiveness either alone or in combination with conventional therapies, and how future immunocytotherapeutics can be further improved from investigations in tumour immunology.     

New gene therapy strategies for cancer treatment: a review of recent patents

Cancer is the second leading cause of death in the Western world. The limited successes of available treatments for cancer mean that new strategies need to be developed. The possibility of modifying the cancer cell with the introduction of genetic material opens the way to a new approach based on gene therapy. There are still many technical difficulties to be overcome, but recent advances in the molecular and cellular biology of gene transfer have made it likely that gene therapy will soon start to play an increasing role in clinical practice, particularly in the treatment of cancer. Gene therapy will probably be the therapeutic option in cases in which conventional treatments such as surgery, radiotherapy and chemotherapy have failed. The development of modified vectors, and an improved understanding of interactions between the vector and the human host, are generating inventions that are being protected by patents due to the considerable interest of industry for their possible commercialization. We review the latest strategies, patented and/or under clinical trial, in cancer gene therapy. These include patents that cover the use of modified vectors to increase the security and specificity, recombining adenovirus that leads to loss or gain of gene function, activation of the patient's own immune cells to eliminate cancer cells by expression of molecules that enhance immune responses, silencing genes related to the development of drug resistance in patients, inhibition of angiogenesis of solid tumors by targeting the tumor vasculature, and the development of enzymes that destroy viral or cancerous genetic material.     

The sialoglycan-Siglec glyco-immune checkpoint – a target for improving innate and adaptive anti-cancer immunity

ABSTRACT

Introduction: During cancer progression, tumor cells develop several mechanisms to prevent killing and to shape the immune system into a tumor-promoting environment. One of such regulatory mechanism is the overexpression of sialic acid (Sia) on carbohydrates of proteins and lipids on tumor cells. Sia-containing glycans or sialoglycans were shown to inhibit immune effector functions of NK cells and T cells by engaging inhibitory Siglec receptors on the surface of these cells. They can also modulate the differentiation of myeloid cells into tumor-promoting M2 macrophages.

Areas covered: We review the role of sialoglycans in cancer and introduce the Siglecs, their expression on different immune cells and their interaction with cancer-associated sialoglycans. The targeting of this sialoglycan-Siglec glyco-immune checkpoint is discussed along with potential therapeutic approaches. Pubmed was searched for publications on Siglecs, sialic acid, and cancer.

Expert opinion: The targeting of sialoglycan-Siglec interactions has become a major focus in cancer research. New approaches have been developed that directly target sialic acids in tumor lesions. Targeted sialidases that cleave sialic acid specifically in the tumor, have already shown efficacy; efforts targeting the sialoglycan-Siglec pathway for improvement of CAR T cell therapy are ongoing. The sialoglycan-Siglec immune checkpoint is a promising new target for cancer immunotherapy.     

Impact of immune infiltration on tumor development and progression

Recently, immune infiltration has a crucial role in modulating tumor progression and response to therapy which comprised cells from the innate and adaptive immune response. Infiltrating immune cells can be detected in biopsy specimens and exploited to promote cancer metastasis, angiogenesis and growth. Mounting evidence demonstrates that many cancer-associated cell types within the tumor stromal support tumor growth and development, greatly modifying cancer cell behavior,facilitating invasion and metastasis and controlling sensitivity to drug therapy. Furthermore,immune infiltration of the tumor microenvironment has been associated with improved survival for some patients with solid tumors which have prognostic value. Infiltrating immune cells are both prognostic and predictive of response to cancer therapies. Understanding the interactions between tumor and immune infiltration is critical to find prognostic biomarkers,reduce drug resistance, and developnew therapies.Therefore, cancer immunotherapy based on tumor-infiltrating cell populations has become arguably the most promising advancement in cancer research and therapy in recent years. In this review, we provide an updated overview of key components of the immune infiltrating cells in the tumor microenvironment and the impact of immune infiltration on tumor development and progression. Moreover, we discuss the intricacy of the reciprocal interactions between cancer-associated immune cell types and signal transduction pathways, which appear to be crucially linked to cancer progression in response to the tumor microenvironment. Finally, we focus on the current immunotherapeutic strategies and emerging results from ongoing clinical trials are presented.