New directions in natural killer cell-based immunotherapy of human cancer

Efforts at harnessing the antitumour activity of natural killer (NK) cells have been investigated for the immunotherapy of human cancer for over two decades. Initial trials, focusing on the use of ex vivo-generated lymphokine activated killer (LAK) cells or activated NK cells, or in vivo cytokine therapy to expand and activate NK cells against autologous tumours, have yielded only modest success. Recent understanding of the means by which NK cells kill target cells through a complex set of activating and inhibitory receptors recognising corresponding ligands on tumour cells has paved the way for the design of improved strategies for NK cell-based immunotherapy. The net balance of activating and inhibitory signals through NK cell receptors determines whether an NK cell becomes activated or not. Successful therapeutic strategies should now focus on manipulating the balance in favour of activating receptor signalling. In the case of autologous cancers, such strategies may include the use of monoclonal antibodies with cytokines to better direct NK cells to their tumour targets through the process of antibody-dependent cellular cytotoxicity (ADCC) or the in vivo blocking of inhibitory interactions between NK receptors (NKRs) and ligands on tumour cells. Alternatively, allogeneic NK cells can be used whenever there is mismatching of inhibitory NK cell receptors and ligands. Finally, methods to modulate expression of NK cell receptors and their ligands on tumour cells by cytokines and other agents should be explored. In this review, the impact of NKR biology on the development of novel strategies for the use of NK cells in the treatment of human cancer is discussed.     

The rise of human stem cell-derived natural killer cells for cancer immunotherapy

Introduction: Natural killer (NK) cell therapy has been proven to be safe and clinically effective for the treatment of multiple cancers, in particular blood cancers. Most of the clinical trials use primary NK cells from peripheral blood or umbilical cord blood, or NK-92 cells. Each cell source is confined by limitations, such as donor dependence, low persistence in vivo, and its difficulty to genetically modify. Thus, there is an urgent need to explore novel NK cell sources for clinical use.

Areas covered: This article highlights the recent progress in utilizing stem cell-derived NK cells as anticancer therapies and strategies to improve their antitumor activities.

Expert commentary: Stem cell-derived NK cells are homogenous, easy to genetically modify on a clonal level, and can be expanded to clinical scale. They may therefore arise as an ideal population for developing off-the-shelf, standardized adoptive NK cell therapeutic products.     

Cellular liaisons of natural killer lymphocytes in immunology and immunotherapy of cancer

There is compelling evidence for the role of natural killer (NK) cells in tumor immunosurveillance and their beneficial effects on many experimentally successful immunotherapy strategies. NK cells mediate cell contact-dependent cellular cytotoxicity and produce pro-inflammatory cytokines, but do not rearrange antigen receptors. Their activation depends on various germline-encoded receptors, including CD16, which mediates recognition of antibody-coated target cells. NK cytotoxicity is checked by a repertoire of inhibitory receptors that scan adequate expression of major histocompatibility complex class I molecules on the potential target cell. Functional cross-talk of NK and dendritic cells suggests a critical role for NK cells in the initiation and regulation of cellular immunity. Considerable knowledge on the molecular basis of NK recognition/activation contrasts with a lack of successful translational research on these matters. However, there is plenty of opportunity for targeted intervention of inhibitory/activatory surface receptors and for adoptive cell therapy with autologous or allogeneic NK cells.     

Designing multivalent proteins based on natural killer cell receptors and their ligands as immunotherapy for cancer

ABSTRACT

Introduction: Natural killer (NK) cells are an important component of the innate immune system that play a key role in host immunity against cancer. NK cell recognition and activation is based on cell surface receptors recognizing specific ligands that are expressed on many types of tumor cells. Some of these receptors are capable of activating NK cell function while other receptors inhibit NK cell function. Therapeutic approaches to treat cancer have been developed based on preventing NK cell inhibition or using NK cell receptors and their ligands to activate NK cells or T cells to destroy tumor cells.

Areas covered: This article describes the various strategies for targeting NK cell receptors and NK cell receptor ligands using multivalent proteins to activate immunity against cancer.

Expert opinion: NK cell receptors work in synergy to activate NK cell effector responses. Effective anti-cancer strategies will need to not only kill tumor cells but must also lead to the destruction of the tumor microenvironment. Immunotherapy based on NK cells and their receptors has the capacity to accomplish this through triggering lymphocyte cytotoxicity and cytokine production.     

Recent clinical development of dendritic cell-based immunotherapy for prostate cancer

Dendritic cells (DCs) are the most powerful immune cells that present antigens to T cells, resulting in a T cell response. Therapeutic strategies involving DCs have been explored in many malignancies, including prostate cancer. These strategies are designed to stimulate DC proliferation, promote antigen uptake and processing by DCs, or to directly provide antigen-loaded DCs. All approaches are designed to stimulate an antitumour T cell response leading to clinical benefit. Many approaches in prostate cancer have demonstrated successful induction of the desired immune response. Clinical effect has also been observed, prompting larger definitive trials.     

γδ cell-based immunotherapy for cancer

Introduction: Cancer immunotherapy relies on the development of an efficient and long-lasting anti-tumor response, generally mediated by cytotoxic T cells. γδ T cells possess distinctive features that justify their use in cancer immunotherapy.

Areas covered: Here we will review our current knowledge on the functions of human γδ T cells that may be relevant in tumor immunity and the most recent advances in our understanding of how these functions are regulated in the tumor microenvironment. We will also discuss the major achievements and limitations of γδ T cell-based immunotherapy of cancer.

Expert opinion: Several small-scale clinical trials have been conducted in cancer patients using either in vivo activation of γδ T cells or adoptive transfer of ex vivo-expanded γδ T cells. Both strategies are safe and give some clinical benefit to patients, thus providing a proof of principle for their utilization in addition to conventional therapies. However, low objective response rates have been obtained in both settings and therefore larger and well-controlled trials are needed. Discovering the factors which influence the success of γδ T cell-based immunotherapy will lead to a better understanding of their mechanism of action and to harness these cells for effective and durable anti-tumor responses.     

自然杀伤细胞在血液肿瘤免疫治疗中的应用及研究进展

自然杀伤(NK)细胞为机体固有免疫系统效应细胞,无需抗原预先致敏即可识别并杀伤肿瘤等异常细胞,参与免疫监视功能,移植物排斥反应与自身免疫疾病的发生.NK细胞对血液肿瘤细胞的杀伤活性主要取决于其细胞表面活化性受体与抑制性受体分别识别血液肿瘤细胞相应配体后产生的信号强度的综合.随着对NK细胞对肿瘤细胞杀伤作用机制的深入研究,以NK细胞为基础的血液肿瘤过继免疫治疗备受关注.     

Cellular immunotherapy for ovarian cancer

Background: Ovarian cancer is frequently diagnosed at an advanced stage, and although initially responsive to surgery and chemotherapy, has a high rate of recurrence and mortality. Cellular immunotherapy may offer the prospect of treatment to prevent or delay recurrent metastatic disease. Objective: To provide an overview of current innovations in cellular immunotherapy for ovarian cancer, with an emphasis on dendritic cell vaccination and adoptive T-cell immunotherapy. Methods: Three key areas are explored in this review: first, an appraisal of the current state of the art of cellular immunotherapy for treatment of ovarian cancer; second, a discussion of the immunological defenses erected by ovarian cancer to prevent immunological attack, with an emphasis on the role of tumor-associated regulatory T cells; and third, an exploration of innovative techniques that may enhance the ability of cellular immunotherapy to overcome ovarian tumor-associated immune suppression. Results/conclusion: Ovarian cancer is recognized as a paradigm for tumor-associated immune suppression. Innovative approaches for antagonism of tumor-associated regulatory T-cell infiltration and redirection of self antigen-driven regulatory T-cell activation may provide the key to development of future strategies for cellular immunotherapy against ovarian cancer.     

Potential approaches for more successful dendritic cell-based immunotherapy

Introduction: Dendritic cells (DCs) are the most important antigen-presenting cell population for activating antitumor T-cell responses; therefore, they offer a unique opportunity for specific targeting of tumors.

Areas covered: We will discuss the critical factors for the enhancement of DC vaccine efficacy: different DC subsets, types of in vitro DC manufacturing protocol, types of tumor antigen to be loaded and finally different adjuvants for activating them. We will cover potential combinatorial strategies with immunomodulatory therapies: depleting T-regulatory (Treg) cells, blocking VEGF and blocking inhibitory signals. Furthermore, recommendations to incorporate these criteria into DC-based tumor immunotherapy will be suggested.

Expert opinion: Monocyte-derived DCs are the most widely used DC subset in the clinic, whereas Langerhans cells and plasmacytoid DCs are two emerging DC subsets that are highly effective in eliciting cytotoxic T lymphocyte responses. Depending on the type of tumor antigens selected for loading DCs, it is important to optimize a protocol that will generate highly potent DCs. The future aim of DC-based immunotherapy is to combine it with one or more immunomodulatory therapies, for example, Treg cell depletion, VEGF blockage and T-cell checkpoint blockage, to elicit the most optimal antitumor immunity to induce long-term remission or even cure cancer patients.     

Maximizing dendritic cell migration in cancer immunotherapy

Background: The success of dendritic cell (DC)-based immunotherapy in inducing cellular immunity against tumors is highly dependent on accurate delivery and trafficking of the DC to T-cell-rich areas of secondary lymphoid tissues. Objective: To provide an overview of DC migration in vivo and how migration to peripheral lymph nodes might be improved to optimize DC therapy. Methods: We focused on DC migration in preclinical models and human skin explants and on clinical vaccination trials studying migration of in vitro-generated DC. Results/conclusions: DC migration requires an intricate interplay between the cell and its environment. To maximize migration for cellular therapy, it is important to optimize the generation of migratory DC as well as treatment strategies.     

Dendritic cell immunotherapy for breast cancer

Novel adjuvant therapies are urgently needed to complement the existing treatment options for breast cancer. The advent of the use of dendritic cells (DCs) for cancer immunotherapy provides a unique opportunity to overcome the relative non-immunogenic property of breast tumours and address the underlying immunodeficiency. To date, the success of this approach has been limited, possibly due to the targeting of specific tumour antigens that rapidly mutate and, thus, become undetectable to the immune system. A more efficient approach would include preparations encompassing multiple antigens, such as those provided by loading of whole tumour cells or tumour RNA. It is proposed that targeting mammary stem cells responsible for resistance to chemo/immunotherapy, through the expression of a broad array of wild-type and mutated tumour antigens in the context of DCs, will become a mainstay for immunotherapy of breast cancer.     

NKG2D在NK细胞杀伤血液肿瘤细胞中的作用

本研究旨在探讨NKG2D在NK细胞杀伤血液肿瘤细胞时是否发挥作用。将多种血液肿瘤细胞株作为靶细胞,并在靶细胞中检测NKG2D相应配体的表达,而后进行杀伤实验。将靶细胞与羧基荧光素二醋酸盐琥珀酰亚胺酯(CFSE)共孵育,同时将NK细胞系NK92MI分别与NKG2D特异性封闭抗体或同型对照抗体共孵育。之后将NK92MI分别与多种血液肿瘤细胞共同培养,2 h后用流式细胞分析方法检测靶细胞的凋亡率。结果显示:加入NKG2D特异性封闭抗体后,NK细胞对于急性髓系白血病细胞Kasumi-1的杀伤作用减弱约30%,而在其他血液肿瘤细胞株中封闭NKG2D并未明显影响NK细胞对于靶细胞的杀伤。结论:在NK细胞作用于某些靶细胞时,NKG2D促进NK细胞的杀伤作用。     

Natural killer cells: from bench to cancer therapy

Natural killer (NK) cells are effectors of the innate immune system that play an important role in host response against viruses and tumour cells through the production of cytokines and direct cytolytic activity. There has been limited success reported from clinical trials in cancer patients treated with activated NK cells. Over the last decade, a better understanding of the biology of NK cells, NK cell receptors and the role of interleukin-15 has led to the development of new strategies using NK cells as immunotherapy for cancer treatment in the transplant and non-transplant settings.     

调节性T细胞在胰腺癌免疫治疗中的作用机制与应用策略

免疫治疗在胰腺癌的临床试验中疗效欠佳,主要原因在于胰腺癌具有高度免疫抑制的肿瘤微环境（tumor microenvironment, TME）。调节性T细胞（regulatory T cells, Tregs）是一类控制自身免疫反应的T细胞亚群,也是免疫抑制性TME的主要组成成分之一。Tregs能调控机体免疫反应强度,抑制效应T细胞的功能和活性进而诱导免疫耐受,维持免疫应答稳态。在胰腺癌TME中,Tregs通过抑制机体免疫反应从而介导肿瘤细胞发生免疫逃逸,影响患者的疗效与预后。本综述总结Tregs在胰腺癌免疫微环境中的作用机制及在胰腺癌中的临床意义,以期为胰腺癌免疫治疗提供更多的新思路。     

Natural killer–dendritic cell cross-talk in cancer immunotherapy

ABSTRACT

Introduction: Rheumatoid arthritis (RA) treatment has been revolutionized by the development of highly efficacious biotherapeutics. However, a significant subset of RA patients has persistently active disease and ongoing erosive joint damage despite the available therapies. Sarilumab targets interleukin-6, one of the main cytokines mediating inflammation in RA. Positive results with sarilumab in RA clinical trials support the licensing application currently under review with the US Food and Drug Administration.

Areas covered: The rationale for IL-6 targeting in RA, the pharmacologic properties of sarilumab, and the clinical trial results are reviewed focusing on the pending application for the RA indication. Comparisons with other IL-6 targeting biologics as well as additional potential therapeutic directions are discussed.

Expert opinion: Sarilumab is a highly active therapeutic in patients with RA. While pharmacologic data demonstrate that sarilumab has a higher affinity than tocilizumab for the target receptor, available clinical results suggest that efficacy and adverse event profiles are similar to this other IL-6 blocker, which is currently approved for the treatment of RA. Whether there are other distinct differences or advantages of sarilumab that will support the approval and successful marketing of this drug, over existing therapies, remains to be determined.     

Natural killer cells in haematopoietic stem cell transplantation

Natural killer cells represent the predominant lymphoid cell in the peripheral blood for many months after allogeneic or autologous stem cell transplant and their role in immunity to pathogens during this period is established. However, following the largely unsuccessful trials of NK and IL-2 activated NK cells for the treatment of haematological malignancies in the 1980's and 90's, their role in tumour immunology was discredited. Over the past ten years we have come to understand some of the complex regulatory pathways involved in NK cell activation and we are now in a position to capitalise upon this knowledge. This review presents our current state of understanding of NK cell regulation and highlights the role of these cells in engraftment, graft-versus-host disease, anti-leukaemia activity and post-transplant infection.     

Natural killer activity of peripheral-blood mononuclear cells in breast cancer patients

Natural killer (NK) activity of immune cells plays a central role in host defense against cancer and virus-infected cells. Natural cytotoxic activity of peripheral-blood mononuclear cells was assessed by a Calcein-AM release assay in 89 subjects. In the present study, we here demonstrated that NK activities of peripheral-blood mononuclear cells (PBMCs) from breast cancer patients were significantly lower as compared with that of healthy individuals. There were significant differences in the NK activities of PBMCs from HER2-negative breast cancer patients as compared with HER2-positive patients. Our results suggest that NK activity of PBMCs is lower in breast cancer indicating a role for immunological natural host defense mechanisms against cancer.     

Allogeneic immune replacement as cancer immunotherapy

The graft-versus-leukaemia (GVL) reaction that occurs after allogeneic haematopoietic cell transplantation (HCT) can cure patients with a variety of haematological malignancies. A heightened appreciation of the GVL effect has resulted in the development of reduced intensity transplant approaches, where antitumour effects occur predominantly as a consequence of the transplanted donor immune system. The recent success of these transplants in patients with acute and chronic leukaemias has led to trials investigating for graft-versus-tumour (GVT) effects in patients with treatment-refractory metastatic solid tumours. This review discusses evidence that immune replacement following allogeneic HCT is a potent form of cancer immunotherapy for patients with haematological and non-haematological malignancies.     

A critical review of T cell targeting immunotherapy in pancreatic cancer: only a hypothesis or a real hope for the patients?

T cell targeting immunotherapy is now being investigated in patients with pancreatic carcinomas. Until recently this therapeutic strategy has been used as a single specific treatment and clinical studies have demonstrated that tumour-specific T cell responses can be induced in a subset of patients and even in patients with advanced disease. However, it remains to be demonstrated whether these T cell responses can mediate clinically relevant antitumour reactivity. Furthermore, in vitro studies of cancer cell susceptibility to antitumour T cell reactivity are often limited to cancer cell lines because native tumour cells are frequently not available from patients. It is therefore still a hypothesis that T cell targeting immunotherapy can be developed into an efficient therapeutic strategy in patients with inoperable pancreatic cancer. Future investigations of this therapeutic strategy should probably focus on its incorporation into treatment regimens that also include other newer treatment strategies, for example tumour-reactive antibodies coupled with toxins or cytotoxic drugs, improved vaccination procedures probably including the use of dendritic cells and enhancement of antigenic presentation in the tumour microenvironment. T cell targeting immunotherapy will contribute to the hope of curative treatment in patients with inoperable tumours if such combinatory approaches can be developed.     

The diterpenoid adenanthin upregulates the expression of natural killer group 2D receptor ligands in hepatocellular carcinoma cells

ObjectiveThe natural killer (NK) group 2D (NKG2D) receptor plays a crucial role in NK cell-mediated anti-tumor immunity. NKG2D anti-proliferative effect is mediated by direct interactions of the receptor with its ligands that may be considered as a potential target for NK-based immunotherapeutic strategy in cancer cells.MethodsHere we report that a natural product adenanthin significantly promotes NKG2D ligands expression in hepatoma cells. The effect was determined using flow cytometry analysis. The activity of NK cell was evaluated by measuring its degranulation activity and cytotoxicity.ResultsOur data indicates that the induction of NKG2D ligand binding to liver cancer cell surface receptors greatly improves the killing activity of NK cells against the cancer cells.ConclusionsThis is the first report of a new mechanism anti-cancer effects of adenanthin mediated by an indirect activation of NK cells. Our data suggests that adenanthin may be used to sensitize NK cells in tumor immunotherapy.