Natural killer cells: the journey from puzzles in biology to treatment of cancer

Activated NK Cells with Pro-inflammatory Features are Associated with Atherogenesis in Perinatally HIV-Acquired Adolescents

Human immunodeficiency virus (HIV) is associated with persistent immune activation and dysfunction in people with HIV despite treatment with antiretroviral therapy (ART). Modulation of the immune system may be driven by: low-level HIV replication, co-pathogens, gut dysbiosis /translocation, altered lipid profiles, and ART toxicities. In addition, perinatally acquired HIV (PHIV) and lifelong ART may alter the development and function of the immune system. Our preliminary data and published literature suggest reprogramming innate immune cells may accelerate aging and increase the risk for future end-organ complications, including cardiovascular disease (CVD). The exact mechanisms, however, are currently unknown. Natural killer (NK) cells are a highly heterogeneous cell population with divergent functions. They play a critical role in HIV transmission and disease progression in adults. Recent studies suggest the important role of NK cells in CVDs; however, little is known about NK cells and their role in HIV-associated cardiovascular risk in PHIV adolescents. Here, we investigated NK cell subsets and their potential role in atherogenesis in PHIV adolescents compared to HIV-negative adolescents in Uganda. Our data suggest, for the first time, that activated NK subsets in PHIV adolescents may contribute to atherogenesis by promoting plasma oxidized low-density lipoprotein (Ox-LDL) uptake by vascular macrophages.

Surgery-mediated tumor-promoting effects on the immune microenvironment

Surgical resection continues to be the mainstay treatment for solid cancers even though chemotherapy and immunotherapy have significantly improved patient overall survival and progression-free survival. Numerous studies have shown that surgery induces the dissemination of circulating tumor cells (CTCs) and that the resultant inflammatory response promotes occult tumor growth and the metastatic process by forming a supportive tumor microenvironment (TME). Surgery-induced platelet activation is one of the initial responses to a wound and the formation of fibrin clots can provide the scaffold for recruited inflammatory cells. Activated platelets can also shield CTCs to protect them from blood shear forces and promote CTCs evasion of immune destruction. Similarly, neutrophils are recruited to the fibrin clot and enhance cancer metastatic dissemination and progression by forming neutrophil extracellular traps (NETs). Activated macrophages are also recruited to surgical sites to facilitate the metastatic spread. More importantly, the body's response to surgical insult results in the recruitment and expansion of immunosuppressive cell populations (i.e. myeloid-derived suppressor cells and regulatory T cells) and in the suppression of natural killer (NK) cells that contribute to postoperative cancer recurrence and metastasis. In this review, we seek to provide an overview of the pro-tumorigenic mechanisms resulting from surgery's impact on these cells in the TME. Further understanding of these events will allow for the development of perioperative therapeutic strategies to prevent surgery-associated metastasis.

Medications for Multiple Sclerosis and Risk of Malignancy: What Next?

Many autoimmune diseases confer a higher risk of cancer on patients compared to the general population. A controversial factor tying autoimmune diseases to malignancy is harm from immunosuppressive treatment. Nonetheless, multiple sclerosis is different from other autoimmune diseases, and findings from other disease populations may not apply. In this issue of Neurotherapeutics, Dolladile and colleagues from France present new evidence about the risks of cancers in patients with multiple sclerosis treated with disease-modifying therapies based on analyses of spontaneous reporting data. This commentary discusses the context, limitations, and implications of these findings.

Beneficial impact of cathelicidin on hypersensitivity pneumonitis treatment-In vivo studies

Cathelicidin (CRAMP) is a defence peptide with a wide range of biological responses including antimicrobial, immunomodulatory and wound healing. Due to its original properties the usefulness of CRAMP in the treatment of pulmonary fibrosis was assessed in a murine model of hypersensitivity pneumonitis (HP). The studies were conducted on mouse strain C57BL/6J exposed to a saline extract of Pantoea agglomerans cells (HP inducer). Cathelicidin was administered in the form of an aerosol during and after HP development. Changes in the composition of immune cell populations (NK cells, macrophages, lymphocytes: Tc, Th, Treg, B), were monitored in lung tissue by flow cytometry. Extracellular matrix deposition (collagens, hydroxyproline), the concentration of cytokines involved in inflammatory and the fibrosis process (IFNγ, TNFα, TGFβ1, IL1β, IL4, IL5, IL10, IL12α, IL13) were examined in lung homogenates by the ELISA method. Alterations in lung tissue morphology were examined in mouse lung sections stained with haematoxylin and eosin as well as Masson trichrome dyes. The performed studies revealed that cathelicidin did not cause any negative changes in lung morphology/structure, immune cell composition or cytokines production. At the same time, CRAMP attenuated the immune reaction induced by mice chronic exposure to P. agglomerans and inhibited hydroxyproline and collagen deposition in the lung tissue of mice treated with bacteria extract. The beneficial effect of CRAMP on HP treatment was associated with restoring the balance in quantity of immune cells, cytokines production and synthesis of extracellular matrix components. The presented study suggests the usefulness of cathelicidin in preventing lung fibrosis; however, cathelicidin was not able to reverse pathological changes completely.

Soluble PD-L1 and Circulating CD8+PD-1+ and NK Cells Enclose a Prognostic and Predictive Immune Effector Score in Immunotherapy Treated NSCLC patients

INTRODUCTION

Upfront criteria to foresee immune checkpoint inhibitors (ICIs) efficacy are far from being identified. Thus, we integrated blood descriptors of pro-inflammatory/immunosuppressive or effective anti-tumor response to non-invasively define predictive immune profiles in ICI-treated advanced non-small cell lung cancer (NSCLC).

METHODS

Peripheral blood (PB) was prospectively collected at baseline from 109 consecutive NSCLC patients undergoing ICIs as first or more line treatment. Soluble PD-L1 (sPD-L1) (immunoassay), CD8+PD-1+ and NK (FACS) cells were assessed and interlaced to generate an Immune effector Score (I_effS). Lung Immune Prognostic Index (LIPI) was computed by LDH levels and derived Neutrophil-to-Lymphocyte Ratio (dNLR). All these parameters were correlated with survival outcome and treatment response.

RESULTS

High sPD-L1 and low CD8+PD-1+ and NK number had negative impact on PFS (P < 0.001), OS (P < 0.01) and ICI-response (P < 0.05). Thus, sPD-L1^high, CD8+PD-1+^low and NK^low were considered as risk factors encompassing I_effS, whose prognostic power outperformed that of individual features and slightly exceeded that of LIPI. Accordingly, the absence of these risk factors portrayed a favorable I_effS characterizing patients with significantly (P < 0.001) prolonged PFS (median NR vs 2.3 months) and OS (median NR vs 4.1) and greater benefit from ICIs (P < 0.01). We then combined each risk parameter composing I_effS and LIPI (LDH^high, dNLR^high), thus defining three distinct prognostic classes. A remarkable impact of I_effS-LIPI integration was documented on survival outcome (PFS, HR = 4.61; 95%CI = 2.32-9.18; P < 0.001; OS, HR=4.03; 95%CI=1.91-8.67; P < 0.001) and ICI-response (AUC=0.90, 95%CI=0.81-0.97, P < 0.001).

CONCLUSION

Composite risk models based on blood parameters featuring the tumor-host interaction might provide accurate prognostic scores able to predict ICI benefit in NSCLC patients.

Combination of Immune Checkpoint Inhibitors with Chemotherapy in Lung Cancer

Tremendous progress has been achieved in the field of immune checkpoint inhibitors (ICIs) therapy in lung cancer in recent years. To generate robust, long-lasting anti-tumor immune responses in lung cancer patients, combinational ICI therapies have been explored deeply. Conventionally, chemotherapy was considered as immunosuppressive. It is now recognized that chemotherapy could also reinstate cancer cell immune-surveillance and enable the perception of cancer cells as dangerous. That is to say that chemotherapeutic drugs are not only a source of direct cytotoxic effects but also an adjuvant for anti-tumor immunity. Recently, multiple clinical studies of ICIs combined with chemotherapeutic drugs have been explored and proved effective. However, there are still crucial questions that are not well addressed, such as the optimal dose and schedule for a given combination may differ across disease indications, and the appropriate strategy of selecting patient population that can benefit from ICIs remains unclear. To facilitate more rational lung cancer ICIs therapy development, this review summarizes the immune-regulatory effects and related mechanisms of chemotherapeutic drugs and the clinical progress of ICIs and their combination with chemotherapies in lung cancer treatment.

WNT Signaling in Tumors: The Way to Evade Drugs and Immunity

WNT/β-catenin signaling is involved in many physiological processes. Its implication in embryonic development, cell migration, and polarization has been shown. Nevertheless, alterations in this signaling have also been related with pathological events such as sustaining and proliferating the cancer stem cell (CSC) subset present in the tumor bulk. Related with this, WNT signaling has been associated with the maintenance, expansion, and epithelial-mesenchymal transition of stem cells, and furthermore with two distinctive features of this tumor population: therapeutic resistance (MDR, multidrug resistance) and immune escape. These mechanisms are developed and maintained by WNT activation through the transcriptional control of the genes involved in such processes. This review focuses on the description of the best known WNT pathways and the molecules involved in them. Special attention is given to the WNT cascade proteins deregulated in tumors, which have a decisive role in tumor survival. Some of these proteins function as extrusion pumps that, in the course of chemotherapy, expel the drugs from the cells; others help the tumoral cells hide from the immune effector mechanisms. Among the WNT targets involved in drug resistance, the drug extrusion pump MDR-1 (P-GP, ABCB1) and the cell adhesion molecules from the CD44 family are highlighted. The chemokine CCL4 and the immune checkpoint proteins CD47 and PD-L1 are included in the list of WNT target molecules with a role in immunity escape. This pathway should be a main target in cancer therapy as WNT signaling activation is essential for tumor progression and survival, even in the presence of the anti-tumoral immune response and/or antineoplastic drugs. The appropriate design and combination of anti-tumoral strategies, based on the modulation of WNT mediators and/or protein targets, could negatively affect the growth of tumoral cells, improving the efficacy of these types of therapies.

The CD26/DPP4-inhibitor vildagliptin suppresses lung cancer growth via macrophage-mediated NK cell activity

CD26/dipeptidyl peptidase 4 (DPP4) is a transmembrane protein which is expressed by various malignant cells. We found that the expression of CD26/DPP4 was significantly higher in lung adenocarcinoma samples in our own patient cohort compared to normal lung tissue. We therefore hypothesize that the inhibition of CD26/DPP4 can potentially suppress lung cancer growth. The CD26/DPP4 inhibitor vildagliptin was employed on Lewis Lung Carcinoma (LLC) cell line and a human lung adenocarcinoma (H460) cell line. Two weeks after subcutaneous injection of tumor cells into C57BL/6 and CD1/nude mice, the size of LLC and H460 tumors was significantly reduced by vildagliptin. Immunohistochemically, the number of macrophages (F4/80+) and NK cells (NKp46+) was significantly increased in vildagliptin-treated tumor samples. Mechanistically, we found in vitro that lung cancer cell lines expressed increased levels of surfactant protein upon vildagliptin treatment thereby promoting the pro-inflammatory activity of macrophages. By the depletion of macrophages with clodronate and by using NK cell deficient (IL-15-/-) mice, tumors reversed to the size of controls, suggesting that indeed macrophages and NK cells were responsible for the observed tumor-suppressing effect upon vildagliptin treatment. FACS analysis showed tumor-infiltrating NK cells to express tumor necrosis-related apoptosis-inducing ligand (TRAIL) which induced the intra-cellular stress marker γH2AX. Accordingly, we found upregulated γH2AX in vildagliptin-treated tumors and TRAIL-treated cell lines. Moreover, the effect of vildagliptin-mediated enhanced NK cell cytotoxicity could be reversed by antagonizing the TRAIL receptor. Our data provide evidence that the CD26/DPP4-inhibitor vildagliptin reduces lung cancer growth. We could demonstrate that this effect is exerted by surfactant-activated macrophages and NK cells that act against the tumor via TRAIL-mediated cytotoxicity.

What Defines NK Cell Functional Fate: Phenotype or Metabolism?

NK cells are capable of an array of functions that range widely from their classic anti-tumor and anti-viral cytotoxic effector functions, to their critical regulatory roles in controlling inflammatory immune responses and promoting tissue growth. However, the mechanisms that polarize NK cells to these distinct and opposing functions are incompletely understood. NK cell functional subsets are primarily identified and studied based on phenotype, which has served as an accessible means for profiling NK cells and does offer information on NK cell activation state. However, inconsistencies have emerged in using classic phenotypes to inform function, which raise the questions: Can phenotype in fact define NK cell functional fate? What factors do profile and drive NK cell fate? In other immune cells, cell metabolism has been shown to critically determine subset polarization. There is a growing body of evidence that cell metabolism is integral to NK cell effector functions. Glucose-driven glycolysis and oxidative metabolism have been shown to drive classic NK cell anti-tumor and anti-viral effector functions. Recent studies have uncovered a critical role for metabolism in NK cell development, education, and memory generation. In this review, we will draw on the evidence to date to investigate the relationship between NK cell phenotype, metabolism, and functional fate. We explore a paradigm in which the differential activity of metabolic pathways within NK cells produce distinct metabolic fingerprints that comprehensively distinguish and drive the range of NK cell functional abilities. We will discuss future areas of study that are needed to develop and test this paradigm and suggest strategies to efficiently profile NK cells based on metabolism. Given the emerging role of metabolism in driving NK cell fates, profiling and modulating NK cell metabolism holds profound therapeutic potential to tune inflammatory and regulatory NK cell responses to treat disease.

Natural killer cell-based immunotherapy: From transplantation toward targeting cancer stem cells

Natural killer (NK) cells are key players of the innate immune system. NK cells provide protection against infectious pathogens and malignancies in cell. This characteristic may be attributable to their intrinsic diverse potentialities and also their cooperation with adaptive immune lymphocytes, known as B and T cells. The growth, recurrence, and metastasis of cancer cells, and the failure of cytoreductive therapies against cancer cells are due to the small population of intratumor stem-like cells, called cancer stem cells (CSCs). Furthermore, NK cells can efficiently eradicate heterogeneous tumor cells after a long-term treatment. Therefore, NK cell-based therapy is a promising strategy to target and break CSC-associated resistance to anticancer drugs treatment. In this review, we have presented an overview of the emerging knowledge of the characteristics, diversities, and mechanism-driven immune surveillance of human NK cells and advances in NK cell-based immunotherapies. Finally, we will discuss how these cells can be applied to introduce the next generation of vaccine- and immune-based approaches to prevent drug resistance.

Immunometabolism of T cells and NK cells: metabolic control of effector and regulatory function

Metabolic flux can dictate cell fate, including immune cell effector and regulatory function. The metabolic regulation of cell function is well characterized with respect to effector, memory, and regulatory T cells. This knowledge may allow for manipulation of T cell metabolic pathways that set the stage for more effective T cell therapy. Natural Killer (NK) and T-lymphocytes have complementary roles in the defense against pathogens. However, studies of NK cell metabolism are only beginning to emerge and there is comparatively little knowledge on the metabolic regulation of NK-cell activation and effector function. Given their common lymphoid lineage, effector functions and cellular memory potential our current knowledge on T cell metabolism could inform investigation of metabolic reprogramming in NK cells. In this review, we compare the current knowledge of metabolic regulation in T cell and NK cell development, activation, effector and memory function. Commonalties in glucose transport, hypoxia-inducible factors and mTOR highlight metabolic control points in both cells types. Contrasting the glycolytic and oxidative nodes of metabolic regulation in T cells versus NK cells may provide insight into the contribution of specific immune responses to disease and promote the development of immunotherapeutic approaches targeting both innate and adaptive immune responses.

CD47-signal regulatory protein α signaling system and its application to cancer immunotherapy

Tumor cells evade immune surveillance through direct or indirect interactions with various types of immune cell, with much recent attention being focused on modifying immune cell responses as the basis for the development of new cancer treatments. Signal regulatory protein α (SIRPα) and CD47 are both transmembrane proteins that interact with each other and constitute a cell-cell communication system. SIRPα is particularly abundant in myeloid cells such as macrophages and dendritic cells, whereas CD47 is expressed ubiquitously and its expression level is elevated in cancer cells. Recent studies have shown that blockade of CD47-SIRPα interaction enhances the phagocytic activity of phagocytes such as macrophages toward tumor cells in vitro as well as resulting in the efficient eradication of tumor cells in a variety of xenograft or syngeneic mouse models of cancer. Moreover, CD47 blockade has been shown to promote the stimulation of tumor-specific cytotoxic T cells by macrophages or dendritic cells. Biological agents, such as Abs and recombinant proteins, that target human CD47 or SIRPα have been developed and are being tested in preclinical models of human cancer or in clinical trials with cancer patients. Preclinical studies have also suggested that CD47 or SIRPα blockade may have a synergistic antitumor effect in combination with immune checkpoint inhibitors that target the adaptive immune system. Targeting of the CD47-SIRPα signaling system is thus a promising strategy for cancer treatment based on modulation of both innate and acquired immune responses to tumor cells.

Expression and function of immune ligand-receptor pairs in NK cells and cancer stem cells: therapeutic implications

BACKGROUND

The interplay between the immune system and cancer cells has come to the forefront of cancer therapeutics, with novel immune blockade inhibitors being approved for the treatment of an increasing list of cancers. However, the majority of cancer patients still display or develop resistance to these promising drugs. It is possible that cancer stem cells (CSCs) are contributing to this therapeutic resistance. Although CSCs usually represent a small percentage of the total number of cancer cells, they are endowed with the ability of self-renewal and to produce differentiated progeny. Additionally, they have shown the capacity to establish tumors after transplantation to animals, even in small numbers. CSCs have also been found to be resistant to various anti-cancer therapies, including chemotherapy, radiation therapy and, more recently, immunotherapy. This is true despite the sensitivity of CSCs to lysis in vitro by natural killer (NK) cells, the main effector cells of the innate immune system. In this paper the expression of ligands specific for NK cells on CSCs, the intracellular network responsible for the expression of the NK cytotoxicity receptors, and the status of activation of NK cells in the tumor micro-environment are reviewed. The aim of this review is to highlight potential strategies for overcoming CSC immune resistance, thereby enhancing the efficacy of current and future anti-cancer therapies.

THERAPEUTIC IMPLICATIONS

NK cell activation in the tumor micro-environment through drugs neutralizing inhibitory immune receptors, and combined with other drugs harnessing the potential of the adaptive immune system, could be the most effective approach for attacking both stem cell and non-stem cell cancer populations.

Concise Review: Human Pluripotent Stem Cells to Produce Cell-Based Cancer Immunotherapy

Human pluripotent stem cells (PSCs) provide a promising resource to produce immune cells for adoptive cellular immunotherapy to better treat and potentially cure otherwise lethal cancers. Cytotoxic T cells and natural killer (NK) cells can now be routinely produced from human PSCs. These PSC-derived lymphocytes have phenotype and function similar to primary lymphocytes isolated from peripheral blood. PSC-derived T and NK cells have advantages compared with primary immune cells, as they can be precisely engineered to introduce improved anti-tumor activity and produced in essentially unlimited numbers. Stem Cells 2018;36:134-145.

M1-like macrophages change tumor blood vessels and microenvironment in murine melanoma

Tumor-associated macrophages (TAMs) play a significant role in at least two key processes underlying neoplastic progression: angiogenesis and immune surveillance. TAMs phenotypic changes play important role in tumor vessel abnormalization/ normalization. M2-like TAMs stimulate immunosuppression and formation of defective tumor blood vessels leading to tumor progression. In contrast M1-like TAMs trigger immune response and normalize irregular tumor vascular network which should sensitize cancer cells to chemo- and radiotherapy and lead to tumor growth regression. Here, we demonstrated that combination of endoglin-based DNA vaccine with interleukin 12 repolarizes TAMs from tumor growth-promoting M2-like phenotype to tumor growth-inhibiting M1-like phenotype. Combined therapy enhances tumor infiltration by CD4⁺, CD8⁺ lymphocytes and NK cells. Depletion of TAMs as well as CD8⁺ lymphocytes and NK cells, but not CD4⁺ lymphocytes, reduces the effect of combined therapy. Furthermore, combined therapy improves tumor vessel maturation, perfusion and reduces hypoxia. It caused that suboptimal doses of doxorubicin reduced the growth of tumors in mice treated with combined therapy. To summarize, combination of antiangiogenic drug and immunostimulatory agent repolarizes TAMs phenotype from M2-like (pro-tumor) into M1-like (anti-tumor) which affects the structure of tumor blood vessels, improves the effect of chemotherapy and leads to tumor growth regression.

The immune system in cancer metastasis: friend or foe?

Metastatic disease is the leading cause of death among cancer patients and involves a complex and inefficient process. Every step of the metastatic process can be rate limiting and is influenced by non-malignant host cells interacting with the tumor cell. Over a century ago, experiments first indicated a link between the immune system and metastasis. This phenomenon, called concomitant immunity, indicates that the primary tumor induces an immune response, which may not be sufficient to destroy the primary tumor, but prevents the growth of a secondary tumor or metastases. Since that time, many different immune cells have been shown to play a role in both inhibiting and promoting metastatic disease. Here we review classic and new observations, describing the links between the immune system and metastasis that inform the development of cancer therapies.

Dysfunctional Natural Killer Cells in the Aftermath of Cancer Surgery

The physiological changes that occur immediately following cancer surgeries initiate a chain of events that ultimately result in a short pro-, followed by a prolonged anti-, inflammatory period. Natural Killer (NK) cells are severely affected during this period in the recovering cancer patient. NK cells play a crucial role in anti-tumour immunity because of their innate ability to differentiate between malignant versus normal cells. Therefore, an opportunity arises in the aftermath of cancer surgery for residual cancer cells, including distant metastases, to gain a foothold in the absence of NK cell surveillance. Here, we describe the post-operative environment and how the release of sympathetic stress-related factors (e.g., cortisol, prostaglandins, catecholamines), anti-inflammatory cytokines (e.g., IL-6, TGF-β), and myeloid derived suppressor cells, mediate NK cell dysfunction. A snapshot of current and recently completed clinical trials specifically addressing NK cell dysfunction post-surgery is also discussed. In collecting and summarizing results from these different aspects of the surgical stress response, a comprehensive view of the NK cell suppressive effects of surgery is presented. Peri-operative therapies to mitigate NK cell suppression in the post-operative period could improve curative outcomes following cancer surgery.

Combined Stimulation with Interleukin-18 and Interleukin-12 Potently Induces Interleukin-8 Production by Natural Killer Cells

The combination of interleukin (IL)-18 and IL-12 (IL-18+IL-12) potently stimulates natural killer (NK) cells, triggering an innate immune response to infections and cancers. Strategies exploiting the effects of IL-18+IL-12 have shown promise for cancer immunotherapy. However, studies have primarily characterized the NK cell response to IL-18+IL-12 in terms of interferon (IFN)-γ production, with little focus on other cytokines produced. IL-8 plays a critical role in activating and recruiting immune cells, but it also has tumor-promoting functions. IL-8 is classically produced by regulatory NK cells; however, cytotoxic NK cells do not typically produce IL-8. In this study, we uncover that stimulation with IL-18+IL-12 induces high levels of IL-8 production by ex vivo expanded and freshly isolated NK cells and NK cells in peripheral blood mononuclear cells. We further report that tumor necrosis factor (TNF)-α, produced by NK cells following IL-18+IL-12 stimulation, regulates IL-8 production. The IL-8 produced is in turn required for maximal IFN-γ and TNF-α production. These findings may have important implications for the immune response to infections and cancer immunotherapies. This study broadens our understanding of NK cell function and IL-18+IL-12 synergy by uncovering an unprecedented ability of IL-18+IL-12-activated peripheral blood NK cells to produce elevated levels of IL-8 and identifying the requirement for intermediates induced by IL-18+IL-12 for maximal cytokine production following stimulation.

IL-18/IL-15/IL-12 synergy induces elevated and prolonged IFN-γ production by ex vivo expanded NK cells which is not due to enhanced STAT4 activation

The synergistic effect of IL-18/IL-15/IL-12 stimulation potently activates NK cells, inducing high levels of IFN-γ production. As a result of this potent stimulatory effect, NK cell pre-activation with IL-18/IL-15/IL-12 is being developed as a cancer immunotherapy. Ex vivo expansion of NK cells enables the efficient generation of large numbers of NK cells for wide-scale and repeated therapeutic use, and is thus an important source of NK cells for clinical application. However, the effects of IL-18/IL-15/IL-12 stimulation on ex vivo expanded NK cells have not yet been assessed. Thus, the present study assessed the effects of IL-18/IL-15/IL-12 stimulation on NK cells expanded ex vivo using K562-based artificial antigen presenting cells expressing membrane-bound IL-21. We report that ex vivo expanded NK cells stimulated with IL-18/IL-15/IL-12 produce high levels of IFN-γ and TNFα, have potent cytotoxicity, and maintain prolonged IFN-γ production following removal of stimulation. IL-18/IL-15/IL-12 stimulation induces a phenotypically unique IFN-γ-producing population with reduced CD16 expression and greater CD25 expression as compared to stimulated IFN-γ- NK cells and unstimulated NK cells. We elucidate that the mechanism of synergy for induction and maintenance of IFN-γ production is not due to a further enhancement of STAT4 activation compared to stimulation with IL-12 alone. Furthermore, we demonstrate that the synergistic increase in IFN-γ is not solely under translational regulation, as elevated levels of IFN-γ mRNA contribute to the synergistic increase in IFN-γ. Overall, this study characterizes the response of ex vivo expanded NK cells to IL-18/IL-15/IL-12 stimulation and supports the use of ex vivo expanded NK cells as a feasible and efficient source of IL-18/IL-15/IL-12 pre-activated NK cells for adoptive transfer in cancer immunotherapies.

Human CD56dimCD16dim Cells As an Individualized Natural Killer Cell Subset

Human natural killer (NK) cells can be subdivided in several subpopulations on the basis of the relative expression of the adhesion molecule CD56 and the activating receptor CD16. Whereas blood CD56^brightCD16^dim/− NK cells are classically viewed as immature precursors and cytokine producers, the larger CD56^dimCD16^bright subset is considered as the most cytotoxic one. In peripheral blood of healthy donors, we noticed the existence of a population of CD56^dimCD16^dim NK cells that was frequently higher in number than the CD56^bright subsets and even expanded in occasional control donors but also in transporter associated with antigen processing-deficient patients, two familial hemophagocytic lymphohistiocytosis type II patients, and several common variable immunodeficiency patients. This population was detected but globally reduced in a longitudinal cohort of 18 HIV-1-infected individuals. Phenotypically, the new subset contained a high percentage of relatively immature cells, as reflected by a significantly stronger representation of NKG2A⁺ and CD57⁻ cells compared to their CD56^dimCD16^bright counterparts. The phenotype of the CD56^dimCD16^dim population was differentially affected by HIV-1 infection as compared to the other NK cell subsets and only partly restored to normal by antiretroviral therapy. From the functional point of view, sorted CD56^dimCD16^dim cells degranulated more than CD56^dimCD16^bright cells but less than CD56^dimCD16⁻ NK cells. The population was also identified in various organs of immunodeficient mice with a human immune system (“humanized” mice) reconstituted from human cord blood stem cells. In conclusion, the CD56^dimCD16^dim NK cell subpopulation displays distinct phenotypic and functional features. It remains to be clarified if these cells are the immediate precursors of the CD56^dimCD16^bright subset or placed somewhere else in the NK cell differentiation and maturation pathway.

Dietary flavonoids and modulation of natural killer cells: implications in malignant and viral diseases

Flavonoids are a large group of secondary plant metabolites present in the diet with numerous potentially health-beneficial biological activities. In addition to antioxidant, anti-inflammatory, cholesterol-lowering, and many other biological functions reported in the literature, flavonoids appear to inhibit cancer cell proliferation and stimulate immune function. Although the immunomodulatory potential of flavonoids has been intensively investigated, only little is known about their impact on natural killer (NK) cells. Enhancing NK cell activity, however, would have strong implications for a possible clinical use of flavonoids, especially in the treatment and prevention of diseases like cancer and viral infections. Therefore, the purpose of this review is to summarize the currently available information on NK cell modulation by flavonoids. Many of the structurally diverse flavonoids stimulate NK cell activity and have thus great potential as diet-derived immune-modulatory chemopreventive agents and may even serve as therapeutic compounds or lead structures for the development of novel drugs for the treatment of both malignant and viral diseases.

Anti-SIRP antibodies as a potential new tool for cancer immunotherapy

Tumor cells are thought to evade immune surveillance through interaction with immune cells. Much recent attention has focused on the modification of immune responses as a basis for new cancer treatments. SIRPα is an Ig superfamily protein that inhibits phagocytosis in macrophages upon interaction with its ligand CD47 expressed on the surface of target cells. Here, we show that SIRPα is highly expressed in human renal cell carcinoma and melanoma. Furthermore, an anti-SIRPα Ab that blocks the interaction with CD47 markedly suppressed tumor formation by renal cell carcinoma or melanoma cells in immunocompetent syngeneic mice. This inhibitory effect of the Ab appeared to be mediated by dual mechanisms: direct induction of Ab-dependent cellular phagocytosis of tumor cells by macrophages and blockade of CD47-SIRPα signaling that negatively regulates such phagocytosis. The antitumor effect of the Ab was greatly attenuated by selective depletion not only of macrophages but also of NK cells or CD8⁺ T cells. In addition, the anti-SIRPα Ab also enhances the inhibitory effects of Abs against CD20 and programmed cell death 1 (PD-1) on tumor formation in mice injected with SIRPα-nonexpressing tumor cells. Anti-SIRPα Abs thus warrant further study as a potential new therapy for a broad range of cancers.

Augmentation of Cytolytic Activity in Murine Natural Killer Cells and Inhibition of Tumor Growth by the Ethanol Fraction of Oyster Extract

A reduced number and/or reduced activity of natural killer (NK) cells, which are important for defense against a variety of cancers and viral infections, occur under various stress conditions and in patients with various diseases. In this article, we report that the 30% to 50% ethanol precipitate of oyster extract (EPOE50) dose-dependently enhanced the activity of mouse spleen NK cells in vitro and in vivo. The activity of EPOE50 was eluted with a molecular weight of about 2000 by gel filtration and was inactivated by periodate but not by proteinase K. The activity of highly purified NK cells was also augmented by EPOE50 but not by oligodeoxyribonucleotide 1585, which mimics bacterial DNA. Administration of EPOE50 to mice stimulated splenic NK cell activity without a change in splenic NK cell populations. Although the proliferation of B16 tumor cells in vitro was slightly stimulated by EPOE50, the growth of B16 melanoma in vivo was dose-dependently suppressed by administration of EPOE50. Taken together, our results indicate that EPOE50 augmented NK cell activity and that its administration to mice inhibited tumor growth presumably through the activation of NK cells and also suggest that the active substance is a sugar-containing oligomer or polymer and is not of bacterial origin.

Dynamic Regulation of NK Cell Responsiveness

Natural killer (NK) cells deliver cytotoxic granules and immunomodulatory cytokines in response to transformed and virally infected cells. NK cell functions are under the control of a large number of germline-encoded receptors that recognize various ligands on target cells, but NK cells also respond to cytokines in the surrounding environment. The interaction between NK cell receptors and their ligands delivers either inhibitory or activating signals. The cytokine milieu further shapes NK cell responses, either directly or by influencing the way inhibitory or activating signals are perceived by NK cells. In this review, we discuss how NK cell function is controlled by inhibitory receptors and MHC-I molecules, how activating receptors contribute to NK cell education, and finally, how cytokines secreted by the surrounding cells affect NK cell responsiveness. Inputs at these three levels involve different cell types and are seamlessly integrated to form a functional NK cell population.

A bispecific protein rG7S-MICA recruits natural killer cells and enhances NKG2D-mediated immunosurveillance against hepatocellular carcinoma

MHC class I-related chain A (MICA) is a principal immunoligand of the natural killer (NK) cell receptor NK group 2, member D (NKG2D) and plays a key role in NK cell-mediated immune recognition. Shedding of MICA from tumor cells leads to immunosuppression. To reconstitute the immunosurveilance function of NK cells, we constructed a fusion protein rG7S-MICA and explored its potential anti-tumor activity against hepatocellular carcinoma (HCC). rG7S-MICA consists of human MICA and a single-chain antibody fragment (scFv) targeting the tumor-associated antigen cluster of differentiation 24 (CD24). In vitro, rG7S-MICA engaged both NK cells and CD24(+) human HCC cells, and triggered NK cell-mediated cytolysis. Furthermore, in CD24(+) HCC-bearing nude mice, rG7S-MICA specifically targeted to the tumor tissue, where it effectively recruited NK cells and induced the release of cytokines, and showed superior anti-tumor activity. In conclusion, rG7S-MICA provides a new approach for HCC-targeting immunotherapy and has attracting potentials for clinical applications.

Neutrophils in Cancer: Two Sides of the Same Coin

Neutrophils are the most abundant leukocytes in blood and are considered to be the first line of defense during inflammation and infections. In addition, neutrophils are also found infiltrating many types of tumors. Tumor-associated neutrophils (TANs) have relevant roles in malignant disease. Indeed neutrophils may be potent antitumor effector cells. However, increasing clinical evidence shows TANs correlate with poor prognosis. The tumor microenvironment controls neutrophil recruitment and in turn TANs help tumor progression. Hence, TANs can be beneficial or detrimental to the host. It is the purpose of this review to highlight these two sides of the neutrophil coin in cancer and to describe recent studies that provide some light on the mechanisms for neutrophil recruitment to the tumor, for neutrophils supporting tumor progression, and for neutrophil activation to enhance their antitumor functions.

Induced Pluripotent Stem Cell-Derived Natural Killer Cells for Treatment of Ovarian Cancer

Natural killer (NK) cells can provide effective immunotherapy for ovarian cancer. Here, we evaluated the ability of NK cells isolated from peripheral blood (PB) and NK cells derived from induced pluripotent stem cell (iPSC) to mediate killing of ovarian cancer cells in a mouse xenograft model. A mouse xenograft model was used to evaluate the intraperitoneal delivery of three different NK cell populations: iPSC-derived NK cells, PB-NK cells that had been activated and expanded in long-term culture, and overnight activated PB-NK cells that were isolated through CD3/CD19 depletion of PB B and T cells. Bioluminescent imaging was used to monitor tumor burden of luciferase expressing tumor lines. Tumors were allowed to establish prior to administering NK cells via intraperitoneal injection. These studies demonstrate a single dose of any of the three NK cell populations significantly reduced tumor burden. When mice were given three doses of either iPSC-NK cells or expanded PB-NK cells, the median survival improved from 73 days in mice untreated to 98 and 97 days for treated mice, respectively. From these studies, we conclude iPSC-derived NK cells mediate antiovarian cancer killing at least as well as PB-NK cells, making these cells a viable resource for immunotherapy for ovarian cancer. Due to their ability to be easily differentiated into NK cells and their long-term expansion potential, iPSCs can be used to produce large numbers of well-defined NK cells that can be banked and used to treat a large number of patients including treatment with multiple doses if necessary.

Role of HLA-B associated transcript 3 in immune diseases

HLA-B associated transcript 3 (BAT3/Scythe/BAG6) is a member of the BAG protein family which can regulate the cell cycle. Recently, BAT3 has also been identified to have immunoregulatory function through kinds of mechanisms. First, BAT3 can promote the maturation of dendritic cells (DCs), the activity of macrophages and the expression of major histocompatibility complex (MHC)-Ⅱ on antigen presenting cells (APCs) to regulate chronic inflammation. Second, BAT3 can suppress T cell immunoglobulin and mucin domain 3 (Tim-3)-mediated cell death and exhaustion of T helper cell type 1 (Th1) to exacerbate autoimmune diseases. Finally, BAT3 can regulate the cytotoxicity of natural killer cells (NKs) in a NKp30-dependent manner to play a part in tumor immune evasion and tumor rejection. Further details about BAT3 and its involvement in immunity and immunity-associated diseases will benefit the novel strategy for treatment of immune diseases.

The potential of cytotherapeutics in hematologic reconstitution and in the treatment and prophylaxis of graft-versus-host disease. Chapter II: emerging transformational cytotherapies

Hematopoietic stem cell transplantation (HSCT) is a life-saving treatment for inherited anemias, immunodeficiencies or hematologic malignancies. A major complication of allo-HSCT associated with high transplant-related mortality rates is graft-versus-host disease (GvHD). Current and future clinical benefits in HSCT enabled by advances in hematopoietic stem cells, mesenchymal stem cells, Tregs and natural killer cells technologies are reviewed here and discussed. Among these evolutions, based on the need for mesenchymal stem cells to be recruited by an inflammatory environment, the development and use of novel GvHD biomarkers could be explored further to deliver the right pharmaceutical to the right patient at the right time. The successful commercialization of cytotherapeutics to efficiently manage GvHD will create a virtuous ‘halo’ effect for regenerative medicine.