Natural cytotoxicity receptors that trigger human NK-cell-mediated cytolysis

Lacticaseibacillus casei K11 exerts immunomodulatory effects by enhancing natural killer cell cytotoxicity via the extracellular regulated-protein kinase pathway

PURPOSE

Probiotics can serve as immunomodulators that regulate the activation of immune cells. This study aimed to screen potential probiotic strains that can enhance NK cell toxicity to improve host immunity.

METHODS

In this investigation, we examined three potential probiotic strains, namely Lactiplantibacillus plantarum YZX21 (YZX21), Bifidobacterium bifidum FL-276.1 (FL-276.1) and Lacticaseibacillus casei K11 (K11), to assess their capacity in modulating NK cytotoxicity both in vitro and in vivo, while elucidating the underlying mechanisms involved.

RESULTS

The findings demonstrated that K11 exhibited superior efficacy in enhancing NK cytotoxicity. Subsequent analysis revealed that K11 significantly augmented the secretion of perforin and granzyme B by NK cells through activation of receptors NKp30 and NKp46 via the extracellular signal-regulated kinase (ERK) pathway. Furthermore, heat-inactivated K11 also enhanced NK cell activity to an extent comparable to live bacteria, with lipoteichoic acid from K11 identified as a crucial factor mediating the activation of NK cell cytotoxicity.

CONCLUSION

Our study suggests that K11 may have potential applications as probiotics or postbiotics for regulating NK cell cytotoxicity to enhance immunity.

Immunology of amyotrophic lateral sclerosis - role of the innate and adaptive immunity

This review aims to summarize the latest evidence about the role of innate and adaptive immunity in Amyotrophic Lateral Sclerosis (ALS). ALS is a devastating neurodegenerative disease affecting upper and lower motor neurons, which involves essential cells of the immune system that play a basic role in innate or adaptive immunity, that can be neurotoxic or neuroprotective for neurons. However, distinguishing between the sole neurotoxic or neuroprotective function of certain cells such as astrocytes can be challenging due to intricate nature of these cells, the complexity of the microenvironment and the contextual factors. In this review, in regard to innate immunity we focus on the involvement of monocytes/macrophages, microglia, the complement, NK cells, neutrophils, mast cells, and astrocytes, while regarding adaptive immunity, in addition to humoral immunity the most important features and roles of T and B cells are highlighted, specifically different subsets of CD4+ as well as CD8+ T cells. The role of autoantibodies and cytokines is also discussed in distinct sections of this review.

Enhanced expression of natural cytotoxicity receptors on cytokine-induced memory-like natural killer cells correlates with effector function

Introduction

Natural killer (NK) cells are a key component of the innate immune system, involved in defending the host against virus-infected cells and tumor immunosurveillance. Under in vitro culture conditions, IL-12/15/18 can induce a memory-like phenotype in NK cells. These cytokine-induced memory-like (CIML) NK cells possess desirable characteristics for immunotherapies, including a longer lifespan and increased cytotoxicity.

Methods

In this study, NK cells were isolated from peripheral blood of healthy donors and stimulated with IL-12/15/18 to induce a memory-like phenotype or with IL-15 alone as a control. After seven days of culture, multiparametric flow cytometry analysis was performed to evaluate the phenotypic and functional profiles of CIML and control NK cells.

Results

Our results showed a significantly higher expression of CD25, CD69, NKG2D, NKp30, NKp44, NKp46, TACTILE, and Granzyme B in CIML NK cells compared to control NK cells. In contrast, KIR2D expression was significantly lower in CIML NK cells than in control NK cells. Moreover, functional experiments demonstrated that CIML NK cells displayed enhanced degranulation capacity and increased intracellular IFN-γ production against the target cell line K562. Interestingly, the degranulation capacity of CIML NK cells was positively correlated with the expression of the activating receptors NKp46 and NKp30, as well as with the inhibitory receptor TACTILE.

Discussion

In conclusion, this study provides a deep phenotypic characterization of in vitro-expanded CIML NK cells. Moreover, the correlations found between NK cell receptors and degranulation capacity of CIML NK cells allowed the identification of several biomarkers that could be useful in clinical settings.

mAb14, a Monoclonal Antibody against Cell Surface PCNA: A Potential Tool for Sezary Syndrome Diagnosis and Targeted Immunotherapy

Mycosis fungoides (MF) and Sézary syndrome (SS) are the most common types of primary cutaneous T-cell lymphoma (CTCL). Proliferating cell nuclear antigen (PCNA) is expressed on the cell surface of cancer cells (csPCNA), but not on normal cells. It functions as an immune checkpoint ligand by interacting with natural killer (NK) cells through the NK inhibitory receptor NKp44, leading to the inhibition of NK cytotoxicity. A monoclonal antibody (mAb14) was established to detect csPCNA on cancer cells and block their interaction with NKp44. In this study, three CTCL cell lines and peripheral blood mononuclear cells (PBMCs) from patients with SS and healthy donors were analyzed for csPCNA using mAb14, compared to monoclonal antibody PC10, against nuclear PCNA (nPCNA). The following assays were used: immunostaining, imaging flow cytometry, flow cytometry, cell sorting, cell cycle analysis, ELISA, and the NK-cell cytotoxic assay. mAb14 successfully detected PCNA on the membrane and in the cytoplasm of viable CTCL cell lines associated with the G2/M phase. In the Sézary PBMCs, csPCNA was expressed on lymphoma cells that had an atypical morphology and not on normal cells. Furthermore, it was not expressed on PBMCs from healthy donors. In the co-culture of peripheral blood NK (pNK) cells with CTCL lines, mAb14 increased the secretion of IFN-γ, indicating the reactivation of pNK activity. However, mAb14 did not enhance the cytotoxic activity of pNK cells against CTCL cell lines. The unique expression of csPCNA detected by mAb14 suggests that csPCNA and mAb14 may serve as a potential biomarker and tool, respectively, for detecting malignant cells in SS and possibly other CTCL variants.

NK cell defects: implication in acute myeloid leukemia

Acute Myeloid Leukemia (AML) is a complex disease with rapid progression and poor/unsatisfactory outcomes. In the past few years, the focus has been on developing newer therapies for AML; however, relapse remains a significant problem. Natural Killer cells have strong anti-tumor potential against AML. This NK-mediated cytotoxicity is often restricted by cellular defects caused by disease-associated mechanisms, which can lead to disease progression. A stark feature of AML is the low/no expression of the cognate HLA ligands for the activating KIR receptors, due to which these tumor cells evade NK-mediated lysis. Recently, different Natural Killer cell therapies have been implicated in treating AML, such as the adoptive NK cell transfer, Chimeric antigen receptor-modified NK (CAR-NK) cell therapy, antibodies, cytokine, and drug treatment. However, the data available is scarce, and the outcomes vary between different transplant settings and different types of leukemia. Moreover, remission achieved by some of these therapies is only for a short time. In this mini-review, we will discuss the role of NK cell defects in AML progression, particularly the expression of different cell surface markers, the available NK cell therapies, and the results from various preclinical and clinical trials.

NK cells with decreased expression of multiple activating receptors is a dominant phenotype in pediatric patients with acute lymphoblastic leukemia

NK cells have unique attributes to react towards cells undergoing malignant transformation or viral infection. This reactivity is regulated by activating or inhibitory germline encoded receptors. An impaired NK cell function may result from an aberrant expression of such receptors, a condition often seen in patients with hematological cancers. Acute lymphoblastic leukemia (ALL) is the most common pediatric cancer worldwide and NK cells have emerged as crucial targets for developing immunotherapies. However, there are important gaps concerning the phenotype and behavior of NK cells during emergence of ALL. In this study we analyze the phenotype and function of NK cells from peripheral blood in pediatric patients with ALL at diagnosis. Our results showed that NK cells exhibited an altered phenotype highlighted by a significant reduction in the overall expression and percent representation of activating receptors compared to age-matched controls. No significant differences were found for the expression of inhibitory receptors. Moreover, NK cells with a concurrent reduced expression in various activating receptors, was the dominant phenotype among patients. An alteration in the relative frequencies of NK cells expressing NKG2A and CD57 within the mature NK cell pool was also observed. In addition, NK cells from patients displayed a significant reduction in the ability to sustain antibody-dependent cellular cytotoxicity (ADCC). Finally, an aberrant expression of activating receptors is associated with the phenomenon of leukemia during childhood.

Ginsenoside 20(R)-Rg3 enhances natural killer cell activity by increasing activating receptor expression through the MAPK/ERK signaling pathway

Ginseng is one of the most widely used herbal remedies for various diseases worldwide. Ginsenoside Rg3 (G-Rg3), the main component of ginseng, possesses several pharmacological properties, including anti-inflammatory, anti-tumor, antioxidant, anti-obesity, and immunomodulatory activities. However, the effect of G-Rg3 on natural killer (NK) cells in humans is not fully understood. Here, we investigated the effect of G-Rg3 on NK cell function and differentiation and elucidated the underlying mechanism. G-Rg3 increased NK cell cytotoxicity and simultaneously increased the expression of NK-activating receptors, NKp44, NKp46, and NKp30. Additionally, G-Rg3 increased the mRNA expression of NK cytolytic molecules, granzyme B and perforin. The expression of CD107a, a marker of NK cell degranulation, also increased in G-Rg3-treated NK cells. We therefore proceeded to identify which MAPK signaling pathway was involved in G-Rg3-mediated cytolytic activity. Treatment with G-Rg3 increased the phosphorylation levels of extracellular signal-regulated kinase (ERK), whereas ERK inhibition eliminated G-Rg3-induced NK cell cytotoxicity, suggesting the involvement of the ERK pathway. G-Rg3 did not affect the rate of differentiation of human cord-blood-derived NK cells; however, it increased the functional maturation of differentiated NK cells and promoted their cytotoxicity. The G-Rg3 isomer, 20(R)-Rg3, effectively activated NK cells via the extracellular signal-regulated kinase (ERK) signaling pathway, whereas 20(S)-Rg3 had no effect on NK cell activity. Altogether, the results demonstrated that 20(R)-Rg3 promoted NK cell activity via activation of the MAPK/ERK pathway, suggesting that 20(R)-Rg3 may be used as an activator of NK cell cytotoxicity for the treatment of diverse types of cancers.

Adoptive NK Cell Therapy: A Promising Treatment Prospect for Metastatic Melanoma

Simple Summary

The incidence of metastatic melanoma has been increasing over the past years with current therapies showing limited efficacy to cure the disease. Therefore, other options are being investigated, such as adoptive cell therapy (ACT) where activated immune cells are infused into a patient to attack melanoma. Natural killer (NK) cells are part of the innate immune system and extremely suitable for this kind of therapy since they show minimal toxicities in the clinical setting. In this review, we focus on current strategies for NK cell therapy and the development of new approaches that hold great promise for the treatment of advanced melanoma.

Abstract

Adoptive cell therapy (ACT) represents a promising alternative approach for patients with treatment-resistant metastatic melanoma. Lately, tumor infiltrating lymphocyte (TIL) therapy and chimeric antigen receptor (CAR)-T cell therapy have shown improved clinical outcome, compared to conventional chemotherapy or immunotherapy. Nevertheless, they are limited by immune escape of the tumor, cytokine release syndrome, and manufacturing challenges of autologous therapies. Conversely, the clinical use of Natural Killer (NK) cells has demonstrated a favorable clinical safety profile with minimal toxicities, providing an encouraging treatment alternative. Unlike T cells, NK cells are activated, amongst other mechanisms, by the downregulation of HLA class I molecules, thereby overcoming the hurdle of tumor immune escape. However, impairment of NK cell function has been observed in melanoma patients, resulting in deteriorated natural defense. To overcome this limitation, “activated” autologous or allogeneic NK cells have been infused into melanoma patients in early clinical trials, showing encouraging clinical benefit. Furthermore, as several NK cell-based therapeutics are being developed for different cancers, an emerging variety of approaches to increase migration and infiltration of adoptively transferred NK cells towards solid tumors is under preclinical investigation. These developments point to adoptive NK cell therapy as a highly promising treatment for metastatic melanoma in the future.

NK cells associate with ALS in a sex- and age-dependent manner

NK cells are innate immune cells implicated in ALS; whether NK cells impact ALS in a sex- and age-specific manner was investigated. Herein, NK cells were depleted in male and female SOD1G93A ALS mice, survival and neuroinflammation were assessed, and data were stratified by sex. NK cell depletion extended survival in female but not male ALS mice with sex-specific effects on spinal cord microglia. In humans, NK cell numbers, NK cell subpopulations, and NK cell surface markers were examined in prospectively blood collected from subjects with ALS and control subjects; longitudinal changes in these metrics were correlated to revised ALS functional rating scale (ALSFRS-R) slope and stratified by sex and age. Expression of NK cell trafficking and cytotoxicity markers was elevated in subjects with ALS, and changes in CXCR3+ NK cells and 7 trafficking and cytotoxicity markers (CD11a, CD11b, CD38, CX3CR1, NKG2D, NKp30, NKp46) correlated with disease progression. Age affected the associations between ALSFRS-R and markers NKG2D and NKp46, whereas sex impacted the NKp30 association. Collectively, these findings suggest that NK cells contribute to ALS progression in a sex- and age-specific manner and demonstrate that age and sex are critical variables when designing and assessing ALS immunotherapy.

The Role of Tim-3 on dNK Cells Dysfunction During Abnormal Pregnancy With Toxoplasma gondii Infection

Vertical transmission of Toxoplasma gondii (T. gondii) infection during gestation can result in severe complications such as abortion, congenital malformation, fetal teratogenesis, etc. Immune inhibitory molecule Tim-3 was discovered to be expressed on some decidual immune cells and participates in the maintenance of maternal-fetal tolerance. Dysregulation of Tim-3 expression on decidual NK (dNK) cells was observed in several cases of pregnancy complications, whereas the role of Tim-3 on dNK cells during T. gondii infection remains unclear. In the present study, T. gondii infected Tim-3^-/- pregnant mice, and anti-Tim-3 neutralizing antibody treated and infected human dNK cells were successfully established to explore the role of Tim-3 in dysfunction of dNK cells during abnormal pregnancy. Our results illustrated that Tim-3^-/- pregnant mice displayed more worse pregnancy outcomes with T. gondii infection compared to infected WT pregnant mice. Also, it demonstrated that Tim-3 expression on dNK cells was significantly down-regulated following T. gondii infection. Data suggested a remarkable activation of dNK cells in Tim-3^-/- mice and anti-Tim-3 neutralizing antibody treated and infected groups, with higher ratios of activating receptor NKG2D to inhibitory receptor NKG2A or KIR2DL4, IFN-γ/IL-10, and increased granule production compared with that of the infected group. Mechanism analysis proved that T. gondii-induced Tim-3 down-regulation significantly activated the phosphatidylinositol-3-kinase (PI3K)-AKT and JAK-STAT signaling pathway, by which the GranzymeB, Perforin, IFN-γ, and IL-10 production were further up-regulated. Our research demonstrated that the decrease of Tim-3 on dNK cells caused by T. gondii infection further led to dNK cells function disorder, which finally contributed to the development of abnormal pregnancy outcomes.

Influenza A Virus Hemagglutinin and Other Pathogen Glycoprotein Interactions with NK Cell Natural Cytotoxicity Receptors NKp46, NKp44, and NKp30

Natural killer (NK) cells are part of the innate immunity repertoire, and function in the recognition and destruction of tumorigenic and pathogen-infected cells. Engagement of NK cell activating receptors can lead to functional activation of NK cells, resulting in lysis of target cells. NK cell activating receptors specific for non-major histocompatibility complex ligands are NKp46, NKp44, NKp30, NKG2D, and CD16 (also known as FcγRIII). The natural cytotoxicity receptors (NCRs), NKp46, NKp44, and NKp30, have been implicated in functional activation of NK cells following influenza virus infection via binding with influenza virus hemagglutinin (HA). In this review we describe NK cell and influenza A virus biology, and the interactions of influenza A virus HA and other pathogen lectins with NK cell natural cytotoxicity receptors (NCRs). We review concepts which intersect viral immunology, traditional virology and glycobiology to provide insights into the interactions between influenza virus HA and the NCRs. Furthermore, we provide expert opinion on future directions that would provide insights into currently unanswered questions.

Immunogenetics of xenotransplantation

Xenotransplantation may become the highly desired solution to close the gap between the availability of donated organs and number of patients on the waiting list. In recent years, enormous progress has been made in the development of genetically engineered donor pigs. The introduced genetic modifications showed to be efficient in prolonging xenograft survival. In this review, we focus on the type of immune responses that may target xeno-organs after transplantation and promising immunogenetic modifications that show a beneficial effect in ameliorating or eliminating harmful xenogeneic immune responses. Increasing histocompatibility of xenografts by eliminating genetic discrepancies between species will pave their way into clinical application.

Non-KIR NK cell receptors: Role in transplantation of allogeneic haematopoietic stem cells

Natural killer (NK) cells are of major significance in patients after allogeneic haematopoietic stem cell transplantation (HSCT). They are the first subset of lymphocytes to appear in peripheral blood after transplantation and play an important role in the immune responses against cancer and viral infections. The function of NK cells is controlled by various surface receptors, of which type I integral proteins with immunoglobulin-like domains (killer-cell immunoglobulin-like receptors, KIRs) have been the most extensively studied. The present review focuses on less studied NK cell receptors, such as type II integral proteins with lectin-like domains (CD94/NKG2, NKG2D), natural cytotoxicity receptors (NCRs), immunoglobulin-like transcripts (ILTs) and their ligands. Their potential role in patients with haematological disorders subjected to HSC transplant procedure in the context of post-transplant complications such as viral reactivation and acute graft-versus-host disease (GvHD) will be presented and discussed.

Control of HCV Infection by Natural Killer Cells and Macrophages

Host defense against invading pathogens within the liver is dominated by innate immunity. Natural killer (NK) cells have been implicated at all stages of hepatitis C virus (HCV) infection, from providing innate protection to contributing to treatment-induced clearance. Decreased NK cell levels, altered NK cell subset distribution, activation marker expression, and functional polarization toward a cytolytic phenotype are hallmarks of chronic HCV infection. Interferon α (IFN-α) is a potent activator of NK cells; therefore, it is not surprising that NK cell activation has been identified as a key factor associated with sustained virological response (SVR) to IFN-α-based therapies. Understanding the role of NK cells, macrophages, and other innate immune cells post-SVR remains paramount for prevention of disease pathogenesis and progression. Novel strategies to treat liver disease may be aimed at targeting these cells.

Innate lymphoid cells control signaling circuits to regulate tissue-specific immunity

The multifaceted organization of the immune system involves not only patrolling lymphocytes that constantly monitor antigen-presenting cells in secondary lymphoid organs but also immune cells that establish permanent tissue-residency. The integration in the respective tissue and the adaption to the organ milieu enable tissue-resident cells to establish signaling circuits with parenchymal cells to coordinate immune responses and maintain tissue homeostasis. Innate lymphoid cells (ILCs) are tissue-resident innate immune cells that have a similar functional diversity to T cells including lineage-specifying transcription factors that drive certain effector programs. Since their formal discovery 10 years ago, it has become clear that ILCs are present in almost every tissue but strongly enriched at barrier surfaces, where they regulate immunity to infection, chronic inflammation, and tissue maintenance. In this context, recent research has identified ILCs as key in orchestrating tissue homeostasis through their ability to sustain bidirectional interactions with epithelial cells, neurons, stromal cells, adipocytes, and many other tissue-resident cells. In this review, we provide a comprehensive discussion of recent studies that define the development and heterogeneity of ILC populations and their impact on innate and adaptive immunity. Further, we discuss emerging research on the influence of the nervous system, circadian rhythm, and developmental plasticity on ILC function. Uncovering the signaling circuits that control development and function of ILCs will provide an integrated view on how immune responses in tissues are synchronized with functional relevance far beyond the classical view of the role of the immune system in discrimination between self/non-self and host defense.

Non-linear multidimensional flow cytometry analyses delineate NK cell phenotypes in normal and HIV-infected chimpanzees

Natural killer (NK) cells are primary immune effector cells with both innate and potentially adaptive functions against viral infections, but commonly become exhausted or dysfunctional during chronic diseases such as human immunodeficiency virus (HIV). Chimpanzees are the closest genetic relatives of humans and have been previously used in immunology, behavior and disease models. Due to their similarities to humans, a better understanding of chimpanzee immunology, particularly innate immune cells, can lend insight into the evolution of human immunology, as well as response to disease. However, the phenotype of NK cells has been poorly defined. In order to define NK cell phenotypes, we unbiasedly quantified NK cell markers among mononuclear cells in both naive and HIV-infected chimpanzees by flow cytometry. We identified NKG2D and NKp46 as the most dominant stable NK cells markers using multidimensional data reduction analyses. Other traditional NK cell markers such as CD8α, CD16 and perforin fluctuated during infection, while some such as CD56, NKG2A and NKp30 were generally unaltered by HIV infection, but did not delineate the full NK cell repertoire. Taken together, these data indicate that phenotypic dysregulation may not be pronounced during HIV infection of chimpanzees, but traditional NK cell phenotyping used for both humans and other non-human primate species may need to be revised to accurately identify chimpanzee NK cells.

Natural Killer Cell-Mediated Cellular Therapy of Hematological Malignancies

Our understanding on the mechanisms of graft versus tumor/leukemia (GvT/GvL) and graft versus host (GvH) effects has tremendously evolved within the past decades. During the search for a mechanism that augments GvT/GvL without increasing GvH effects, natural killer (NK) cells have clearly attracted attention. Current approaches of NK cell immunotherapy for hematological malignancies involve using methods for in vivo potentiation of NK cell proliferation and activity; adoptive transfer of NK cells from autologous and allogeneic sources [cord blood mononuclear cells, peripheral blood mononuclear cells, CD34⁺ stem cells] and NK cell lines; and genetic modification of NK cells. Several cytokines, including interleukin-2 and interleukin-15 take part in the development of NK cells and have been shown to boost NK cell effects both in vivo and ex vivo. Monoclonal antibodies directed towards certain targets, including stimulating CD16, blockade of NK cell receptors, and redirection of cytotoxicity to tumor cells via bi- or tri-specific engagers may promote NK cell function. Despite the relative disappointment with autologous NK cell infusions, the future holds promise in adoptive transfer of allogeneic NK cells and the development of novel cellular therapeutic strategies, such as chimeric antigen receptor-modified NK cell immunotherapy. In this review, we summarize the current status of NK cell-related mechanisms in the therapy of hematologic malignancies, and discuss the future perspectives on adoptive NK cell transfer and other novel cellular immunotherapeutic strategies.

Inhibition of the NKp44-PCNA Immune Checkpoint Using a mAb to PCNA

mAb-based blocking of the immune checkpoints involving the CTLA4-B7 and PD1-PDL1 inhibitory axes enhance T-cell-based adaptive immune responses in patients with cancer. We show here that antitumor responses by natural killer (NK) cells can be enhanced by a checkpoint-blocking mAb, 14-25-9, which we developed against proliferating cell nuclear antigen (PCNA). PCNA is expressed on the surface of cancer cells and acts as an inhibitory ligand for the NK-cell receptor, NKp44-isoform1. We tested for cytoplasmic- and membrane-associated PCNA by FACS- and ImageStream-based staining of cell lines and IHC of human cancer formalin fixed, paraffin embedded tissues. The mAb, 14-25-9, inhibited binding of chimeric NKp44 receptor to PCNA and mostly stained the cytoplasm and membrane of tumor cells, whereas commercial antibody (clone PC10) stained nuclear PCNA. NK functions were measured using ELISA-based IFNγ secretion assays and FACS-based killing assays. The NK92-NKp44-1 cell line and primary human NK cells showed increased IFNγ release upon coincubation with mAb 14-25-9 and various solid tumor cell lines and leukemias. Treatment with 14-25-9 also increased NK cytotoxic activity. In vivo efficacy was evaluated on patient-derived xenografts (PDX)-bearing NSG mice. In PDX-bearing mice, intravenous administration of mAb 14-25-9 increased degranulation (CD107a expression) of intratumorally injected patient autologous or allogeneic NK cells, as well as inhibited tumor growth when treated long term. Our study describes a mAb against the NKp44-PCNA innate immune checkpoint that can enhance NK-cell antitumor activity both in vitro and in vivo.

STAT3 directly regulates NKp46 transcription in NK cells of HBeAg-negative CHB patients

NK cells play an important role in early control of HBV infection. The function of NK cells is inhibited in chronic hepatitis B virus (CHB) infection, although the underlying mechanism remains unknown. We found that the expression of STAT3 decreased in peripheral NK cells of CHB patients, and was associated with low levels of degranulation and IFN-γ secretion. In addition, STAT3 levels were positively correlated with cytolysis-associated molecules and antiviral cytokines, such as CD107a, granzyme B, perforin, and IFN-γ. HBsAg directly inhibited the expression and activation of STAT3 in NK cells, and knocking down STAT3 expression in NK cells inhibited proliferation, decreased cyclin d1 levels, and suppressed responsiveness to IL-21 stimulation. Furthermore, STAT3 directly bound to the promoter of NKp46, an important activating receptor of NK cells, to regulate its transcription and expression. Taken together, our findings indicate that STAT3 is an important positive regulator of NK cells, and provide a new mechanism of NK cell dysfunction in CHB.

Monkeying Around: Using Non-human Primate Models to Study NK Cell Biology in HIV Infections

Natural killer (NK) cells are the major innate effectors primed to eliminate virus-infected and tumor or neoplastic cells. Recent studies also suggest nuances in phenotypic and functional characteristics among NK cell subsets may further permit execution of regulatory and adaptive roles. Animal models, particularly non-human primate (NHP) models, are critical for characterizing NK cell biology in disease and under homeostatic conditions. In HIV infection, NK cells mediate multiple antiviral functions via upregulation of activating receptors, inflammatory cytokine secretion, and antibody dependent cell cytotoxicity through antibody Fc-FcR interaction and others. However, HIV infection can also reciprocally modulate NK cells directly or indirectly, leading to impaired/ineffective NK cell responses. In this review, we will describe multiple aspects of NK cell biology in HIV/SIV infections and their association with viral control and disease progression, and how NHP models were critical in detailing each finding. Further, we will discuss the effect of NK cell depletion in SIV-infected NHP and the characteristics of newly described memory NK cells in NHP models and different mouse strains. Overall, we propose that the role of NK cells in controlling viral infections remains incompletely understood and that NHP models are indispensable in order to efficiently address these deficits.

Human Natural Killer Receptors, Co-Receptors, and Their Ligands

In the last 20 years, the study of human natural killer (NK) cells has moved from the first molecular characterizations of very few receptor molecules to the identification of a plethora of receptors displaying surprisingly divergent functions. We have contributed to the description of inhibitory receptors and their signaling pathways, important in fine regulation in many cell types, but unknown until their discovery in the NK cells. Inhibitory function is central to regulating NK-mediated cytolysis, with different molecular structures evolving during speciation to assure its persistence. More recently, it has become possible to characterize the NK triggering receptors mediating natural cytotoxicity, unveiling the existence of a network of cellular interactions between effectors of both natural and adaptive immunity. This unit reviews the contemporary history of molecular studies of receptors and ligands involved in NK cell function, characterizing the ligands of the triggering receptor and the mechanisms for finely regulating their expression in pathogen-infected or tumor cells. © 2018 by John Wiley & Sons, Inc.

Tuning Natural Killer Cell Anti-multiple Myeloma Reactivity by Targeting Inhibitory Signaling via KIR and NKG2A

Natural killer (NK) cells are attractive candidates for allogeneic cell-based immunotherapy due to their potent antitumor effector function and good safety profile. NK cells express killer immunoglobulin-like receptors (KIRs) and the NKG2A receptor important for NK cells education as well as providing inhibitory signals upon encountering HLA-expressing target cells. Multiple myeloma (MM) is an example of a tumor expressing relatively high levels of HLA molecules. In this review, we discuss the functional relevance of inhibitory KIRs and NKG2A for NK cells anti-MM response and strategies to lower these inhibitory signaling to enhance clinical efficacy of allogeneic NK cells in MM.

Recovery of natural killer cells is mainly in post-treatment period in chronic hepatitis C patients treated with sofosbuvir plus ledipasvir

AIM

To investigate how natural killer (NK) cells are affected in the elimination of hepatitis C virus (HCV) by sofosbuvir/ledipasvir, two highly effective direct-acting antivirals (DAAs).

METHODS

Thirteen treatment-naïve and treatment-experienced chronic hepatitis C (CHC) patients were treated with sofosbuvir/ledipasvir, and NK cells were detected at baseline, weeks 2, 4, 8 and 12 during therapy, and week post of treatment (Pt)-12 and 24 after the end of therapy by multicolor flow cytometry and compared with those from 13 healthy controls.

RESULTS

All patients achieved sustained virological response. There was a significant decline in CD56bright NK cell frequencies at week 8 (P = 0.002) and week 12 (P = 0.003), which were altered to the level comparable to healthy controls at week Pt-12, but no difference was observed in the frequency of CD56dim NK cells. Compared with healthy controls, the expression levels of NKG2A, NKp30 and CD94 on NK cells from CHC patients at baseline were higher. NKG2A, NKp30 and CD94 started to recover at week 12 and reached the levels similar to those of healthy controls at week Pt-12 or Pt-24. Before treatment, patients have higher interferon (IFN)-γ and perforin levels than healthy controls, and IFN-γ started to recover at week 8 and reached the normalized level at week Pt-12.

CONCLUSION

NK cells of CHC patients can be affected by DAAs, and phenotypes and function of NK cells recover not at early stage but mainly after the end of sofosbuvir/ledipasvir treatment.

IXA Honorary Member Lecture, 2017: The long and winding road to tolerance

The last 15 years or so have seen exciting progress in xenotransplantation, with porcine organ grafts surviving months or even years in non-human primates. These advances reflect the application of new scientific knowledge, improved immunosuppressive agents, and genetic engineering. The field has recently enjoyed a renaissance of interest and hope, largely due to the exponential increase in our capacity to genetically engineer porcine source animals. However, immune responses to xenografts are very powerful and widespread clinical application of xenotransplantation will depend on the ability to suppress these immune responses while preserving the capacity to protect both the recipient and the graft from infectious microorganisms. Our work over the last three decades has aimed to engineer the immune system of the recipient in a manner that achieves specific tolerance to the xenogeneic donor while preserving otherwise normal immune function. Important proofs of principle have been obtained, first in rodents, and later in human immune systems in "humanized mice" and finally in non-human primates, demonstrating the capacity and potential synergy of mixed xenogeneic chimerism and xenogeneic thymic transplantation in tolerizing multiple arms of the immune system. Considering the fact that clinical tolerance has recently been achieved for allografts and the even greater importance of avoiding excessive immunosuppression for xenografts, it is my belief that it is both possible and imperative that we likewise achieve xenograft tolerance. I expect this to be accomplished through the availability of targeted approaches to recipient immune conditioning, understanding of immunological mechanisms of tolerance, advanced knowledge of physiological incompatibilities, and the availability of inbred miniature swine with optimized use of genetic engineering.

Haemagglutinin-neuraminidase from HPIV3 mediates human NK regulation of T cell proliferation via NKp44 and NKp46

HPIV3 is a respiratory virus causing airway diseases, including pneumonia, croup, and bronchiolitis, during infancy and childhood. Currently there is no effective vaccine or anti-viral therapy for this virus. Studies have suggested that poor T cell proliferation following HPIV3 infection is responsible for impaired immunological memory associated with this virus. We have previously demonstrated that NK cells mediate regulation of T cell proliferation during HPIV3 infection. Here we add to these studies by demonstrating that the regulation of T cell proliferation during HPIV3 infection is mediated via NK receptors NKp44 and NKp46 and involves the surface glycoprotein haemagglutinin-neuraminidase but not the fusion protein of the virus. These studies extend our knowledge of the regulatory repertoire of NK cells and provide mechanistic insights which may explain reoccurring failures of vaccines against this virus.

A Developed NK-92MI Cell Line with Siglec-7neg Phenotype Exhibits High and Sustainable Cytotoxicity against Leukemia Cells

Altered sialic acid processing that leads to upregulation of cell surface sialylation is recognized as a key change in malignant tissue glycosylation. This cancer-associated hypersialylation directly impacts the signaling interactions between tumor cells and their surrounding microenvironment, especially the interactions mediated by immune cell surface sialic acid-binding immunoglobulin-like lectins (Siglecs) to relay inhibitory signals for cytotoxicity. First, we obtained a Siglec-7^neg NK-92MI cell line, NK-92MI-S7N, by separating a group of Siglec-7^neg cell population from an eight-month-long-term NK-92MI in vitro culture by fluorescence-activated cell sorting (FACS). The effect of Siglec-7 loss on NK-92MI-S7N cells was characterized by the cell morphology, proliferation, and cytotoxic activity via FACS, MTS assay, cytotoxic assay, and natural killer (NK) degranulation assay. We found the expression levels of Siglec-7 in NK-92MI were negatively correlated with NK cytotoxicity against leukemia cells. This NK-92MI-S7N cell not only shared very similar phenotypes with its parental cells but also possessed a high and sustainable killing activity. Furthermore, this Siglec-7^neg NK line was unexpectedly capable of eliminating a NK-92MI-resistant leukemia cell, THP-1, through enhancing the effector-target interaction. In this study, a NK cell line with high and sustainable cytotoxicity was established and this cell may provide a potential application in NK-based treatment for leukemia patients.

Survival in acute myeloid leukemia is associated with NKp44 splice variants

NKp44 is a receptor encoded by the NCR2 gene, which is expressed by cytokine-activated natural killer (NK) cells that are involved in anti-AML immunity. NKp44 has three splice variants corresponding to NKp44^ITIM+ (NKp44-1) and NKp44^ITIM− (NKp44-2, and NKp44-3) isoforms. RNAseq data of AML patients revealed similar survival of NKp46⁺NKp44⁺ and NKp46⁺NKp44⁻ patients. However, if grouped according to the NKp44 splice variant profile, NKp44-1 expression was significantly associated with poor survival of AML patients. Moreover, activation of PBMC from healthy controls showed co-dominant expression of NKp44-1 and NKp44-3, while primary NK clones show more diverse NKp44 splice variant profiles. Cultured primary NK cells resulted in NKp44-1 dominance and impaired function associated with PCNA over-expression by target cells. This impaired functional phenotype could be rescued by blocking of NKp44 receptor. Human NK cell lines revealed co-dominant expression of NKp44-1 and NKp44-3 and showed a functional phenotype that was not inhibited by PCNA over-expression. Furthermore, transfection-based overexpression of NKp44-1, but not NKp44-2/NKp44-3, reversed the endogenous resistance of NK-92 cells to PCNA-mediated inhibition, and resulted in poor formation of stable lytic immune synapses. This research contributes to the understanding of AML prognosis by shedding new light on the functional implications of differential splicing of NKp44.

Natural killer cells in HIV-1 infection and therapy

: Natural killer (NK) cells are important effectors of innate immunity playing a key role in the eradication and clearance of viral infections. Over the recent years, several studies have shown that HIV-1 pathologically changes NK cell homeostasis and hampers their antiviral effector functions. Moreover, high levels of chronic HIV-1 viremia markedly impair those NK cell regulatory features that normally regulate the cross talks between innate and adaptive immune responses. These pathogenic events take place early in the infection and are associated with a pathologic redistribution of NK cell subsets that includes the expansion of anergic CD56/CD16 NK cells with an aberrant repertoire of activating and inhibitory receptors. Nevertheless, the presence of specific haplotypes for NK cell receptors and the engagement of NK cell antibody-dependent cell cytotocity have been reported to control HIV-1 infection. This dichotomy can be extremely useful to both predict the clinical outcome of the infection and to develop alternative antiviral pharmacological approaches. Indeed, the administration of antiretroviral therapy in HIV-1-infected patients restores NK cell phenotype and functions to normal levels. Thus, antiretroviral therapy can help to develop NK cell-directed therapeutic strategies that include the use of broadly neutralizing antibodies and toll-like receptor agonists. The present review discusses how our current knowledge of NK cell pathophysiology in HIV-1 infection is being translated both in experimental and clinical trials aimed at controlling the infection and disease.

Branched I antigens on leukemia cells enhanced sensitivity against natural killer-cell cytotoxicity through affecting the target-effector interaction

BACKGROUND

The aberrant glycosylation on proteins and lipids has been implicated in malignant transformations for promoting the tumorigenesis, metastasis, and evasion from the host immunity. The I-branching β-1,6-N-acetylglucosaminyltransferase, converting the straight i to branched I histo-blood group antigens, reportedly could influence the migration, invasion, and metastasis of solid tumors.

STUDY DESIGN AND METHODS

We first chose the highly cytotoxic natural killer (NK)-92MI cells as effector against leukemia for this cell line has been used in several clinical trials. Fluorescence-activated cell sorting and nonradioactive cytotoxicity assay were performed to reexamine the role of NK-activating receptors, their corresponding ligands, and the tumor-associated carbohydrate antigens in this NK-92MI-leukemia in vitro system. The I role on cytotoxic mechanism was further studied especially on the effector-target interactions by cytotoxic analysis and conjugate formation assay.

RESULTS

We showed that expression levels of leukemia surface ligands for NK-activating receptors did not positively reflect susceptibility to NK-92MI. Instead, the expression of I antigen on the leukemia cells was found important in mediating the susceptibility to NK targeting by affecting the interaction with effector cells. Furthermore, susceptibility was shown to dramatically increase while overexpressing branched I antigens on the I- cells. By both conjugate and cytotoxicity assay, we revealed that the presence of I antigen on leukemia cells enhanced the interaction with NK-92MI cells, increasing susceptibility to cell-mediated lysis.

CONCLUSION

In our system, branched I antigens on the leukemia were involved in the immunosurveillance mediated by NK cells specifically through affecting the effector-target interaction.

Impact of Mixed Xenogeneic Porcine Hematopoietic Chimerism on Human NK Cell Recognition in a Humanized Mouse Model

Mixed chimerism is a promising approach to inducing allograft and xenograft tolerance. Mixed allogeneic and xenogeneic chimerism in mouse models induced specific tolerance and global hyporesponsiveness, respectively, of host mouse natural killer (NK) cells. In this study, we investigated whether pig/human mixed chimerism could tolerize human NK cells in a humanized mouse model. Our results showed no impact of induced human NK cell reconstitution on porcine chimerism. NK cells from most pig/human mixed chimeric mice showed either specifically decreased cytotoxicity to pig cells or global hyporesponsiveness in an in vitro cytotoxicity assay. Mixed xenogeneic chimerism did not hamper the maturation of human NK cells but was associated with an alteration in NK cell subset distribution and interferon gamma (IFN-γ) production in the bone marrow. In summary, we demonstrate that mixed xenogeneic chimerism induces human NK cell hyporesponsiveness to pig cells. Our results support the use of this approach to inducing xenogeneic tolerance in the clinical setting. However, additional approaches are required to improve the efficacy of tolerance induction while ensuring adequate NK cell functions.

Cytotoxicity and infiltration of human NK cells in in vivo-like tumor spheroids

Background

The complex cellular networks within tumors, the cytokine milieu, and tumor immune escape mechanisms affecting infiltration and anti-tumor activity of immune cells are of great interest to understand tumor formation and to decipher novel access points for cancer therapy. However, cellular in vitro assays, which rely on monolayer cultures of mammalian cell lines, neglect the three-dimensional architecture of a tumor, thus limiting their validity for the in vivo situation.

Methods

Three-dimensional in vivo-like tumor spheroid were established from human cervical carcinoma cell lines as proof of concept to investigate infiltration and cytotoxicity of NK cells in a 96-well plate format, which is applicable for high-throughput screening. Tumor spheroids were monitored for NK cell infiltration and cytotoxicity by flow cytometry. Infiltrated NK cells, could be recovered by magnetic cell separation.

Results

The tumor spheroids were stable over several days with minor alterations in phenotypic appearance. The tumor spheroids expressed high levels of cellular ligands for the natural killer (NK) group 2D receptor (NKG2D), mediating spheroid destruction by primary human NK cells. Interestingly, destruction of a three-dimensional tumor spheroid took much longer when compared to the parental monolayer cultures. Moreover, destruction of tumor spheroids was accompanied by infiltration of a fraction of NK cells, which could be recovered at high purity.

Conclusion

Tumor spheroids represent a versatile in vivo-like model system to study cytotoxicity and infiltration of immune cells in high-throughput screening. This system might proof useful for the investigation of the modulatory potential of soluble factors and cells of the tumor microenvironment on immune cell activity as well as profiling of patient-/donor-derived immune cells to personalize cellular immunotherapy.

Electronic supplementary material

The online version of this article (doi:10.1186/s12885-015-1321-y) contains supplementary material, which is available to authorized users.

Mechanisms regulating NK cell activation during viral infection

ABSTRACT 

NK cells constitute a population of lymphocytes involved in innate immune functions. They play a critical role in antiviral immune surveillance. Viruses have evolved with their host species for millions of years, each exerting a selective pressure upon the other. As a corollary, the pathways used by the immune system that are critical to control viral infection can be revealed by defining the role of viral gene products that are nonessential for virus replication. We relate here the battery of resources available to NK cells to recognize and eliminate viruses and reciprocally the immune evasion mechanisms developed by viruses to prevent NK cell activation.

NK cells after transplantation: friend or foe

Natural killer (NK) cells are effector cells of the innate immune system that can lyse target cells without prior sensitization and have an important role in host defense to pathogens and transformed cells. A balance between negative and positive signals transmitted via germ line-encoded inhibitory and activating receptors controls the function of NK cells. Although the concept of "missing-self" would suggest that NK cells could target foreign allografts, the prevailing dogma has been that NK cells are not active participants in the mechanisms that culminate in the rejection of solid organ allografts. Recent studies, however, challenge this conclusion and instead implicate NK cells in contributing to both graft rejection and tolerance to an allograft. In this review, we highlight recent studies with the goal of understanding the complex NK cell interactions that impact alloimmunity.

Extracellular HCV-core protein induces an immature regulatory phenotype in NK cells: implications for outcome of acute infection

Background

Hepatitis C viral (HCV) proteins, including core, demonstrate immuno-modulatory properties; however, the effect of extracellular core on natural killer (NK) cells has not previously been investigated.

Aims

To characterise NKs in acute HCV infection over time, and, to examine the effect of exogenous HCV-core protein on NK cell phenotype and function.

Methods

Acute HCV patients (n = 22), including 10 subjects who spontaneously recovered, were prospectively studied. Flow-cytometry was used to measure natural cytotoxicity and to phenotype NKs directly ex vivo and after culture with HCV-core protein. Microarray analysis was used to identify pathways involved in the NK cell response to exogenous HCV-core.

Results

Direct ex vivo analysis demonstrated an increased frequency of immature/regulatory CD56^bright NKs early in acute HCV infection per se which normalized with viral clearance. Natural cytotoxicity was reduced and did not recover after viral clearance. There was a statistically significant correlation between the frequency of CD56^bright NKs and circulating serum levels of HCV core protein. In vitro culture of purified CD56^bright NK cells with HCV-core protein in the presence of IL-15 maintained a significant proportion of NKs in the CD56^bright state. The in vitro effect of core closely correlates with NK characteristics measured directly ex vivo in acute HCV infection. Pathway analysis suggests that HCV-core protein attenuates NK interferon type I responses.

Conclusions

Our data suggest that HCV-core protein alters NK cell maturation and may influence the outcome of acute infection.

HLA-G expression is an independent predictor for improved survival in high grade ovarian carcinomas

Aberrant expression of human leukocyte antigens (HLA) class I has prognostic importance in various cancers. Here, we evaluated the prognostic value of classical (A/B/C) and nonclassical (G/E) HLA expression in 169 high grade epithelial ovarian cancer samples and linked that to clinicopathological characteristics and survival. Expression of HLA-A, -B/C, or -E was not correlated with survival. Survival was prolonged when tumours expressed HLA-G (P = 0.008) and HLA-G was an independent predictor for better survival (P = 0.011). In addition, HLA-G expression was associated with longer progression-free survival (P = 0.036) and response to chemotherapy (P = 0.014). Accordingly, high expression of HLA-G mRNA was associated with prolonged disease-free survival (P = 0.037) in 65 corresponding samples. Elevated serum-soluble HLA-G levels as measured by enzyme-linked immunosorbent assay in 50 matched patients were not correlated to HLA-G protein expression or gene expression nor with survival. During treatment, sHLA-G levels declined (P = 0.038). In conclusion, expression of HLA-G is an independent prognostic factor for improved survival in high grade epithelial ovarian cancer and a predictor for platinum sensitivity.

Soluble HLA-I/peptide monomers mediate antigen-specific CD8 T cell activation through passive peptide exchange with cell-bound HLA-I molecules

Accumulating evidence that serum levels of soluble class I HLA molecules (sHLA-I) can, under various pathological conditions, correlate with disease stage and/or patient survival, has stimulated interest in defining whether sHLA-I can exert immunological functions. However, despite a mounting number of publications suggesting the ability of sHLA-I to affect immune effectors in vitro, the precise underlying mechanism still remains controversial. In this article, we address potential functions of both classical and nonclassical sHLA-I, using soluble recombinant HLA-I/peptide monomers, and clearly demonstrate their ability to trigger Ag-specific activation of CD8 T cells in vitro. Furthermore, we provide strong evidence that this behavior results from the passive transfer of peptides from monomers to T cell-bound HLA-I molecules, allowing for fratricide representation and activation. Hence, we proposed a unifying model of T cell activation by HLA-I/peptide monomers, reappraising the potential involvement of sHLA-I molecules in the immune response.

Leukemia-induced phenotypic and functional defects in natural killer cells predict failure to achieve remission in acute myeloid leukemia

The majority of patients with acute myeloid leukemia will relapse, and older patients often fail to achieve remission with induction chemotherapy. We explored the possibility that leukemic suppression of innate immunity might contribute to treatment failure. Natural killer cell phenotype and function was measured in 32 consecutive acute myeloid leukemia patients at presentation, including 12 achieving complete remission. Compared to 15 healthy age-matched controls, natural killer cells from acute myeloid leukemia patients were abnormal at presentation, with downregulation of the activating receptor NKp46 (P=0.007) and upregulation of the inhibitory receptor NKG2A (P=0.04). Natural killer cells from acute myeloid leukemia patients had impaired effector function against autologous blasts and K562 targets, with significantly reduced CD107a degranulation, TNF-α and IFN-γ production. Failure to achieve remission was associated with NKG2A overexpression and reduced TNF-α production. These phenotypic and functional abnormalities were partially restored in the 12 patients achieving remission. In vitro co-incubation of acute myeloid leukemia blasts with natural killer cells from healthy donors induced significant impairment in natural killer cell TNF-α and IFN-γ production (P=0.02 and P=0.01, respectively) against K562 targets and a trend to reduced CD107a degranulation (P=0.07). Under transwell conditions, the inhibitory effect of AML blasts on NK cytotoxicity and effector function was still present, and this inhibitory effect was primarily mediated by IL-10. These results suggest that acute myeloid leukemia blasts induce long-lasting changes in natural killer cells, impairing their effector function and reducing the competence of the innate immune system, favoring leukemia survival.

Natural killer cells modulation in hematological malignancies

Hematological malignancies (HM) treatment improved over the last years resulting in increased achievement of complete or partial remission, but unfortunately high relapse rates are still observed, due to remaining minimal residual disease. Therefore, sustainment of long-term remission is crucial, using either drug maintenance treatment or by boosting or prolonging an immune response. Immune system has a key role in tumor surveillance. Nonetheless, tumor-cells evade the specific T-lymphocyte mediated immune surveillance using many mechanisms but especially by the down-regulation of the expression of HLA class I antigens. In theory, these tumor-cells lacking normal expression of HLA class I molecules should be destroyed by natural killer (NK) cells, according to the missing-self hypothesis. NK cells, at the frontier of innate and adaptive immune system, have a central role in tumor-cells surveillance as demonstrated in the setting of allogenic stem cell transplantation. Nevertheless, tumors develop various mechanisms to escape from NK innate immune pressure. Abnormal NK cytolytic functions have been described in many HM. We present here various mechanisms involved in the escape of HM from NK-cell surveillance, i.e., NK-cells quantitative and qualitative abnormalities.

Occurrence of nodular lymphocyte-predominant hodgkin lymphoma in hermansky-pudlak type 2 syndrome is associated to natural killer and natural killer T cell defects

Hermansky Pudlak type 2 syndrome (HPS2) is a rare autosomal recessive primary immune deficiency caused by mutations on β3A gene (AP3B1 gene). The defect results in the impairment of the adaptor protein 3 (AP-3) complex, responsible for protein sorting to secretory lysosomes leading to oculo-cutaneous albinism, bleeding disorders and immunodeficiency. We have studied peripheral blood and lymph node biopsies from two siblings affected by HPS2. Lymph node histology showed a nodular lymphocyte predominance type Hodgkin lymphoma (NLPHL) in both HPS2 siblings. By immunohistochemistry, CD8 T-cells from HPS2 NLPHL contained an increased amount of perforin (Prf) + suggesting a defect in the release of this granules-associated protein. By analyzing peripheral blood immune cells we found a significant reduction of circulating NKT cells and of CD56(bright)CD16(-) Natural Killer (NK) cells subset. Functionally, NK cells were defective in their cytotoxic activity against tumor cell lines including Hodgkin Lymphoma as well as in IFN-γ production. This defect was associated with increased baseline level of CD107a and CD63 at the surface level of unstimulated and IL-2-activated NK cells. In summary, these results suggest that a combined and profound defect of innate and adaptive effector cells might explain the susceptibility to infections and lymphoma in these HPS2 patients.

Emerging concepts in immunity to hepatitis C virus infection

Since the discovery of hepatitis C virus (HCV) by molecular cloning almost a quarter of a century ago, unprecedented at the time because the virus had never been grown in cell culture or detected serologically, there have been impressive strides in many facets of our understanding of the natural history of the disease, the viral life cycle, the pathogenesis, and antiviral therapy. It is apparent that the virus has developed multiple strategies to evade immune surveillance and eradication. This Review covers what we currently understand of the temporal and spatial immunological changes within the human innate and adaptive host immune responses that ultimately determine the outcomes of HCV infection.

Understanding human NK cell differentiation: clues for improving the haploidentical hematopoietic stem cell transplantation

The study of in vitro and in vivo NK cell differentiation from hematopoietic precursors revealed the existence of discrete stages of development. These stages are characterized by the progressive acquisition of markers and receptors that play a crucial role in NK cell function. The knowledge acquired has revealed particularly relevant for improving the HSCT to cure high-risk leukemias in the haplo-HSCT setting, in which NK cells play a central role in the clearance of leukemic cells and in the positive clinical outcome.

Natural killer cells: multifaceted players with key roles in hepatitis C immunity

Natural killer cells (NKs) are involved in every stage of hepatitis C viral (HCV) infection, from protection against HCV acquisition and resolution in the acute phase to treatment-induced clearance. In addition to their direct antiviral actions, NKs are involved in the induction and priming of appropriate downstream T-cell responses. In the setting of chronic HCV, overall NK cell levels are decreased, subset distribution is altered, and changes in NK receptor (NKR) expression have been demonstrated, although the contribution of individual NKRs to viral clearance or persistence remains to be clarified. Enhanced NK cell cytotoxicity accompanied by insufficient interferon-γ production may promote liver damage in the setting of chronic infection. Treatment-induced clearance is associated with activation of NK cells, and it will be of interest to monitor NK cell responses to triple therapy. Activated NK cells also have anti-fibrotic properties, and the same hepatic NK cell populations that are actively involved in control of HCV may also be involved in control of HCV-associated liver damage. We still have much to learn, in particular: how do liver-derived NKs influence the outcome of HCV infection? Do NK receptors recognize HCV-specific components? And, are HCV-specific memory NK populations generated?

Protein Kinase Inhibitors CK59 and CID755673 Alter Primary Human NK Cell Effector Functions

Natural killer (NK) cells are part of the innate immune response and play a crucial role in the defense against tumors and virus-infected cells. Their effector functions include the specific killing of target cells, as well as the modulation of other immune cells by cytokine release. Kinases constitute a relevant part in signaling, are prime targets in drug research and the protein kinase inhibitor Dasatinib is already used for immune-modulatory therapies. In this study, we tested the effects of the kinase inhibitors CK59 and CID755673. These inhibitors are directed against calmodulin kinase II (CaMKII; CK59) and PKD family kinases (CID755673) that were previously suggested as novel components of NK activation pathways. Here, we use a multi-parameter, FACS-based assay to validate the influence of CK59 and CID755673 on the effector functions of primary NK cells. Treatment with CK59 and CID755673 indeed resulted in a significant dose-dependent reduction of NK cell degranulation markers and cytokine release in freshly isolated Peripheral blood mononuclear cell populations from healthy blood donors. These results underline the importance of CaMKII for NK cell signaling and suggest protein kinase D2 as a novel signaling component in NK cell activation. Notably, kinase inhibition studies on pure NK cell populations indicate significant donor variations.