The killer's kiss: the many functions of NK cell immunological synapses

NK-cell receptor modulation in viral infections

Natural killer (NK) cells play a crucial role in controlling viral infections. The ability to kill infected cells without prior immunization, yet being tolerant to self, healthy cells, depends on the balance of germ-line encoded surface receptors. NK-cell receptors are divided into either activating, leading to activation of NK cell and its cytotoxic and pro-inflammatory activity, or inhibitory, providing tolerance for a target cell. The signals from inhibitory receptors dominate and NK-cell activation requires stimulation of activating receptors. In viral infections, NK-cell interaction with infected cells can result in activation, memory-like NK-cell differentiation, or NK-cell exhaustion, which constitutes one of the viral immune evasion mechanisms. All of these states are associated with the modulation of NK-cell receptor expression. In this review, we summarize the current knowledge of NK-cell receptors and their role in viral infection control, as well as the alterations of their expression observed in acute or chronic infections. We present recently discovered SARS-CoV-2-mediated modulation of NK-cell receptor expression and compare them with other human viral infections. Finally, since modulation of NK-cell receptor activation gives a promising addition to currently used antiviral therapies, we briefly discuss the clinical significance and future perspective of the application of agonists or antagonists of activating and inhibitory receptors, respectively. In sum, our review shows that although much is known about NK-cell receptor biology, a deeper understanding of NK-cell receptors role in viral infections is still needed.

Effector and cytolytic function of natural killer cells in anticancer immunity

Adaptive immune cells play an important role in mounting antigen-specific antitumor immunity. The contribution of innate immune cells such as monocytes, macrophages, natural killer (NK) cells, dendritic cells, and gamma-delta T cells is well studied in cancer immunology. NK cells are innate lymphoid cells that show effector and regulatory function in a contact-dependent and contact-independent manner. The cytotoxic function of NK cells plays an important role in killing the infected and transformed host cells and controlling infection and tumor growth. However, several studies have also ascribed the role of NK cells in inducing pathophysiology in autoimmune diseases, promoting immune tolerance in the uterus, and antitumor function in the tumor microenvironment. We discuss the fundamentals of NK cell biology, its distribution in different organs, cellular and molecular interactions, and its cytotoxic and noncytotoxic functions in cancer biology. We also highlight the use of NK cell-based adoptive cellular therapy in cancer.

Altered serum levels of cytokines in patients with myasthenia gravis

Background

Myasthenia gravis (MG) is an autoimmune disease characterized by generalized skeletal muscle contraction weakness due to autoantibodies targeting neural-muscular junctions. Here, we investigated the relationship between key cytokines and MG type, disease course, antibodies, and comorbidities.

Method

Cytokine levels in serum samples collected from MG (n = 45) and healthy control (HC, n = 38) patients from January 2020 to June 2022 were quantified via flow cytometry.

Results

Levels of IL-6 were higher in the MG group versus healthy individuals (p = 0.026) and in patients with generalized versus ocular MG (p = 0.019). IL-6 levels were positively correlated with QMG score. In patients with MG with both AChR and Titin antibodies, serum levels of sFas and granulysin were higher than in those with AChR alone (p = 0.036, and p = 0.028, respectively). LOMG had a reduction in serum levels of IL-2 compared to EOMG (p = 0.036). LOMG patients with diabetes had lower serum levels of IL-2, IL-4, and IFN-γ (p = 0.044, p = 0.038, and p = 0.047, respectively) versus those without diabetes. sFas in the MG with Abnormal thymus were reduced compared to those in MG with Normal thymus (p = 0.008).

Conclusions

This study revealed a positive correlation between IL-6 level and MG status. Serum cytokine levels of the AChR + Titin MG group differed from those of the AChR group. LOMG had a lower IL-2 level. Comorbidities affect some cytokines in peripheral blood in MG serum.

Vitamin A deficiency and vitamin A supplementation affect innate and T cell immune responses to rotavirus A infection in a conventional sow model

Rotavirus A (RVA) causes ~200,000 diarrheal deaths annually in children <5yrs, mostly in low- and middle-income countries. Risk factors include nutritional status, social factors, breastfeeding status, and immunodeficiency. We evaluated the effects of vitamin A (VA) deficiency/VA supplementation and RVA exposure (anamnestic) on innate and T cell immune responses in RVA seropositive pregnant and lactating sows and passive protection of their piglets post-RVA challenge. Sows were fed VA deficient (VAD) or sufficient (VAS) diets starting at gestation day (GD)30. A subset of VAD sows received VA supplementation from GD|76 (30,000IU/day, VAD+VA). Sows (6 groups) were inoculated with porcine RVA G5P[7] (OSU strain) or Minimal Essential Medium (mock) at GD~90: VAD+RVA; VAS+RVA; VAD+VA+RVA; VAD-mock; VAS-mock; and VAD+VA-mock. Blood, milk, and gut-associated tissues were collected from sows at several time points to examine innate [natural killer (NK), dendritic (DC) cells], T cell responses and changes in genes involved in the gut-mammary gland (MG)-immunological axis trafficking. Clinical signs of RVA were evaluated post inoculation of sows and post-challenge of piglets. We observed decreased frequencies of NK cells, total and MHCII+ plasmacytoid DCs, conventional DCs, CD103+ DCs and CD4+/CD8+ and T regulatory cells (Tregs) and NK cell activity in VAD+RVA sows. Polymeric Ig receptor and retinoic acid receptor alpha (RARα) genes were downregulated in mesenteric lymph nodes and ileum of VAD+RVA sows. Interestingly, RVA-specific IFN-γ producing CD4+/CD8+ T cells were increased in VAD-Mock sows, coinciding with increased IL-22 suggesting inflammation in these sows. VA supplementation to VAD+RVA sows restored frequencies of NK cells and pDCs, and NK activity, but not tissue cDCs and blood Tregs. In conclusion, similar to our recent observations of decreased B cell responses in VAD sows that led to decreased passive immune protection of their piglets, VAD impaired innate and T cell responses in sows, while VA supplementation to VAD sows restored some, but not all responses. Our data reiterate the importance of maintaining adequate VA levels and RVA immunization in pregnant and lactating mothers to achieve optimal immune responses, efficient function of the gut-MG-immune cell-axis and to improve passive protection of their piglets.

Potential of resveratrol in the treatment of interstitial lung disease

Interstitial lung disease (ILD) is a heterogeneous group of diseases characterized by lung injury caused by lung fibroblast proliferation, interstitial inflammation, and fibrosis. Different cell signal transduction pathways are activated in response to various proinflammatory or fibrotic cytokines, such as IL-6, and these cytokines are increased in different ILDs. The overexpressed cytokines and growth factors in ILD can activate TGF-β/Smad2/3/4, NF-κB, and JAK/STAT signal transduction pathways, promote the activation of immune cells, increase the release of pro-inflammatory and pro-fibrotic factors, differentiate fibroblasts into myofibroblasts, and promote the occurrence and development of ILD. This finding suggests the importance of signal transduction pathways in patients with ILD. Recent evidence suggests that resveratrol (RSV) attenuates excessive inflammation and pulmonary fibrosis by inhibiting the TGF-β/Smad2/3/4, NF-κB, and JAK/STAT signal transduction pathways and overactivation of immune cells. In this review, advances in lung protection and the underlying mechanisms of RSV are summarized, and the potential efficacy of RSV as a promising treatment option for ILD is highlighted.

The innate and T-cell mediated immune response during acute and chronic gammaherpesvirus infection

Immediately after entry into host cells, viruses are sensed by the innate immune system, leading to the activation of innate antiviral effector mechanisms including the type I interferon (IFN) response and natural killer (NK) cells. This innate immune response helps to shape an effective adaptive T cell immune response mediated by cytotoxic T cells and CD4+ T helper cells and is also critical for the maintenance of protective T cells during chronic infection. The human gammaherpesvirus Epstein-Barr virus (EBV) is a highly prevalent lymphotropic oncovirus that establishes chronic lifelong infections in the vast majority of the adult population. Although acute EBV infection is controlled in an immunocompetent host, chronic EBV infection can lead to severe complications in immunosuppressed patients. Given that EBV is strictly host-specific, its murine homolog murid herpesvirus 4 or MHV68 is a widely used model to obtain in vivo insights into the interaction between gammaherpesviruses and their host. Despite the fact that EBV and MHV68 have developed strategies to evade the innate and adaptive immune response, innate antiviral effector mechanisms still play a vital role in not only controlling the acute infection but also shaping an efficient long-lasting adaptive immune response. Here, we summarize the current knowledge about the innate immune response mediated by the type I IFN system and NK cells, and the adaptive T cell-mediated response during EBV and MHV68 infection. Investigating the fine-tuned interplay between the innate immune and T cell response will provide valuable insights which may be exploited to design better therapeutic strategies to vanquish chronic herpesviral infection.

TCR-NK Cells: A Novel Source for Adoptive Immunotherapy of Cancer

Antigen-specific retargeting of cytotoxic lymphocytes against tumor-associated antigens has thus far remained largely dependent on chimeric antigen receptors (CARs) that can be constructed by the fusion of an extracellular targeting domain (classically a single-chain variable fragment from an antibody) fused with intracellular signaling domains to trigger activation of T or natural killer (NK) cells. A major limitation of CAR-based therapies is that this technology only allows for the targeting of antigens that would be located on the surface of target cells while non-surface antigens, which affect approximately three-fourths of all human genes, remain out of reach. The targeting of non-surface antigens is only possible using inherent T cell receptor (TCR) mechanisms. However, introducing a second TCR into T cells via genetic modification is problematic due to the heterodimeric nature of the TCR ligand-binding domain, which is composed of TCR α and β chains. It has been observed that the delivery of a second TCR α/β pair may lead to the mispairing of new TCR chains with the endogenously expressed ones and create mixed TCR dimers, and this has negatively affected the advancement of TCR-based T cell therapies. Recently, NK cells have been put forward as possible effectors for TCR gene therapy. Since NK cells do not endogenously express TCR chains, this seems to be an infallible approach to circumventing the problem of mispairing. Moreover, the similarity of intracellular signaling pathways and mechanisms of cytotoxicity between NK and T cells ensures that the triggering of antigen-specific responses by the TCR/CD3 complex can be used to induce antigen-specific cytotoxicity by TCR-modified NK (TCR-NK) cells. This review provides an overview of the initial studies of TCR-NK cells, identifies open questions in the field, and defines the place of this approach within the spectrum of adoptive immunotherapy techniques that rely on cytotoxic lymphocytes.

Role of natural killer and B cell interaction in inducing pathogen specific immune responses

The innate lymphoid cell (ILC) system comprising of the circulating and tissue-resident cells is known to clear infectious pathogens, establish immune homeostasis as well as confer antitumor immunity. Human natural killer cells (hNKs) and other ILCs carry out mopping of the infectious pathogens and perform cytolytic activity regulated by the non-adaptive immune system. The NK cells generate immunological memory and rapid recall response tightly regulated by the adaptive immunity. The interaction of NK and B cell, and its role to induce the pathogen specific immunity is not fully understood. Hence, present article sheds light on the interaction between NK and B cells and resulting immune responses in the infectious diseases. The immune responses elicited by the NK-B cell interaction is of particular importance for developing therapeutic vaccines against the infectious pathogens. Further, experimental evidences suggest the immune-response driven by NK cell population elicits the host-specific antibodies and memory B cells. Also, recently developed humanized immune system (HIS) mice and their importance in to understanding the NK-B cell interaction and resulting pathogen specific immunity has been discussed.

Natural killer cell exhaustion in SARS-CoV-2 infection

At the end of 2019, an outbreak of a severe respiratory disease occurred in Wuhan China, and an increase in cases of unknown pneumonia was alerted. In January 2020, a new coronavirus named SARS-CoV-2 was identified as the cause. The virus spreads primarily through the respiratory tract, and lymphopenia and cytokine storms have been observed in severely ill patients. This suggests the existence of an immune dysregulation as an accompanying event during a serious illness caused by this virus. Natural killer (NK) cells are innate immune responders, critical for virus shedding and immunomodulation. Despite its importance in viral infections, the contribution of NK cells in the fight against SARS-CoV-2 has yet to be deciphered. Different studies in patients with COVID-19 suggest a significant reduction in the number and function of NK cells due to their exhaustion. In this review, we summarize the current understanding of how NK cells respond to SARS-CoV-2 infection.

Targeting WEE1/AKT restores p53-dependent NK cell activation to induce immune checkpoint blockade responses in 'cold' melanoma

Immunotherapy has revolutionized cancer treatment. Unfortunately, most tumor types do not respond to immunotherapy due to a lack of immune infiltration or 'cold' tumor microenvironment (TME), a contributing factor in treatment failure. Activation of the p53 pathway can increase apoptosis of cancer cells, leading to enhanced antigen presentation, and can stimulate natural killer (NK) cells through expression of stress ligands. Therefore, modulation of the p53 pathway in cancer cells with wildtype TP53 has the potential to enhance tumor immunogenicity to NK cells, produce an inflammatory TME, and ultimately lead to tumor regression. In this study, we report simultaneous targeting of the AKT/WEE1 pathways is a novel and tolerable approach to synergistically induce p53 activation to inhibit tumor development. This approach reduced the growth of melanoma cells and induced plasma membrane surface localization of the ER-resident protein calreticulin, an indicator of immunogenic cell death (ICD). Increase in ICD led to enhanced expression of stress ligands recognized by the activating NK cell receptor NKG2D, promoting tumor lysis. WEE1/AKT inhibition resulted in recruitment and activation of immune cells, including NK cells, in the TME, triggering an inflammatory cascade that transformed the 'cold' TME of B16F10 melanoma into a 'hot' TME that responded to anti-PD-1, resulting in complete regression of established tumors. These results suggest that AKT/WEE1 pathway inhibition is a potential approach to broaden the utility of class-leading anti-PD-1 therapies by enhancing p53-mediated, NK cell-dependent tumor inflammation and supports the translation of this novel approach to further improve response rates for metastatic melanoma.

Filamin A Is Required for NK Cell Cytotoxicity at the Expense of Cytokine Production via Synaptic Filamentous Actin Modulation

Natural killer (NK) cells are innate cytotoxic lymphocytes that efficiently eliminate malignant and virus-infected cells without prior activation via the directed and focused release of lytic granule contents for target cell lysis. This cytolytic process is tightly regulated at discrete checkpoint stages to ensure the selective killing of diseased target cells and is highly dependent on the coordinated regulation of cytoskeletal components. The actin-binding protein filamin crosslinks cortical actin filaments into orthogonal networks and links actin filament webs to cellular membranes to modulate cell migration, adhesion, and signaling. However, its role in the regulation of NK cell functions remains poorly understood. Here, we show that filamin A (FLNa), a filamin isoform with preferential expression in leukocytes, is recruited to the NK cell lytic synapse and is required for NK cell cytotoxicity through the modulation of conjugate formation with target cells, synaptic filamentous actin (F-actin) accumulation, and cytotoxic degranulation, but not granule polarization. Interestingly, we also find that the loss of FLNa augments the target cell-induced expression of IFN-γ and TNF-α by NK cells, correlating with enhanced activation signals such as Ca²⁺ mobilization, ERK, and NF-κB, and a delayed down-modulation of the NKG2D receptor. Thus, our results identify FLNa as a new regulator of NK cell effector functions during their decision to kill target cells through a balanced regulation of NK cell cytotoxicity vs cytokine production. Moreover, this study implicates the cross-linking/bundling of F-actin mediated by FLNa as a necessary process coordinating optimal NK effector functions.

Resveratrol and Immune Cells: A Link to Improve Human Health

The use of polyphenols as adjuvants in lowering risk factors for various debilitating diseases has been investigated in recent years due to their possible antioxidant action. Polyphenols represent a fascinating and relatively new subject of research in nutraceuticals and nutrition, with interest rapidly expanding since they can help maintain health by controlling metabolism, weight, chronic diseases, and cell proliferation. Resveratrol is a phenolic compound found mostly in the pulp, peels, seeds, and stems of red grapes. It has a wide variety of biological actions that can be used to prevent the beginning of various diseases or manage their symptoms. Resveratrol can influence multiple inflammatory and non-inflammatory responses, protecting organs and tissues, thanks to its interaction with immune cells and its activity on SIRT1. This compound has anti-inflammatory, antioxidant, anti-apoptotic, neuroprotective, cardioprotective, anticancer, and antiviral properties, making it a potential adjunct to traditional pharmaceutical therapy in public health. This review aims to provide a comprehensive analysis of resveratrol in terms of active biological effects and mechanism of action in modifying the immune cellular response to promote human psychophysical health.

Natural Killer (NK) cells in immunotherapy and perspectives in antitumour approaches

Natural Killer (NK) cells comprise a group of specialized innate lymphoid cells endowed with multiple cytotoxicity mechanisms while also harnessed with the ability to enhance other immune cells with cytokine production. This exclusive advantage of them to recognize and eliminate virally infected cells and tumour cells has been unmasked for decades, and previous clinical trials are also successfully tested for both efficacy and safety. With the emerging strategies in CAR-T cell therapy, such technologies can also be capable of further enhancing the viability of NK cell immunotherapy through cytokine armouring, chimeric antigen receptor (CAR) transduction, checkpoint inhibition, and co-stimulatory signals. Other than the conventional approach of engineering CAR to target tumour antigens, they are also capable of acting as blockers to the inhibitory compartments on tumour cells within the harsh environment to reduce the negative effects. Despite all these aspects, the tumour microenvironment (TME) is another essential facet when discussing cancer therapy owing to its characteristic setting that contributes immensely to immune evasion and immune function inhibition. In this review, I introduce the foundational mechanism for NK cytotoxicity and its signalling routes, discuss the impacts of TME on immune cells and their antitumour effects, evaluate possible strategies that overcome the current challenges, and propose a few potentially adoptive measures for future research in general immunotherapy from a perspective of molecular biology.

Role of Toll-like receptors in natural killer cell function in acute lymphoblastic leukemia

Natural killer (NK) cells are specialized lymphocytes primarily involved in the response to infection and tumors. NK cells are characterized by the presence of specific surface molecules, as well as a wide repertoire of receptors that impart microenvironment-dependent effector functions. Among these receptors, Toll-like receptors (TLRs) can be activated to condition the NK response to either a cytotoxic or immunoregulatory phenotype. However, cellular function is frequently impaired during disorders such as cancer. In the last decade, it has become increasingly evident that the stimulation of NK cells is a requirement for their increased cytotoxic activity. TLR activation has been suggested as an alternative route for reestablishing the antitumor activity of NK cells. The present review summarizes the characteristics of NK cells, their receptors, the expression and function of NK cell TLRs, and their functional status in cancer, primarily acute lymphoblastic leukemia.

Tumor-derived NKG2D ligand sMIC reprograms NK cells to an inflammatory phenotype through CBM signalosome activation

Natural Killer (NK) cell dysfunction is associated with poorer clinical outcome in cancer patients. What regulates NK cell dysfunction in tumor microenvironment is not well understood. Here, we demonstrate that the human tumor-derived NKG2D ligand soluble MIC (sMIC) reprograms NK cell to secrete pro-tumorigenic cytokines with diminished cytotoxicity and polyfunctional potential. Antibody clearing sMIC restores NK cell to a normal cytotoxic effector functional state. We discovered that sMIC selectively activates the CBM-signalosome inflammatory pathways in NK cells. Conversely, tumor cell membrane-bound MIC (mMIC) stimulates NK cell cytotoxicity through activating PLC2γ2/SLP-76/Vav1 pathway. Ultimately, antibody targeting sMIC effectuated the in vivo anti-tumor effect of adoptively transferred NK cells. Our findings uncover an unrecognized mechanism that could instruct NK cell to a dysfunctional state in response to cues in the tumor microenvironment. Our findings provide a rationale for co-targeting sMIC to enhance the efficacy of the ongoing NK cell-based cancer immunotherapy.

Immunological considerations and challenges for regenerative cellular therapies

The central goal of regenerative medicine is to replace damaged or diseased tissue with cells that integrate and function optimally. The capacity of pluripotent stem cells to produce unlimited numbers of differentiated cells is of considerable therapeutic interest, with several clinical trials underway. However, the host immune response represents an important barrier to clinical translation. Here we describe the role of the host innate and adaptive immune responses as triggers of allogeneic graft rejection. We discuss how the immune response is determined by the cellular therapy. Additionally, we describe the range of available in vitro and in vivo experimental approaches to examine the immunogenicity of cellular therapies, and finally we review potential strategies to ameliorate immune rejection. In conclusion, we advocate establishment of platforms that bring together the multidisciplinary expertise and infrastructure necessary to comprehensively investigate the immunogenicity of cellular therapies to ensure their clinical safety and efficacy.

The Role of Natural Killer Cells in Autoimmune Diseases

Natural killer (NK) cells, the large granular lymphocytes differentiated from the common lymphoid progenitors, were discovered in early 1970's. They are members of innate immunity and were initially defined by their strong cytotoxicity against virus-infected cells and by their important effector functions in anti-tumoral immune responses. Nowadays, NK cells are classified among the recently discovered innate lymphoid cell subsets and have capacity to influence both innate and adaptive immune responses. Therefore, they can be considered as innate immune cells that stands between the innate and adaptive arms of immunity. NK cells don't express T or B cell receptors and are recognized by absence of CD3. There are two major subgroups of NK cells according to their differential expression of CD16 and CD56. While CD16+CD56dim subset is best-known by their cytotoxic functions, CD16-CD56bright NK cell subset produces a bunch of cytokines comparable to CD4+ T helper cell subsets. Another subset of NK cells with production of interleukin (IL)-10 was named as NK regulatory cells, which has suppressive properties and could take part in immune-regulatory responses. Activation of NK cells is determined by a delicate balance of cell-surface receptors that have either activating or inhibitory properties. On the other hand, a variety of cytokines including IL-2, IL-12, IL-15, and IL-18 influence NK cell activity. NK-derived cytokines and their cytotoxic functions through induction of apoptosis take part in regulation of the immune responses and could contribute to the pathogenesis of many immune mediated diseases including ankylosing spondylitis, Behçet's disease, multiple sclerosis, rheumatoid arthritis, psoriasis, systemic lupus erythematosus and type-1 diabetes. Dysregulation of NK cells in autoimmune disorders may occur through multiple mechanisms. Thanks to the rapid developments in biotechnology, progressive research in immunology enables better characterization of cells and their delicate roles in the complex network of immunity. As NK cells stand in between innate and adaptive arms of immunity and "bridge" them, their contribution in inflammation and immune regulation deserves intense investigations. Better understanding of NK-cell biology and their contribution in both exacerbation and regulation of inflammatory disorders is a requisite for possible utilization of these multi-faceted cells in novel therapeutic interventions.

Immunomodulatory effects of flavonoids: An experimental study on natural-killer-cell-mediated cytotoxicity against lung cancer and cytotoxic granule secretion profile

Background:

A new approach involving immune-cell-mediated cancer therapy has been adopted extensively for the sake of lung cancer treatments by utilizing natural killer (NK) cells. NK cell activity can be enhanced with certain agents, and among them are flavonoids. Thus, this study was conducted to investigate the immunomodulatory roles of apigenin, luteolin and quercetin on NK cell activity against lung cancer cells and on the secretions of perforin and granulysin profile.

Methods:

The NK-92 cells were grown in complete α-Minimum Essential Medium (MEM). NCI-H460 lung cancer cells were cultured in Roswell Park Memorial Institute 1640 media. NK cell activity against lung cancer cells were done using MTT(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assay. The secretions of perforin and granulysin profiles were then analysed using enzyme-linked immunosorbent assay.

Results:

Apigenin, luteolin and quercetin significantly increased the NK-cell-mediated cytotoxic activity against lung cancer cells at concentrations 12.5 µg/ml and 25µg/ml ( P < 0.001). The secretion levels of perforin and granulysin from NK cells were also significantly enhanced with apigenin and luteolin treatment but not with quercetin.

Conclusions:

All three flavonoid compounds possessed some significant immunomodulatory actions on NK cell cytotoxic activity and granule secretion profiles towards lung cancer therapy.

Harnessing the Formation of Natural Killer-Tumor Cell Immunological Synapses for Enhanced Therapeutic Effect in Solid Tumors

The formation of an immunological synapse (IS) on recognition of a cancer cell is the main mechanism underlying the natural killer (NK)-cell-mediated killing of tumor cells. Herein, an integrative strategy for cancer therapy against solid tumors is reported, in which alterations in the cleft of IS, following the secretion of acidic granular content, are utilized as a trigger for the delivery of chemotherapeutic drugs. NK cells are decorated with the IS-environment-responsive micellar system to ensure the release of the payload when they attack cancer cells. Using this strategy, the immunological cytotoxic killing effect of NK cells against solid tumors is reinforced with the site-specific diffusion of chemotherapeutic agents. Harnessing the intrinsic mechanism for the recognition of abnormal cells and the tumor-homing effect of NK cells limit the adverse systemic effects of chemotherapeutic drugs. This approach may provide a pragmatic platform for the universal and effective utilization of IS formation.

Natural killer cells: From surface receptors to the cure of high-risk leukemia (Ceppellini Lecture)

Natural killer (NK) cells are innate immune effector cells involved in the first line of defense against viral infections and malignancies. In the last three decades, the identification of HLA class I‐specific inhibitory killer immunoglobulin‐like receptors (KIR) and of the main activating receptors has strongly improved our understanding of the mechanisms regulating NK cell functions. The increased knowledge on how NK cells discriminate healthy cells from damaged cells has made it possible to transfer basic research notions to clinical applications. Of particular relevance is the strong NK‐mediated anti‐leukemia effect in haploidentical hematopoietic stem cell transplantation to cure high‐risk leukemia.

HSP70/IL-2 Treated NK Cells Effectively Cross the Blood Brain Barrier and Target Tumor Cells in a Rat Model of Induced Glioblastoma Multiforme (GBM)

Natural killer (NK) cell therapy is one of the most promising treatments for Glioblastoma Multiforme (GBM). However, this emerging technology is limited by the availability of sufficient numbers of fully functional cells. Here, we investigated the efficacy of NK cells that were expanded and treated by interleukin-2 (IL-2) and heat shock protein 70 (HSP70), both in vitro and in vivo. Proliferation and cytotoxicity assays were used to assess the functionality of NK cells in vitro, after which treated and naïve NK cells were administrated intracranially and systemically to compare the potential antitumor activities in our in vivo rat GBM models. In vitro assays provided strong evidence of NK cell efficacy against C6 tumor cells. In vivo tracking of NK cells showed efficient homing around and within the tumor site. Furthermore, significant amelioration of the tumor in rats treated with HSP70/Il-2-treated NK cells as compared to those subjected to nontreated NK cells, as confirmed by MRI, proved the efficacy of adoptive NK cell therapy. Moreover, results obtained with systemic injection confirmed migration of activated NK cells over the blood brain barrier and subsequent targeting of GBM tumor cells. Our data suggest that administration of HSP70/Il-2-treated NK cells may be a promising therapeutic approach to be considered in the treatment of GBM.

Measurement of Natural Killer Cell-Mediated Cytotoxicity and Migration in the Context of Hepatic Tumor Cells

Natural killer (NK) cells are a subset of the cytotoxic lymphocyte population of the innate immune system and participate as a first line of defense by clearing pathogen-infected, malignant, and stressed cells. The ability of NK cells to eradicate cancer cells makes them an important tool in the fight against cancer. Several new immune-based therapies are under investigation for cancer treatment which rely either on enhancing NK cell activity or increasing the sensitivity of cancer cells to NK cell-mediated eradication. However, to effectively develop these therapeutic approaches, cost-effective in vitro assays to monitor NK cell-mediated cytotoxicity and migration are also needed. Here, we present two in vitro protocols that can reliably and reproducibly monitor the effect of NK-cell cytotoxicity on cancer cells (or other target cells). These protocols are non-radioactivity-based, simple to set up, and can be scaled up for high-throughput screening. We also present a flow cytometry-based protocol to quantitatively monitor NK cell migration, which can also be scaled up for high-throughput screening. Collectively, these three protocols can be used to monitor key aspects of NK cell activity that are necessary for the cells' ability to eradicate dysfunctional target cells.

Potential of NK cells in multiple Myeloma therapy

Introduction: Despite rapid advances in myeloma treatment with the development of new drugs, curative therapies remain elusive. Relapsed/refractory disease related to progressive dysregulation of immune system and acquired genetic abnormalities continues to be a major obstacle in achieving cure. Immune-based therapy harnessing the host defense mechanism of natural killer (NK) cells is a promising avenue in the treatment of myeloma. Areas covered: Here, we discuss the biology and cytotoxic activity of NK cells and the potential role of these innate immune cells in defense against cancer and specifically multiple myeloma. We also discuss the role of NK cells in the anti-myeloma effects of autologous and allogeneic stem cell transplantation, various novel drugs, and treatment modalities such as chimeric antigen receptor therapy. Immune evasion, either directly or indirectly involving NK cell dysfunction, may be a key and under-recognized mechanism in myeloma progression. We reviewed extensive literature identified using the keywords immunotherapy, natural killer cells, and multiple myeloma. Expert opinion: Novel treatment approaches in myeloma utilizing the immunomodulatory and cytotoxic properties of NK cells to eradicate resistant and quiescent clones could pave the way for potentially curative interventions.

Influence of Resveratrol on the Immune Response

Resveratrol is the most well-known polyphenolic stilbenoid, present in grapes, mulberries, peanuts, rhubarb, and in several other plants. Resveratrol can play a beneficial role in the prevention and in the progression of chronic diseases related to inflammation such as diabetes, obesity, cardiovascular diseases, neurodegeneration, and cancers among other conditions. Moreover, resveratrol regulates immunity by interfering with immune cell regulation, proinflammatory cytokines’ synthesis, and gene expression. At the molecular level, it targets sirtuin, adenosine monophosphate kinase, nuclear factor-κB, inflammatory cytokines, anti-oxidant enzymes along with cellular processes such as gluconeogenesis, lipid metabolism, mitochondrial biogenesis, angiogenesis, and apoptosis. Resveratrol can suppress the toll-like receptor (TLR) and pro-inflammatory genes’ expression. The antioxidant activity of resveratrol and the ability to inhibit enzymes involved in the production of eicosanoids contribute to its anti-inflammation properties. The effects of this biologically active compound on the immune system are associated with widespread health benefits for different autoimmune and chronic inflammatory diseases. This review offers a systematic understanding of how resveratrol targets multiple inflammatory components and exerts immune-regulatory effects on immune cells.

Rational use of mesenchymal stem cells in the treatment of autism spectrum disorders

Autism and autism spectrum disorders (ASD) refer to a range of conditions characterized by impaired social and communication skills and repetitive behaviors caused by different combinations of genetic and environmental influences. Although the pathophysiology underlying ASD is still unclear, recent evidence suggests that immune dysregulation and neuroinflammation play a role in the etiology of ASD. In particular, there is direct evidence supporting a role for maternal immune activation during prenatal life in neurodevelopmental conditions. Currently, the available options of behavioral therapies and pharmacological and supportive nutritional treatments in ASD are only symptomatic. Given the disturbing rise in the incidence of ASD, and the fact that there is no effective pharmacological therapy for ASD, there is an urgent need for new therapeutic options. Mesenchymal stem cells (MSCs) possess immunomodulatory properties that make them relevant to several diseases associated with inflammation and tissue damage. The paracrine regenerative mechanisms of MSCs are also suggested to be therapeutically beneficial for ASD. Thus the underlying pathology in ASD, including immune system dysregulation and inflammation, represent potential targets for MSC therapy. This review will focus on immune dysfunction in the pathogenesis of ASD and will further discuss the therapeutic potential for MSCs in mediating ASD-related immunological disorders.

Glycation interferes with natural killer cell function

One hallmark of molecular aging is glycation, better known as formation of so-called advanced glycation end products (AGEs), where reactive carbonyls react with amino-groups of proteins. AGEs accumulate over time and are responsible for various age-dependent diseases and impairments. Two very potent dicarbonyls to generate AGEs are glyoxal (GO) and methylglyoxal (MGO). The plasma level of such dicarbonyls is higher in aging and age-related diseases. Natural killer (NK) cells are cells of the innate immune system and provide a major defense against tumor cells and virus infected cells. They are able to kill modified or infected cells and produce different cytokines to modulate the function of other immune cells. Here we investigated the effect of GO- and MGO-induced glycation on the function of NK cells. Using the human NK cell line NK-92, we could demonstrate that both GO and MGO lead to glycation of cellular proteins, but that MGO interferes much stronger with NK cell function (cytotoxicity) than GO. In addition, glycation of NK cell targets, such as K562 tumor cells, also interferes with their lysis by NK cells. From this data we conclude that glycation acts negatively on NK cells function and reduces their cytotoxic potential towards tumor cells.

Natural Killer Cells: Development, Maturation, and Clinical Utilization

Natural killer (NK) cells are the predominant innate lymphocyte subsets that mediate anti-tumor and anti-viral responses, and therefore possess promising clinical utilization. NK cells do not express polymorphic clonotypic receptors and utilize inhibitory receptors (killer immunoglobulin-like receptor and Ly49) to develop, mature, and recognize “self” from “non-self.” The essential roles of common gamma cytokines such as interleukin (IL)-2, IL-7, and IL-15 in the commitment and development of NK cells are well established. However, the critical functions of pro-inflammatory cytokines IL-12, IL-18, IL-27, and IL-35 in the transcriptional-priming of NK cells are only starting to emerge. Recent studies have highlighted multiple shared characteristics between NK cells the adaptive immune lymphocytes. NK cells utilize unique signaling pathways that offer exclusive ways to genetically manipulate to improve their effector functions. Here, we summarize the recent advances made in the understanding of how NK cells develop, mature, and their potential translational use in the clinic.

Decrease of perforin positive CD3+γδ-T cells in patients with obstructive sleep disordered breathing

Introduction

Sleep related breathing disorders (SRBD) cause sleep fragmentation, intermittent hypoxia or a combination of both leading to homeostasis perturbations, including in the immune system. We investigated whether SRBD patients with or without intermittent hypoxia show substantial differences in perforin and granzyme-B positive peripheral blood lymphocytes.

Methods

A total of 87 subjects were included and distributed as follows: 24 controls (C), 19 patients with respiratory effort related arousals due to increased upper airway resistance (UAR) without hypoxic events, 24 obese patients with obstructive sleep apnea (OSA) (oOSA), and 20 without obesity (noOSA). After polysomnographic recording, we analyzed in fasting blood samples routine hematologic and biochemical parameters and the percentage of lymphocytes containing the proteins perforin and granzyme-B (GrB). Kruskal-Wallis tests and a posteriori multiple comparisons were applied for statistical analysis of results.

Results

Perforin-positive γδ-cells revealed significant differences between groups (p = 0.017), especially between the Control group and the oOSA (p-value = 0.04); the remaining SRBD groups also showed differences from the control (C vs UAR: p = 0.08; C vs noOSA = 0.09), but they did not raise to statistical significance. There were no differences among the SRBD groups. Granzyme-B cells were decreased in SRBD patients, but the differences were not statistically significant. No additional statistical significant result was found in the other investigated lymphocyte subsets.

Conclusions

Obstructive sleep-disordered breathing is associated with a decrease in perforin-positive CD3⁺γδ-T cells. Although this finding was detected in lean patients without intermittent hypoxia, the reduction was only statistically significant in obese patients with severe OSA. Because CD3⁺γδ-T cells play an important role in the control of tumor cells, our findings are directly relevant for the study of the association of OSA and cancer.

Electronic supplementary material

The online version of this article (10.1007/s11325-017-1602-6) contains supplementary material, which is available to authorized users.

An actin cytoskeletal barrier inhibits lytic granule release from natural killer cells in patients with Chediak-Higashi syndrome

Background

Chediak-Higashi syndrome (CHS) is a rare disorder caused by biallelic mutations in the lysosomal trafficking regulator gene (LYST), resulting in formation of giant lysosomes or lysosome-related organelles in several cell types. The disease is characterized by immunodeficiency and a fatal hemophagocytic lymphohistiocytosis caused by impaired function of cytotoxic lymphocytes, including natural killer (NK) cells.

Objective

We sought to determine the underlying biochemical cause of the impaired cytotoxicity of NK cells in patients with CHS.

Methods

We generated a human cell model of CHS using Clustered Regularly Interspaced Short Palindromic Repeats (CRISPR) technology. We used a combination of classical techniques to evaluate lysosomal function and cell activity in the model system and super-resolution microscopy to visualize F-actin and lytic granules in normal and LYST-deficient NK cells.

Results

Loss of LYST function in a human NK cell line, NK92mi, resulted in inhibition of NK cell cytotoxicity and reproduced other aspects of the CHS cellular phenotype, including the presence of significantly enlarged lytic granules with defective exocytosis and impaired integrity of endolysosomal compartments. The large granules had an acidic pH and normal activity of lysosomal enzymes and were positive for the proteins essential for lytic granule exocytosis. Visualization of the actin meshwork openings at the immunologic synapse revealed that the cortical actin acts as a barrier for secretion of such large granules at the cell-cell contact site. Decreasing the cortical actin density at the immunologic synapse or decreasing the lytic granule size restored the ability of LYST-deficient NK cells to degranulate and kill target cells.

Conclusion

The cortical actin and granule size play significant roles in NK cell cytotoxic function. We present evidence that the periodicity of subsynaptic actin is an important factor limiting the release of large lytic granules from NK cells from patients with CHS and could be a novel target for pharmaceutical intervention.

Phenotypic and Functional Dysregulated Blood NK Cells in Colorectal Cancer Patients Can Be Activated by Cetuximab Plus IL-2 or IL-15

The clinical outcome of colorectal cancer (CRC) is associated with the immune response; thus, these tumors could be responsive to different immune therapy approaches. Natural killer (NK) cells are key antitumor primary effectors that can eliminate CRC cells without prior immunization. We previously determined that NK cells from the local tumor environment of CRC tumors display a profoundly altered phenotype compared with circulating NK cells from healthy donors (HD). In this study, we evaluated peripheral blood NK cells from untreated patients and their possible role in metastasis progression. We observed profound deregulation in receptor expression even in early stages of disease compared with HD. CRC-NK cells displayed underexpression of CD16, NKG2D, DNAM-1, CD161, NKp46, and NKp30 activating receptors, while inhibitory receptors CD85j and NKG2A were overexpressed. This inhibited phenotype affected cytotoxic functionality against CRC cells and interferon-γ production. We also determined that NKp30 and NKp46 are the key receptors involved in detriment of CRC-NK cells’ antitumor activity. Moreover, NKp46 expression correlated with relapse-free survival of CRC patients with a maximum follow-up of 71 months. CRC-NK cells also exhibited altered antibody-dependent cellular cytotoxicity function responding poorly to cetuximab. IL-2 and IL-15 in combination with cetuximab stimulated NK cell, improving cytotoxicity. These results show potential strategies to enhance CRC-NK cell activity.

Nutritional immunology: function of natural killer cells and their modulation by resveratrol for cancer prevention and treatment

Natural killer (NK) cells as part of the innate immune system represent the first line of defence against (virus-) infected and malignantly transformed cells. The emerging field of nutritional immunology focuses on compounds featuring immune-modulating activities in particular on NK cells, which e.g. can be exploited for cancer prevention and treatment. The plant-based nutrition resveratrol is a ternary hydroxylated stilbene, which is present in many foods and beverages, respectively. In humans it comprises a large variety of distinct biological activities. Interestingly, resveratrol strongly modulates the immune response including the activity of NK cells. This review will give an overview on NK cell functions and summarize the resveratrol-mediated modulation thereof.

Chediak-Higashi syndrome: Lysosomal trafficking regulator domains regulate exocytosis of lytic granules but not cytokine secretion by natural killer cells

BACKGROUND

Mutations in lysosomal trafficking regulator (LYST) cause Chediak-Higashi syndrome (CHS), a rare immunodeficiency with impaired cytotoxic lymphocyte function, mainly that of natural killer (NK) cells. Our understanding of NK cell function deficiency in patients with CHS and how LYST regulates lytic granule exocytosis is very limited.

OBJECTIVE

We sought to delineate cellular defects associated with LYST mutations responsible for the impaired NK cell function seen in patients with CHS.

METHODS

We analyzed NK cells from patients with CHS with missense mutations in the LYST ARM/HEAT (armadillo/huntingtin, elongation factor 3, protein phosphatase 2A, and the yeast kinase TOR1) or BEACH (beige and Chediak-Higashi) domains.

RESULTS

NK cells from patients with CHS displayed severely reduced cytotoxicity. Mutations in the ARM/HEAT domain led to a reduced number of perforin-containing granules, which were significantly increased in size but able to polarize to the immunologic synapse; however, they were unable to properly fuse with the plasma membrane. Mutations in the BEACH domain resulted in formation of normal or slightly enlarged granules that had markedly impaired polarization to the IS but could be exocytosed on reaching the immunologic synapse. Perforin-containing granules in NK cells from patients with CHS did not acquire certain lysosomal markers (lysosome-associated membrane protein 1/2) but were positive for markers of transport vesicles (cation-independent mannose 6-phosphate receptor), late endosomes (Ras-associated binding protein 27a), and, to some extent, early endosomes (early endosome antigen 1), indicating a lack of integrity in the endolysosomal compartments. NK cells from patients with CHS had normal cytokine compartments and cytokine secretion.

CONCLUSION

LYST is involved in regulation of multiple aspects of NK cell lytic activity, ranging from governance of lytic granule size to control of their polarization and exocytosis, as well as regulation of endolysosomal compartment identity. LYST functions in the regulated exocytosis but not in the constitutive secretion pathway.

Tricking the balance: NK cells in anti-cancer immunity

Natural Killer (NK) cells are classically considered innate immune effector cells involved in the first line of defense against infected and malignant cells. More recently, NK cells have emerged to acquire properties of adaptive immunity in response to certain viral infections such as expansion of specific NK cell subsets and long-lasting virus-specific responses to secondary challenges. NK cells distinguish healthy cells from abnormal cells by measuring the net input of activating and inhibitory signals perceived from target cells through NK cell surface receptors. Acquisition of activating ligands in combination with reduced expression of MHC class I molecules on virus-infected and cancer cells activates NK cell cytotoxicity and release of immunostimulatory cytokines like IFN-γ. In the cancer microenvironment however, NK cells become functionally impaired by inhibitory factors produced by immunosuppressive immune cells and cancer cells. Here we review recent progress on the role of NK cells in cancer immunity. We describe regulatory factors of the tumor microenvironment on NK cell function which determine cancer cell destruction or escape from immune recognition. Finally, recent strategies that focus on exploiting NK cell anti-cancer responses for immunotherapeutic approaches are outlined.

Understanding of molecular mechanisms in natural killer cell therapy

Cancer cells and the immune system are closely related and thus influence each other. Although immune cells can suppress cancer cell growth, cancer cells can evade immune cell attack via immune escape mechanisms. Natural killer (NK) cells kill cancer cells by secreting perforins and granzymes. Upon contact with cancer cells, NK cells form immune synapses to deliver the lethal hit. Mature NK cells are differentiated from hematopoietic stem cells in the bone marrow. They move to lymph nodes, where they are activated through interactions with dendritic cells. Interleukin-15 (IL-15) is a key molecule that activates mature NK cells. The adoptive transfer of NK cells to treat incurable cancer is an attractive approach. A certain number of activated NK cells are required for adoptive NK cell therapy. To prepare these NK cells, mature NK cells can be amplified to obtain sufficient numbers of NK cells. Alternatively, NK cells can be differentiated and amplified from hematopoietic stem cells. In addition, the selection of donors is important to achieve maximal efficacy. In this review, we discuss the overall procedures and strategies of NK cell therapy against cancer.

Cysteine cathepsins as regulators of the cytotoxicity of NK and T cells

Cysteine cathepsins are lysosomal peptidases involved at different levels in the processes of the innate and adaptive immune responses. Some, such as cathepsins B, L, and H are expressed constitutively in most immune cells. In cells of innate immunity they play a role in cell adhesion and phagocytosis. Other cysteine cathepsins are expressed more specifically. Cathepsin X promotes dendritic cell maturation, adhesion of macrophages, and migration of T cells. Cathepsin S is implicated in major histocompatibility complex class II antigen presentation, whereas cathepsin C, expressed in cytotoxic T lymphocytes and natural killer (NK) cells, is involved in processing pro-granzymes into proteolytically active forms, which trigger cell death in their target cells. The activity of cysteine cathepsins is controlled by endogenous cystatins, cysteine protease inhibitors. Of these, cystatin F is the only cystatin that is localized in endosomal/lysosomal vesicles. After proteolytic removal of its N-terminal peptide, cystatin F becomes a potent inhibitor of cathepsin C with the potential to regulate pro-granzyme processing and cell cytotoxicity. This review is focused on the role of cysteine cathepsins and their inhibitors in the molecular mechanisms leading to the cytotoxic activity of T lymphocytes and NK cells in order to address new possibilities for regulation of their function in pathological processes.

Concentration-dependent biphasic effects of resveratrol on human natural killer cells in vitro

Resveratrol (RES) is a polyphenol phytoalexin from plants, which has been reported to possess a variety of biological effects. The properties of RES on human natural killer (NK) cells were assessed in this study. Results showed that RES has concentration-dependent biphasic effects on NK cells. In high concentration (50 μM), RES can inhibit viability and promoted apoptosis of NK cells and human lymphoblastoid T (Jurkat) cells, which may affect the caspase signaling pathway. The Jurkat cells were more sensitive than NK cells on the RES caused cell death. However, when the concentration range reduced from 3.13 to 1.56 μM, RES showed the positive effects on NK cells by increasing the NK cells cytotoxicity via up-regulating the expression of NKG2D and IFN-γ (in mRNA and protein levels). These results indicated that one needs to pay more attention to the dosage and biphasic effects when RES was applied as antitumor drugs or health products.

The central role of the cytoskeleton in mechanisms and functions of the NK cell immune synapse

Natural killer (NK) cells discriminate between healthy and unhealthy target cells through a balance of activating and inhibitory signals at direct intercellular contacts called immune synapses. Rearrangements in the cellular cytoskeleton have long been known to be critical in assembly of immune synapses. Here, through bringing together the vast literature on this subject, the number of different ways in which the cytoskeleton is important becomes evident. The dynamics of filamentous actin are critical in (i) creating the nanometer-scale organization of NK cell receptors, (ii) establishing cellular polarity, (iii) coordinating immune receptor and integrin-mediated signaling, and (iv) directing secretion of lytic granules and cytokines. The microtubule network also is important in the delivery of lytic granules and vesicles containing cytokines to the immune synapse. Together, these data establish that the cytoskeleton acts as a central regulator of this complex and dynamic process - and an enormous amount of NK cell biology is controlled through the cytoskeleton.

Major histocompatibility complex I in brain development and schizophrenia

Although the etiology of schizophrenia (SZ) remains unknown, it is increasingly clear that immune dysregulation plays a central role. Genome-wide association studies reproducibly indicate an association of SZ with immune genes within the major histocompatibility complex (MHC). Moreover, environmental factors that increase risk for SZ, such as maternal infection, alter peripheral immune responses as well as the expression of immune molecules in the brain. MHC class I (MHCI) molecules might mediate both genetic and environmental contributions to SZ through direct effects on brain development in addition to mediating immunity. MHCI molecules are expressed on neurons in the central nervous system throughout development and into adulthood, where they regulate many aspects of brain development, including neurite outgrowth, synapse formation and function, long-term and homeostatic plasticity, and activity-dependent synaptic refinement. This review summarizes our current understanding of MHCI expression and function in the developing brain as well as its involvement in maternal immune activation, from the perspective of how these roles for MHCI molecules might contribute to the pathogenesis of SZ.

Effects of KIR ligand incompatibility on clinical outcomes of umbilical cord blood transplantation without ATG for acute leukemia in complete remission

To clarify the effect of killer cell immunoglobulin-like receptor (KIR) ligand incompatibility on outcomes of acute myeloid leukemia (AML) and acute lymphoblastic leukemia (ALL) patients in complete remission after single cord blood transplantation (CBT), we assessed the outcomes of CBT registered in the Japan Society for Hematopoietic Cell Transplantation (JSHCT) database. A total of 643 acute leukemia (357 AML and 286 ALL) patient and donor pairs were categorized according to their KIR ligand incompatibility by determining whether or not they expressed HLA-C, Bw4 or A3/A11 by DNA typing. A total of 128 patient–donor pairs were KIR ligand-incompatible in the graft-versus-host (GVH) direction and 139 patient–donor pairs were incompatible in the host-versus-graft (HVG) direction. Univariate and multivariate analyses showed no significant differences between the KIR ligand-incompatible and compatible groups in the GVH direction for both AML and ALL patients of overall survival, disease-free survival, relapse incidence, non-relapse mortality and acute GVH disease. However, KIR incompatibility in the HVG direction ameliorated engraftment in ALL patients (hazard ratio 0.66, 95% confidence interval 0.47–0.91, P=0.013). Therefore, there were no effects of KIR ligand incompatibility in the GVH direction on single CBT outcomes for acute leukemia patients without anti-thymocyte globulin use. However, it is necessary to pay attention to KIR incompatibility in the HVG direction for engraftment.

Macrophage and NK-mediated killing of precursor-B acute lymphoblastic leukemia cells targeted with a-fucosylated anti-CD19 humanized antibodies

This work reports the tumoricidal effects of a novel investigational humanized anti-CD19 monoclonal antibody (Medi-551). An a-fucosylated antibody with increased affinity for human FcγRIIIA, Medi-551 is shown to mediate both antibody-dependent cellular cytotoxicity (ADCC) and antibody-dependent cellular phagocytosis (ADCP). Medi-551/CD19 complexes internalize slowly (>5 h) and thus remain accessible to effector cells for prolonged periods. We evaluated in vitro ADCC and ADCP activities of primary human natural killer (NK) cells and macrophages against precursor-B (pre-B) acute lymphoblastic leukemia (ALL) cell lines and pediatric patient blasts. Fluorescent imaging studies document immunological synapses formed between anti-CD19-bound target leukemia cells and effector cells and capture the kinetics of both NK-mediated killing and macrophage phagocytosis. Genetic polymorphisms in FcγRIIIA-158F/V modulate in vitro activities of effector cells, with FcγRIIIA-158V homozygotes or heterozygotes showing the strongest activity. Medi-551 treatment of severe combined immunodeficiency (SCID) mice engrafted with human pre-B cells led to prolonged animal survival and markedly reduced disease burden in blood, liver and bone marrow. These data show that anti-CD19 antibodies effectively recruit immune cells to pre-B ALL cells and support a move forward to early phase trials in this disease.

Classification of human natural killer cells based on migration behavior and cytotoxic response

Despite intense scrutiny of the molecular interactions between natural killer (NK) and target cells, few studies have been devoted to dissection of the basic functional heterogeneity in individual NK cell behavior. Using a microchip-based, time-lapse imaging approach allowing the entire contact history of each NK cell to be recorded, in the present study, we were able to quantify how the cytotoxic response varied between individual NK cells. Strikingly, approximately half of the NK cells did not kill any target cells at all, whereas a minority of NK cells was responsible for a majority of the target cell deaths. These dynamic cytotoxicity data allowed categorization of NK cells into 5 distinct classes. A small but particularly active subclass of NK cells killed several target cells in a consecutive fashion. These "serial killers" delivered their lytic hits faster and induced faster target cell death than other NK cells. Fast, necrotic target cell death was correlated with the amount of perforin released by the NK cells. Our data are consistent with a model in which a small fraction of NK cells drives tumor elimination and inflammation.

Human NK cell lytic granules and regulation of their exocytosis

Natural killer (NK) cells form a subset of lymphocytes that play a key role in immuno-surveillance and host defense against cancer and viral infections. They recognize stressed cells through a variety of germline-encoded activating cell surface receptors and utilize their cytotoxic ability to eliminate abnormal cells. Killing of target cells is a complex, multi-stage process that concludes in the directed secretion of lytic granules, containing perforin and granzymes, at the immunological synapse. Upon delivery to a target cell, perforin mediates generation of pores in membranes of target cells, allowing granzymes to access target cell cytoplasm and induce apoptosis. Therefore, lytic granules of NK cells are indispensable for normal NK cell cytolytic function. Indeed, defects in lytic granule secretion lead or are related to serious and often fatal diseases, such as familial hemophagocytic lymphohistiocytosis (FHL) type 2–5 or Griscelli syndrome type 2. A number of reports highlight the role of several proteins involved in lytic granule release and NK cell-mediated killing of tumor cells. This review focuses on lytic granules of human NK cells and the advancements in understanding the mechanisms controlling their exocytosis.

The major histocompatibility complex and autism spectrum disorder

Autism spectrum disorder (ASD) is a complex disorder that appears to be caused by interactions between genetic changes and environmental insults during early development. A wide range of factors have been linked to the onset of ASD, but recently both genetic associations and environmental factors point to a central role for immune-related genes and immune responses to environmental stimuli. Specifically, many of the proteins encoded by the major histocompatibility complex (MHC) play a vital role in the formation, refinement, maintenance, and plasticity of the brain. Manipulations of levels of MHC molecules have illustrated how disrupted MHC signaling can significantly alter brain connectivity and function. Thus, an emerging hypothesis in our field is that disruptions in MHC expression in the developing brain caused by mutations and/or immune dysregulation may contribute to the altered brain connectivity and function characteristic of ASD. This review provides an overview of the structure and function of the three classes of MHC molecules in the immune system, healthy brain, and their possible involvement in ASD.

Super-resolution imaging of remodeled synaptic actin reveals different synergies between NK cell receptors and integrins

Natural killer (NK) cells secrete lytic granules to directly kill virus-infected or transformed cells and secrete cytokines to communicate with other cells. Three-dimensional super-resolved images of F-actin, lytic granules, and IFN-γ in primary human NK cells stimulated through different activating receptors reveal that both IFN-γ and lytic granules accumulated in domains where the periodicity of the cortical actin mesh at the synapse opened up to be penetrable. Ligation of some activating receptors alone (eg, CD16 or NKG2D) was sufficient to increase the periodicity of the actin mesh, but surprisingly, ligation of others (eg, NKp46 or CD2) was not sufficient to induce cortical actin remodeling unless LFA-1 was coligated. Importantly, influenza virus particles that can be recognized by NK cells similarly did not open the actin mesh but could if LFA-1 was coligated. This leads us to propose that immune cells using germline-encoded receptors to directly recognize foreign proteins can use integrin recognition to differentiate between free pathogens and pathogen-infected cells that will both be present in blood. This distinction would not be required for NK cell receptors, such as NKG2D, which recognize host cell-encoded proteins that can only be found on diseased cells and not pathogens.

Major histocompatibility complex class I proteins in brain development and plasticity

Proper development of the central nervous system (CNS) requires the establishment of appropriate connections between neurons. Recent work suggests that this process is controlled by a balance between synaptogenic molecules and proteins that negatively regulate synapse formation and plasticity. Surprisingly, many of these newly identified synapse-limiting molecules are classic 'immune' proteins. In particular, major histocompatibility complex class I (MHCI) molecules regulate neurite outgrowth, the establishment and function of cortical connections, activity-dependent refinement in the visual system, and long-term and homeostatic plasticity. This review summarizes our current understanding of MHCI expression and function in the CNS, as well as the potential mechanisms used by MHCI to regulate brain development and plasticity.

Protein Kinase C-θ (PKC-θ) in Natural Killer Cell Function and Anti-Tumor Immunity

The protein kinase C-θ (PKCθ), which is essential for T cell function and survival, is also required for efficient anti-tumor immune surveillance. Natural killer (NK) cells, which express PKCθ, play a prominent role in this process, mainly by elimination of tumor cells with reduced or absent major histocompatibility complex class-I (MHC-I) expression. This justifies the increased interest of the use of activated NK cells in anti-tumor immunotherapy in the clinic. The in vivo development of MHC-I-deficient tumors is much favored in PKCθ^−/− mice compared with wild-type mice. Recent data offer some clues on the mechanism that could explain the important role of PKCθ in NK cell-mediated anti-tumor immune surveillance: some studies show that PKCθ is implicated in signal transduction and anti-tumoral activity of NK cells elicited by interleukin (IL)-12 or IL-15, while others show that it is implicated in NK cell functional activation mediated by certain killer-activating receptors. Alternatively, the possibility that PKCθ is involved in NK cell degranulation is discussed, since recent data indicate that it is implicated in microtubule-organizing center polarization to the immune synapse in CD4⁺ T cells. The implication of PKC isoforms in degranulation has been more extensively studied in cytotoxic T lymphocyte, and these studies will be also summarized.

Important role for NKp30 in synapse formation and activation of NK cells

Natural killer (NK) cells play an important role in host defense against viral infections and tumor cells. NK cells require contact with target cells and must subsequently form an NK cell immunological synapse (NKIS). The NKIS represents the interface formed between NK cells and their target cells via receptor recognition and adhesion molecule binding, and it is essential for NK cell cytotoxicity, which is mediated through degranulation and release of cytolytic enzymes. In this study, NKp30-mediated signaling and the role of NKp30 in the formation of the NKIS were investigated. The results from confocal microscopy studies showed that the activating receptor, NKp30, and the adhesion molecule, LFA-1 (CD11a), accumulated at the interface between NK92 cells, which are a human NK cell line, and HeLa cells, which are a human tumor cell line (NK92-HeLa). Blockade of NKp30 inhibited NK cell degranulation, cytotoxicity and cytokine secretion but did not affect the conjugation between NK and target cells. Additionally, ligation with HeLa cells activated the Erk1/2 signaling pathway in NK92 cells, and blockade of NKp30 decreased the phosphorylation of Erk1/2. Therefore, NKp30 is a triggering receptor downstream of adhesion and plays an important role in NK cell activation, degranulation and cytotoxicity.