Lymphocyte cytotoxicity reactions to leukemia-associated antigens in identical twins

Recent Progress of Gold-Based Nanostructures towards Future Emblem of Photo-Triggered Cancer Theranostics: A Special Focus on Combinatorial Phototherapies

Cancer is one of the most dangerous health problems in the millennium and it is the third foremost human cause of death in the universe. Traditional cancer treatments face several disadvantages and cannot often afford adequate outcomes. It has been exhibited that the outcome of several therapies can be improved when associated with nanostructures. In addition, a modern tendency is being developed in cancer therapy to convert single-modal into multi-modal therapies with the help of existing various nanostructures. Among them, gold is the most successful nanostructure for biomedical applications due to its flexibility in preparation, stabilization, surface modifications, less cytotoxicity, and ease of bio-detection. In the past few decades, gold-based nanomaterials rule cancer treatment applications, currently, gold nanostructures were the leading nanomaterials for synergetic cancer therapies. In this review article, the synthesis, stabilization, and optical properties of gold nanostructures have been discussed. Then, the surface modifications and targeting mechanisms of gold nanomaterials will be described. Recent signs of progress in the application of gold nanomaterials for synergetic cancer therapies such as photodynamic and photo-thermal therapies in combination with other common interventions such as radiotherapy, chemotherapy, and will be reviewed. Also, a summary of the pharmacokinetics of gold nanostructures will be delivered. Finally, the challenges and outlooks of the gold nanostructures in the clinics for applications in cancer treatments are debated.

Tissue Immunity in the Bladder

The bladder is a major component of the urinary tract, an organ system that expels metabolic waste and excess water, which necessitates proximity to the external environment and its pathogens. It also houses a commensal microbiome. Therefore, its tissue immunity must resist pathogen invasion while maintaining tolerance to commensals. Bacterial infection of the bladder is common, with half of women globally experiencing one or more episodes of cystitis in their lifetime. Despite this, our knowledge of bladder immunity, particularly in humans, is incomplete. Here we consider the current view of tissue immunity in the bladder, with a focus on defense against infection. The urothelium has robust immune functionality, and its defensive capabilities are supported by resident immune cells, including macrophages, dendritic cells, natural killer cells, and γδ T cells. We discuss each in turn and consider why adaptive immune responses are often ineffective in preventing recurrent infection, as well as areas of priority for future research.

The War Is on: The Immune System against Glioblastoma—How Can NK Cells Drive This Battle?

Natural killer (NK) cells are innate lymphocytes that play an important role in immunosurveillance, acting alongside other immune cells in the response against various types of malignant tumors and the prevention of metastasis. Since their discovery in the 1970s, they have been thoroughly studied for their capacity to kill neoplastic cells without the need for previous sensitization, executing rapid and robust cytotoxic activity, but also helper functions. In agreement with this, NK cells are being exploited in many ways to treat cancer. The broad arsenal of NK-based therapies includes adoptive transfer of in vitro expanded and activated cells, genetically engineered cells to contain chimeric antigen receptors (CAR-NKs), in vivo stimulation of NK cells (by cytokine therapy, checkpoint blockade therapies, etc.), and tumor-specific antibody-guided NK cells, among others. In this article, we review pivotal aspects of NK cells’ biology and their contribution to immune responses against tumors, as well as providing a wide perspective on the many antineoplastic strategies using NK cells. Finally, we also discuss those approaches that have the potential to control glioblastoma—a disease that, currently, causes inevitable death, usually in a short time after diagnosis.

Determining Activation Status of Natural Killer Cells Following Stimulation via Cytokines and Surface Receptors

Stimulation of Natural Killer (NK) cells with cytokines, target cell interaction, or antibody mediated activation of receptors on the NK cell surface enables the dissection of specific signaling intermediates in different activation pathways. NK cell activation status is commonly measured by production of interferon gamma (IFNγ) and expression of the degranulation marker LAMP-1 (CD107a). Cytotoxic potency can also be assessed by the production of perforin, granzymes, and tumor necrosis factor alpha (TNFα). NK cell receptor mediated activation by antibodies requires crosslinking of the receptor-specific antibodies; thus, in vitro activation assays are performed by binding antibodies to cell culture plates. All parameters can be measured by flow cytometry.

Making a Killer: Selecting the Optimal Natural Killer Cells for Improved Immunotherapies

Over the past 20 years natural killer (NK) cell-based immunotherapies have emerged as a safe and effective treatment option for patients with relapsed or refractory leukemia. Unlike T cell-based therapies, NK cells harbor an innate capacity to eliminate malignant cells without prior sensitization and can be adoptively transferred between individuals without the need for extensive HLA matching. A wide variety of therapeutic NK cell sources are currently being investigated clinically, including allogeneic donor-derived NK cells, stem cell-derived NK cells and NK cell lines. However, it is becoming increasingly clear that not all NK cells are endowed with the same antitumor potential. Despite advances in techniques to enhance NK cell cytotoxicity and persistence, the initial identification and utilization of highly functional NK cells remains essential to ensure the future success of adoptive NK cell therapies. Indeed, little consideration has been given to the identification and selection of donors who harbor NK cells with potent antitumor activity. In this regard, there is currently no standard donor selection criteria for adoptive NK cell therapy. Here, we review our current understanding of the factors which govern NK cell functional fate, and propose a paradigm shift away from traditional phenotypic characterization of NK cell subsets towards a functional profile based on molecular and metabolic characteristics. We also discuss previous selection models for NK cell-based immunotherapies and highlight important considerations for the selection of optimal NK cell donors for future adoptive cell therapies.

Recalcitrant Herpes Zoster Ophthalmicus in a Patient Discovered to Have Underlying Functional Natural Killer Cell Deficiency

PURPOSE

To report the management of a patient with chronic herpes zoster ophthalmicus with previously undiagnosed natural killer cell deficiency.

METHODS

A 50-year-old female presented with herpes zoster ophthalmicus that despite appropriate treatment progressed to uveitis and expansion of the lesions. Multiple attempts to wean the patient off therapeutic anti-viral medications continued to result in reoccurrence of the disease. Discovery of underlying natural killer cell deficiency prompted indefinite treatment with therapeutic anti-viral medication.

RESULTS

After multiple flares of herpes zoster ophthalmicus over 3 years, seven prior to the discovery of the immunodeficiency, she developed unilateral corneal scarring on the affected side. At this time, her visual acuity was measured to be uncorrected at 20/150 with improvement to 20/25-1 with refraction.

CONCLUSIONS

This case highlights the need for further immunological investigation and unconventional medical management with recurrent viral infections to prevent visual morbidity.

Role of immune cells in the removal of deleterious senescent cells

Cellular senescence is an essentially irreversible arrest of cell proliferation coupled to a complex senescence-associated secretory phenotype (SASP). The senescence arrest prevents the development of cancer, and the SASP can promote tissue repair. Recent data suggest that the prolonged presence of senescent cells, and especially the SASP, could be deleterious, and their beneficial effects early in life can become maladaptive such that they drive aging phenotypes and pathologies late in life. It is therefore important to develop strategies to eliminate senescent cells. There are currently under development or approved several immune cell-based therapies for cancer, which could be redesigned to target senescent cells. This review focuses on this possible use of immune cells and discusses how current cell-based therapies could be used for senescent cell removal.

Natural Killer Cells: Tumor Surveillance and Signaling

Natural killer (NK) cells play a pivotal role in cancer immunotherapy due to their innate ability to detect and kill tumorigenic cells. The decision to kill is determined by the expression of a myriad of activating and inhibitory receptors on the NK cell surface. Cell-to-cell engagement results in either self-tolerance or a cytotoxic response, governed by a fine balance between the signaling cascades downstream of the activating and inhibitory receptors. To evade a cytotoxic immune response, tumor cells can modulate the surface expression of receptor ligands and additionally, alter the conditions in the tumor microenvironment (TME), tilting the scales toward a suppressed cytotoxic NK response. To fully harness the killing power of NK cells for clinical benefit, we need to understand what defines the threshold for activation and what is required to break tolerance. This review will focus on the intracellular signaling pathways activated or suppressed in NK cells and the roles signaling intermediates play during an NK cytotoxic response.

On the Way to Become a Natural Killer Cell

Natural Killer (NK) cells are innate lymphocytes playing pivotal roles in host defense and immune-surveillance. The homeostatic modulation of germ-line encoded/non-rearranged activating and inhibitory NK cell receptors (NKRs) determines the capability of these innate lymphocytes to either spare "self" cells or to kill viral-infected, tumor-transformed and heterologous cell targets. However, despite being discovered more than 40 years ago, several aspects of NK cell biology remain unknown or are still being debated. In particular, our knowledge of human NK cell ontogenesis and differentiation is still in its infancy as the majority of our experimental evidence on this topic mainly comes from findings obtained in vitro or with animal models in vivo. Although both the generation and the maintenance of human NK cells are sustained by hematopoietic stem cells (HSCs), the precise site(s) of NK cell development are still poorly defined. Indeed, HSCs and hematopoietic precursors are localized in different anatomical compartments that also change their ontogenic commitments before and after birth as well as in aging. Currently, the main site of NK cell generation and maturation in adulthood is considered the bone marrow, where their interactions with stromal cells, cytokines, growth factors, and other soluble molecules support and drive maturation. Different sequential stages of NK cell development have been identified on the basis of the differential expression of specific markers and NKRs as well as on the acquisition of specific effector-functions. All these phenotypic and functional features are key in inducing and regulating homing, activation and tissue-residency of NK cells in different human anatomic sites, where different homeostatic mechanisms ensure a perfect balance between immune tolerance and immune-surveillance. The present review summarizes our current knowledge on human NK cell ontogenesis and on the related pathways orchestrating a proper maturation, functions, and distributions.

Development of c‑MET‑specific chimeric antigen receptor‑engineered natural killer cells with cytotoxic effects on human liver cancer HepG2 cells

In recent years, cellular immunotherapy has served an important role in the combined treatment of hepatocellular carcinoma. The possibility of specific cell therapies for the treatment of solid tumours has been further explored following the success of chimeric antigen receptor (CAR)-T cell therapy in the treatment of haematological tumours. The present study aimed to evaluate the specificity and efficiency of c-MET-targeted CAR-NK cell immunotherapy on human liver cancer in vitro. A CAR structure that targeted and recognised a c-MET antigen was constructed. c-MET-CAR was transferred into primary NK cells using lentiviral infection. c-MET-positive HepG2 cells were used as an in vitro study model. The cytotoxicity assay results revealed that c-MET-CAR-NK cells exhibited more specific cytotoxicity for HepG2 cells with high c-MET expression compared with the lung cancer cell line H1299, which has low levels of c-MET expression. The results of the present study demonstrated that c-MET may be a specific and effective target for human liver cancer cell CAR-NK immunotherapy. Based on these results, CAR-NK cell-based immunotherapy may provide a potential biotherapeutic approach for liver cancer treatment in the future.

Inflammation fires up cancer metastasis

Metastatic disease is the major challenge of cancer that accounts for over 90% of total cancer lethality. Mounting clinical and preclinical data now indicate that inflammation, a potent immune and repair response, is indispensable for metastasis. In this review we describe our current understanding of how major inflammatory cells contribute to metastatic cascade with a focus on the primary tumour. We also discuss exciting new directions for future research and novel therapeutic approaches to tackle metastatic disease through targeting inflammation.

Control of the HIV-1 DNA Reservoir Is Associated In Vivo and In Vitro with NKp46/NKp30 (CD335 CD337) Inducibility and Interferon Gamma Production by Transcriptionally Unique NK Cells

The size of lentiviral DNA reservoirs reflects the effectiveness of immune responses against lentiviruses. So far, abundant information has been gathered on the control of HIV-1 replication. Understanding the innate mechanisms contributing to containment of the HIV DNA reservoir, however, are only partly clarified and are relevant to guiding interventions for reservoir containment or eradication. We studied the contribution of natural killer (NK) cell functional features in HIV patients controlling replication either spontaneously (HIV controllers [HIC]) or after progression and antiretroviral treatment (progressor patients [PP]). An inverse correlation between HIV DNA copy numbers (either total or integrated) in circulating CD4⁺ cells and NK cell function was observed. Induced interferon gamma (IFN-γ) production and NKp46/NKp30 activating receptor-induced expression correlated inversely with reservoir size. The correlation was present not only for a homogeneous cohort of HIC patients but also when PP were included in the analysis. Adaptive (NKG2C⁺ CD57⁺) NK cell features were not associated with reservoir size. However, a distinct set of 370 differentially expressed transcripts was found to underlie functional differences in NK cells controlling HIV DNA reservoir size. In proof-of-principle in vitro experiments of CD4⁺ cell infection with HIV-1, purified NK cells with the above-mentioned functional/transcriptional features displayed 10- and 30-fold higher abilities to control HIV replication and DNA burdens in vitro, respectively, than those of other NK cells. Thus, NK cells with a specific functional and transcriptional signature contribute to control of the HIV reservoir in CD4⁺ cells. Their selection, expansion, and/or adoptive transfer may support strategies to eradicate HIV-1 infection or to safely deescalate antiretroviral treatment.IMPORTANCE The most relevant feature of HIV-1 infection is represented by its DNA reservoir size in the body, which guarantees lifelong infection and resumption of virus replication after antiretroviral treatment interruption. So far, there has been little success in the identification of factors contributing to HIV-1 reservoir containment. In this study, by studying quantitative total and integrated HIV-1 DNA levels and NK cells in HIV-1 patients with either progressive or nonprogressive disease, we observed that inducible IFN-γ and natural cytotoxicity receptor (NCR) expression in a specific subset of NK cells with a characteristic transcriptional signature represents a correlate for HIV-1 reservoir control. This represents an advance in our understanding of the mechanism(s) that controls the lentivirus reservoir. Monitoring, selection, expansion, and adoptive transfer of these NK cells may allow monitoring of treatment efficacy and the likelihood of reservoir control and may support protocols for HIV-1 eradication.

Markers and function of human NK cells in normal and pathological conditions

Natural killer (NK) cells, the most important effectors of the innate lymphoid cells (ILCs), play a fundamental role in tumor immune-surveillance, defense against viruses and, in general, in innate immune responses. NK cell activation is mediated by several activating receptors and co-receptors able to recognize ligands on virus-infected or tumor cells. To prevent healthy cells from auto-aggression, NK cells are provided with strong inhibitory receptors (KIRs and NKG2A) which recognize HLA class I molecules on target cells and, sensing their level of expression, allow killing of targets underexpressing HLA-class I. In vivo, NK cell-mediated anti-tumor function may be suppressed by tumor or tumor-associated cells via inhibitory soluble factors/cytokines or the engagement of the so called immune-check point molecules (e.g., PD1-PDL1). The study of these immune check-points is now offering new important opportunities for the therapy of cancer. In haemopoietic stem cell transplantation, alloreactive NK cells (i.e., those that express KIRs, which do not recognize HLA class I molecules on patient cells), derived from HSC of haploidentical donors, are able to kill leukemia blasts and patient's DC, thus preventing both tumor relapses and graft-versus-host disease. A clear correlation exists between size of the alloreactive NK cell population and clinical outcome. Thus, in view of the recent major advances in cancer therapy based on immuno-mediated mechanisms, the phenotypic analysis of cells and molecules involved in these mechanisms plays an increasingly major role. © 2017 International Clinical Cytometry Society.

Identification of CD245 as myosin 18A, a receptor for surfactant A: A novel pathway for activating human NK lymphocytes

CD245 is a human surface antigen expressed on peripheral blood lymphocytes, initially delineated by two monoclonal antibodies DY12 and DY35. Until now, CD245 molecular and functional characteristics remained largely unknown. We combined immunological and proteomic approaches and identified CD245 as the unconventional myosin 18A, a highly conserved motor enzyme reported as a receptor for the surfactant protein A (SP-A), that plays a critical role in cytoskeleton organization and Golgi budding. We report that the recruitment of CD245 strongly enhanced NK cell cytotoxicity. Further, we show that the enhancement of the NK lymphocytes killing ability toward CD137-ligand expressing target cells could result from the induction of CD137 expression following CD245 engagement. The SP-A receptor could therefore represent a novel and promising target in cancer immunotherapy.

Electroporation of siRNA to Silence Gene Expression in Primary NK Cells

Gene silencing through siRNA is an effective experimental tool to unravel molecular mechanisms involved in cellular processes. Here we describe a method to silence gene expression in primary human natural killer (NK) cells by transfecting ON-TARGETplus SMART pool siRNA using an electroporation-based method called Nucleofection(®). The technique yields effective silencing of the target gene without any off-target effects.

Interleukin-12: a master regulator

Early resistance to pathogens requires a swift response from NK cells. In 1989, Giorgio Trinchieri identified an NK growth factor and activator, later called interleukin-12 (IL-12). This discovery helped reveal the regulatory link between innate and adaptive immunity.

Natural killer activity: early days, advances, and seminal observations

This manuscript describes the early history of NK cell discovery, with emphasis on the events in the first decade of NK cell studies, 1972-1982. The authors highlight some of the earliest and most important observations that would later prove to be milestones in the study of NK cells and their activity.

Human NK cell receptors/markers: a tool to analyze NK cell development, subsets and function

Natural killer (NK) cells are important components of the innate immunity and play a key role in host defense by virtue of their ability to release cytokines and to mediate cytolytic activity against tumor cells and virus-infected cells. NK cells were first described more than 30 years ago on the basis of their peculiar functional capabilities. Subsequently, thanks to the production of a variety of monoclonal antibodies, it became possible to identify surface receptors and markers expressed by NK cells as well as to characterize their functional properties. Here, we provide a brief historical overview about the discovery of human NK cell receptors and we delineate the main phenotypic features of differentiating and mature NK cells in healthy donors as well as their alterations in certain pathologic conditions.

Natural killer cell mediated antibody-dependent cellular cytotoxicity in tumor immunotherapy with therapeutic antibodies

In the last decade several therapeutic antibodies have been Federal Drug Administration (FDA) and European Medicines Agency (EMEA) approved. Although their mechanisms of action in vivo is not fully elucidated, antibody-dependent cellular cytotoxicity (ADCC) mediated by natural killer (NK) cells is presumed to be a key effector function. A substantial role of ADCC has been demonstrated in vitro and in mouse tumor models. However, a direct in vivo effect of ADCC in tumor reactivity in humans remains to be shown. Several studies revealed a predictive value of FcγRIIIa-V158F polymorphism in monoclonal antibody treatment, indicating a potential effect of ADCC on outcome for certain indications. Furthermore, the use of therapeutic antibodies after allogeneic hematopoietic stem cell transplantation is an interesting option. Studying the role of the FcγRIIIa-V158F polymorphism and the influence of Killer-cell Immunoglobuline-like Receptor (KIR) receptor ligand incompatibility on ADCC in this approach may contribute to future transplantation strategies. Despite the success of approved second-generation antibodies in the treatment of several malignancies, efforts are made to further augment ADCC in vivo by antibody engineering. Here, we review currently used therapeutic antibodies for which ADCC has been suggested as effector function.

The dysfunction of NK cells in patients with type 2 diabetes and colon cancer

Glucose metabolism disorders influence anticarcinogenic function of natural killer (NK) cells. The aim of this study was to evaluate the number and cytotoxic activity of NK cells in type 2 diabetic (T2D) patients with negative family history of cancer, type 2 diabetic subjects with newly diagnosed untreated colon cancer (T2DCC) and patients without type 2 diabetes with newly diagnosed, untreated colon cancer (CC). Incubation tests were performed in 18 T2D patients, treated with diet and oral antidiabetic agents, 16 T2DCC; cT1-4N0M0 (c-clinical diagnosis based on computed tomography, colonoscopy and histopathology) treated with diet and oral antidiabetic agents and 16 normoglycemic CC; cT1-4N0M0. Control group included 18 metabolically healthy (with normal fasting glucose and normal glucose tolerance) subjects (HS) with negative family history of cancer, matched by age, BMI and waist circumference. Peripheral blood mononuclear cells were isolated by means of gradient centrifugation. The K562 human erythroleukemia cell line served as the standard target for human NK cytotoxicity assay. The T2D revealed an increased number of NK cells (13.56 ± 5.9 vs 9.50 ± 4.8 %; p < 0.05) when compared with HS, yet these cells had a decreased activity (3.3 ± 2.5 vs 9.4 ± 3.6 %; p < 0.01). The CC demonstrated a decreased activity (2.9 ± 1.8 %; p < 0.01) but a similar number (8.82 ± 3.7 %; not significant) of NK cells when compared to HS. The T2DCC NK cells were characterized by trace cytotoxic activity (1.1 ± 0.7 %; p < 0.01) and nearly three times greater amount (21.24 ± 7.5 %; p < 0.01) when compared to T2D. Type 2 diabetes and CC are associated with disadvantageous alterations of NK cells, leading to impairment in their cytotoxic activity. The impaired activity of NK cells in T2D can be involved in the increased carcinogenic risk and can promote a higher incidence of CC.

Use of NK cell activity in cure by transplant

Analogous to T cells, Natural Killer (NK) cells may facilitate engraftment, combat infection, and control cancer in bone marrow or haematopoietic stem cell transplantation (HSCT); however, NK cells do not cause graft-versus-host disease. Killer immunoglobulin-like receptors (KIRs) regulate NK cell function, and recent data suggest that KIR is as important as its ligand (human leucocyte antigen; HLA) in HSCT for both malignant and non-malignant conditions. Because there is substantial variability in KIR gene content, allelic polymorphism, and cell-surface expression among people, careful selection of donors based on HLA and KIR is essential to optimize HSCT outcomes. Furthermore, NK cells may be used for adoptive immunotherapy after HSCT in place of conventional donor lymphocyte infusion, as part of pre-transplant cytoreductive therapy, or as an independent therapeutic agent in high-risk leukaemia in place of sibling donor HSCT.

NKG2D and its ligands: active factors in the outcome of solid organ transplantation?

The role of natural killer (NK) cells in solid organ transplantation is not well established, although several recent reports highlight the importance of the activating receptor NKG2D and its ligands in the development of rejection during transplantation. The human NKG2D ligands (MICA and MICB) are induced in allografts during acute and chronic rejection, and the presence of anti-MICA antibodies is correlated with a higher incidence of rejection. The binding of these ligands to its receptor NKG2D activates NK cells, enhances the functions of effectors, and allows NK cells to function as a bridge between innate and adaptive immunity associated with the transplantation. In fact, blockage of NKG2D with the anti-NKG2D monoclonal antibodies prolongs graft survival and prevents CD28-independent rejection in heart and skin allograft mouse models. Furthermore, the current immunosuppressive therapies can modulate the expression of NK cell receptors and consequently the effector functions of NK cells. That is particularly important during the first few months after transplantation, when the susceptibility to opportunistic viral infections is higher and NKG2D has an essential role. In this review, we analyze in detail the potential role of the NKG2D-activating receptor and its ligands in the immune responses during the outcome of solid organ transplantation. These findings open a new pathway for therapeutic intervention that can contribute to tolerance in solid organ transplantation.

Suppressive effect of a standardized mistletoe extract on the expression of activatory NK receptors and function of human NK cells

Despite long-term use of mistletoe extracts for cancer treatment, their mode of action remains elusive. In this study, it was studied in vitro if mistletoe extract is able to modulate the expression of natural cytotoxic receptors (NCRs) and NKG2D receptor, which stimulate natural killer cell-mediated cytotoxicity. Unexpectedly, a mistletoe extract, ABNOBA viscum Fraxini, inhibited the expression level of NKp46 and NKG2D receptors in dose- and time-dependent manners. The levels of NKp30 and NKG2D receptors were remarkably induced and NKp44 was slightly induced after 48 h treatment with IL-2 and IL-15 in both mRNA and surface expression. The activatory NK receptors were not induced significantly after treatment with IL-12, IL-18, and IL-21 for 48 h. Induction of activatory NK receptors by IL-2 and IL-15 was suppressed almost to the untreated levels by treatment with mistletoe extract, which appeared to induce apoptosis of NK cells in a dose-dependent manner. However, the treatment with IL-2 and IL-15 did not prevent the mistletoe-induced NK-cell death. Mistletoe extract inhibited significantly the cytotoxic activity of resting and IL-2- or IL-15-stimulated NK cells. These results suggest that inhibition of survival and function of NK cells by mistletoe extract may curtail in part the therapeutic effects of mistletoe.

Natural killer cells: from bench to cancer therapy

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

Putting the natural killer cell in its place

Natural killer (NK) cells were originally described as 'null' lymphocytes, but we have increasing evidence of their role in recognizing pathogen, and our knowledge of NK cell receptors continues to expand exponentially. Human NK cells have many receptors for human leucocyte antigen (HLA) class I. These killer immunoglobulin-like receptors (KIRs) and CD94/NKG2 receptors can signal in both positive and negative ways to regulate NK cell functions. The inhibitory receptors are the best characterized, but even in these cases much of their functional biology remains elusive. In this review, some recent advances in terms of the three-immunoglobulin (3Ig)-domain KIRs are discussed. Natural cytotoxicity receptors (NCRs) are among the activatory receptors found on NK cells. While pathogen ligands for these receptors have been described, endogenous ligands remain elusive. NCRs and NKG2D, a receptor for stress-induced antigens, appear to play complementary functional roles in terms of NK cell activation. More recently described on NK cells are the Toll-like receptors. In particular, these receptors of the innate immune system allow NK cells to directly sense pathogen, and their ligation on accessory cells indirectly activates NK cells through cytokine production. It is becoming clear that none of these receptor systems functions in isolation and that it is the sum of the signals (which will reflect the pathogenic situation), in addition to the cytokine milieu, that will direct NK cell activation. The resulting cytotoxicity, cytokine production and direct cell-cell regulatory interactions with other cells of the immune system, for example dendritic cells, ultimately determine the role of the NK cell in the context of an overall immune response.

Comparative study and effects of macrophage colony-stimulating factor (M-CSF) administration on NK1.1+ cells in mouse spleen and bone marrow

We conducted a comparative study of NK1.1+ cells in spleen and bone marrow and the effects of administration of M-CSF on them. Administration of M-CSF to mice increased the number of NK1.1+ cells in spleen but not in bone marrow. The NK1.1+ cells in spleen (Spl-NK1.1) and bone marrow (BM-NK1.1) were purified by magnetic cell sorter. Their cell surface markers and functions were then examined. The percentage of Mac-1 antigen-positive cells (and F4/80 antigen-positive cells) was higher among BM-NK1.1 than Spl-NK1.1. Moreover, the administration of M-CSF increased the number of Mac-1 and F4/80 antigen-positive cells in both Spl-Nk1.1 and BM-NK1.1. The functions (cytolytic activity and IFN-gamma production) of Spl-NK1.1 and BM-NK1.1 were the same and were enhanced by the administration of M-CSF. But Spl-NK1.1 produced more IFN-gamma than BM-NK1.1 when M-CSF was administered. BM-NK1.1 showed a greater proliferative response to IL-2 than Spl-NK1.1. Administration of M-CSF augmented this response. BM-NK1.1 proliferated in response to IL-4 and IL-15, but Spl-NK1.1 responded only slightly. However, administration of M-CSF stimulated Spl-NK1.1 to respond to these cytokines. Both Spl-NK1.1 and BM-NK1.1 showed only a weak response to M-CSF in vitro. But the expression of c-fms antigen (M-CSFR) increased after the M-CSF injections in vivo. These results suggested that there are phenotypical and functional differences between Spl-NK1.1 and BM-NK1.1. The administration of M-CSF led to an accumulation of NK1.1+ cells which were mobilized from bone marrow in spleen.

Spontaneous cell-mediated cytotoxicity (SCMC) in various mammalian species and chickens: selective reaction pattern and different mechanisms

Cultured cell lines derived from donors of various species served as 75Se- or 51Cr-labelled targets in microcytotoxicity assays. As in human donors, considerable spontaneous cell-mediated cytotoxicity (SCMC) was exhibited by peripheral blood lymphoid effector cells from healthy chickens, mink, swine, cattle, horses and tigers. Although all target lines tested could be lysed in SCMC, there was no 'general SCMC target' for all species or all individuals of one species. The selectivity, the kinetics, and the strength of SCMC reflected the capacity of the effector cells rather than a 'susceptibility' of the target to lysis. Classical major histocompatibility complex products, determinants specific for distinct cell types or subpopulations, or antigens associated with Epstein-Barr virus, herpes virus ateles, herpes virus papio, or Marek's disease virus were not appreciably involved in SCMC. No 'malignant phenotype' on targets was required for the cytotoxic effect. Yet undefined xenogeneic, allogeneic, and individual structures seem to be involved in SCMC. Depending on their expression, a target can be classified as 'species-related' or as 'individual-related'. Intermediate forms are conceivable. SCMC might comprise different cytotoxic mechanisms. Antibodies are not required for lysis to occur, but serum factors including immunoglobulins can have considerable influence on SCMC.

Murine natural killer cell differentiation: past, present, and future

Natural killer cells are bone marrow-derived lymphocytes capable of lysing a variety of target cells without prior exposure. While the biological activities and function of mature NK cells have been extensively investigated, the differentiation of NK cells from primitive hematopoietic stem cells is poorly understood. Recently, we have reported on the identification of a highly enriched bone marrow population capable of repopulating recipient mice with mature NK cells. In this review, we will summarize our findings and those of others in an attempt to clarify the current status of murine natural killer cell differentiation.

Positive selection of NK1.1+ cells on a magnetic cell separator (MACS)

Natural killer (NK) cells are involved not only in resistance to tumors and infection, but also in some transplantation reactions. A specific, inexpensive method for purifying large numbers of NK cells is often required. All NK cells in H-2b mice express the surface marker NK1.1. We report a method for positively selecting NK1.1+ spleen cells from normal and Poly I:C-stimulated C56Bl/6 mice using a magnetic cell separation technique known as MACS. Our results show that cytotoxic activity directed at YAC-1 target cells by normal and Poly I:C-stimulated spleen cells could be increased five-fold using this method. We also found that spleen cells from mice given Poly I:C could lyse NK-resistant, BW1100 target cells, and that this activity could be increased two-fold. Flow cytometry analysis of Poly I:C-stimulated, MACS enriched, NK1.1+ spleen cells revealed the presence of two subpopulations: one consisting of LGL and the other consisting of smaller, agranular lymphocytes (SAL). After enrichment, the percentage of NK1.1+ spleen cells increased from 69% to 91% in the LGL subpopulation and from 33% to 73% in the SAL subpopulation. These results clearly demonstrate the effectiveness of the MACS technique for purifying large numbers of NK1.1+ cells for both flow cytometric and functional analyses.

Selective inhibition by alcohol and cortisol of natural killer cell activity of lymphocytes from cord blood

1. The immunosuppressive effects of drugs such as alcohol or hormones such as cortisol may be age-related. To test this hypothesis, the authors investigated the in vitro effects of ethanol (EtOH) and cortisol on Natural Killer (NK) cell activity of lymphocytes from normal cord blood in comparison with that of lymphocytes from normal adult peripheral blood. 2. K562, an erythroleukemia cell line, was used as a target in a 4 hr 51Cr release assay. 3. Ethanol at 0.3% (V/V) and cortisol at 0.05, 0.1 and 0.2 microgram/ml concentrations, added directly to a mixture of effector and target cells significantly suppressed the NK activity of cord blood lymphocytes in a dose dependent fashion, whereas similar concentrations of either EtOH or cortisol did not manifest significant immunoregulatory effects on NK cell activity of normal adult lymphocytes. 4. Pre-treatment of the target with either EtOH or cortisol for 4 hours did not affect cytotoxicity. Inhibition of cytotoxicity was also not due to direct toxicity of effector cells because lymphocytes treated with either EtOH or cortisol showed normal 51Cr release and their viability was comparable to that of untreated control cells. 5. This suggests a selective inhibitory effect of EtOH and cortisol on NK activity of neonatal lymphocytes that may be of clinical significance.

Enumeration of organ-associated natural killer cells in mice: application of a new stereological method

We here describe a method for estimation of the absolute number of NK cells in various organs of C57BL/6 mice. Using anti-asialo-GM1 heteroantisera to identify NK cells in tissue sections routinely stained by two-layer immunoperoxidase techniques, scoring was performed using light microscopy. Extrapolation to the absolute number of NK cells/organ was done after counting 10 systematically sampled sections of each organ. Due to the thinness of the sections (8 microns) many cells are cut and will appear in at least two sections, and a correction factor was constructed to eliminate this bias. With this method we show that spleens of eight-week-old C57BL/6 male mice contain about 4 x 10(6) NK cells, which is consistent with previous findings obtained by other methods. However, application of this stereological method to liver and lungs revealed the existence of as many as 0.75 and 2.5 x 10(6) NK cells in these organs, respectively, i.e. three to 10 times as many as previously found in single-cell suspensions obtained by enzymatic dissociation of liver and lung tissue. This stereological method for enumeration of the absolute number of small subpopulations of cells is generally applicable to other organs and to other antigens, and does not require the application of cumbersome single-cell isolation procedures, during which an unknown number of cells might be lost.

Absence of natural killer (NK) cell activity against oligodendrocytes in multiple sclerosis

The cytotoxicity of natural killer (NK) cells directed to enriched cultures of bovine oligodendrocytes was investigated in multiple sclerosis (MS) patients and controls. Macrophage-depleted peripheral blood lymphocytes were used as effector cells in a 4-h 51Cr release assay. No significant cytotoxic activity to oligodendrocytes was identified in either MS or control groups. In contrast, a definite cytotoxic activity directed toward K562 cells was observed in the study populations. No statistically significant difference was observed between chronic progressive or stable MS, other neurological diseases (OND), and normal controls. These results indicate that NK cell activity directed toward intact bovine oligodendrocytes is not significantly different between MS and control groups and question the significance of studies employing K562 cells as the target in NK assays in MS. Furthermore, these observations suggest that NK-mediated cytotoxicity against oligodendrocytes is unlikely to be a specific mechanism mediating demyelination in MS.

Lymphokine activated killer cells

Various subpopulations of human leukocytes may be induced by lymphokines to exert cytotoxic activity. In man major histocompatibility complex non-restricted tumor cell lysis by interleukin-2 (IL-2) induced peripheral blood lymphocytes is attributed mainly to natural killer cells. These T cell receptor negative large granular lymphocytes are called lymphokine activated killer (LAK) cells. In order to explore the potential of LAK cells in tumor therapy, several clinical studies have been conducted, using IL-2 alone or in combination with ex vivo IL-2-activated peripheral blood lymphocytes. Objective responses have reproducibly been achieved only in renal cell carcinoma and malignant melanoma and were associated with considerable toxicity. In view of restricted efficacy and increasing doubts as to whether LAK cells indeed account for the in vivo observed responses, more recent strategies focus on tumor antigen specific cytotoxic T cells or tumor infiltrating lymphocytes. Successful translation of this approach into clinical practice, however, may be dependent on some basic problems of tumor immunology to be solved which were thought to be by-passed by the LAK cell approach.

[Development of Eimeria tenella in MDBK cell culture with a note on enhancing effect of preincubation with chicken spleen cells]

Eimeria tenella, an intracellular protozoan parasite infecting the epithelial cells of the ceca of chickens, causes severe diarrhea and bleeding that can lead its host to death. It is of interest that E. tenella first penetrate into the mucosal intraepithelial lymphocytes (IEL) before they parasitize crypt or villous epithelial cells. This in vitro study was undertaken to know whether the penetration of E. tenella into such a lymphoid cell is a beneficial step for the parasite survival and development. Three sequential experiments were performed. First, the in vitro established bovine kidney cell line, MDBK cells, were evaluated for use as host cells for E. tenella, through morphological observation. Second, the degree of parasite development and multiplication in MDBK cells was quantitatively assayed using radioisotope-labelled uracil (3H-uracil). Third, the E. tenella sporozoites viability was assayed after preincubation of them with chicken spleen cells. E. tenella oöcysts obtained from the ceca of the infected chickens were used for the source of the sporozoites. Spleen cells (E) obtained from normal chickens (FP strain) were preincubated with the sporozoites (T) at the E:T ratio of 100:1, 50:1 or 25:1 for 4 or 12 hours, and then the mixture was inoculated into the MDBK cell monolayer. Morphologically the infected MDBK cells revealed active schizogonic cycle of E. tenella in 3-4 days, which was characterized by the appearance of trophozoites, and immature and mature schizonts containing merozoites. The 3H-uracil uptake by E. tenella increased gradually in the MDBK cells, which made a plateau after 48-60 hours, and decreased thereafter. The uptake amount of 3H-uracil depended not only upon the inoculum size of the sporozoites but also on the degree of time delay (preincubation; sporozoites only) from excystation to inoculation into MDBK cells. The 3H-uracil uptake became lower as the preincubation time was prolonged. In comparison, after preincubation of sporozoites with spleen cells for 4 or 12 hours, the 3H-uracil uptake was significantly increased compared with that of control group. From the results, it was inferred that, although the penetration of E. tenella sporozoites into the lymphoid cells such as IEL is not an essential step, it should be at least a beneficial one for the survival and development of sporozoites in the chicken intestine.

Natural killer activity in Fischer-344 rat lungs as a method to assess pulmonary immunocompetence: immunosuppression by phosgene inhalation

Phosgene, also known as carbonyl chloride, carbon oxychloride, and chloroformyl chloride, is a toxic air pollutant and a potential occupational health hazard. Studies were initiated (a) to evaluate the measurement of pulmonary natural killer (NK) activity as a method to assess pulmonary immunocompetence, and (b) to determine whether exposure to phosgene resulted in local pulmonary or systemic immune dysfunction. Fischer-344 male rats were exposed either to filtered air or to 1.0 ppm phosgene gas for four hours. The effect of phosgene on lung NK activity was quantified at different times after acute phosgene exposure. Pulmonary NK activity was measured by mincing lung tissue into small pieces prior to incubation with collagenase. Whole-lung homogenate was assayed for NK activity utilizing a 4 hour 51-Cr-release assay with YAC-1 cells as target cells. Acute phosgene exposure resulted in a suppressed pulmonary NK activity on days 1, 2, and 4 after exposure; however, normal levels of biological activity were observed 7 days after exposure. The suppressed NK activity was not restored after removal of adherent cells from the lung homogenate, thus indicating that the effect of phosgene on NK activity was not due to immunosuppression via mobilization of suppressor alveolar macrophages. Pulmonary immunotoxicity was also observed after exposure at 0.5 ppm, while no adverse effects were observed at 0.1 ppm phosgene. Systemic immunotoxic effects were observed for NK activity in the spleen, but not in the peripheral blood. It is thus important in pulmonary immunotoxicology to evaluate systemic immune functions, since secondary effects--distant to the original interaction--may occur with potentially serious consequences. Cells exhibiting natural killer activity comprise a part of the nonspecific innate immunity that is important in defense against both neoplastic and viral diseases. Any perturbation of this important nonspecific immunological mechanism may result in a compromised host more susceptible to infectious and neoplastic disease.

Measurement of natural killer cell cytotoxicity by area under a cytotoxic curve. A method suitable for rheumatoid arthritis

Calculation of the area under a curve derived from a 51Cr cellular release assay gives a reproducible expression of cellular cytotoxicity and correlates well with results at fixed lymphocyte-to-target cell ratios and with lytic units at 20% and 30% cytotoxicity. This method is suitable for quantifying the low cytotoxicity seen in rheumatoid arthritis. The area under the cellular cytotoxic curve may be calculated using a simple mathematical formula or by computer analysis.

A multi-step isolation scheme for obtaining CD16+ human natural killer cells

A multi-step isolation scheme capitalizing on negative selection protocols is described for obtaining an enriched population of CD16+ human natural killer (NK) cells. The isolation scheme consists of incubating peripheral blood mononuclear cells (MNC) on nylon wool, rosetting the nylon wool non-adherent cells with sheep red blood cells (SRBCs) for 1 h at 29 degrees C and then utilizing a 'panning' technique to remove CD3+, non-rosetting cells. The final working cell population contained 70-80% CD16+ cells, 15% CD2+ cells, 1-3% CD3+ cells, 5-7% SIg+ cells and no detectable MO2+ cells. In comparing the final NK cell population from the multi-step isolation protocol to NK cells obtained by the Percoll density gradient centrifugation technique, the multistep method: (1) yielded a higher percentage of CD16+ cells, (2) mediated a greater degree of cytotoxicity at a 25:1 E:T ratio, and (3) contained fewer contaminating monocytes/macrophages (none were detectable). In addition, the multi-step scheme allowed recovery of 30% of the total CD16+ cells present compared to only 7% recovered by the Percoll density gradient technique. Pretreatment of the enriched NK cells, obtained from the multi-step scheme, with interleukin-2 (3.5 and 7.0 U/ml of activity) resulted in an increase in NK cell-mediated cytotoxicity. In addition, these cells were as effective at synthesizing the cytotoxin, NKCF, at a 25:1 E:T ratio as at 50:1 and 100:1 E:T ratios. This multi-step isolation scheme consistently yields a high percentage of CD16+ NK cells and thus may greatly facilitate studies on the mechanism(s) involved in NK cell-mediated cytotoxicity and may further the study of the cytotoxins involved.

Effects of protein depletion on NK cell cytotoxicity and bone marrow cellularity

Tumor bearing patients have repeatedly been shown to develop states of protein (PD). PD has frequently been associated with depression of acquired immunity. In contrast, little is known about the effects of PD on natural killer (NK) cell cytotoxicity and on bone marrow cellularity and how modulation of these parameters by maleic anhydride divinyl ether copolymer (MVE-2) would be affected. BALB/c mice 6-10 weeks old were fed normal diets (18% protein) (ND mice) or protein deficient isocaloric diets (PD mice) for 35 days. On days 5, 9, 15, 23, and 35 assays were performed. Three days prior to each assay day, some groups received MVE-2 i.p. In PD mice spontaneous NK activity was reduced by some 80%. After MVE-2 the levels only rose to half the amount of activity of ND mice, although in both groups an increase of NK activity took place. BMC levels of PD mice were also strongly decreased. After MVE-2, increases of BMC in PD mice were quite weak and did not reach the level of normal unstimulated BMC. In PD mice we found body weight loss of 46%, reduction in albumin and total protein of 22% and complete disappearance of prealbumin after 5 days of diets. Preliminary results indicate that repletion with amino acids (NeoAminomel L12.5 o.K.H. Salvia, Boehringer Mannheim Co.) is able restore NK activities and BMC levels.

Association of decreased natural and antibody-dependent cellular cytotoxicity and production of natural killer cytotoxic factor and interferon in neonates

Cord blood lymphocytes (CBL) were compared with adult peripheral blood lymphocytes (a-PBL) for their: (i) natural killer (NK) and antibody-dependent cellular cytotoxic (ADCC) activities, (ii) target-binding capacity, (iii) ability to induce soluble natural killer cytotoxic factor (NKCF), (iv) interferon (IFN)-, interleukin 2 (IL-2)-, and lectin-induced augmentation of NK activity, and (v) ability to produce IFN against tumor targets in vitro. CBL depleted of adherent cells and Percoll-separated, NK-enriched subpopulations demonstrated significantly lower NK, ADCC, and target-binding activities compared to a-PBL. CBL produced significantly lower levels of NKCF directed against K562 tumor targets in comparison with a-PBL. Although the NK activity of CBL was not stimulated by either IFN or IL-2 to the same levels shown by a-PBL, the percentage enhancement of cytotoxicity of CBL by IFN and IL-2 was greater than that of a-PBL. Lectin-induced enhancement of cytotoxicity was significantly greater for CBL in comparison with a-PBL. Further, the ability of CBL lymphocytes to produce IFN-gamma in vitro against K562 target cells was significantly lower than that of adult PBL. These studies suggest an association between decreased NK, ADCC, and target-binding activities, induction of NKCF and IFN production by CBL, and increased susceptibility of neonates to infection.

Functional properties of natural killer cells in carcinoma of the prostate

Functional properties of natural killer cells were analyzed in a 51chromium-release assay by modulating their activity with human beta-interferon using 1) peripheral mononuclear cells of 16 patients with carcinoma of the prostate and 7 healthy male donors, and 2) mononuclear cells from the periprostatic lymph nodes of 6 patients with stage pT2N0M0 prostatic cancer and 5 without malignancy. Cell lines EB 33, PC 3, DU 145 and CaKi 1 were used as target cells. Spontaneous cell-mediated cytotoxicity of peripheral mononuclear cells was depressed in patients with advanced prostatic cancer; however, the natural killer cells responded as those of the healthy controls to beta-interferon. The beta-interferon effect was time and dose dependent. In mononuclear periprostatic lymph node cells virtually no spontaneous cell-mediated cytotoxicity was detected. The reactivity of mononuclear periprostatic lymph node cells from patients with prostatic cancer was significantly less improved by beta-interferon stimulation than the mononuclear periprostatic lymph node cells of healthy subjects. The stimulation of mononuclear periprostatic lymph node cells by beta-interferon was reduced significantly compared to simultaneously tested autologous peripheral mononuclear cells.