CD56bright cells differ in their KIR repertoire and cytotoxic features from CD56dim NK cells

Tissue-specific features of innate lymphoid cells in antiviral defense

Innate lymphocytes (ILCs) rapidly respond to and protect against invading pathogens and cancer. ILCs include natural killer (NK) cells, ILC1s, ILC2s, ILC3s, and lymphoid tissue inducer (LTi) cells and include type I, type II, and type III immune cells. While NK cells have been well recognized for their role in antiviral immunity, other ILC subtypes are emerging as players in antiviral defense. Each ILC subset has specialized functions that uniquely impact the antiviral immunity and health of the host depending on the tissue microenvironment. This review focuses on the specialized functions of each ILC subtype and their roles in antiviral immune responses across tissues. Several viruses within infection-prone tissues will be highlighted to provide an overview of the extent of the ILC immunity within tissues and emphasize common versus virus-specific responses.

Relapsing-remitting multiple sclerosis patients exhibit differential natural killer functional subpopulations

BACKGROUND

Multiple sclerosis (MS) is a chronic inflammatory disease of the central nervous system (CNS) and has been known as T-cell mediated. However, the contribution of multiple cell types, notably natural killer (NK) cells, has also been reported.

AIM

To quantify circulating total NK cells and its subpopulations, CD56 dim and bright, and to characterize the functional phenotype and IFN-γ and TNF-α production in relapsing-remitting patients treated with IFN-β and in apparently healthy controls.

RESULTS

CD56bright NK cells were found to be the least represented subpopulation. In relapse patients, the frequencies of IFN-γ-producing NK cells and their subpopulations were significantly decreased. In remission patients, CD56dim NK cells expressed high levels of HLA-DR and CD54.

CONCLUSION

These results suggest that remission RRMS patients, although in an inactive stage of MS, present circulating NK cells with an activation phenotype, supporting the idea that NK cells may be relevant mediators in the MS pathophysiology.

Single-cell transcriptomics reveals comprehensive microenvironment and highlights the dysfuntional state of NK cells in endometrioid carcinoma

Endometrioid endometrial cancer (EEC) is one of the most common gynecologic malignancies. The interaction between cancer cells and the cells in the tumor microenvironment (TME) plays a crucial role in determining disease progression and response to treatment. To better understand the diversity in the TME of ECC, we conducted a comprehensive analysis using single-cell RNA sequencing across 21 samples, including 16 ECC and 5 adjacent normal tissues. We primarily focused on tumor-infiltrating natural killer (NK) cells and their cell-cell interactions with other immune cell types. We identified a CD56dim_DNAJB1 NK cells subset, which had low cytotoxic capability and high stress levels, suggesting a dysfunctional state. This subset showed strong interactions with tumor-associated macrophages through several ligand-receptor pairs. Additionally, we observed that tumor-infiltrating LAMP3+ dendritic cells may inhibit CD8+ T cells or attract regulatory T cells to the tumor area. These dendritic cells also had impaired activation effects on NK cells within the TME. Our study provides valuable insights into the role of NK cells in cancer immunity and highlights the potential of targeting specific NK cell subsets for therapeutic purposes.

Distinctive CD56dim NK subset profiles and increased NKG2D expression in blood NK cells of Parkinson's disease patients

Mounting data suggest an important role for the immune system in Parkinson's disease (PD). Previous evidence of increased natural killer (NK) cell populations in PD suggests a potential role of NK cells in the pathogenesis of the disease. Previous studies have analyzed NK cell populations using aggregation by variable expression of CD56 and CD16. It remains unknown what differences may exist between NK cell subpopulations when stratified using more nuanced classification. Here, we profile NK cell subpopulations and elucidate the expressions of activating, NKG2D, inhibitory, NKG2A, and homing, CX3CR1, receptors on NK cell subpopulations in PD and healthy controls (HC). We analyzed cryopreserved PMBC samples using a 10-color flow cytometry panel to evaluate NK cell subpopulations in 31 individuals with sporadic PD and 27 HC participants. Here we identified significant differences in the CD56dim NK subset that changes with disease severity in PD. Furthermore, the expressions of NKG2D in all three NK cell subsets were significantly elevated in PD patients compared to HC. Notably, NKG2A expression in the CD56bright NK subset increased in PD patients with longer disease duration but there were no changes in CX3CR1. In summary, our data suggests that changes in NK cells may be influenced by the clinical severity and duration of PD.

CAR-NK cells for cancer immunotherapy: recent advances and future directions

Natural Killer (NK) cells, intrinsic to the innate immune system, are pivotal in combating cancer due to their independent cytotoxic capabilities in antitumor immune response. Unlike predominant treatments that target T cell immunity, the limited success of T cell immunotherapy emphasizes the urgency for innovative approaches, with a spotlight on harnessing the potential of NK cells. Despite tumors adapting mechanisms to evade NK cell-induced cytotoxicity, there is optimism surrounding Chimeric Antigen Receptor (CAR) NK cells. This comprehensive review delves into the foundational features and recent breakthroughs in comprehending the dynamics of NK cells within the tumor microenvironment. It critically evaluates the potential applications and challenges associated with emerging CAR-NK cell therapeutic strategies, positioning them as promising tools in the evolving landscape of precision medicine. As research progresses, the unique attributes of CAR-NK cells offer a new avenue for therapeutic interventions, paving the way for a more effective and precise approach to cancer treatment.

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.

Unraveling the dynamic mechanisms of natural killer cells in viral infections: insights and implications

Viruses pose a constant threat to human well-being, necessitating the immune system to develop robust defenses. Natural killer (NK) cells, which play a crucial role in the immune system, have become recognized as vital participants in protecting the body against viral infections. These remarkable innate immune cells possess the unique ability to directly recognize and eliminate infected cells, thereby contributing to the early control and containment of viral pathogens. However, recent research has uncovered an intriguing phenomenon: the alteration of NK cells during viral infections. In addition to their well-established role in antiviral defense, NK cells undergo dynamic changes in their phenotype, function, and regulatory mechanisms upon encountering viral pathogens. These alterations can significantly impact the effectiveness of NK cell responses during viral infections. This review explores the multifaceted role of NK cells in antiviral immunity, highlighting their conventional effector functions as well as the emerging concept of NK cell alteration in the context of viral infections. Understanding the intricate interplay between NK cells and viral infections is crucial for advancing our knowledge of antiviral immune responses and could offer valuable information for the creation of innovative therapeutic approaches to combat viral diseases.

The Potential of Siglecs and Sialic Acids as Biomarkers and Therapeutic Targets in Tumor Immunotherapy

The dysregulation of sialic acid is closely associated with oncogenesis and tumor progression. Most tumor cells exhibit sialic acid upregulation. Sialic acid-binding immunoglobulin-like lectins (Siglecs) are receptors that recognize sialic acid and are expressed in various immune cells. The activity of Siglecs in the tumor microenvironment promotes immune escape, mirroring the mechanisms of the well-characterized PD-1/PD-L1 pathway in cancer. Cancer cells utilize sialic acid-linked glycans to evade immune surveillance. As Siglecs exhibit similar mechanisms as the established immune checkpoint inhibitors (ICIs), they are potential therapeutic targets for different forms of cancer, especially ICI-resistant malignancies. Additionally, the upregulation of sialic acid serves as a potential tumor biomarker. This review examines the feasibility of using sialic acid and Siglecs for early malignant tumor detection and discusses the potential of targeting Siglec-sialic acid interaction as a novel cancer therapeutic strategy.

Perforin and granzyme A release as novel tool to measure NK cell activation in chickens

Natural killer (NK) cells are cytotoxic lymphocytes that are present in the circulation but also in many organs including spleen and gut, where they play an important role in the defense against infections. Interaction of NK cells with target cells leads to degranulation, which results in the release of perforin and granzymes in the direct vicinity of the target cell. Chicken NK cells have many characteristics similar to their mammalian counterparts and based on similarities with studies on human NK cells, surface expression of CD107 was always presumed to correlate with granule release. However, proof of this degranulation or in fact the actual presence of perforin (PFN) and granzyme A (GrA) in chicken NK cells and their release upon activation is lacking. Therefore, the purpose of the present study was to determine the presence of perforin and granzyme A in primary chicken NK cells and to measure their release upon degranulation, as an additional tool to study the function of chicken NK cells. Using human specific antibodies against PFN and GrA in fluorescent and confocal microscopy resulted in staining in chicken NK cells. The presence of PFN and GrA was also confirmed by Western blot analyses and its gene expression by PCR. Stimulation of NK cells with the pectin SPE6 followed by flow cytometry resulted in reduced levels of intracellular PFN and GrA, suggesting release of PFN and GrA. Expression of PFN and GrA reversely correlated with increased surface expression of the lysosomal marker CD107. Finally it was shown that the supernatant of activated NK cells, containing the NK cell granule content including PFN and GrA, was able to kill Escherichia coli. This study correlates PFN and GrA release to activation of chicken NK cells and establishes an additional tool to study activity of cytotoxic lymphocytes in chickens.

Balancing act: the complex role of NK cells in immune regulation

Natural killer (NK) cells, as fundamental components of innate immunity, can quickly react to abnormalities within the body. In-depth research has revealed that NK cells possess regulatory functions not only in innate immunity but also in adaptive immunity under various conditions. Multiple aspects of the adaptive immune process are regulated through NK cells. In our review, we have integrated multiple studies to illuminate the regulatory function of NK cells in regulating B cell and T cell responses during adaptive immune processes, focusing on aspects including viral infections and the tumor microenvironment (TME). These insights provide us with many new understandings on how NK cells regulate different phases of the adaptive immune response.

Impact of a new liver immune status index among patients with hepatocellular carcinoma after initial hepatectomy

Aim

The anti-tumor effects of natural killer (NK) cells vary among individuals. Tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) expressed on liver NK cells is a marker of anti-tumor cytotoxicity against hepatocellular carcinoma (HCC) in immune cell therapy. This study aimed to develop a liver immune status index (LISI) that predicts low TRAIL expression and validates its ability to predict recurrence after initial hepatectomy for primary HCC.

Methods

A functional analysis of liver NK cells co-cultured with interleukin-2 for 3 days was performed of 40 liver transplant donors. The LISI, which predicted low TRAIL expression (25% quartile: <33%) in liver NK cells, was calculated using multiple logistic regression analysis. Next, 586 initial hepatectomy cases were analyzed based on the LISI.

Results

Our model was based on the Fibrosis-4 index+0.1 (odds ratio [OR], 1.33), body mass index (OR, 0.61), and albumin levels+0.1 (OR, 0.54). The area under the receiver operating characteristic curve (AUC) of the LISI for low TRAIL expression was 0.89. Stratification of the recurrence rates (RR) revealed that LISI was an independent predictive factor of RR (moderate risk: hazard ratio, 1.44; high risk: hazard ratio, 3.02). The AUC was similar for the LISI, albumin-indocyanine green evaluation grade, albumin-bilirubin score, and geriatric nutritional risk index for predicting RR. Among the vascular invasion cases, the LISI was more useful than the other indexes.

Conclusion

Our model facilitates the prediction of RR in high-risk patients by providing LISI to predict the anti-tumor effects of NK cells.

NK cell subsets and dysfunction during viral infection: a new avenue for therapeutics?

In the setting of viral challenge, natural killer (NK) cells play an important role as an early immune responder against infection. During this response, significant changes in the NK cell population occur, particularly in terms of their frequency, location, and subtype prevalence. In this review, changes in the NK cell repertoire associated with several pathogenic viral infections are summarized, with a particular focus placed on changes that contribute to NK cell dysregulation in these settings. This dysregulation, in turn, can contribute to host pathology either by causing NK cells to be hyperresponsive or hyporesponsive. Hyperresponsive NK cells mediate significant host cell death and contribute to generating a hyperinflammatory environment. Hyporesponsive NK cell populations shift toward exhaustion and often fail to limit viral pathogenesis, possibly enabling viral persistence. Several emerging therapeutic approaches aimed at addressing NK cell dysregulation have arisen in the last three decades in the setting of cancer and may prove to hold promise in treating viral diseases. However, the application of such therapeutics to treat viral infections remains critically underexplored. This review briefly explores several therapeutic approaches, including the administration of TGF-β inhibitors, immune checkpoint inhibitors, adoptive NK cell therapies, CAR NK cells, and NK cell engagers among other therapeutics.

NK cells vs. obesity: A tale of dysfunction & redemption

Natural killer (NK) cells are critical in protecting the body against infection and cancer. NK cells can rapidly respond to these threats by directly targeting the infected or transformed cell using their cytotoxic machinery or by initiating and amplifying the immune response via their production of cytokines. Additionally, NK cells are resident across many tissues including adipose, were their role extends from host protection to tissue homeostasis. Adipose resident NK cells can control macrophage polarization via cytokine production, whilst also regulating stressed adipocyte fate using their cytotoxic machinery. Obesity is strongly associated with increased rates of cancer and a heightened susceptibility to severe infections. This is in part due to significant obesity-related immune dysregulation, including defects in both peripheral and adipose tissue NK cells. In this review, we detail the literature to date on NK cells in the setting of obesity - outlining the consequences, mechanisms and therapeutic interventions.

Investigating the relationship between the number and activity of natural killer cells with increased cytomegalovirus and CMV disease after kidney transplantation

BACKGROUND

Cytomegalovirus (CMV) infections caused by the cytomegalovirus are one of the most common problems in patients after kidney transplant. We examined the association of the relationship between the number and activity of natural killer cells with increased cytomegalovirus and its related disease after kidney transplantation.

MATERIAL AND METHODS

In this analytical study, 58 new transplant patients in the Labbafinejad Hospital, who did not have any evidence of CMV infection, were evaluated based on the number and percentage of CD56+/16+, CD56+/16-, and CD69+ Natural Killer (NK) cells.

RESULTS

The results of this study showed that CD16+ and CD56+ cells in the group of CMV Ag-positive patients are less than negative patients (p = 0.003) and the difference between the two groups are significant (p = 0.01). However, CD69+ cells did not differ significantly between the two groups (p = 0.1). Moreover, the absolute number of CD16+ and CD56+ cells declined significantly after infection with CMV unlike the CMV Ag - group(p = 0.003).

DISCUSSION

These results indicate that kidney transplant patients suffering from CMV infection after transplantation have a significantly reduced total number of NK cells. On the other hand, a slight decrease in the number of NK subgroups was observed with an increase in the peak serum levels of cyclosporine. As a consequence of these findings, it can be assumed that more dosage and a higher level of the drug will result in more severe immunosuppression and, consequently, increased susceptibility to CMV infections. Thus, taking the right dose of the drug would prevent viral infections and immune system from over-activation.

A pan-cancer single-cell panorama of human natural killer cells

Natural killer (NK) cells play indispensable roles in innate immune responses against tumor progression. To depict their phenotypic and functional diversities in the tumor microenvironment, we perform integrative single-cell RNA sequencing analyses on NK cells from 716 patients with cancer, covering 24 cancer types. We observed heterogeneity in NK cell composition in a tumor-type-specific manner. Notably, we have identified a group of tumor-associated NK cells that are enriched in tumors, show impaired anti-tumor functions, and are associated with unfavorable prognosis and resistance to immunotherapy. Specific myeloid cell subpopulations, in particular LAMP3+ dendritic cells, appear to mediate the regulation of NK cell anti-tumor immunity. Our study provides insights into NK-cell-based cancer immunity and highlights potential clinical utilities of NK cell subsets as therapeutic targets.

Decreased Expression of CD314 by NK Cells Correlates with Their Ability to Respond by Producing IFN-γ after BCG Moscow Vaccination and Is Associated with Distinct Early Immune Responses

The immune response to vaccines is complex and results in various outcomes. BCG vaccination induces innate and specific responses that can lead to protection against tuberculosis, and cross-protection against other infections. NK cells have been associated with BCG-induced protection. Therefore, we hypothesize that differences in NK cell status before BCG vaccination may have a role in the ability of BCG to activate the immune response. Participants of a clinical trial were evaluated after BCG vaccination. The participants were assigned to different groups according to variation in IFN-γ expression by NK cells between days 1 and 15 after BCG vaccination. Individuals that presented a higher increase in IFN-γ expression by NK cells presented reduced CD314 expression at day 1, and after vaccination an increase in inflammatory NK cells and CD4 T-cell expression of IL-17. A negative correlation between expression of CD314 at day 1 and that of IFN-γ by NK cells after BCG vaccination was observed. Participants with lower of IFN-γ expression by NK cells after BCG vaccination presented an increase in the cytotoxic NK subpopulation and CD4 T-cell expression of IL-17 and IFN-γ. In conclusion, the expression of CD314 by NK cells before BCG vaccination influences their IFN-γ responses, generation of NK subpopulations, and the specific T immune response at 15 days after vaccination.

Alterations of natural killer cells activatory molecules phenotype and function in mothers of ASD children: a pilot study

Introduction

Autism spectrum disorder (ASD) is accompanied by complex immune alterations and inflammation, and the possible role played by Natural Killer (NK) in such alterations is only barely understood.

Methods

To address this question we analysed activating and inhibitory NK receptors, as well as NK cells phenotype and function in a group of mothers of children who developed ASD (ASD-MO; N=24) comparing results to those obtained in mothers of healthy children who did not develop (HC-MO; N=25).

Results

Results showed that in ASD-MO compared to HC-MO: 1) NK cells expressing the inhibitory receptor ILT2 are significantly decreased; 2) the activating HLA-G14bp+ polymorphism is more frequently observed and is correlated with the decrease of ILT2-expressing cells; 3) the CD56bright and CD56dim NK subsets are increased; 4) IFNγ and TNF production is reduced; and 5) perforin- and granzymes-releasing NK cells are increased even in unstimulated conditions and could not be upregulated by mitogenic stimulation.

Discussion

Results herein reinforce the hypothesis that ASD relatives present traits similar to, but not as severe as the defining features of ASD (Autism endophenotype) and identify a role for NK cells impairment in generating the inflammatory milieu that is observed in ASD.

Understanding NK cell biology for harnessing NK cell therapies: targeting cancer and beyond

Gene-engineered immune cell therapies have partially transformed cancer treatment, as exemplified by the use of chimeric antigen receptor (CAR)-T cells in certain hematologic malignancies. However, there are several limitations that need to be addressed to target more cancer types. Natural killer (NK) cells are a type of innate immune cells that represent a unique biology in cancer immune surveillance. In particular, NK cells obtained from heathy donors can serve as a source for genetically engineered immune cell therapies. Therefore, NK-based therapies, including NK cells, CAR-NK cells, and antibodies that induce antibody-dependent cellular cytotoxicity of NK cells, have emerged. With recent advances in genetic engineering and cell biology techniques, NK cell-based therapies have become promising approaches for a wide range of cancers, viral infections, and senescence. This review provides a brief overview of NK cell characteristics and summarizes diseases that could benefit from NK-based therapies. In addition, we discuss recent preclinical and clinical investigations on the use of adoptive NK cell transfer and agents that can modulate NK cell activity.

Expression of placental glycans and its role in regulating peripheral blood NK cells during preeclampsia: a perspective

Preeclampsia is a pregnancy-related multisystem disorder characterized by altered trophoblast invasion, oxidative stress, exacerbation of systemic inflammatory response, and endothelial damage. The pathogenesis includes hypertension and mild-to-severe microangiopathy in the kidney, liver, placenta, and brain. The main mechanisms involved in its pathogenesis have been proposed to limit trophoblast invasion and increase the release of extracellular vesicles from the syncytiotrophoblast into the maternal circulation, exacerbating the systemic inflammatory response. The placenta expresses glycans as part of its development and maternal immune tolerance during gestation. The expression profile of glycans at the maternal-fetal interface may play a fundamental role in physiological pregnancy changes and disorders such as preeclampsia. It is unclear whether glycans and their lectin-like receptors are involved in the mechanisms of maternal-fetal recognition by immune cells during pregnancy homeostasis. The expression profile of glycans appears to be altered in hypertensive disorders of pregnancy, which could lead to alterations in the placental microenvironment and vascular endothelium in pregnancy conditions such as preeclampsia. Glycans with immunomodulatory properties at the maternal-fetal interface are altered in early-onset severe preeclampsia, implying that innate immune system components, such as NK cells, exacerbate the systemic inflammatory response observed in preeclampsia. In this article, we discuss the evidence for the role of glycans in gestational physiology and the perspective of glycobiology on the pathophysiology of hypertensive disorders in gestation.

Immunomodulatory effect of locoregional therapy in the tumor microenvironment

Cancer immunotherapy appears to be a promising treatment option; however, only a subset of patients with cancer responds favorably to treatment. Locoregional therapy initiates a local antitumor immune response by disrupting immunosuppressive components, releasing immunostimulatory damage-associated molecular patterns, recruiting immune effectors, and remodeling the tumor microenvironment. Many studies have shown that locoregional therapy can produce specific antitumor immunity alone; nevertheless, the effect is relatively weak and transient. Furthermore, increasing research efforts have explored the potential synergy between locoregional therapy and immunotherapy to enhance the long-term systemic antitumor immune effect and improve survival. Therefore, further research is needed into the immunomodulatory effects of locoregional therapy and immunotherapy to augment antitumor effects. This review article summarizes the key components of the tumor microenvironment, discusses the immunomodulatory role of locoregional therapy in the tumor microenvironment, and emphasizes the therapeutic potential of locoregional therapy in combination with immune checkpoint inhibitors.

Characterization of circulating immune cells and correlation with Tie2/Angiopoietins level in well differentiated neuroendocrine gastroenteropancreatic tumors: a cross-sectional analysis

PURPOSE

The immune environment represents a new, but little explored, tool for understanding neuroendocrine neoplasms (NENs) behavior. An immunosuppressed microenvironment is hypothesized to promote NENs progression. A missing profiling of circulating leukocyte and peripheral blood mononuclear cells (PBMCs) subpopulations would open new perspectives in the still limited diagnostic-therapeutic management of NENs.

METHODS

A cross-sectional case-control pilot study was performed recruiting 30 consecutive subjects: 15 patients naïve to treatment, with histologically proven gastroenteropancreatic (GEP) neuroendocrine tumors (NETs) and 15 healthy controls, matched for age and sex. PBMCs subpopulations were studied by flow cytometry. Soluble Tie2 (sTie2), Angiopoietin-1 (Ang-1), Angiopoietin-2 (Ang-2) were evaluated by ELISA.

RESULTS

Immune cell profiling revealed a significant lower CD3^-CD56⁺ natural killer (NK) cell count in NETs vs controls (p = 0.04). NK subset analysis showed a reduced relative count of CD56⁺CD16⁺ NK cells (p =0.002) in NETs vs controls. Patients with NET showed a higher percentage of CD14⁺CD16⁺⁺ non-classical monocytes (p = 0.01), and a lower percentage of CD14⁺CD16⁺ intermediate monocytes (p = 0.04). A decrease in percentage (p = 0.004) of CD4⁺ T-helper lymphocytes was found in NET patients. Evaluation of cellular and serum angiopoietin pathway mediators revealed in NET patients a higher relative count of Tie2-expressing monocytes (TEMs) (p < 0.001), and high levels of Ang-1 (p = 0.003) and Ang-2 (p = 0.002).

CONCLUSIONS

Patients with GEP-NET presented an immunosuppressed environment characterized by a low count of cytotoxic NK cells, a high count of anti-inflammatory non-classical monocytes, and a low count of T-helper lymphocytes. Higher levels of TEMs and angiopoietins suggest a crosstalk between innate immunity and angiogenic pathways in NETs.

Weaponizing natural killer cells for solid cancer immunotherapy

Enhancing natural killer (NK) cell-based innate immunity has become a promising strategy for immunotherapy against hard-to-cure solid cancers. Monoclonal antibody (mAb) therapy has been used to activate NK-cell-mediated antibody-dependent cellular cytotoxicity (ADCC) towards solid cancers. Cancer cells, however, can subvert immunosurveillance using multiple immunosuppressive mechanisms, which may hamper NK cell ADCC. Mechanisms to safely enhance ADCC by NK cells, such as utilizing temporary inhibition of receptor endocytosis to increase antibody presentation from target to effector cells can now be used to enhance NK-cell-mediated ADCC against solid tumors. This review summarizes and discusses the recent advances in the field and highlights current and potential future use of immunotherapies to maximize the therapeutic efficacy of innate anticancer immunity.

Clinical application and prospect of immune checkpoint inhibitors for CAR-NK cell in tumor immunotherapy

Chimeric antigen receptor (CAR) engineering of natural killer (NK) cells is an attractive research field in tumor immunotherapy. While CAR is genetically engineered to express certain molecules, it retains the intrinsic ability to recognize tumor cells through its own receptors. Additionally, NK cells do not depend on T cell receptors for cytotoxic killing. CAR-NK cells exhibit some differences to CAR-T cells in terms of more precise killing, numerous cell sources, and increased effectiveness in solid tumors. However, some problems still exist with CAR-NK cell therapy, such as cytotoxicity, low transfection efficiency, and storage issues. Immune checkpoints inhibit immune cells from performing their normal killing function, and the clinical application of immune checkpoint inhibitors for cancer treatment has become a key therapeutic strategy. The application of CAR-T cells and immune checkpoint inhibitors is being evaluated in numerous ongoing basic research and clinical studies. Immune checkpoints may affect the function of CAR-NK cell therapy. In this review, we describe the combination of existing CAR-NK cell technology with immune checkpoint therapy and discuss the research of CAR-NK cell technology and future clinical treatments. We also summarize the progress of clinical trials of CAR-NK cells and immune checkpoint therapy.

Phenotypic diversity of human adipose tissue-resident NK cells in obesity

Natural killer (NK) cells have emerged as key mediators of obesity-related adipose tissue inflammation. However, the phenotype of NK cell subsets residing in human adipose tissue are poorly defined, preventing a detailed understanding of their role in metabolic disorders. In this study, we applied multicolor flow cytometry to characterize CD56^bright and CD56^dim NK cells in blood and adipose tissue depots in individuals with obesity and identified surface proteins enriched on adipose tissue-resident CD56^bright NK cells. Particularly, we found that adipose tissue harbored clusters of tissue-resident CD56^bright NK cells signatured by the expression of CD26, CCR5 and CD63, possibly reflecting an adaptation to the microenvironment. Together, our findings provide broad insights into the identity of NK cells in blood and adipose tissue in relation to obesity.

The Role of NK Cells and Their Exosomes in Graft Versus Host Disease and Graft Versus Leukemia

Natural killer (NK) cells are one of the innate immune cells that play an important role in preventing and controlling tumors and viral diseases, but their role in hematopoietic stem cell transplantation (HCT) is not yet fully understood. However, according to some research, these cells can prevent infections and tumor relapse without causing graft versus host disease (GVHD). In addition to NK cells, several studies are about the anti-leukemia effects of NK cell-derived exosomes that can highlight their roles in graft-versus-leukemia (GVL). In this paper, we intend to investigate the results of various articles on the role of NK cells in allogeneic hematopoietic cell transplantation and also their exosomes in GVL. Also, we have discussed the antiviral effects of these cells in post-HCT cytomegalovirus infection.

Mucosa associated invariant T and natural killer cells in active and budesonide treated collagenous colitis patients

Introduction

Collagenous colitis (CC) is an inflammatory bowel disease, which usually responds to budesonide treatment. Our aim was to study the immunological background of the disease.

Methods

Analyses of peripheral and mucosal MAIT (mucosa associated invariant T cells) and NK (natural killer) cells were performed with flow cytometry. Numbers of mucosal cells were calculated using immunohistochemistry. We studied the same patients with active untreated CC (au-CC) and again while in remission on budesonide treatment. Budesonide refractory patients and healthy controls were also included. The memory marker CD45R0 and activation marker CD154 and CD69 were used to further study the cells. Finally B cells, CD4⁺ and CD8⁺ T cells were also analysed.

Results

The percentages of circulating CD56^dimCD16⁺ NK cells as well as MAIT cells (CD3⁺TCRVa7.2⁺CD161⁺) were decreased in au-CC compared to healthy controls. This difference was not seen in the mucosa; where we instead found increased numbers of mucosal CD4⁺ T cells and CD8⁺ T cells in au-CC. Mucosal immune cell numbers were not affected by budesonide treatment. In refractory CC we found increased mucosal numbers of MAIT cells, CD4⁺ and CD8⁺ T cells compared to au-CC.

Discussion

Patients with active collagenous colitis have lower percentages of circulating MAIT and NK cells. However, there was no change of these cells in the colonic mucosa. Most mucosal cell populations were increased in budesonide refractory as compared to au-CC patients, particularly the number of MAIT cells. This may indicate that T cell targeting therapy could be an alternative in budesonide refractory CC.

Inflammatory-driven NK cell maturation and its impact on pathology

NK cells are innate lymphocytes involved in a large variety of contexts and are crucial in the immunity to intracellular pathogens as well as cancer due to their ability to kill infected or malignant cells. Thus, they harbor a strong potential for clinical and therapeutic use. NK cells do not require antigen exposure to get activated; their functional response is rather based on a balance between inhibitory/activating signals and on the diversity of germline-encoded receptors they express. In order to reach optimal functional status, NK cells go through a step-wise development in the bone marrow before their egress, and dissemination into peripheral organs via the circulation. In this review, we summarize bone marrow NK cell developmental stages and list key factors involved in their differentiation before presenting newly discovered and emerging factors that regulate NK cell central and peripheral maturation. Lastly, we focus on the impact inflammatory contexts themselves can have on NK cell development and functional maturation.

The Value of Single-cell Technologies in Solid Organ Transplantation Studies

Single-cell technologies open up new opportunities to explore the behavior of cells at the individual level. For solid organ transplantation, single-cell technologies can provide in-depth insights into the underlying mechanisms of the immunological processes involved in alloimmune responses after transplantation by investigating the role of individual cells in tolerance and rejection. Here, we review the value of single-cell technologies, including cytometry by time-of-flight and single-cell RNA sequencing, in the context of solid organ transplantation research. Various applications of single-cell technologies are addressed, such as the characterization and identification of immune cell subsets involved in rejection or tolerance. In addition, we explore the opportunities for analyzing specific alloreactive T- or B-cell clones by linking phenotype data to T- or B-cell receptor data, and for distinguishing donor- from recipient-derived immune cells. Moreover, we discuss the use of single-cell technologies in biomarker identification and risk stratification, as well as the remaining challenges. Together, this review highlights that single-cell approaches contribute to a better understanding of underlying immunological mechanisms of rejection and tolerance, thereby potentially accelerating the development of new or improved therapies to avoid allograft rejection.

New Insights and Implications of Natural Killer Cells in Parkinson's Disease

Parkinson's disease (PD) is the second most common neurodegenerative disease and is characterized by the loss of dopaminergic neurons in the substantia nigra and the abnormal aggregation and accumulation of the alpha-synuclein (α-syn) protein into Lewy bodies. It is established that there is an association between inflammation and PD; however, the time course of the inflammatory process as well as the immune cells involved are still debated. Natural killer (NK) cells are innate lymphocytes with numerous functions including targeting and killing infected or malignant cells, antimicrobial defense, and resolving inflammation. NK cell subsets differ in their effector function capacities which are modulated by activating and inhibitory receptors expressed at the cell surface. Alterations in NK cell numbers and receptor expression have been reported in PD patients. Recently, NK cell numbers and frequency were shown to be altered in the periphery and in the central nervous system in a preclinical mouse model of PD. Moreover, NK cells have recently been shown to internalize and degrade α-syn aggregates and systemic NK cell depletion exacerbated synuclein pathology in a preclinical mouse model of PD, indicating a potential protective role of NK cells. Here, we review the inflammatory process in PD with a particular focus on alterations in NK cell numbers, phenotypes, and functions.

Identification of aging-associated immunotypes and immune stability as indicators of post-vaccination immune activation

Immunosenescence describes immune dysfunction observed in older individuals. To identify individuals at-risk for immune dysfunction, it is crucial to understand the diverse immune phenotypes and their intrinsic functional capabilities. We investigated immune cell subsets and variation in the aging population. We observed that inter-individual immune variation was associated with age and cytomegalovirus seropositivity. Based on the similarities of immune subset composition among individuals, we identified nine immunotypes that displayed different aging-associated immune signatures, which explained inter-individual variation better than age. Additionally, we correlated the immune subset composition of individuals over approximately a year as a measure of stability of immune parameters. Immune stability was significantly lower in immunotypes that contained aging-associated immune subsets and correlated with a circulating CD38 + CD4+ T follicular helper cell increase 7 days after influenza vaccination. In conclusion, immune stability is a feature of immunotypes and could be a potential indicator of post-vaccination cellular kinetics.

Ebola virus protein VP40 stimulates IL-12- and IL-18-dependent activation of human natural killer cells

Accumulation of activated natural killer (NK) cells in tissues during Ebola virus infection contributes to Ebola virus disease (EVD) pathogenesis. Yet, immunization with Ebola virus-like particles (VLPs) comprising glycoprotein and matrix protein VP40 provides rapid, NK cell–mediated protection against Ebola challenge. We used Ebola VLPs as the viral surrogates to elucidate the molecular mechanism by which Ebola virus triggers heightened NK cell activity. Incubation of human peripheral blood mononuclear cells with Ebola VLPs or VP40 protein led to increased expression of IFN-γ, TNF-α, granzyme B, and perforin by CD3^–CD56⁺ NK cells, along with increases in degranulation and cytotoxic activity of these cells. Optimal activation required accessory cells like CD14⁺ myeloid and CD14^– cells and triggered increased secretion of numerous inflammatory cytokines. VP40-induced IFN-γ and TNF-α secretion by NK cells was dependent on IL-12 and IL-18 and suppressed by IL-10. In contrast, their increased degranulation was dependent on IL-12 with little influence of IL-18 or IL-10. These results demonstrate that Ebola VP40 stimulates NK cell functions in an IL-12– and IL-18–dependent manner that involves CD14⁺ and CD14^– accessory cells. These potentially novel findings may help in designing improved intervention strategies required to control viral transmission during Ebola outbreaks.

Recruited and Tissue-Resident Natural Killer Cells in the Lung During Infection and Cancer

Natural killer (NK) cells are an important component of the innate immune system, and have a key role in host defense against infection and in tumor surveillance. Tumors and viruses employ remarkably similar strategies to avoid recognition and killing by NK cells and so much can be learnt by comparing NK cells in these disparate diseases. The lung is a unique tissue environment and immune cells in this organ, including NK cells, exist in a hypofunctional state to prevent activation against innocuous stimuli. Upon infection, rapid NK cell infiltration into the lung occurs, the amplitude of which is determined by the extent of inflammation and damage. Activated NK cells kill infected cells and produce pro-inflammatory cytokines and chemokines to recruit cells of the adaptive immune system. More recent evidence has shown that NK cells also play an additional role in resolution of inflammation. In lung cancer however, NK cell recruitment is impaired and those that are present have reduced functionality. The majority of lung NK cells are circulatory, however recently a small population of tissue-resident lung NK cells has been described. The specific role of this subset is yet to be determined, but they show similarity to resident memory T cell subsets. Whether resident or recruited, NK cells are important in the control of pulmonary infections, but equally, can drive excessive inflammation if not regulated. In this review we discuss how NK cells are recruited, controlled and retained in the specific environment of the lung in health and disease. Understanding these mechanisms in the context of infection may provide opportunities to promote NK cell recruitment and function in the lung tumor setting.

What Inhibits Natural Killers’ Performance in Tumour

Natural killer cells are innate lymphocytes with the ability to lyse tumour cells depending on the balance of their activating and inhibiting receptors. Growing numbers of clinical trials show promising results of NK cell-based immunotherapies. Unlike T cells, NK cells can lyse tumour cells independent of antigen presentation, based simply on their activation and inhibition receptors. Various strategies to improve NK cell-based therapies are being developed, all with one goal: to shift the balance to activation. In this review, we discuss the current understanding of ways NK cells can lyse tumour cells and all the inhibitory signals stopping their cytotoxic potential.

Acute portal hypertension using portal vein ligation abrogates TRAIL expression of liver-resident NK cells

The effects of acute portal hypertension (PHT), which is reported as poor prognostic factors in patients with hepatocellular carcinoma, are not well known on the liver immune system, including natural killer (NK) cells. The aim of this study, therefore, was to investigate how acute PHT influences the functions and characteristics of liver‐resident NK (lr‐NK) cells using an acute PHT mouse model. Acute PHT decreased the number of tumor necrosis factor–related apoptosis‐inducing ligand (TRAIL⁺) lr‐NK cells by about 20% and attenuated cytotoxic activity against the Hepa1‐6 cell line by about 40%. Among various cytokine, only interleukin‐33 (IL‐33), which inhibits NK activity, significantly increased after portal vein ligation (PVL). Because lr‐NK cells highly expressed ST2/IL‐33R, IL‐33 co‐culture significantly suppressed TRAIL expression on lr‐NK cells by about 50%, and IL‐33 administration markedly decreased TRAIL expression and cytotoxic activity of lr‐NK cells. Furthermore, the TRAIL⁺ NK cells population was maintained by anti‐IL33 antibody or following portosystemic shunt procedure even after PVL. Finally, we demonstrated that IL‐33 decreased TRAIL expression in lr‐NK cells via AKT–forkhead box O (FoxO) and mitogen‐activated protein kinase (MAPK) signaling. Conclusion: This work demonstrates that PHT suppresses the TRAIL⁺ lr‐NK cell population and antitumor activities in the liver. Additionally, Akt‐FoxO and MAPK signaling pathways attenuate the TRAIL expression in lt‐NK cells via IL‐33 receptor in mice.

All About (NK Cell-Mediated) Death in Two Acts and an Unexpected Encore: Initiation, Execution and Activation of Adaptive Immunity

NK cells are key mediators of immune cell-mediated cytotoxicity toward infected and transformed cells, being one of the main executors of cell death in the immune system. NK cells recognize target cells through an array of inhibitory and activating receptors for endogenous or exogenous pathogen-derived ligands, which together with adhesion molecules form a structure known as immunological synapse that regulates NK cell effector functions. The main and best characterized mechanisms involved in NK cell-mediated cytotoxicity are the granule exocytosis pathway (perforin/granzymes) and the expression of death ligands. These pathways are recognized as activators of different cell death programmes on the target cells leading to their destruction. However, most studies analyzing these pathways have used pure recombinant or native proteins instead of intact NK cells and, thus, extrapolation of the results to NK cell-mediated cell death might be difficult. Specially, since the activation of granule exocytosis and/or death ligands during NK cell-mediated elimination of target cells might be influenced by the stimulus received from target cells and other microenvironment components, which might affect the cell death pathways activated on target cells. Here we will review and discuss the available experimental evidence on how NK cells kill target cells, with a special focus on the different cell death modalities that have been found to be activated during NK cell-mediated cytotoxicity; including apoptosis and more inflammatory pathways like necroptosis and pyroptosis. In light of this new evidence, we will develop the new concept of cell death induced by NK cells as a new regulatory mechanism linking innate immune response with the activation of tumour adaptive T cell responses, which might be the initiating stimulus that trigger the cancer-immunity cycle. The use of the different cell death pathways and the modulation of the tumour cell molecular machinery regulating them might affect not only tumour cell elimination by NK cells but, in addition, the generation of T cell responses against the tumour that would contribute to efficient tumour elimination and generate cancer immune memory preventing potential recurrences.

Cellular Origins and Pathogenesis of Gastrointestinal NK- and T-Cell Lymphoproliferative Disorders

The intestinal immune system, which must ensure appropriate immune responses to both pathogens and commensal microflora, comprises innate lymphoid cells and various T-cell subsets, including intra-epithelial lymphocytes (IELs). An example of innate lymphoid cells is natural killer cells, which may be classified into tissue-resident, CD56bright NK-cells that serve a regulatory function and more mature, circulating CD56dim NK-cells with effector cytolytic properties. CD56bright NK-cells in the gastrointestinal tract give rise to indolent NK-cell enteropathy and lymphomatoid gastropathy, as well as the aggressive extranodal NK/T cell lymphoma, the latter following activation by EBV infection and neoplastic transformation. Conventional CD4+ TCRαβ+ and CD8αβ+ TCRαβ+ T-cells are located in the lamina propria and the intraepithelial compartment of intestinal mucosa as type 'a' IELs. They are the putative cells of origin for CD4+ and CD8+ indolent T-cell lymphoproliferative disorders of the gastrointestinal tract and intestinal T-cell lymphoma, NOS. In addition to such conventional T-cells, there are non-conventional T-cells in the intra-epithelial compartment that express CD8αα and innate lymphoid cells that lack TCRs. The central feature of type 'b' IELs is the expression of CD8αα homodimers, seen in monomorphic epitheliotropic intestinal T-cell lymphoma (MEITL), which primarily arises from both CD8αα+ TCRαβ+ and CD8αα+ TCRγδ+ IELs. EATL is the other epitheliotropic T-cell lymphoma in the GI tract, a subset of which arises from the expansion and reprograming of intracytoplasmic CD3+ innate lymphoid cells, driven by IL15 and mutations of the JAK-STAT pathway.

HLA-B*57:01 Complexed to a CD8 T-Cell Epitope from the HSV-2 ICP22 Protein Binds NK and T Cells through KIR3DL1

HLA-B*57:01 is an HLA allelic variant associated with positive outcomes during viral infections through interactions with T cells and NK cells, but severe disease in persons treated with the anti-HIV-1 drug abacavir. The role of HLA-B*57:01 in the context of HSV infection is unknown. We identified an HLA-B*57:01-restricted CD8 T-cell epitope in the ICP22 (US1) protein of HSV-2. CD8 T cells reactive to the HSV-2 ICP22 epitope recognized the orthologous HSV-1 peptide, but not closely related peptides in human IFNL2 or IFNL3. Abacavir did not alter the CD8 T-cell recognition of the HSV or self-derived peptides. Unexpectedly, a tetramer of HSV-2 ICP22 epitope (228–236) and HLA-B*57:01 bound both CD8 T cells and NK cells. Tetramer specificity for KIR3DL1 was confirmed using KIR3DL1 overexpression on non-human primate cells lacking human KIR and studies with blocking anti-KIR3DL1 antibody. Interaction with KIR3DL1 was generalizable to donors lacking the HLA-B*57:01 genotype or HSV seropositivity. These findings suggest a mechanism for the recognition of HSV infection by NK cells or KIR-expressing T cells via KIR3DL1.

Advances of research of Fc-fusion protein that activate NK cells for tumor immunotherapy

The rapid development of bioengineering technology has introduced Fc-fusion proteins, representing a novel kind of recombinant protein, as promising biopharmaceutical products in tumor therapy. Numerous related anti-tumor Fc-fusion proteins have been investigated and are in different stages of development. Fc-fusion proteins are constructed by fusing the Fc-region of the antibody with functional proteins or peptides. They retain the bioactivity of the latter and partial properties of the former. This structural and functional advantage makes Fc-fusion proteins an effective tool in tumor immunotherapy, especially for the recruitment and activation of natural killer (NK) cells, which play a critical role in tumor immunotherapy. Even though tumor cells have developed mechanisms to circumvent the cytotoxic effect of NK cells or induce defective NK cells, Fc-fusion proteins have been proven to effectively activate NK cells to kill tumor cells in different ways, such as antibody-dependent cell-mediated cytotoxicity (ADCC), activate NK cells in different ways in order to promote killing of tumor cells. In this review, we focus on NK cell-based immunity for cancers and current research progress of the Fc-fusion proteins for anti-tumor therapy by activating NK cells.

Engineering CAR-NK cells: how to tune innate killer cells for cancer immunotherapy

Cell therapy is an innovative approach that permits numerous possibilities in the field of cancer treatment. CAR-T cells have been successfully used in patients with hematologic relapsed/refractory. However, the need for autologous sources for T cells is still a major drawback. CAR-NK cells have emerged as a promising resource using allogeneic cells that could be established as an off-the-shelf treatment. NK cells can be obtained from various sources, such as peripheral blood (PB), bone marrow, umbilical cord blood (CB), and induced pluripotent stem cells (iPSC), as well as cell lines. Genetic engineering of NK cells to express different CAR constructs for hematological cancers and solid tumors has shown promising preclinical results and they are currently being explored in multiple clinical trials. Several strategies have been employed to improve CAR-NK-cell expansion and cytotoxicity efficiency. In this article, we review the latest achievements and progress made in the field of CAR-NK-cell therapy.

The role of NK and NKT cells in the pathogenesis and improvement of multiple sclerosis following disease‐modifying therapies

Background

Multiple sclerosis (MS) is an autoimmune inflammatory disease of the central nervous system (CNS) that T cells become autoreactive by recognizing CNS antigens. Both innate and adaptive immune systems are involved in the pathogenesis of MS. In recent years, the impact of innate immune cells on MS pathogenesis has received more attention. CD56^bright NK cells, as an immunoregulatory subset of NK cells, can increase the production of cytokines that modulate adaptive immune responses, whereas CD56^dim NK cells are more active in cytolysis functions. These two main subsets of NK cells may have different effects on the onset or progression of MS. Invariant NKT (iNKT) cells are other immune cells involved in the control of autoimmune diseases; however, variant NKT (vNKT) cells, despite limited information, could play a role in MS remission via an immunoregulatory pathway.

Aim

We aimed to evaluate the influence of MS therapeutic agents on NK and NKT cells and NK cell subtypes.

Materials and Methods

The possible mechanism of each MS therapeutic agent has been presented here, focusing on the effects of different disease‐modifying therapies on the number of NK and NKT subtypes.

Results

Expansion of CD56^bright NK cells, reduction in the CD56^dim cells, and enhancement in NKT cells are the more important innate immune cells alterations following the disease‐modifying therapies.

Conclusion

Expansion of CD56^bright NK cells or reduction in the CD56^dim cells has been associated with a successful response to different treatments in MS. iNKT and vNKT cells could have beneficial effects on MS improving. It seems that they are enhanced due to some of MS drugs, leading to disease improvement. However, a reduction in the number of NKT cells could be due to the adverse effects of some of MS drugs on the bone marrow.

Understanding human immunity in idiopathic recurrent pregnancy loss

Miscarriage, defined as the loss of a pregnancy before a viable gestation, affects 1 in 6 couples. Recurrent pregnancy loss (RPL), defined as two or more miscarriages, affects up to 1.9% of couples. The physical, psychological, and financial impact of miscarriage can be substantial. However, despite its multifactorial etiology, for up to 50% of couples a reason behind this condition cannot be identified, termed 'idiopathic RPL'. Much recent research has strived to understand this, with immune dysregulation being a source of particular interest. In this short review we summarize the current evidence on the complex role of the immune system both pre- and early post-conception in RPL. A key question is whether systemic peripheral blood markers, in particular natural killer cell and T cells, may be utilized to accurately predict and/ or diagnose those pregnancies at high risk of loss. Given the invasive nature of endometrial testing, identification of reliable peripheral immune biomarkers is particularly appealing. Clinical trials using potent immunomodulatory agents, including intravenous immunoglobulin, donor leukocyte immunization, and tumor necrosis factor (TNF)-α inhibitors, have been undertaken with the primary objective of preventing miscarriage in women with RPL. Standardisation of both diagnostic and prognostic immune cell testing assays is required to permit accurate identification of those women who may benefit from immunomodulation. Prompt clarification is required to meet the increasing expectation from couples and clinicians, as without these advancements women are at risk of exposure to potent immune-therapies and subsequent studies are at risk of failure, generating further controversy regarding the role of immune dysregulation in women with RPL. Through this review we highlight clear gaps in our current knowledge on immune activity in RPL.

Immunotherapy for Hepatocellular Carcinoma: New Prospects for the Cancer Therapy

Hepatocellular carcinoma (HCC) is the fourth leading cause of cancer-related death worldwide. HCC patients may benefit from liver transplantation, hepatic resection, radiofrequency ablation, transcatheter arterial chemoembolization, and targeted therapies. The increased infiltration of immunosuppressive immune cells and the elevated expression of immunosuppressive factors in the HCC microenvironment are the main culprits of the immunosuppressive nature of the HCC milieu. The immunosuppressive tumor microenvironment can substantially attenuate antitumoral immune responses and facilitate the immune evasion of tumoral cells. Immunotherapy is an innovative treatment method that has been promising in treating HCC. Immune checkpoint inhibitors (ICIs), adoptive cell transfer (ACT), and cell-based (primarily dendritic cells) and non-cell-based vaccines are the most common immunotherapeutic approaches for HCC treatment. However, these therapeutic approaches have not generally induced robust antitumoral responses in clinical settings. To answer to this, growing evidence has characterized immune cell populations and delineated intercellular cross-talk using single-cell RNA sequencing (scRNA-seq) technologies. This review aims to discuss the various types of tumor-infiltrating immune cells and highlight their roles in HCC development. Besides, we discuss the recent advances in immunotherapeutic approaches for treating HCC, e.g., ICIs, dendritic cell (DC)-based vaccines, non-cell-based vaccines, oncolytic viruses (OVs), and ACT. Finally, we discuss the potentiality of scRNA-seq to improve the response rate of HCC patients to immunotherapeutic approaches.

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.

Directly reprogrammed natural killer cells for cancer immunotherapy

Efficacious and accessible sources of natural killer (NK) cells would widen their use as immunotherapeutics, particularly for solid cancers. Here, we show that human somatic cells can be directly reprogrammed into NK cells with a CD56^brightCD16^bright phenotype using pluripotency transcription factors and an optimized reprogramming medium. The directly reprogrammed NK cells have strong innate-adaptive immunomodulatory activity and are highly potent against a wide range of cancer cells, including difficult-to-treat solid cancers and cancer stem cells. Both directly reprogrammed NK cells bearing a cancer-specific chimeric antigen receptor and reprogrammed NK cells in combination with antibodies competent for antibody-dependent cell-mediated cytotoxicity led to selective anticancer effects with augmented potency. The direct reprogramming of human somatic cells into NK cells is amenable to the production of autologous and allogeneic NK cells, and will facilitate the design and testing of cancer immunotherapies and combination therapies.

Activated natural killer cells predict poor clinical prognosis in high-risk B- and T-cell acute lymphoblastic leukemia

B- and T-cell acute lymphoblastic leukemia (B/T-ALL) may be refractory or recur after therapy by suppressing host anticancer immune surveillance mediated specifically by natural killer (NK) cells. We delineated the phenotypic and functional defects in NK cells from high-risk patients with B/T-ALL using mass cytometry, flow cytometry, and in silico cytometry, with the goal of further elucidating the role of NK cells in sustaining acute lymphoblastic leukemia (ALL) regression. We found that, compared with their normal counterparts, NK cells from patients with B/T-ALL are less cytotoxic but exhibit an activated signature that is characterized by high CD56, high CD69, production of activated NK cell-origin cytokines, and calcium (Ca2+) signaling. We demonstrated that defective maturation of NK cells into cytotoxic effectors prevents NK cells from ALL from lysing NK cell-sensitive targets as efficiently as do normal NK cells. Additionally, we showed that NK cells in ALL are exhausted, which is likely caused by their chronic activation. We found that increased frequencies of activated cytokine-producing NK cells are associated with increased disease severity and independently predict poor clinical outcome in patients with ALL. Our studies highlight the benefits of developing NK cell profiling as a diagnostic tool to predict clinical outcome in patients with ALL and underscore the clinical potential of allogeneic NK cell infusions to prevent ALL recurrence.

Transcription factor Zhx2 restricts NK cell maturation and suppresses their antitumor immunity

The maturation and functional competence of natural killer (NK) cells is a tightly controlled process that relies on transcription factors (TFs). Here, we identify transcriptional repressor zinc fingers and homeoboxes 2 (Zhx2) as a novel regulator that restricts NK cell maturation and function. Mice with Zhx2 conditional deletion in NK cells (Zhx2Δ/Δ) showed accumulation of matured NK cells. Loss of Zhx2 enhanced NK cell survival and NK cell response to IL-15. Transcriptomic analysis revealed Zeb2, a key TF in NK cell terminal maturation, as a direct downstream target of Zhx2. Therapeutically, transfer of Zhx2-deficient NK cells resulted in inhibition of tumor growth and metastasis in different murine models. Our findings collectively unmask a previously unrecognized role of Zhx2 as a novel negative regulator in NK cell maturation and highlight its therapeutic potential as a promising strategy to enhance NK cell-mediated tumor surveillance.

Natural killer cells: functional differences in recurrent spontaneous abortion†

Recurrent spontaneous abortion (RSA) is one of the major pregnancy disorders and poses a serious risk to both the mother and the fetus. Although a number of research efforts have been conducted, therapeutic advances for treating RSA have not lived up to their expectations. Hence, other treatments should be explored. The important role of natural killer (NK) cells in immunotherapy is attracting increasing attention, both as a pharmaceutical target and for cell therapies. NK cells are abundant in the endometrium and play a role in implantation and placentation in normal pregnancy. As research progresses, NK cells are increasingly regarded as playing essential roles in the emergence and development of RSA. In this article, I review recent findings on the role of uterine NK cells in the pathophysiology of RSA. These cells may become therapeutic NK cell-related targets. In conclusion, although several issues regarding NK cells in RSA remain unresolved and require further investigation, extensive evidence is available for the treatment of RSA.

Tumor infiltrating NK cell (TINK) subsets and functional molecules in patients with breast cancer

INTRODUCTION

NK cells have been introduced as the main innate arm of immunity against malignancies. Recent advances introduced new subsets of, and new effector molecules on NK cells suggesting new paradigms for NK cell functions in tumor immunity. Considering these new paradigms, in the current research we investigated the frequency of tumor infiltrating NK cell (TINK) subsets and their functional molecules in breast tumor tissues by flowcytometry method.

METHODS

Breast tumor tissues were obtained from 32 untreated patients with breast cancer. The tissues were then minced mechanically to acquire a single cell suspension and surface-stained with monoclonal antibodies against CD3, CD56, CD11b, CD27, NKG2A, NKG2D and CXCR3. For intracellular staining (ICS), the surface-stained cells were then fixed, permeabilized and stained with anti-Perforin and anti-Granzyme B antibodies. The samples were run and the data were acquired on a four-color flowcytometer.

RESULTS

The cell suspension derived from tumor tissue encompassed 3.10 ± 0.52 % CD3^-CD56^{+(bright/dim)} total NK cells. Based on the conventional classification the percentages of cytotoxic (CD3^- CD56^dim) and regulatory (CD3^- CD56^bright) NK cells were respectively 1.74 ± 0.24 % and 1.36 ± 0.48 %. According to the new classification the percentages of cytotoxic (CD3- CD56⁺ CD11b⁺ CD27^-), regulatory (CD3^-CD56⁺ CD11b^+/- CD27⁺) and tolerant (CD3^-CD56⁺ CD27- CD11b^-) NK cells were respectively 0.48 ± 0.07, 1.55 ± 0.34 and 1.15 ± 0.51. A significant higher frequency of total NK cells (CD3^-CD56^{+ (bright/dim)}) in the breast tumor tissues of the patients whose tumor draining lymph nodes (TDLNs) has not been yet involved by tumor cells (LN^- patients) compared with the ones with lymph nodes involvement (LN⁺) (5.91 ± 1.79 % Vs. 2.20 ± 0.20 %, P < 0.004). Furthermore, NK cells with overexpressed activating receptor; NKGD2 (CD3- CD56^{+(bright/dim)} NKG2D⁺ NK cells) was observed to be elevated in LN^- patients compared with the LN⁺ ones (70.01 ± 7.96 Vs. 42.5 ± 4.81, P < 0.011). Correlation analysis revealed the percentages of conventional regulatory NK cells (CD3- CD56^bright) in breast tumor tissue to be in positive correlation with the tumor size (R = 0.380, P < 0.04). The mean percentage of this cell subset was also observed to be higher in patients with T3 tumor size compared with smaller T1 tumor size (1.61 ± 0.20 % vs. 0.75 ± 0.15 %, P < 0.023.

CONCLUSION

Our observations suggest that accumulation of NK cells as well as the expression of activating NKG2D receptor by TINKs may play roles in breast tumor regression especially in the LN^- patients. As the tumor growths and the size of tumor increases the accumulation of regulatory NK cells may facilitate the tumor improvement. These observations may have implications in cancer NK cell-based immunotherapy.

Uterine natural killer cells: from foe to friend in reproduction

BACKGROUND

Recurrent miscarriage and pre-eclampsia are common reproductive disorders, but their causes are often unknown. Recent evidence has provided new insight into immune system influences in reproductive disorders. A subset of lymphocytes of the innate immune system known as uterine natural killer (uNK) cells are now recognized as fundamental to achieving embryo implantation and successful pregnancy, but were initially attributed a bad reputation. Indeed, immune therapies have been developed to treat the 'exaggerated' immune response from uNK cells. These treatments have been based on studies of peripheral blood natural killer (pbNK) cells. However, uNK cells and pbNK cells have different phenotypic and functional characteristics. The functions of uNK cells are closely related to their interactions with the extravillous trophoblast cells (EVTs) and spiral arteries, which underlie an essential role in regulating vascular function, controlling trophoblast invasion and promoting placental development. EVTs express MHC molecules of class I HLA-C/E/G/F, while uNK cells express, among other receptors, killer cell immunoglobulin-like receptors (KIRs) that bind to HLA-C or CD94/NKG2A inhibitory receptors, and then bind HLA-E. Associations of certain KIR/HLA-C combinations with recurrent miscarriage, pre-eclampsia, and foetal growth restriction and the interactions between uNK cells, trophoblasts and vascular cells have led to the hypothesis that uNK cells may play a role in embryo implantation.

OBJECTIVE AND RATIONALE

Our objective was to review the evolution of our understanding of uNK cells, their functions, and their increasingly relevant role in reproduction.

SEARCH METHODS

Relevant literature through June 2020 was retrieved using Google Scholar and PubMed. Search terms comprised uNK cells, human pregnancy, reproductive failure, maternal KIR and HLA-C, HLA-E/G/F in EVT cells, angiogenic cytokines, CD56+ NK cells, spiral artery, oestrogen and progesterone receptors, KIR haplotype and paternal HLA-C2.

OUTCOMES

This review provides key insights into the evolving conceptualization of uNK cells, from their not-so-promising beginnings to now, when they are considered allies in reproduction. We synthesized current knowledge about uNK cells, their involvement in reproduction and their main functions in placental vascular remodeling and trophoblast invasion. One of the issues that this review presents is the enormous complexity involved in studying the immune system in reproduction. The complexity in the immunology of the maternal-foetal interface lies in the great variety of participating molecules, the processes and interactions that occur at different levels (molecular, cellular, tissue, etc.) and the great diversity of genetic combinations that are translated into different types of responses.

WIDER IMPLICATIONS

Insights into uNK cells could offer an important breakthrough for ART outcomes, since each patient could be assessed based on the combination of HLA and its receptors in their uNK cells, evaluating the critical interactions at the materno-foetal interface. However, owing to the technical challenges in studying uNK cells in vivo, there is still much knowledge to gain, particularly regarding their exact origin and functions. New studies using novel molecular and genetic approaches can facilitate the identification of mechanisms by which uNK cells interact with other cells at the materno-foetal interface, perhaps translating this knowledge into clinical applicability.