The Rise of NK Cell Checkpoints as Promising Therapeutic Targets in Cancer Immunotherapy

Targeted immune cell therapy for hepatocellular carcinoma using expanded liver mononuclear cell-derived natural killer cells

Natural killer (NK) cells are a promising cellular therapy for T cell-refractory cancers but are frequently deficient or dysfunctional in patients with hepatocellular carcinoma (HCC). In the present study, we explored a novel therapy for HCC using NK cells derived from donor liver graft perfusate. These liver-derived NK cells, named LMNC-NK cells, are more abundant in liver mononuclear cells (LMNCs) than in peripheral blood mononuclear cells (PBMCs) from the same donor. We developed a method to expand LMNC-NK cells by 33.8±54.4-fold, enhancing their cytotoxic properties and cytokine production, including granzyme B, CD107a, TNF-α, and IFN-γ. These cells also showed an increased expression of cytotoxicity receptors. An RNA-seq analysis revealed considerable differences in gene expression between LMNC-NK and PBMC-NK cells, with 453 genes upregulated and 449 downregulated in LMNC-NK cells. These genes are involved in the mitogen-activated protein kinase cascade and cell differentiation, explaining the increased activity of LMNC-NK cells. Quantitative reverse transcription polymerase chain reaction confirmed the significant upregulation of TLR6, KIT, MMP14, IRF8, TCF7, FCERIG, LEF1, NLRp3, and IL16 in LMNC-NK cells. LMNC-NK cells effectively eliminated HepG-2-Luc cells in vitro, and in an orthotopic murine model of HCC, they exhibited a potent anti-tumor effect, outperforming PBMC-NK cells. The expression of the activation marker CD69+ in LMNC-NK cells was also significantly higher among tumor-infiltrating lymphocytes compared to PBMC-NK cells. Our research suggests that the adoptive transfer of LMNC-NK cells could be a promising treatment for HCC, offering a novel and effective source of NK cells with superior cytotoxic functions.

The basic biology of NK cells and its application in tumor immunotherapy

Natural Killer (NK) cells play a crucial role as effector cells within the tumor immune microenvironment, capable of identifying and eliminating tumor cells through the expression of diverse activating and inhibitory receptors that recognize tumor-related ligands. Therefore, harnessing NK cells for therapeutic purposes represents a significant adjunct to T cell-based tumor immunotherapy strategies. Presently, NK cell-based tumor immunotherapy strategies encompass various approaches, including adoptive NK cell therapy, cytokine therapy, antibody-based NK cell therapy (enhancing ADCC mediated by NK cells, NK cell engagers, immune checkpoint blockade therapy) and the utilization of nanoparticles and small molecules to modulate NK cell anti-tumor functionality. This article presents a comprehensive overview of the latest advances in NK cell-based anti-tumor immunotherapy, with the aim of offering insights and methodologies for the clinical treatment of cancer patients.

Advances in CAR-NK cell therapy for hematological malignancies

Chimeric antigen receptor T (CAR-T) cell therapy has revolutionized the treatment of hematological malignancies, demonstrably improving patient outcomes and prognosis. However, its application has introduced new challenges, such as safety concerns, off-target toxicities, and significant costs. Natural killer (NK) cells are crucial components of the innate immune system, capable of eliminating tumor cells without prior exposure to specific antigens or pre-activation. This inherent advantage complements the limitations of T cells, making CAR-NK cell therapy a promising avenue for hematological tumor immunotherapy. In recent years, preclinical and clinical studies have yielded preliminary evidence supporting the safety and efficacy of CAR-NK cell therapy in hematological malignancies, paving the way for future advancements in immunotherapy. This review aims to succinctly discuss the characteristics, significant therapeutic progress, and potential challenges associated with CAR-NK cell therapy.

Immunotherapy of Clear-Cell Renal-Cell Carcinoma

Clear-cell Renal-Cell Carcinoma (ccRCC) is the most common type of renal-cell carcinoma (RCC). In many cases, RCC patients manifest the first symptoms during the advanced stage of the disease. For this reason, immunotherapy appears to be one of the dominant treatments to achieve a resolution. In this review, we focus on the presentation of the main immune checkpoint proteins that act as negative regulators of immune responses, such as PD-1, CTLA-4, LAG-3, TIGIT, and TIM-3, and their respective inhibitors. Interleukin-2, another potential component of the treatment of ccRCC patients, has also been covered. The synergy between several immunotherapies is one of the main aspects that unites the conclusions of research in recent years. To date, the combination of several immunotherapies enhances the efficacy of a monotherapy, which often manifests important limitations. Immunotherapy aimed at restoring the anti-cancer immune response in ccRCC, involved in the recognition and elimination of cancer cells, may also be a valid solution for many other types of immunogenic tumors that are diagnosed in the final stages.

Exercise-induced β2-adrenergic Receptor Activation Enhances the Antileukemic Activity of Expanded γδ T-Cells via DNAM-1 Upregulation and PVR/Nectin-2 Recognition

Exercise mobilizes cytotoxic lymphocytes to blood which may allow superior cell products to be harvested and manufactured for cancer therapy. Gamma-Delta (γδ) T-cells have shown promise for treating solid tumors, but there is a need to increase their potency against hematologic malignancies. Here, we show that human γδ T-cells mobilized to blood in response to just 20 minutes of graded exercise have surface phenotypes and transcriptomic profiles associated with cytotoxicity, adhesion, migration, and cytokine signaling. Following 14 days ex vivo expansion with zoledronic acid and IL2, exercise mobilized γδ T-cells had surface phenotypes and transcriptomic profiles associated with enhanced effector functions and demonstrated superior cytotoxic activity against multiple hematologic tumors in vitro and in vivo in leukemia-bearing xenogeneic mice. Infusing humans with the β1+β2-agonist isoproterenol and administering β1 or β1+β2 antagonists prior to exercise revealed these effects to be β2-adrenergic receptor (AR) dependent. Antibody blocking of DNAM-1 on expanded γδ T-cells, as well as the DNAM-1 ligands PVR and Nectin-2 on leukemic targets, abolished the enhanced antileukemic effects of exercise. These findings provide a mechanistic link between exercise, β2-AR activation, and the manufacture of superior γδ T-cell products for adoptive cell therapy against hematologic malignancies.

SIGNIFICANCE

Exercise mobilizes effector γδ T-cells to blood via β2-adrenergic signaling which allows for generation of a potent expanded γδ T-cell product that is highly cytotoxic against hematologic malignancies.

The role of exhausted natural killer cells in the immunopathogenesis and treatment of leukemia

The immune responses to cancer cells involve both innate and acquired immune cells. In the meantime, the most attention has been drawn to the adaptive immune cells, especially T cells, while, it is now well known that the innate immune cells, especially natural killer (NK) cells, play a vital role in defending against malignancies. While the immune cells are trying to eliminate malignant cells, cancer cells try to prevent the function of these cells and suppress immune responses. The suppression of NK cells in various cancers can lead to the induction of an exhausted phenotype in NK cells, which will impair their function. Recent studies have shown that the occurrence of this phenotype in various types of leukemic malignancies can affect the prognosis of the disease, and targeting these cells may be considered a new immunotherapy method in the treatment of leukemia. Therefore, a detailed study of exhausted NK cells in leukemic diseases can help both to understand the mechanisms of leukemia progression and to design new treatment methods by creating a deeper understanding of these cells. Here, we will comprehensively review the immunobiology of exhausted NK cells and their role in various leukemic malignancies. Video Abstract.

Chimeric antigen receptor-based natural killer cell immunotherapy in cancer: from bench to bedside

Immunotherapy has rapidly evolved in the past decades in the battle against cancer. Chimeric antigen receptor (CAR)-engineered T cells have demonstrated significant success in certain hematologic malignancies, although they still face certain limitations, including high costs and toxic effects. Natural killer cells (NK cells), as a vital component of the immune system, serve as the "first responders" in the context of cancer development. In this literature review, we provide an updated understanding of NK cell development, functions, and their applications in disease therapy. Furthermore, we explore the rationale for utilizing engineered NK cell therapies, such as CAR-NK cells, and discuss the differences between CAR-T and CAR-NK cells. We also provide insights into the key elements and strategies involved in CAR design for engineered NK cells. In addition, we highlight the challenges currently encountered and discuss the future directions in NK cell research and utilization, including pre-clinical investigations and ongoing clinical trials. Based on the outstanding antitumor potential of NK cells, it is highly likely that they will lead to groundbreaking advancements in cancer treatment in the future.

The elevation of plasma galectin-9 levels in patients with psoriasis and its associations with inflammatory and immune checkpoint molecules in skin tissues

Psoriasis is a chronic, immune-mediated disorder that mainly affects the skin, with an estimated global prevalence of 2-3%. Galectin-9 (Gal-9) is a β-galactoside-binding lectin capable of promoting or suppressing the progression of infectious and immune-mediated diseases. Here, we determined if the expression of Gal-9 is observed in psoriasis. Gal-9 levels were measured in plasma of psoriasis (n = 62) and healthy control (HC) (n = 31) using an enzyme-linked immunosorbent assay. In addition, skin samples from seven patients were screened for RNA transcriptomes and the expression of Gal-9 was compared with inflammatory, immune checkpoint molecules (ICMs) and Foxp3. The plasma Gal-9 levels in patients with psoriasis were significantly higher (841 pg/mL) than in HCs (617 pg/mL) (P < 0.0001) and were associated with white blood cell numbers, eosinophils (%) and alanine transaminase. The levels of inflammatory molecules IL-36B, IL-17RA, IL-6R, IL-10, IRF8, TGFb1, and IL-37, and those of ICMs of Tim-3, CTLA-4, CD86, CD80, PD-1LG2, CLEC4G, and Foxp3 were significantly correlated with Gal-9 (LGALS9) in skin. However, HMGB1, CD44, CEACAM1 and PDL1-known to be associated with a variety of Gal-9 biological functions were not correlated with LGALS9. Thus, it is likely that Gal-9 expression affects the disease state of PS.

An integrated study to decipher immunosuppressive cellular communication in the PDAC environment

Pancreatic ductal adenocarcinoma (PDAC) is one the most aggressive cancers and characterized by a highly rigid and immunosuppressive tumor microenvironment (TME). The extensive cellular interactions are known to play key roles in the immune evasion, chemoresistance, and poor prognosis. Here, we used the spatial transcriptomics, scRNA-seq, and bulk RNA-seq datasets to enhance the insights obtained from each to decipher the cellular communication in the TME. The complex crosstalk in PDAC samples was revealed by the single-cell and spatial transcriptomics profiles of the samples. We show that tumor-associated macrophages (TAMs) are the central cell types in the regulation of microenvironment in PDAC. They colocalize with the cancer cells and tumor-suppressor immune cells and take roles to provide an immunosuppressive environment. LGALS9 gene which is upregulated in PDAC tumor samples in comparison to healthy samples was also found to be upregulated in TAMs compared to tumor-suppressor immune cells in cancer samples. Additionally, LGALS9 was found to be the primary component in the crosstalk between TAMs and the other cells. The widespread expression of P4HB gene and its interaction with LGALS9 was also notable. Our findings point to a profound role of TAMs via LGALS9 and its interaction with P4HB that should be considered for further elucidation as target in the combinatory immunotherapies for PDAC.

NK cell exhaustion in the tumor microenvironment

Natural killer (NK) cells kill mutant cells through death receptors and cytotoxic granules, playing an essential role in controlling cancer progression. However, in the tumor microenvironment (TME), NK cells frequently exhibit an exhausted status, which impairs their immunosurveillance function and contributes to tumor immune evasion. Emerging studies are ongoing to reveal the properties and mechanisms of NK cell exhaustion in the TME. In this review, we will briefly introduce the maturation, localization, homeostasis, and cytotoxicity of NK cells. We will then summarize the current understanding of the main mechanisms underlying NK cell exhaustion in the TME in four aspects: dysregulation of inhibitory and activating signaling, tumor cell-derived factors, immunosuppressive cells, and metabolism and exhaustion. We will also discuss the therapeutic approaches currently being developed to reverse NK cell exhaustion and enhance NK cell cytotoxicity in the TME.

CD47: The Next Frontier in Immune Checkpoint Blockade for Non-Small Cell Lung Cancer

The success of PD-1/PD-L1-targeted therapy in lung cancer has resulted in great enthusiasm for additional immunotherapies in development to elicit similar survival benefits, particularly in patients who do not respond to or are ineligible for PD-1 blockade. CD47 is an immunosuppressive molecule that binds SIRPα on antigen-presenting cells to regulate an innate immune checkpoint that blocks phagocytosis and subsequent activation of adaptive tumor immunity. In lung cancer, CD47 expression is associated with poor survival and tumors with EGFR mutations, which do not typically respond to PD-1 blockade. Given its prognostic relevance, its role in facilitating immune escape, and the number of agents currently in clinical development, CD47 blockade represents a promising next-generation immunotherapy for lung cancer. In this review, we briefly summarize how tumors disrupt the cancer immunity cycle to facilitate immune evasion and their exploitation of immune checkpoints like the CD47-SIRPα axis. We also discuss approved immune checkpoint inhibitors and strategies for targeting CD47 that are currently being investigated. Finally, we review the literature supporting CD47 as a promising immunotherapeutic target in lung cancer and offer our perspective on key obstacles that must be overcome to establish CD47 blockade as the next standard of care for lung cancer therapy.

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

Introduction

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

Methods

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

Results

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

Discussion

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

Shaping the "hot" immunogenic tumor microenvironment by nanoparticles co-delivering oncolytic peptide and TGF-β1 siRNA for boosting checkpoint blockade therapy

Induction of potent immune responses toward tumors remains challenging in cancer immunotherapy, in which it only showed benefits in a minority of patients with "hot" tumors, which possess pre-existing effector immune cells within the tumor. In this study, we proposed a nanoparticle-based strategy to fire up the "cold" tumor by upregulating the components associated with T and NK cell recruitment and activation and suppressing TGF-β1 secretion by tumor cells. Specifically, LTX-315, a first-in-class oncolytic cationic peptide, and TGF-β1 siRNA were co-entrapped in a polymer-lipid hybrid nanoparticle comprising PLGA, DSPE-mPEG, and DSPE-PEG-conjugated with cRGD peptide (LTX/siR-NPs). The LTX/siR-NPs showed significant inhibition of TGF-β1 expression, induction of type I interferon release, and triggering immunogenic cell death (ICD) in treated tumor cells, indicated via the increased levels of danger molecules, an in vitro setting. The in vivo data showed that the LTX/siR-NPs could effectively protect the LTX-315 peptide from degradation in serum, which highly accumulated in tumor tissue. Consequently, the LTX/siR-NPs robustly suppressed TGF-β1 production by tumor cells and created an immunologically active tumor with high infiltration of antitumor effector immune cells. As a result, the combination of LTX/siR-NP treatment with NKG2A checkpoint inhibitor therapy remarkably increased numbers of CD8+NKG2D+ and NK1.1+NKG2D+ within tumor masses, and importantly, inhibited the tumor growth and prolonged survival rate of treated mice. Taken together, this study suggests the potential of the LTX/siR-NPs for inflaming the "cold" tumor for potentiating the efficacy of cancer immunotherapy.

Early expansion of activated adaptive but also exhausted NK cells during acute severe SARS-CoV-2 infection

The analysis of immunological parameters during the course of a SARS-CoV-2 infection is of great importance, both to identify diagnostic markers for the risk of a severe course of COVID-19, and to better understand the role of the immune system during the infection. By using multicolor flow cytometry we compared the phenotype of Natural Killer (NK) cells from hospitalized COVID-19 patients during early SARS-CoV-2 infection with samples from recovered and SARS-CoV-2 naïve subjects. Unsupervised high-dimensional analysis of 28-color flow cytometric data revealed a strong enrichment of NKG2C expressing NK cells in response to the acute viral infection. In addition, we found an overrepresentation of highly activated NK cell subsets with an exhausted phenotype. Moreover, our data show long-lasting phenotypic changes within the NK cell compartment that did not completely reverse up to 2 months after recovery. This demonstrates that NK cells are involved in the early innate immune response against SARS-CoV-2.

TIGIT Expression on Activated NK Cells Correlates with Greater Anti-Tumor Activity but Promotes Functional Decline upon Lung Cancer Exposure: Implications for Adoptive Cell Therapy and TIGIT-Targeted Therapies

Treatments targeting TIGIT have gained a lot of attention due to strong preclinical and early clinical results, particularly with anti-PD-(L)1 therapeutics. However, this combination has failed to meet progression-free survival endpoints in phase III trials. Most of our understanding of TIGIT comes from studies of T cell function. Yet, this inhibitory receptor is often upregulated to the same, or higher, extent on NK cells in cancers. Studies in murine models have demonstrated that TIGIT inhibits NK cells and promotes exhaustion, with its effects on tumor control also being dependent on NK cells. However, there are limited studies assessing the role of TIGIT on the function of human NK cells (hNK), particularly in lung cancer. Most studies used NK cell lines or tested TIGIT blockade to reactivate exhausted cells obtained from cancer patients. For therapeutic advancement, a better understanding of TIGIT in the context of activated hNK cells is crucial, which is different than exhausted NK cells, and critical in the context of adoptive NK cell therapeutics that may be combined with TIGIT blockade. In this study, the effect of TIGIT blockade on the anti-tumor activities of human ex vivo-expanded NK cells was evaluated in vitro in the context of lung cancer. TIGIT expression was higher on activated and/or expanded NK cells compared to resting NK cells. More TIGIT+ NK cells expressed major activating receptors and exerted anti-tumor response as compared to TIGIT- cells, indicating that NK cells with greater anti-tumor function express more TIGIT. However, long-term TIGIT engagement upon exposure to PVR+ tumors downregulated the cytotoxic function of expanded NK cells while the inclusion of TIGIT blockade increased cytotoxicity, restored the effector functions against PVR-positive targets, and upregulated immune inflammation-related gene sets. These combined results indicate that TIGIT blockade can preserve the activation state of NK cells during exposure to PVR+ tumors. These results support the notion that a functional NK cell compartment is critical for anti-tumor response and anti-TIGIT/adoptive NK cell combinations have the potential to improve outcomes.

Tumor-associated NK cells facilitate tumor growth via NKp46 in immunocompetent murine hepatocellular carcinoma

Natural killer(NK) cells comprise one subset of the innate lymphoid cells family. Despite reported anti-tumor activity of NK cells, their tangible contribution to tumor control remains controversial. This is due to the incomplete understanding of NK alterations within tumor microenvironment(TME). Here we showed, using murine hepatocellular carcinoma(HCC) model, that early NK cells deletion markedly attenuated tumor growth in a CD8⁺ T cells dependent manner. This effect was accompanied by an enhanced CD8⁺ T cells effector function in tumor rather than circulating blood. Then, we demonstrated that abundant NKp46⁺ NK subset, but not NKp46^- NK, were recruited towards tumor microenvironment during tumor progression. Frequency of intratumor NKP46⁺ NK cells were inversely related to CD8⁺ T cells activation, and positively correlated with tumor growth. Intratumor NKp46⁺ NK cells exhibited dysfunction and increased expression of inhibitory receptors, when compared with NKp46^- NK cells. Blockade of NK cells-associated NKp46 effectively attenuated HCC growth. Infusion of tumor-derived NKp46⁺ NK cells markedly enhanced HCC growth in vivo, in contrast to tumor cells inoculation alone. The further mechanistic investigations unveiled that NK cells boosted tumor growth by NKp46-mediated impairment of CD8⁺T cells effector function. Overall, this work supported a previously unappreciated regulatory property of tumor-associated NK cells in HCC, and NKp46 as a potential target against HCC in clinical setting.

The Immune Checkpoint Receptor CD96: A Local and Systemic Immune Modulator in Oral Cancer?

Background: As immunotherapy of oral squamous cell carcinomas (OSCCs), using PD1 inhibitors, is only efficient in a small proportion of patients, additional immune checkpoints need to be identified as potential therapeutic targets. There is evidence that a blockade of CD96 might positively affect the anti-tumor immune response. The aim of this study was to analyze the gene and protein expression of CD96 in the tissue and peripheral blood of OSCC patients compared to healthy controls, while also checking for potential associations with a differential expression to the histomorphological parameters. In addition, possible correlations with the expression of PD1 and PD-L1 as well as the macrophage markers CD68 and CD163 should be tested to obtain further insights into the potential effectiveness of combined checkpoint blockage. Material and Methods: For real-time quantitative polymerase chain reaction (RT-qPCR), a total of 183 blood and tissue samples, divided into a patient and a control group, were included. Additionally, 141 tissue samples were examined by immunohistochemistry (IHC). The relative expression differences between the groups were calculated using statistical tests including the Mann–Whitney U test and AUC method. The Chi-square test was used to determine whether CD96 overexpression in individual samples is associated with malignancy. Correlation analysis was performed using the Spearman correlation test. Results: There was a significant CD96 mRNA and protein overexpression in the OSCC group compared to the controls (p = 0.001). In contrast, CD96 mRNA expression in the peripheral blood of the OSCC patients was significantly lower compared to the control group (p = 0.007). In the Chi-square test, the OSCC tissue samples showed a highly significant upregulation of CD96 mRNA expression (p < 0.001) and protein expression (p = 0.005) compared to the healthy mucosa. CD96 mRNA and protein expression correlated significantly (p = 0.005). In addition, there was a significant positive correlation of CD96 expression with PD1 (p ≤ 0.001), PD-L1 (p ≤ 0.001), and CD163 (p = 0.006) at the mRNA level. Conclusions: CD96 expression in the tumor tissue and peripheral blood of OSCC patients is differentially regulated and appears to be a relevant immune checkpoint.

Chimeric Antigen Receptor-Natural Killer Cells: A New Breakthrough in the Treatment of Solid Tumours

Natural killer (NK) cells can quickly and directly eradicate tumour cells without recognising tumour-specific antigens. NK cells also participate in immune surveillance, which arouses great interest in the development of novel cancer therapies. The chimeric antigen receptor (CAR) family is composed of receptor proteins that give immune cells extra capabilities to target specific antigen proteins or enhance their killing effects. CAR-T cell therapy has achieved initial success in haematological tumours, but is prone to adverse reactions, especially with cytokine release syndrome in clinical applications. Currently, CAR-NK cell therapy has been shown to successfully kill haematological tumour cells with allogeneic NK cells in clinical trials without adverse reactions, proving its potential to become an off-the-shelf product with broad clinical application prospects. Meanwhile, clinical trials of CAR-NK cells for solid tumours are currently underway. Here we will focus on the latest advances in CAR-NK cells, including preclinical and clinical trials in solid tumours, the advantages and challenges of CAR-NK cell therapy and new strategies to improve the safety and efficacy of CAR-NK cell therapy.

Adoptive cellular immunotherapy for solid neoplasms beyond CAR-T

In recent decades, immune checkpoint blockade and chimeric antigen receptor T cell (CAR-T) therapy are two milestone achievements in clinical immunotherapy. However, both show limited efficacies in most solid neoplasms, which necessitates the exploration of new immunotherapeutic modalities. The failure of CAR-T and immune checkpoint blockade in several solid neoplasms is attributed to multiple factors, including low antigenicity of tumor cells, low infiltration of effector T cells, and diverse mechanisms of immunosuppression in the tumor microenvironment. New adoptive cell therapies have been attempted for solid neoplasms, including TCR-T, CAR-natural killer cells (CAR-NK), and CAR-macrophages (CAR-M). Compared to CAR-T, these new adoptive cell therapies have certain advantages in treating solid neoplasms. In this review, we summarized the 40-year evolution of adoptive cell therapies, then focused on the advances of TCR-T, CAR-NK, and CAR-M in solid neoplasms and discussed their potential clinical applications.

Downregulation of AT-rich interaction domain 2 underlies natural killer cell dysfunction in oral squamous cell carcinoma

The immune system plays a significant role in controlling oral squamous cell carcinoma (OSCC) initiation and progression. Natural killer (NK) cells actively participate in antitumor immunity but become dysfunctional or exhausted in the tumor microenvironment. To explore the mechanisms of NK cell dysfunction in OSCC, we characterized the expression and function of AT-rich interaction domain 2 (ARID2) in NK cells in a murine OSCC model. ARID2 was downregulated in tongue NK cells compared with splenic NK cells. Notably, ARID2 was significantly decreased in NK cells with an exhausted phenotype and weakened antitumor function. ARID2 knockdown resulted in the upregulation of programmed cell death protein 1 (PD-1) and downregulation of interferon-gamma (IFN-γ), tumor necrosis factor (TNF), granzyme B and perforin in NK cells. As a result, ARID2 knockdown impaired NK cell cytotoxicity. Besides, ARID2 overexpression suppressed the expression of PD-1 and lymphocyte-activation gene 3, and promoted the expression of IFN-γ, TNF, granzyme B and perforin in NK cells which were adoptively transferred into OSCC-bearing mice. Taken together, our study implies that the OSCC microenvironment triggers ARID2 downregulation in intratumoral NK cells. In turn, ARID2 downregulation results in PD-1 upregulation on NK cells and subsequently impairs NK cell cytotoxicity. Therefore, we uncovered a novel mechanism of NK cell dysfunction in OSCC.

Targeting immune checkpoints: how to use natural killer cells for fighting against solid tumors

Natural killer (NK) cells are unique innate immune cells that mediate anti-viral and anti-tumor responses. Thus, they might hold great potential for cancer immunotherapy. NK cell adoptive immunotherapy in humans has shown modest efficacy. In particular, it has failed to demonstrate therapeutic efficiency in the treatment of solid tumors, possibly due in part to the immunosuppressive tumor microenvironment (TME), which reduces NK cell immunotherapy's efficiencies. It is known that immune checkpoints play a prominent role in creating an immunosuppressive TME, leading to NK cell exhaustion and tumor immune escape. Therefore, NK cells must be reversed from their dysfunctional status and increased in their effector roles in order to improve the efficiency of cancer immunotherapy. Blockade of immune checkpoints can not only rescue NK cells from exhaustion but also augment their robust anti-tumor activity. In this review, we discussed immune checkpoint blockade strategies with a focus on chimeric antigen receptor (CAR)-NK cells to redirect NK cells to cancer cells in the treatment of solid tumors.

Disruption of the NKG2A:HLA-E Immune Checkpoint Axis to Enhance NK Cell Activation against Cancer

Ligation of the inhibitory receptor NKG2A by its ligand HLA-E negatively regulates the activation of natural killer (NK) cells, as well as subsets of CD8+ T cells and innate T cell populations. NKG2A has recently become a novel immune checkpoint target for the treatment of cancer and direct antibody mediated blockade of NKG2A function is currently under assessment in two phase 3 clinical trials. In addition to direct targeting, the NKG2A:HLA-E axis can also be disrupted indirectly via multiple different targeted cancer agents that were not previously recognised to possess immunomodulatory properties. Increased understanding of immune cell modulation by targeted cancer therapies will allow for the design of rational and more efficacious drug combination strategies to improve cancer patient outcomes. In this review, we summarise and discuss the various strategies currently in development which either directly or indirectly disrupt the NKG2A:HLA-E interaction to enhance NK cell activation against cancer.

Immunotherapy targeting inhibitory checkpoints: The role of NK and other innate lymphoid cells

Monoclonal antibodies that target specific ligand-receptor signaling pathways and act as immune checkpoint inhibitors have been designed to remove the brakes in T cells and restore strong and long-term antitumor-immunity. Of note, many of these inhibitory receptors are also expressed by Innate Lymphoid Cells (ILCs), suggesting that also blockade of inhibitory pathways in innate lymphocytes has a role in the response to the treatment with checkpoint inhibitors. ILCs comprise cytotoxic NK cells and "helper" subsets and are important cellular components in the tumor microenvironment. In addition to killing tumor cells, ILCs release inflammatory cytokines, thus contributing to shape adaptive cell activation in the context of immunotherapy. Therefore, ILCs play both a direct and indirect role in the response to checkpoint blockade. Understanding the impact of ILC-mediated response on the treatment outcome would contribute to enhance immunotherapy efficacy, as still numerous patients resist or relapse.

Increased circulating TGF-β1 is associated with impairment in NK cell effector functions in metastatic melanoma patients

Transforming growth factor beta (TGF-β) plays a complex role in carcinogenesis. In 30 melanoma patients and 20 healthy controls (HC) we analysed functional and phenotypic characteristics of NK cells by Flow cytometry, gene expression of TGF-β1 in peripheral blood mononuclear cells by qPCR and serum and supernatant level of free TGF-β1 by ELISA. Melanoma patients had significantly higher serum level of circulatingTGF-β1 compared to HC, especially those with metastasis into the central nervous system (subclass M1d) and high LDH serum values. Melanoma patients compared to HC had significantly higher level of TGF-β1 gene in PBMC. TGF-β1 serum values negatively correlate with NK cell activity analysed by CD107a (degranulation marker), IFN-γ, NKG2D, and NKp46 in patients. Study shows the association of high level of TGF-β1 with NK cell inhibition in patients represents the main mechanism of tumour immune evasion. Targeting TGF-β may become an important cancer treatment for improving antitumor immunity.

CD96 as a Potential Diagnostic Biomarker and New Target for Skin Cutaneous Melanoma

Skin cutaneous melanoma has high morbidity and mortality. Identification of reliable and quantitative melanoma biomarkers could facilitate an early diagnosis and improve survival and morbidity rates. CD96 has a significant role in adjusting immune function. Although the abnormal expression of CD96 has been reported to participate in carcinogenesis in many human types of cancer, the bioinformatics role of the CD96 in melanoma is unknown. Expression degrees and their underlying functions were first studied by this study. According to TCGA, GTEx, and gene expression profile interaction analysis dataset in this paper, compared with normal skin tissues, CD96 was expressed at higher levels in human cutaneous melanoma skin tissues. Meanwhile, we detected the relative CD96 expression levels by immunohistochemistry. Gene functional enrichment analyses were applied through cBioPortal database analysis. CD96 was clearly upregulated in skin cutaneous melanoma patients and carried out its effects through regulating several signaling pathways, containing the JAK-STAT, PI3K-Akt, and MAPK. Taken together, the analysis results indicated that CD96 could be used as a new clinical bioindicator as well as an underlying medicinal target for cutaneous melanoma.

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.

Down-regulation of MLLT1 super elongation complex subunit impairs the anti-tumor activity of natural killer cells in esophageal cancer

Natural killer (NK) cells actively participate in anti-tumor immunity and are thus regarded as a promising tool in immunotherapy against esophageal cancer (EC). However, the mechanisms regulating NK cell activation and exhaustion have not been completely elucidated. In this study, we characterized the expression and function of MLLT1 super elongation complex subunit (MLLT1) in esophageal NK cells in a mouse EC model. MLLT1 was down-regulated in esophageal NK cells, especially NK cells expressing both T cell immunoglobulin and mucin-domain containing-3 (TIM-3) and lymphocyte activation gene3(LAG-3). In vitro knockdown of MLLT1 in NK cells resulted in significant decreases in the expression of IFN-γ and perforin, as well as impaired NK cell cytotoxicity on tumor cells. Adoptive transfer of MLLT-deficient NK cells into EC-bearing mice showed consistent impairment of NK cell anti-tumor activity, as evidenced by decreases in IFN-γ and perforin but not granzyme B. Furthermore, EC tissue cells, which were enriched from the esophagus of EC-bearing mice, induced down-regulation of MLLT1 in splenic NK cells. This down-regulation was partially restored by a TIM-3 blocking antibody. Therefore, this study indicated that TIM-3 signaling down-regulated MLLT1 in esophageal NK cells, and MLLT1 down-regulation undermined the tumoricidal function of NK cells in EC. Our study unveils a novel mechanism underlying NK cell exhaustion/dysfunction in the EC microenvironment. MLLT1 could be a potential target in future NK cell-mediated immunotherapy against EC.

Overcoming Resistance to Checkpoint Inhibitors: Natural Killer Cells in Non-Small Cell Lung Cancer

Immune checkpoint inhibitors (ICIs) have revolutionized cancer treatments over the last 10 years, with even increasing indications in many neoplasms. Non-small cell lung cancer (NSCLC) is considered highly immunogenic, and ICIs have found a wide set of applications in this area, in both early and advanced lines of treatment, significantly changing the prognosis of these patients. Unfortunately, not all patients can benefit from the treatment, and resistance to ICIs can develop at any time. In addition to T lymphocytes, which are the major target, a variety of other cells present in the tumor microenvironment (TME) act in a complex cross-talk between tumor, stromal, and immune cells. An imbalance between activating and inhibitory signals can shift TME from an “anti-” to a “pro-tumorigenic” phenotype and vice versa. Natural killer cells (NKs) are able to recognize cancer cells, based on MHC I (self and non-self) and independently from antigen presentation. They represent an important link between innate and adaptive immune responses. Little data are available about the role of pro-inflammatory NKs in NSCLC and how they can influence the response to ICIs. NKs express several ligands of the checkpoint family, such as PD-1, TIGIT, TIM-3, LAG3, CD96, IL1R8, and NKG2A. We and others have shown that TME can also shape NKs, converting them into a pro-tumoral, pro-angiogenic “nurturing” phenotype through “decidualization.” The features of these NKs include expression of CD56, CD9, CD49a, and CXCR3; low CD16; and poor cytotoxicity. During ICI therapy, tumor-infiltrating or associated NKs can respond to the inhibitors or counteract the effect by acting as pro-inflammatory. There is a growing interest in NKs as a promising therapeutic target, as a basis for adoptive therapy and chimeric antigen receptor (CAR)-NK technology. In this review, we analyzed current evidence on NK function in NSCLC, focusing on their possible influence in response to ICI treatment and resistance development, addressing their prognostic and predictive roles and the rationale for exploiting NKs as a tool to overcome resistance in NSCLC, and envisaging a way to repolarize decidual NK (dNK)-like cells in lung cancer.

Targeting CISH enhances natural cytotoxicity receptor signaling and reduces NK cell exhaustion to improve solid tumor immunity

Background

The success and limitations of current immunotherapies have pushed research toward the development of alternative approaches and the possibility to manipulate other cytotoxic immune cells such as natural killer (NK) cells. Here, we targeted an intracellular inhibiting protein ‘cytokine inducible SH2-containing protein’ (CISH) in NK cells to evaluate the impact on their functions and antitumor properties.

Methods

To further understand CISH functions in NK cells, we developed a conditional Cish-deficient mouse model in NK cells (Cish^fl/flNcr1^Ki/+). NK cells cytokine expression, signaling and cytotoxicity has been evaluated in vitro. Using intravenous injection of B16F10 melanoma cell line and EO711 triple negative breast cancer cell line, metastasis evaluation was performed. Then, orthotopic implantation of breast tumors was performed and tumor growth was followed using bioluminescence. Infiltration and phenotype of NK cells in the tumor was evaluated. Finally, we targeted CISH in human NK-92 or primary NK cells, using a technology combining the CRISPR(i)-dCas9 tool with a new lentiviral pseudotype. We then tested human NK cells functions.

Results

In Cish^fl/flNcr1^Ki/+ mice, we detected no developmental or homeostatic difference in NK cells. Global gene expression of Cish^fl/flNcr1^Ki/+ NK cells compared with Cish^+/+Ncr1^Ki/+ NK cells revealed upregulation of pathways and genes associated with NK cell cycling and activation. We show that CISH does not only regulate interleukin-15 (IL-15) signaling pathways but also natural cytotoxicity receptors (NCR) pathways, triggering CISH protein expression. Primed Cish^fl/flNcr1^Ki/+ NK cells display increased activation upon NCR stimulation. Cish^fl/flNcr1^Ki/+ NK cells display lower activation thresholds and Cish^fl/flNcr1^Ki/+ mice are more resistant to tumor metastasis and to primary breast cancer growth. CISH deletion favors NK cell accumulation to the primary tumor, optimizes NK cell killing properties and decreases TIGIT immune checkpoint receptor expression, limiting NK cell exhaustion. Finally, using CRISPRi, we then targeted CISH in human NK-92 or primary NK cells. In human NK cells, CISH deletion also favors NCR signaling and antitumor functions.

Conclusion

This study represents a crucial step in the mechanistic understanding and safety of Cish targeting to unleash NK cell antitumor function in solid tumors. Our results validate CISH as an emerging therapeutic target to enhance NK cell immunotherapy.

Modulation of intrinsic inhibitory checkpoints using nano-carriers to unleash NK cell activity

Natural killer (NK) cells provide a powerful weapon mediating immune defense against viral infections, tumor growth, and metastatic spread. NK cells demonstrate great potential for cancer immunotherapy; they can rapidly and directly kill cancer cells in the absence of MHC-dependent antigen presentation and can initiate a robust immune response in the tumor microenvironment (TME). Nevertheless, current NK cell-based immunotherapies have several drawbacks, such as the requirement for ex vivo expansion of modified NK cells, and low transduction efficiency. Furthermore, to date, no clinical trial has demonstrated a significant benefit for NK-based therapies in patients with advanced solid tumors, mainly due to the suppressive TME. To overcome current obstacles in NK cell-based immunotherapies, we describe here a non-viral lipid nanoparticle-based delivery system that encapsulates small interfering RNAs (siRNAs) to gene silence the key intrinsic inhibitory NK cell molecules, SHP-1, Cbl-b, and c-Cbl. The nanoparticles (NPs) target NK cells in vivo, silence inhibitory checkpoint signaling molecules, and unleash NK cell activity to eliminate tumors. Thus, the novel NP-based system developed here may serve as a powerful tool for future NK cell-based therapeutic approaches.

Resveratrol and Immune Cells: A Link to Improve Human Health

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

CAR-NK Cells: From Natural Basis to Design for Kill

Chimeric antigen receptors (CARs) are fusion proteins with an extracellular antigen recognition domain and numerous intracellular signaling domains that have been genetically modified. CAR-engineered T lymphocyte-based therapies have shown great success against blood cancers; however, potential fatal toxicity, such as in cytokine release syndrome, and high costs are some shortcomings that limit the clinical application of CAR-engineered T lymphocytes and remain to overcome. Natural killer (NK) cells are the focal point of current immunological research owing to their receptors that prove to be promising immunotherapeutic candidates for treating cancer. However, to date, manipulation of NK cells to treat malignancies has been moderately successful. Recent progress in the biology of NK cell receptors has greatly transformed our understanding of how NK cells recognize and kill tumor and infected cells. CAR-NK cells may serve as an alternative candidate for retargeting cancer because of their unique recognition mechanisms, powerful cytotoxic effects especially on cancer cells in both CAR-dependent and CAR-independent manners and clinical safety. Moreover, NK cells can serve as an ‘off-the-shelf product’ because NK cells from allogeneic sources can also be used in immunotherapies owing to their reduced risk of alloreactivity. Although ongoing fundamental research is in the beginning stages, this review provides an overview of recent developments implemented to design CAR constructs to stimulate NK activation and manipulate NK receptors for improving the efficiency of immunotherapy against cancer, summarizes the preclinical and clinical advances of CAR-NK cells against both hematological malignancies and solid tumors and confronts current challenges and obstacles of their applications. In addition, this review provides insights into prospective novel approaches that further enhance the efficiency of CAR-NK therapies and highlights potential questions that require to be addressed in the future.

IgE-Based Therapeutic Combination Enhances Antitumor Response in Preclinical Models of Pancreatic Cancer

Pancreatic ductal adenocarcinoma (PDAC) represents 3% of all cancer cases and 7% of all cancer deaths in the United States. Late diagnosis and inadequate response to standard chemotherapies contribute to an unfavorable prognosis and an overall 5-year survival rate of less than 10% in PDAC. Despite recent advances in tumor immunology, tumor-induced immunosuppression attenuates the immunotherapy response in PDAC. To date, studies have focused on IgG-based therapeutic strategies in PDAC. With the recent interest in IgE-based therapies in multiple solid tumors, we explored the MUC1-targeted IgE potential against pancreatic cancer. Our study demonstrates the notable expression of FceRI (receptor for IgE antibody) in tumors from PDAC patients. Our study showed that administration of MUC1 targeted-IgE (mouse/human chimeric anti-MUC1.IgE) antibody at intermittent levels in combination with checkpoint inhibitor (anti-PD-L1) and TLR3 agonist (PolyICLC) induces a robust antitumor response that is dependent on NK and CD8 T cells in pancreatic tumor-bearing mice. Subsequently, our study showed that the antigen specificity of the IgE antibody plays a vital role in executing the antitumor response as nonspecific IgE, induced by ovalbumin (OVA), failed to restrict tumor growth in pancreatic tumor-bearing mice. Utilizing the OVA-induced allergic asthma-PDAC model, we demonstrate that allergic phenotype induced by OVA cannot restrain pancreatic tumor growth in orthotopic tumor-bearing mice. Together, our data demonstrate the novel tumor protective benefits of tumor antigen-specific IgE-based therapeutics in a preclinical model of pancreatic cancer, which can open new avenues for future clinical interventions.

Immune cell landscape and immunotherapy of medulloblastoma

Medulloblastoma is the most common primary pediatric malignancy of the central nervous system. Recurrent and refractory patients account for approximately 30% of them. Immune cells are an important component of the brain tumor microenvironment, including tumor-associated macrophages, T lymphocytes, natural killer cells, dendritic cells, neutrophils and B lymphocytes. Understanding how they behave and interact is important in the investigation of the onset and progression of medulloblastoma. Here, we overview the features and recent advances of each component of immune cells in medulloblastoma. Meanwhile, immunotherapy is a promising but also challenging treatment strategy for medulloblastoma. At present, there are a growing number of immunotherapeutic approaches under investigation including immune checkpoint inhibitors, oncolytic viruses, cancer vaccines, chimeric antigen receptor T cell therapies, and natural killer cells in recurrent and refractory medulloblastoma patients.

Chemical screening identifies novel small molecule activators of natural killer cell cytotoxicity against cancer cells

Natural killer (NK) cells are cytotoxic lymphocytes that play a major role in the innate immune system. NK cells exhibit potent cytotoxic activity against cancer cells and virally infected cells without antigen priming. These unique cytotoxic properties make NK cells a promising therapeutic against cancer. Limitations of NK cell therapy include deficiencies in high clinical efficacy often due to a need for a high NK cell to target cell ratio to achieve effective killing. In order to address the suboptimal efficacy of current adoptive NK cell therapy, a high throughput screen (HTS) was designed and performed to identify drug-like compounds that increase NK cytotoxic activity against tumor cells without affecting the normal cells. This screen was performed in a 384-well plate format utilizing an expanded primary NK cell product and ovarian cancer cells as a target cell (TC) line. Of the 8000 diverse small molecules screened, 16 hits were identified (0.2% hit rate) based on both a robust Z (RZ) score < -3 and a greater than 10% increase in NK cell killing. A validation screen had a confirmation rate of 70%. Select compounds were further validated and characterized by additional cytotoxicity assays including activity against multiple blood cancer and solid tumor cell lines, with no effect on primary human T cells. This work demonstrates that high-throughput screening can be reliably used to identify compounds that increase NK tumoricidal activity in vitro that can be further investigated and translated for potential clinical application. Précis: Our work led to the identification of promising compound that potently increases NK cell-mediated killing of a variety of different cancer cells, but no impact on the killing of normal cells. This compound demonstrates the utility of this assay.

The Activating Receptors of Natural Killer Cells and Their Inter-Switching Potentials

The global incidence of cancer is on the increase and researchers are prospecting for specific and non-selective therapies derived from the immune system. The killer activating receptors of NK cells are known to be involved in immunosurveillance against tumor and virally-infected cells. These receptors belong to two main categories, namely the immunoglobulin like and C-lectin like families. Though they have different signal pathways, all the killer activating receptors have similar effector functions which include direct cytotoxicity and the release of inflammatory cytokines such as IFN-gamma and TNF-alpha. To transduce signals that exceed the activation threshold for cytotoxicity, most of these receptors require synergistic effort. This review profiles 21 receptors: 13 immunoglobulin-like, 5 lectin-like, and 3 others. It critically explores their structural uniqueness, role in disease, respective transduction signal pathways and their status as current and prospective targets for cancer immunotherapy. While the native ligands of most of these receptors are known, much work is required to prospect for specific antibodies, peptides and multi-target small molecules with high binding affinities.

Role of KIR Receptor in NK Regulation during Viral Infections

Natural Killer (NK) cells are key effectors of the innate immune system which represent the first line of defense against viral infections. NK cell activation depends on the engagement of a complex receptor repertoire expressed on their surface, consisting of both activating and inhibitory receptors. Among the known NK cell receptors, the family of killer Ig-like receptors (KIRs) consists in activating/inhibitory receptors that interact with specific human leukocyte antigen (HLA) molecules expressed on target cells. In particular, the expression of peculiar KIRs have been reported to be associated to viral infection susceptibility. Interestingly, a significant association between the development and onset of different human pathologies, such as tumors, neurodegeneration and infertility, and a clonal KIRs expression on NK cells has been described in presence of viral infections, supporting the crucial role of KIRs in defining the effect of viral infections in different tissues and organs. This review aims to report the state of art about the role of KIRs receptors in NK cell activation and viral infection control.

Natural killer (NK) cell-based immunotherapies and the many faces of NK cell memory: A look into how nanoparticles enhance NK cell activity

Natural killer (NK) cells are lymphocytes able to exert potent antitumor and antiviral functions by different means. Besides their classification as innate lymphoid cells (ILCs), NK cells exhibit memory-like and memory responses after cytokine preactivation, viral infections and hapten exposure. Multiple NK cell-based immunotherapies have been developed and are currently being tested, including the possibility to translate the NK cell memory responses into the clinic. Nevertheless, still there is a need to improve these therapies, especially for the treatment of solid tumors, and nanotechnology represents an attractive option to increase NK cell effector functions against transformed cells. In this article, we review the basis of NK cell activity, the diversity of the NK cell memory responses and the current NK cell-based immunotherapies that are being used in the clinic. Furthermore, we take a look into nanotechnology-based strategies targeting NK cells to modulate their responses for effective immunotherapy.

Down-regulation of HLA-B-associated transcript 3 impairs the tumoricidal effect of natural killer cells through promoting the T cell immunoglobulin and mucin domain-containing-3 signaling in a mouse head and neck squamous cell carcinoma model

Head and neck squamous cell carcinoma (HNSCC) arises from the malignant mucosal epithelium of the oral cavity, pharynx, and larynx. Natural killer (NK) cells are fundamental immune cells shaping the anti-HNSCC response. Elucidation of the regulatory mechanisms of NK cell activity is crucial for understanding anti-HNSCC immunity. In this study, we characterized the expression and function of HLA-B-associated transcript 3 (Bat3) in NK cells in a mouse HNSCC model. We found that Bat3 expression was down-regulated in HNSCC-infiltrating NK cells. SCC VII, the mouse HNSCC cell line used in this model, induced Bat3 downregulation through direct cell-to-cell contact. By applying lentivirus-mediated silencing of Bat3, we discovered that Bat3 knockdown impaired the tumoricidal effect of NK cells on SCC VII cells and Hepa1-6^RAE1, a genetically modified liver cancer cell line. Furthermore, Bat3 knockdown resulted in a significant decrease in perforin, granzyme B, interferon-γ, and tumor necrosis factor-α in NK cells upon co-culture with SCC VII cells. Further investigations revealed that Bat3 knockdown promoted the binding of T cell immunoglobulin and mucin domain-containing-3 (Tim-3) to Fyn and thus activated the Tim-3 signaling. Blockade of Tim-3 with a neutralizing Tim-3 antibody counteracted the effect of Bat3 knockdown on NK cell cytotoxicity. Taken together, our data suggest that HNSCC might down-regulate Bat3 expression to augment Tim-3 signaling and ultimately suppress the tumoricidal activity of NK cells. This study unveils a novel mechanism by which HNSCC evades NK cell killing, and sheds light on designing novel anti-HNSCC immunotherapy targeting Bat3 and Tim-3 signaling.

Innate lymphoid cells and cancer: Role in tumor progression and inhibition

Innate lymphoid cells (ILCs), a critical component of the immune system, have recently been nominated as emerging players associated with tumor progression and inhibition. ILCs are classified into five groups: natural killer (NK) cells, ILC1s, ILC2s, ILC3s, and lymphoid tissue inducer (LTis) cells. NK cells and ILC1s are mainly involved in antitumor activities due to their cytotoxic and cytokine production capabilities, respectively. The current understanding of the heterogeneous behavior of ILC2s and ILC3s in tumors is limited and incomplete. Mostly, their dual roles are modulated by their resident tissues, released cytokines, cancer types, and plasticity. Based on overlap RORγt and cytokine expression, the LTi cells were previously considered part of the ILC3s ontogeny, which are essential for the formation of the secondary lymphoid organs during embryogenesis. Indeed, these facts highlight the urgency in understanding the respective mechanisms that shape the phenotypes and responses of ILCs, either on the repressive or proliferative side in the tumor microenvironment (TME). This review aims to provide an updated view of ILCs biology with respect to tumorigenesis, including a description of ILC plasticity, their interaction with other immune cells and communication with components of the TME. Taken together, targeting ILCs for cancer immunotherapy could be a promising approach against tumors that needs to be further study.

The Impact of NK Cell-Based Therapeutics for the Treatment of Lung Cancer for Biologics: Targets and Therapy

Lung cancer has a dismal prognosis and novel targeted therapies leave still room for major improvements and better outcomes. Immunotherapy targeting immune checkpoint (IC) proteins, either as single agents or in combination with chemotherapy, is active but responders constitute only approximately 10-15% of non-small cell lung cancer (NSCLC) patients. Other effector immune cells such as CAR-T cells or NK cells may help to overcome the limitations of the IC inhibitor therapies for lung cancer. NK cells can kill tumor cells without previous priming and are present in the circulatory system and lymphoid organs. Tissue-residing NK cells differ from peripheral effector cells and, in case of the lung, comprise CD56bright CD16-negative populations showing high cytokine release but low cytotoxicity in contrast to the circulating CD56dim CD16-positive NK cells exhibiting high cytotoxic efficacy. This local attenuation of NK cell killing potency seems due to a specific stage of NK differentiation, immunosuppressive factors as well as presence of myeloid-derived suppressor cells (MDSCs) and regulatory T cells (TREGs). Improved NK cell-based immunotherapies involve IL-2-stimulated effector cells, NK cells expanded with the help of cytokines, permanent NK cell lines, induced pluripotent stem cell-derived NK cells and NK cells armed with chimeric antigen receptors. Compared to CAR T cell therapy, NK cells administration is devoid of graft-versus-host disease (GvHD) and cytokine-release syndrome. Although NK cells are clearly active against lung cancer cells, the low-cytotoxicity differentiation state in lung tumors, the presence of immunosuppressive leucocyte populations, limited infiltration and adverse conditions of the microenvironment need to be overcome. This goal may be achieved in the future using large numbers of activated and armed NK cells as provided by novel methods in NK cell isolation, expansion and stimulation of cytotoxic activity, including combinations with monoclonal antibodies in antibody-dependent cytotoxicity (ADCC). This review discusses the basic characteristics of NK cells and the potential of NK cell preparations in cancer therapy.

Angiogenic Properties of NK Cells in Cancer and Other Angiogenesis-Dependent Diseases

The pathogenesis of many serious diseases, including cancer, is closely related to disturbances in the angiogenesis process. Angiogenesis is essential for the progression of tumor growth and metastasis. The tumor microenvironment (TME) has immunosuppressive properties, which contribute to tumor expansion and angiogenesis. Similarly, the uterine microenvironment (UME) exerts a tolerogenic (immunosuppressive) and proangiogenic effect on its cells, promoting implantation and development of the embryo and placenta. In the TME and UME natural killer (NK) cells, which otherwise are capable of killing target cells autonomously, enter a state of reduced cytotoxicity or anergy. Both TME and UME are rich with factors (e.g., TGF-β, glycodelin, hypoxia), which support a conversion of NK cells to the low/non-cytotoxic, proangiogenic CD56^brightCD16^low phenotype. It is plausible that the phenomenon of acquiring proangiogenic and low cytotoxic features by NK cells is not only limited to cancer but is a common feature of different angiogenesis-dependent diseases (ADDs). In this review, we will discuss the role of NK cells in angiogenesis disturbances associated with cancer and other selected ADDs. Expanding the knowledge of the mechanisms responsible for angiogenesis and its disorders contributes to a better understanding of ADDs and may have therapeutic implications.

Enhancing a Natural Killer: Modification of NK Cells for Cancer Immunotherapy

Natural killer (NK) cells are potent innate immune system effector lymphocytes armed with multiple mechanisms for killing cancer cells. Given the dynamic roles of NK cells in tumor surveillance, they are fast becoming a next-generation tool for adoptive immunotherapy. Many strategies are being employed to increase their number and improve their ability to overcome cancer resistance and the immunosuppressive tumor microenvironment. These include the use of cytokines and synthetic compounds to bolster propagation and killing capacity, targeting immune-function checkpoints, addition of chimeric antigen receptors (CARs) to provide cancer specificity and genetic ablation of inhibitory molecules. The next generation of NK cell products will ideally be readily available as an “off-the-shelf” product and stem cell derived to enable potentially unlimited supply. However, several considerations regarding NK cell source, genetic modification and scale up first need addressing. Understanding NK cell biology and interaction within specific tumor contexts will help identify necessary NK cell modifications and relevant choice of NK cell source. Further enhancement of manufacturing processes will allow for off-the-shelf NK cell immunotherapies to become key components of multifaceted therapeutic strategies for cancer.

Innate Immune Cells in the Esophageal Tumor Microenvironment

Esophageal cancer (EC) is one of the most common mucosa-associated tumors, and is characterized by aggressiveness, poor prognosis, and unfavorable patient survival rates. As an organ directly exposed to the risk of foodborne infection, the esophageal mucosa harbors distinct populations of innate immune cells, which play vital roles in both maintenance of esophageal homeostasis and immune defense and surveillance during mucosal anti-infection and anti-tumor responses. In this review, we highlight recent progress in research into innate immune cells in the microenvironment of EC, including lymphatic lineages, such as natural killer and γδT cells, and myeloid lineages, including macrophages, dendritic cells, neutrophils, myeloid-derived suppressor cells, mast cells and eosinophils. Further, putative innate immune cellular and molecular mechanisms involved in tumor occurrence and progression are discussed, to highlight potential directions for the development of new biomarkers and effective intervention targets, which can hopefully be applied in long-term multilevel clinical EC treatment. Fully understanding the innate immunological mechanisms involved in esophageal mucosa carcinogenesis is of great significance for clinical immunotherapy and prognosis prediction for patients with EC.

Preclinical Evaluation of Recombinant Human IL15 Protein Fused with Albumin Binding Domain on Anti-PD-L1 Immunotherapy Efficiency and Anti-Tumor Immunity in Colon Cancer and Melanoma

Simple Summary

In this manuscript, we reported that a newly developed recombinant human IL15 fused with albumin binding domain (hIL15-ABD) showed superior biological half-life, pharmacokinetic and anti-tumor immunity than wild-type (WT) hIL15. Our hIL-15-ABD can effectively enhance anti-tumor efficacy of anti-PD-L1 on colon cancer and melanoma animal models. The anti-tumor potential of hIL-15-ABD was associated with tumor microenvironment (TME) regulation, including the activation of NK cells and CD8⁺ T cells, the reduction of immunosuppressive cells (MDSCs and Tregs) and the suppression of immunosuppressive factors (IDO, FOXP3 and VEGF). In conclusion, our new hIL15-ABD combined with anti-PD-L1 antibody increased the activity of anti-tumor effector cells involved in both innate and adaptive immunities, decreased the TME’s immunosuppressive cells, and showed greater anti-tumor effect than that of either monotherapy. We suggested hIL15-ABD as the potential complementary agent may effectively augment the therapeutic efficacy of anti-PD-L1 antibody in colon cancer and melanoma model.

Abstract

Anti-PD-L1 antibody monotherapy shows limited efficacy in a significant proportion of the patients. A common explanation for the inefficacy is a lack of anti-tumor effector cells in the tumor microenvironment (TME). Recombinant human interleukin-15 (hIL15), a potent immune stimulant, has been investigated in clinical trial with encouraging results. However, hIL15 is constrained by the short half-life of hIL15 and a relatively unfavorable pharmacokinetics profile. We developed a recombinant fusion IL15 protein composed of human IL15 (hIL15) and albumin binding domain (hIL15-ABD) and explored the therapeutic efficacy and immune regulation of hIL-15, hIL15-ABD and/or combination with anti-PD-L1 on CT26 murine colon cancer (CC) and B16-F10 murine melanoma models. We demonstrated that hIL15-ABD has significant inhibitory effect on the CT26 and B16-F10 tumor growths as compared to hIL-15. hIL-15-ABD not only showed superior half-life and pharmacokinetics data than hIL-15, but also enhance anti-tumor efficacy of antibody against PD-L1 via suppressive effect on accumulation of Tregs and MDSCs and activation of NK and CD8+T cells. Immune suppressive factors including VEGF and IDO were also decreased by combination treatment. hIL15-ABD combined with anti-PD-L1 antibody increased the activity of anti-tumor effector cells involved in both innate and adaptive immunities, decreased the TME’s immunosuppressive cells, and showed greater anti-tumor effect than that of either monotherapy.

Targeting NK Cells to Enhance Melanoma Response to Immunotherapies

Natural killer (NK) cells are a key component of an innate immune system. They are important not only in initiating, but also in augmenting adaptive immune responses. NK cell activation is mediated by a carefully orchestrated balance between the signals from inhibitory and activating NK cell receptors. NK cells are potent producers of proinflammatory cytokines and are also able to elicit strong antitumor responses through secretion of perforin and granzyme B. Tumors can develop many mechanisms to evade NK cell antitumor responses, such as upregulating ligands for inhibitory receptors, secreting anti-inflammatory cytokines and recruiting immunosuppressive cells. Enhancing NK cell responses will likely augment the effectiveness of immunotherapies, and strategies to accomplish this are currently being evaluated in clinical trials. A comprehensive understanding of NK cell biology will likely provide additional opportunities to further leverage the antitumor effects of NK cells. In this review, we therefore sought to highlight NK cell biology, tumor evasion of NK cells and clinical trials that target NK cells.

Immune checkpoint expression on peripheral cytotoxic lymphocytes in cervical cancer patients: moving beyond the PD-1/PD-L1 axis

Immune checkpoint therapy to reverse natural killer (NK) and T cell exhaustion has emerged as a promising treatment in various cancers. While anti-programmed cell death 1 (PD-1) pembrolizumab has recently gained Food and Drug Administration (FDA) approval for use in recurrent or metastatic cervical cancer, other checkpoint molecules, such as T cell immunoreceptor with immunoglobulin (Ig) and immunoreceptor tyrosine-based inhibition motif (ITIM) domains (TIGIT) and T cell immunoglobulin and mucin-domain containing-3 (Tim-3), have yet to be fully explored in this disease. We report expression of TIGIT, Tim-3 and PD-1 on subsets of peripheral blood NK (CD56^dim/neg CD16^{bright/dim/neg} and CD56^bright CD16^dim/neg ) and T cells. The percentages of these cells were increased in women with cervical cancer and pre-malignant lesions. PD-1⁺ NK and T cells were likely to co-express TIGIT and/or Tim-3. These cells, with an apparently 'exhausted' phenotype, were augmented in patients. A subset of cells were also natural killer group 2 member D (NKG2D)- and DNAX accessory molecule 1 (DNAM-1)-positive. PD-1^int and PD-1^high T cells were notably increased in cervical cancer. Soluble programmed cell death ligand 1 (PD-L1) was higher in cancer patient blood versus healthy donors and we observed a positive correlation between sPD-L1 and PD-1⁺ T cells in women with low-grade lesions. Within the cancer group, there were no significant correlations between sPD-L1 levels and cervical cancer stage. However, when comparing cancer versus healthy donors, we observed an inverse association between sPD-L1 and total T cells and a correlation between sPD-L1 and CD56^dim NK cells. Our results may show an overview of the immune response towards pre-cancerous lesions and cervical cancer, perhaps giving an early clue as to whom to administer blocking therapies. The increase of multiple checkpoint markers may aid in identifying patients uniquely responsive to combined antibody therapies.

Next-Generation Immunotherapies to Improve Anticancer Immunity

Checkpoint inhibitors are widely used immunotherapies for advanced cancer. Nonetheless, checkpoint inhibitors have a relatively low response rate, work in a limited range of cancers, and have some unignorable side effects. Checkpoint inhibitors aim to reinvigorate exhausted or suppressed T cells in the tumor microenvironment (TME). However, the TME contains various other immune cell subsets that interact to determine the fate of cytotoxic T cells. Activation of cytotoxic T cells is initiated by antigen cross-presentation of dendritic cells. Dendritic cells could also release chemokines and cytokines to recruit and foster T cells. B cells, another type of antigen-presenting cell, also foster T cells and can produce tumor-specific antibodies. Neutrophils, a granulocyte cell subset in the TME, impede the proliferation and activation of T cells. The TME also consists of cytotoxic innate natural killer cells, which kill tumor cells efficiently. Natural killer cells can eradicate major histocompatibility complex I-negative tumor cells, which escape cytotoxic T cell–mediated destruction. A thorough understanding of the immune mechanism of the TME, as reviewed here, will lead to further development of more powerful therapeutic strategies. We have also reviewed the clinical outcomes of patients treated with drugs targeting these immune cells to identify strategies for improvement and possible immunotherapy combinations.

Arrested development: suppression of NK cell function in the tumor microenvironment

Natural killer (NK) cells are cytotoxic innate lymphocytes that protect against viral infection and tumor metastasis. Despite their inherent ability to kill a broad range of virally infected, stressed and transformed cells, low numbers of dysfunctional NK cells are often observed in many advanced solid human cancers. Here, we review the potential mechanisms that influence suboptimal mature NK cell recruitment and function in the tumor microenvironment (TME) of solid tumors. We further highlight current immunotherapy approaches aimed to circumvent NK cell dysfunction and discuss next-generation strategies to enhance adoptive NK cell therapy through targeting intrinsic and extrinsic checkpoints the regulate NK cell functionality in the TME. Understanding the mechanisms that drive NK cell dysfunction in the TME will lead to novel immunotherapeutic approaches in the fight against cancer.

Outlook for New CAR-Based Therapies with a Focus on CAR NK Cells: What Lies Beyond CAR-Engineered T Cells in the Race against Cancer

Chimeric antigen receptor (CAR) engineering of T cells has revolutionized the field of cellular therapy for the treatment of cancer. Despite this success, autologous CAR-T cells have recognized limitations that have led to the investigation of other immune effector cells as candidates for CAR modification. Recently, natural killer (NK) cells have emerged as safe and effective platforms for CAR engineering. In this article, we review the advantages, challenges, and preclinical and clinical research advances in CAR NK cell engineering for cancer immunotherapy. We also briefly consider the feasibility and potential benefits of applying other immune effector cells as vehicles for CAR expression. SIGNIFICANCE: CAR engineering can redirect the specificity of immune effector cells, converting them to a much more potent weapon to combat cancer cells. Expanding this strategy to immune effectors beyond conventional T lymphocytes could overcome some of the limitations of CAR T cells, paving the way for safer and more effective off-the-shelf cellular therapy products.