Conditional ablation of NKp46+ cells using a novel Ncr1(greenCre) mouse strain: NK cells are essential for protection against pulmonary B16 metastases

HPK1 Dysregulation-Associated NK Cell Dysfunction and Defective Expansion Promotes Metastatic Melanoma Progression

Distant metastasis, the leading cause of cancer death, is efficiently kept in check by immune surveillance. Studies have uncovered peripheral natural killer (NK) cells as key antimetastatic effectors and their dysregulation during metastasis. However, the molecular mechanism governing NK cell dysfunction links to metastasis remains elusive. Herein, MAP4K1 encoding HPK1 is aberrantly overexpressed in dysfunctional NK cells in the periphery and the metastatic site. Conditional HPK1 overexpression in NK cells suffices to exacerbate melanoma lung metastasis but not primary tumor growth. Conversely, MAP4K1-deficient mice are resistant to metastasis and further protected by combined immune-checkpoint inhibitors. Mechanistically, HPK1 restrains NK cell cytotoxicity and expansion via activating receptors. Likewise, HPK1 limits human NK cell activation and associates with melanoma NK cell dysfunction couples to TGF-β1 and patient response to immune checkpoint therapy. Thus, HPK1 is an intracellular checkpoint controlling NK-target cell responses, which is dysregulated and hijacked by tumors during metastatic progression.

Microenvironmental signals shaping NK-cell reactivity in cancer

Since the postulation of the "missing-self" concept, much progress has been made in defining requirements for NK-cell activation. Unlike T lymphocytes that process signals from receptors in a hierarchic manner dominated by the T-cell receptors, NK cells integrate receptor signals more "democratically." Signals originate not only the downstream of cell-surface receptors triggered by membrane-bound ligands or cytokines, but are also mediated by specialized microenvironmental sensors that perceive the cellular surrounding by detecting metabolites or the availability of oxygen. Thus, NK-cell effector functions are driven in an organ and disease-dependent manner. Here, we review the latest findings on how NK-cell reactivity in cancer is determined by the reception and integration of complex signals. Finally, we discuss how this knowledge can be exploited to guide novel combinatorial approaches for NK-cell-based anticancer therapies.

Divergent roles for STAT4 in shaping differentiation of cytotoxic ILC1 and NK cells during gut inflammation

Natural killer (NK) cells and type 1 innate lymphoid cells (ILC1) require signal transducer and activator of transcription 4 (STAT4) to elicit rapid effector responses and protect against pathogens. By combining genetic and transcriptomic approaches, we uncovered divergent roles for STAT4 in regulating effector differentiation of these functionally related cell types. Stat4 deletion in Ncr1-expressing cells led to impaired NK cell terminal differentiation as well as to an unexpected increased generation of cytotoxic ILC1 during intestinal inflammation. Mechanistically, Stat4-deficient ILC1 exhibited upregulation of gene modules regulated by STAT5 in vivo and an aberrant effector differentiation upon in vitro stimulation with IL-2, used as a prototypical STAT5 activator. Moreover, STAT4 expression in NCR+ innate lymphocytes restrained gut inflammation in the dextran sulfate sodium-induced colitis model limiting pathogenic production of IL-13 from adaptive CD4+ T cells in the large intestine. Collectively, our data shed light on shared and distinctive mechanisms of STAT4-regulated transcriptional control in NK cells and ILC1 required for intestinal inflammatory responses.

Selective targeting of IL2Rβγ combined with radiotherapy triggers CD8- and NK-mediated immunity, abrogating metastasis in HNSCC

The implementation of cancer immunotherapies has seen limited clinical success in head and neck squamous cell carcinoma (HNSCC). Interleukin-2 (IL-2), which modulates the survival and functionality of lymphocytes, is an attractive target for new immunotherapies but one that is limited by presence of regulatory T cells (Tregs) expressing the high-affinity IL-2Rα. The bispecific immunocytokine PD1-IL2v preferentially delivers IL-2 signaling through IL-2Rβγ on PD-1-expressing cells. Selectively targeting the intermediate-affinity IL-2Rβγ can be leveraged to induce anti-tumor immune responses in effector T cells and natural killer (NK) cells while limiting the negative regulation of IL-2Rα activation on Tregs. Using radiation therapy (RT) in combination with PD1-IL2v improves local tumor control and survival, and controls metastatic spread in orthotopic HNSCC tumor models. PD1-IL2v drives systemic activation and expansion of circulating and tumor-infiltrating cytotoxic T cells and NK cells while limiting Treg-mediated immunosuppression. These data show that PD1-L2v induces durable systemic tumor control in HNSCC.

Cycloartenyl ferulate improves natural killer (NK) cell immunity against cancer by binding to IFNγ receptor 1

Cycloartenyl ferulate (CF) is abundant in brown rice with multiple biologic functions. It has been reported to possess antitumor activity; however, the related mechanism of action of CF has not been clarified. Herein, we unexpectedly uncover the immunological regulation effects of CF and its molecular mechanism. We discovered that CF directly enhanced the killing capacity of natural killer (NK) cells for various cancer cells in vitro. In vivo, CF also improved cancer surveillance in mouse models of lymphoma clearance and metastatic melanoma dependent on NK cells. In addition, CF promoted anticancer efficacy of the anti-PD1 antibody with improvement of tumor immune microenvironment. Mechanistically, we first unveiled that CF acted on the canonical JAK1/2-STAT1 signaling pathway to enhance the immunity of the NK cells by selectively binding to interferon γ receptor 1. Collectively, our results indicate that CF is a promising immunoregulation agent worthy of attention in clinical application in the future. Due to broad biological significance of interferon γ, our findings also provide a capability to understand the diverse functions of CF.

The Function of NK Cells in Tumor Metastasis and NK Cell-Based Immunotherapy

Metastatic tumors cause the most deaths in cancer patients. Treating metastasis remains the primary goal of current cancer research. Although the immune system prevents and kills the tumor cells, the function of the immune system in metastatic cancer has been unappreciated for decades because tumors are able to develop complex signaling pathways to suppress immune responses, leading them to escape detection and elimination. Studies showed NK cell-based therapies have many advantages and promise for fighting metastatic cancers. We here review the function of the immune system in tumor progression, specifically focusing on the ability of NK cells in antimetastasis, how metastatic tumors escape the NK cell attack, as well as the recent development of effective antimetastatic immunotherapies.

Innate lymphoid cells in early tumor development

Innate and adaptive immune cells monitor, recognize, and eliminate transformed cells. Innate lymphoid cells (ILCs) are innate counterparts of T cells that play a key role in many facets of the immune response and have a profound impact on disease states, including cancer. ILCs regulate immune responses by responding and integrating a wide range of signals within the local microenvironment. As primarily tissue-resident cells, ILCs are ideally suited to sense malignant transformation and initiate anti-tumor immunity. However, as ILCs have been associated with anti-tumor and pro-tumor activities in established tumors, they could potentially have dual functions during carcinogenesis by promoting or suppressing the malignant outgrowth of premalignant lesions. Here we discuss emerging evidence that shows that ILCs can impact early tumor development by regulating immune responses against transformed cells, as well as the environmental cues that potentially induce ILC activation in premalignant lesions.

Role of the ITAM-Bearing Receptors Expressed by Natural Killer Cells in Cancer

Natural Killer (NK) cells are innate lymphoid cells (ILCs) capable of recognizing and directly killing tumor cells. They also secrete cytokines and chemokines, which participate in the shaping of the adaptive response. NK cells identify tumor cells and are activated through a net positive signal from inhibitory and activating receptors. Several activating NK cell receptors are coupled to adaptor molecules containing an immunoreceptor tyrosine-based activation motif (ITAM). These receptors include CD16 and the natural cytotoxic receptors NKp46, NKp44, NKp30 in humans. The powerful antitumor NK cell response triggered by these activating receptors has made them attractive targets for exploitation in immunotherapy. In this review, we will discuss the different activating receptors associated with ITAM-bearing cell surface receptors expressed on NK cells, their modulations in the tumor context and the various therapeutic tools developed to boost NK cell responses in cancer patients.

Metformin promotes anticancer activity of NK cells in a p38 MAPK dependent manner

Metformin, a drug prescribed to treat type 2 diabetes, has been reported to possess antitumor activity via immunity activation. However, the influence of metformin on natural killer (NK) cells is not fully understood. Here, we investigated whether metformin exerts a potent anticancer effect by activating NK cells. The results showed that sustained exposure to metformin enhances the cytolytic activity of NK-92 cells. Moreover, this enhancement of cytotoxicity by metformin was also observed in NK cells from healthy peripheral blood and cancer patient ascites. Mechanistically, metformin induced activation of the JAK1/2/3/STAT5 and AKT/mTOR pathways in a p38 MAPK-dependent manner rather than an AMPK-dependent manner. In vivo experiments, metformin also improved cancer surveillance of NK cells in mouse models of lymphoma clearance and metastatic melanoma. Additionally, combination treatment with metformin and anti-PD-1 antibodies increased the therapy response rates of B16F10 melanoma. Moreover, metformin treatment increased NK cell and T cell infiltration in tumors. Therefore, these results provide a deeper understanding of metformin on the effector function of NK cells and will contribute to the development and applications of metformin in cancer treatment strategies.

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.

Natural Killer Cells and Type 1 Innate Lymphoid Cells in Hepatocellular Carcinoma: Current Knowledge and Future Perspectives

Natural killer (NK) cells and type 1 innate lymphoid cells (ILC1) are specific innate lymphoid cell subsets that are key for the detection and elimination of pathogens and cancer cells. In liver, while they share a number of characteristics, they differ in many features. These include their developmental pathways, tissue distribution, phenotype and functions. NK cells and ILC1 contribute to organ homeostasis through the production of key cytokines and chemokines and the elimination of potential harmful bacteria and viruses. In addition, they are equipped with a wide range of receptors, allowing them to detect “stressed cells’ such as cancer cells. Our understanding of the role of innate lymphoid cells in hepatocellular carcinoma (HCC) is growing owing to the development of mouse models, the progress in immunotherapeutic treatment and the recent use of scRNA sequencing analyses. In this review, we summarize the current understanding of NK cells and ILC1 in hepatocellular carcinoma and discuss future strategies to take advantage of these innate immune cells in anti-tumor immunity. Immunotherapies hold great promise in HCC, and a better understanding of the role and function of NK cells and ILC1 in liver cancer could pave the way for new NK cell and/or ILC1-targeted treatment.

Endogenous DEL-1 restrains melanoma lung metastasis by limiting myeloid cell-associated lung inflammation

Distant metastasis represents the primary cause of cancer-associated death. Pulmonary metastasis is most frequently seen in many cancers, largely driven by lung inflammation. Components from primary tumor or recruited leukocytes are known to facilitate metastasis formation. However, contribution of target site-specific host factor to metastasis is poorly understood. Here, we show that developmental endothelial locus-1 (DEL-1), an anti-inflammatory factor abundant in the lung and down-regulated by inflammatory insults, protects from melanoma lung metastasis independently of primary tumor development and systemic immunosurveillance. DEL-1 deficiency is associated with gene profiles that favor metastatic progression with inflammation and defective immunosurveillance. Mechanistically, DEL-1 deficiency primarily influences Ly6G⁺ neutrophil accumulation in lung metastatic niche, leading to IL-17A up-regulation from γδ T cells and reduced antimetastatic NK cells. In support, neutrophil depletion or recombinant DEL-1 treatment profoundly reverses these effects. Thus, our results identify DEL-1 as a previously unrecognized link between tumor-induced inflammation and pulmonary metastasis.

NK cells-directed therapies target circulating tumor cells and metastasis

Metastasis is the major cause of cancer-related deaths. Invasive primary cancers often metastasize after circulating tumor cells (CTCs) enter the bloodstream or lymph node to colonize adjacent tissue or distant anatomical locations. CTCs interact with immune cells and metastatic microenvironments, survival signaling, and chemotherapeutic resistance. Among immune cells, natural killer (NK) cells can, directly and indirectly, interact with CTCs to control cancer metastasis. Understanding the molecular mechanisms that drive NK cells mediated recognition and elimination of CTCs may pave the way for a new generation of anti-CTC molecularly targeted immunotherapies. In this review, we will discuss i) the role of CTCs in metastases, ii) CTCs in the context of the tumor microenvironment, iii) CTCs immune escape, and finally, iv) the potentials of NK cell-based therapies alone, or in combination with nanomedicine for targeted-immunotherapies of metastatic diseases.

Natural Killer Cells Suppress T Cell-Associated Tumor Immune Evasion

Despite the clinical success of cancer immunotherapies, the majority of patients fail to respond or develop resistance through disruption of pathways that promote neo-antigen presentation on MHC I molecules. Here, we conducted a series of unbiased, genome-wide CRISPR/Cas9 screens to identify genes that limit natural killer (NK) cell anti-tumor activity. We identified that genes associated with antigen presentation and/or interferon-γ (IFN-γ) signaling protect tumor cells from NK cell killing. Indeed, Jak1-deficient melanoma cells were sensitized to NK cell killing through attenuated NK cell-derived IFN-γ-driven transcriptional events that regulate MHC I expression. Importantly, tumor cells that became resistant to T cell killing through enrichment of MHC I-deficient clones were highly sensitive to NK cell killing. Taken together, we reveal the genes targeted by tumor cells to drive checkpoint blockade resistance but simultaneously increase their vulnerability to NK cells, unveiling NK cell-based immunotherapies as a strategy to antagonize tumor immune escape.

Natural killer and NKT cells in the male reproductive tract

Natural killer (NK) cells are important effector lymphocytes that play a pivotal role in the innate and adaptive immune responses to tumors and viral infection. NKT cells are a heterogeneous group of T cells that share properties with both T cells and NK cells. They display immunoregulatory properties as they facilitate the cell-mediated immune response to tumors and infectious diseases, and inhibit cell-mediated immunity associated with autoimmune diseases and allograft rejection. However, the roles of NK and NKT cells in the male reproductive tract remain largely unexplored, in particular, NKT cells, tissue distribution, and state of health or disease. Infection and inflammation of the male genital tract are thought to be the primary etiological factors of male infertility. In this review, we considered this complex and rapidly growing field. We summarize the recent findings and the characterization and roles of NK and NKT cells in the male reproductive tract, including the testis, epididymis, prostate, seminal vesicle, and semen, to enhance our understanding of the immunological mechanisms of male infertility and for the design effective vaccines for male reproductive health in the future.

NK Cell Development in Times of Innate Lymphoid Cell Diversity

After being described in the 1970s as cytotoxic cells that do not require MHC-dependent pre-activation, natural killer (NK) cells remained the sole member of innate lymphocytes for decades until lymphoid tissue-inducer cells in the 1990s and helper-like innate lymphoid lineages from 2008 onward completed the picture of innate lymphoid cell (ILC) diversity. Since some of the ILC members, such as ILC1s and CCR6^- ILC3s, share specific markers previously used to identify NK cells, these findings provoked the question of how to delineate the development of NK cell and helper-like ILCs and how to properly identify and genetically interfere with NK cells. The description of eomesodermin (EOMES) as a lineage-specifying transcription factor of NK cells provided a candidate that may serve as a selective marker for the genetic targeting and identification of NK cells. Unlike helper-like ILCs, NK cell activation is, to a large degree, regulated by the engagement of activating and inhibitory surface receptors. NK cell research has revealed some elegant mechanisms of immunosurveillance, coined "missing-self" and "induced-self" recognition, thus complementing "non-self recognition", which is predominantly utilized by adaptive lymphocytes and myeloid cells. Notably, the balance of activating and inhibitory signals perceived by surface receptors can be therapeutically harnessed for anti-tumor immunity mediated by NK cells. This review aims to summarize the similarities and the differences in development, function, localization, and phenotype of NK cells and helper-like ILCs, with the purpose to highlight the unique feature of NK cell development and regulation.

Influence of the Tumor Microenvironment on NK Cell Function in Solid Tumors

Natural killer (NK) cells are a population of innate lymphoid cells playing a pivotal role in host immune responses against infection and tumor growth. These cells have a powerful cytotoxic activity orchestrated by an intricate network of inhibitory and activating signals. The importance of NK cells in controlling tumor growth and in mediating a robust anti-metastatic effect has been demonstrated in different experimental mouse cancer models. Consistently, high density of tumor-infiltrating NK cells has been linked with a good prognosis in multiple human solid tumors. However, there are also tumors that appear to be refractory to NK cell-mediated killing for the presence of an immunosuppressive microenvironment affecting NK cell function. Immunotherapeutic strategies aimed at restoring and increasing the cytotoxic activity of NK cells in solid tumors, including the adoptive transfer of NK and CAR-NK cells, are currently employed in preclinical and clinical studies. In this review, we outline recent advances supporting the direct role of NK cells in controlling expansion of solid tumors and their prognostic value in human cancers. We summarize the mechanisms adopted by cancer cells and the tumor microenvironment to affect NK cell function, and finally we evaluate current strategies to augment the antitumor function of NK cells for the treatment of solid tumors.

[Cbl-b gene silencing enhances H9 T lymphocyte-mediated killing of human laryngeal squamous cancer Hep-2 cells]

OBJECTIVE

To investigate the effect of sputum ubiquitin ligase (Cbl-b) gene known-down on the cytotoxicity of H9 T lymphocytes against human laryngeal squamous cancer Hep-2 cells and explore the underlying mechanism.

METHODS

CD4+ T lymphocytes isolated from 12 patients with laryngeal squamous carcinoma and 12 healthy individuals were examined for Cbl-b mRNA expressions using RT-PCR. H9 T lymphocytes cultured in 96-well plates were transfected with Cbl-b siRNA via liposomes followed by treatment with an anti-IL-2 monoclonal antibody, with H9 T lymphocytes transfected with a scrambled sequence as the negative control. The expressions of Cbl-b mRNA and protein in the cells were detected using real-time fluorescent quantitative PCR and Western blotting, respectively. The killing effect of the treated T lymphocytes against Hep-2 cells was assessed using the cell counting kit (CCK-8). The positive expression rates of CD69 and CD25 on the surface of H9 T lymphocytes were determined using flow cytometry, and the levels of interleukin-2 (IL-2) and interferon-gamma (INF-γ) in the culture supernatants of H9 T lymphocytes were detected with ELISA.

RESULTS

The CD4+ T lymphocytes from patients with laryngeal squamous carcinoma showed significantly increased Cbl-b mRNA level compared with those from healthy individuals (P < 0.05). Transfection of H9 T lymphocytes with Cbl-b siRNA significantly reduced the expression levels of Cbl-b mRNA and protein (P < 0.05), which were not significantly affected by subsequent treatment of the cells with the anti-IL-2 antibody (P>0.05). At different target-effector ratios, the Cbl-b siRNA-transfected cells showed significantly higher Hep-2 cell killing rates and higher positivity rates of CD69 and CD25 expressions than the blank and negative control cells and the cells with both Cbl-b siRNA transfection and anti-IL-2 treatment (P < 0.05). Cbl-b silencing in H9 T lymphocytes resulted in significantly increased levels of IL-2 and INF-γ in the supernatant as compared with those in the blank and negative control groups (P < 0.05).

CONCLUSIONS

Cbl-b gene silencing effectively enhances the killing effect of H9 T lymphocytes against Hep-2 cells in vitro probably as the result of enhanced IL-2 secretion and T lymphocyte activation.

The Natural Cytotoxicity Receptors in Health and Disease

The Natural Cytotoxicity Receptors (NCRs), NKp46, NKp44, and NKp30, were some of the first human activating Natural Killer (NK) cell receptors involved in the non-MHC-restricted recognition of tumor cells to be cloned over 20 years ago. Since this time many host- and pathogen-encoded ligands have been proposed to bind the NCRs and regulate the cytotoxic and cytokine-secreting functions of tissue NK cells. This diverse set of NCR ligands can manifest on the surface of tumor or virus-infected cells or can be secreted extracellularly, suggesting a remarkable NCR polyfunctionality that regulates the activity of NK cells in different tissue compartments during steady state or inflammation. Moreover, the NCRs can also be expressed by other innate and adaptive immune cell subsets under certain tissue conditions potentially conferring NK recognition programs to these cells. Here we review NCR biology in health and disease with particular reference to how this important class of receptors regulates the functions of tissue NK cells as well as confer NK cell recognition patterns to other innate and adaptive lymphocyte subsets. Finally, we highlight how NCR biology is being harnessed for novel therapeutic interventions particularly for enhanced tumor surveillance.

Conditional Genetic Ablation Mouse Models as a Tool to Study Cancer Immunosurveillance In Vivo

Over the last decades, it has been established that the immune system is crucial for the impediment of cancer development by recognizing and destroying transformed cells. This process has been termed cancer immunosurveillance. Small animal models have significantly facilitated our understanding of it. Dissecting the contribution of any specific immune cell type participating in this process requires the ability to specifically target it while leaving the other immune components as well as the cancer model system unperturbed in vivo. Here, we provide a simple and rapid protocol for the generation of transgenic mice expressing Cre recombinase in a cell type-specific manner-in our example we chose cells expressing Ncr1, which encodes for the surface protein NKp46-and the use of those mice to ablate NKp46+ cells in order to study their role in a model of cancer immunosurveillance against experimental pulmonary metastases. This protocol can easily be adapted to target other cell types and other cancer models.

Ginsenoside F1 Promotes Cytotoxic Activity of NK Cells via Insulin-Like Growth Factor-1-Dependent Mechanism

Ginsenosides are the principal active components of ginseng and are considered attractive candidates for combination cancer therapy because they can kill tumors and have favorable safety profiles. However, the overall benefit of ginsenosides remains unclear, particularly in cancer immunosurveillance, considering the controversial results showing repression or promotion of immune responses. Here we identify a potentiating role of ginsenoside F1 (G-F1) in cancer surveillance by natural killer (NK) cells. Among 15 different ginsenosides, G-F1 most potently enhanced NK cell cytotoxicity in response to diverse activating receptors and cancer cells. G-F1 also improved cancer surveillance in mouse models of lymphoma clearance and metastatic melanoma that rely on NK cell activity. G-F1-treated NK cells exhibited elevated cytotoxic potential such as upregulation of cytotoxic mediators and of activation signals upon stimulation. NK cell potentiation by G-F1 was antagonized by insulin-like growth factor (IGF)-1 blockade and recapitulated by IGF-1 treatment, suggesting the involvement of IGF-1. Thus, our results suggest that G-F1 enhances NK cell function and may have chemotherapeutic potential in NK cell-based immunotherapy. We anticipate our results to be a starting point for further comprehensive studies of ginsenosides in the immune cells mediating cancer surveillance and the development of putative therapeutics.

Subset- and tissue-defined STAT5 thresholds control homeostasis and function of innate lymphoid cells

Innate lymphoid cells (ILCs) patrol environmental interfaces to defend against infection and protect barrier integrity. Using a genetic tuning model, we demonstrate that the signal-dependent transcription factor (TF) STAT5 is critical for accumulation of all known ILC subsets in mice and reveal a hierarchy of STAT5 dependency for populating lymphoid and nonlymphoid tissues. We apply transcriptome and genomic distribution analyses to define a STAT5 gene signature in natural killer (NK) cells, the prototypical ILC subset, and provide a systems-based molecular rationale for its key functions downstream of IL-15. We also uncover surprising features of STAT5 behavior, most notably the wholesale redistribution that occurs when NK cells shift from tonic signaling to acute cytokine-driven signaling, and genome-wide coordination with T-bet, another key TF in ILC biology. Collectively, our data position STAT5 as a central node in the TF network that instructs ILC development, homeostasis, and function and provide mechanistic insights on how it works at cellular and molecular levels.

Control of Metastasis by NK Cells

The metastatic spread of malignant cells to distant anatomical locations is a prominent cause of cancer-related death. Metastasis is governed by cancer-cell-intrinsic mechanisms that enable neoplastic cells to invade the local microenvironment, reach the circulation, and colonize distant sites, including the so-called epithelial-to-mesenchymal transition. Moreover, metastasis is regulated by microenvironmental and systemic processes, such as immunosurveillance. Here, we outline the cancer-cell-intrinsic and -extrinsic factors that regulate metastasis, discuss the key role of natural killer (NK) cells in the control of metastatic dissemination, and present potential therapeutic approaches to prevent or target metastatic disease by harnessing NK cells.

Innate lymphoid cell function in the context of adaptive immunity

Innate lymphoid cells (ILCs) are a family of innate immune cells that have diverse functions during homeostasis and disease. Subsets of ILCs have phenotypes that mirror those of polarized helper T cell subsets in their expression of core transcription factors and effector cytokines. Given the similarities between these two classes of lymphocytes, it is important to understand which functions of ILCs are specialized and which are redundant with those of T cells. Here we discuss genetic mouse models that have been used to delineate the contributions of ILCs versus those of T cells and review the current understanding of the specialized in vivo functions of ILCs.

Phenotypic and Functional Plasticity of Murine Intestinal NKp46+ Group 3 Innate Lymphoid Cells

Group 3 innate lymphoid cells (ILC3) actively participate in mucosal defense and homeostasis through prompt secretion of IL-17A, IL-22, and IFN-γ. Reports identify two ILC3 lineages: a CCR6(+)T-bet(-) subset that appears early in embryonic development and promotes lymphoid organogenesis and a CCR6(-)T-bet(+) subset that emerges after microbial colonization and harbors NKp46(+) ILC3. We demonstrate that NKp46 expression in the ILC3 subset is highly unstable. Cell fate mapping using Ncr1(CreGFP) × Rosa26(RFP) mice revealed the existence of an intestinal RFP(+) ILC3 subset (Ncr1(FM)) lacking NKp46 expression at the transcript and protein levels. Ncr1(FM) ILC3 produced more IL-22 and were distinguishable from NKp46(+) ILC3 by differential CD117, CD49a, DNAX accessory molecule-1, and, surprisingly, CCR6 expression. Ncr1(FM) ILC3 emerged after birth and persisted in adult mice following broad-spectrum antibiotic treatment. These results identify an unexpected phenotypic instability within NKp46(+) ILC3 that suggests a major role for environmental signals in tuning ILC3 functional plasticity.

Transcriptional regulation of innate lymphoid cell fate

Innate lymphoid cells (ILCs) are a recently described family of lymphoid effector cells that have important roles in immune defence, inflammation and tissue remodelling. It has been proposed that ILCs represent 'innate' homologues of differentiated effector T cells, and they have been categorized into three groups — namely, ILC1s, ILC2s and ILC3s — on the basis of their expression of cytokines and transcription factors that are typically associated with T helper 1 (T(H)1)-, T(H)2- and T(H)17-type immune responses, respectively. Indeed, remarkable similarity is seen between the specific transcription factors required for the development and diversification of different ILC groups and those that drive effector T cell differentiation. The recent identification of dedicated ILC precursors has provided a view of the mechanisms that control this first essential stage of ILC development. Here, we discuss the transcriptional mechanisms that regulate ILC development and diversification into distinct effector subsets with key roles in immunity and tissue homeostasis. We further caution against the current distinction between 'helper' versus 'killer' subsets in the evolving area of ILC nomenclature.

A novel immunoregulatory role for NK-cell cytotoxicity in protection from HLH-like immunopathology in mice

NK cytotoxic activity limits HLH-like immunopathology in cytotoxic-deficient mice. NK cytotoxic activity reduces T-cell activation and tissue infiltration of macrophages.

Lessons from NK Cell Deficiencies in the Mouse

Since their discovery in the late 1970s, in vivo studies on mouse natural killer (NK) cell almost entirely relied on the use of depleting antibodies and were associated with significant limitations. More recently, large-scale gene-expression analyses allowed the identification of NKp46 as one of the best markers of NK cells across mammalian species. Since then, NKp46 has been shown to be expressed on other subsets of innate lymphoid cells (ILCs) such as the closely related ILC1 and the mucosa-associated NCR(+) ILC3. Based on this marker, several mouse models specifically targeting NKp46-expressing cell have recently been produced. Here, we review recent advances in the generation of models of deficiency in NKp46-expressing cells and their use to address the role of NK cells in immunity, notably on the regulation of adaptive immune responses.