Regulation Of Natural Killer Cell Function Research Articles

DNMT1 silencing induces KIR2DL1/2/3 expression via methylation to alleviate graft-versus-host disease after allogeneic hematopoietic stem cell transplantation.

Natural killer (NK) cells are the promoters in graft-versus-host disease (GVHD) after allogeneic hematopoietic stem cell transplantation (allo-HSCT), while demethylation can regulate NK cell function. We explored the mechanism of demethylation regulating NK cell function to affect GVHD after allo-HSCT. BALB/c mice were transfused with C57BL/6 mouse-derived NK and bone marrow cells to establish GVHD models, followed by isolation and in-vitro expansion of NK cells. NK cell purity, cytokine levels, proliferation, and cytokine-producing NK cell levels were measured via flow cytometry. KIR2DL1/2/3 methylation was tested by Methylation-specific polymerase chain reaction (MSP), with determination of mouse survival and GVHD scores. KIR2DL1/2/3 and DNMT1 expression was detected through qRT-PCR and/or western blot. Methylation levels were upregulated and KIR2DL1/2/3 expression was downregulated in GVHD mouse model-derived NK cells following IL-2 stimulation. DNMT1 silencing promoted KIR2DL1/2/3 expression, proliferation, and the secretion of Granzyme, Perforin, and Interferon-γ (IFN-γ) in C57BL/6 mouse-derived NK cells. DNMT1 silencing also enhanced mouse survival, reduced GVHD scores, promoted KIR2DL1/2/3 expression on the NK cell surface, and increased the secretion of Granzyme, Perforin, IFN-γ, and the number of cytokine-producing NK cells in the spleen, liver, and lung tissues of the models. Collectively, DNMT1 silencing induced KIR2DL1/2/3 expression in NK cells through reducing methylation to alleviate GVHD after allo-HSCT.

Overexpressing S100A9 ameliorates NK cell dysfunction in estrogen receptor-positive breast cancer

BackgroundEstrogen receptor (ER) positive human epidermal growth factor receptor 2 (HER2) negative breast cancer (ER+/HER2−BC) and triple-negative breast cancer (TNBC) are two distinct breast cancer molecular subtypes, especially in tumor immune microenvironment (TIME). The TIME of TNBC is considered to be more inflammatory than that of ER+/HER2−BC. Natural killer (NK) cells are innate lymphocytes that play an important role of tumor eradication in TME. However, studies focusing on the different cell states of NK cells in breast cancer subtypes are still inadequate.MethodsIn this study, single-cell mRNA sequencing (scRNA-seq) and bulk mRNA sequencing data from ER+/HER2−BC and TNBC were analyzed. Key regulator of NK cell suppression in ER+/HER2−BC, S100A9, was quantified by qPCR and ELISA in MCF-7, T47D, MDA-MB-468 and MDA-MB-231 cell lines. The prognosis predictability of S100A9 and NK activation markers was evaluated by Kaplan–Meier analyses using TCGA-BRAC data. The phenotype changes of NK cells in ER+/HER2−BC after overexpressing S100A9 in cancer cells were evaluated by the production levels of IFN-gamma, perforin and granzyme B and cytotoxicity assay.ResultsBy analyzing scRNA-seq data, we found that multiple genes involved in cellular stress response were upregulated in ER+/HER2−BC compared with TNBC. Moreover, TLR regulation pathway was significantly enriched using differentially expressed genes (DEGs) from comparing the transcriptome data of ER+/HER2−BC and TNBC cancer cells, and NK cell infiltration high/low groups. Among the DEGs, S100A9 was identified as a key regulator. Patients with higher expression levels of S100A9 and NK cell activation markers had better overall survival. Furthermore, we proved that overexpression of S100A9 in ER+/HER2-cells could improve cocultured NK cell function.ConclusionIn conclusion, the study we presented demonstrated that NK cells in ER+/HER2−BC were hypofunctional, and S100A9 was an important regulator of NK cell function in ER+BC. Our work contributes to elucidate the regulatory networks between cancer cells and NK cells and may provide theoretical basis for novel drug development.

G-CSFR Is a Checkpoint of Natural Killer Cells Against Tumor

G-CSFR is a cell surface receptor that can activate cell proliferation and differentiation after binding to granulocyte colony stimulating factor(G-CSF). However, in natural killer (NK) cells, the biological role of G-CSFR has not been fully elucidated. Here we show that granulocyte colony-stimulating factor receptor, that is encoded by the CSF3R gene, is a novel and potent checkpoint in both human and mouse NK cells fighting against tumors. Previous studies have shown that NK cells under resting state with low expression of G-CSFR, but highly expressed in peripheral blood and bone marrow NK cells after G-CSF mobilization. We therefore used G-CSFR blocking agent in vitro to evaluate the effect of G-CSFR on human NK cells proliferation and cytotoxicity capacity. The results showed that G-CSFR agonist significantly down-regulated the proliferation and cytotoxicity of NK cells in vitro and this is independent of G-CSF stimulation. Since NK92 and YT cell lines highly express G-CSFR, we then knocked down G-CSFR in NK92 and YT cells. The results showed that the low expression of G-CSFR enhanced the expression of CD107a in vitro, indicating G-CSFR may be an inhibitory signaling in NK cells. To the further evaluate the specific role of G-CSFR in NK cells and we therefore constructed NK-specific CSF3R deficiency mice (CSF3R △NK/NK; CSF3Rfl/flNCR1cre, thecre group) and the control group ( CSF3Rfl/fl ( CSF3RWT/WT mice, the flox group). We then evaluated the phenotype, differentiation and functional state of NK cells between the two group. NK-specific CSF3R deficiency increased mature NK subsets in mice, and these CSF3R-deficient NK cells exhibited enhanced activation, cytotoxicity and proliferation, which is in accordance with the role in human NK cells. After constructing four tumor-bearing models, namely MC38 (colon tumor), LLC (lung tumor), MLL-AF8(acute myeloid leukemia), B16-F10(melanoma), we found that CSF3R specific depletion in NK cells reduced the tumor burden, prolonged the survival and reduced tumor metastasis in CSF3R△NK/NK mice (Figure 1A-D), indicating CSF3R depletion in NK cells promotes increased ability against tumors. To further evaluate the molecular mechanism of G-CSFR regulation of NK cell function, single cell RNA sequencing on bone marrow cells from both CSF3R△NK/NK mice and CSF3RWT/WT mice and NK cells were extracted for further subpopulation analysis. UMAP analysis revealed the clustering of bone marrow NK cells from both genotypes into ten subsets and on the basis of the key gene expression of NK cell effector molecules, transcriptional factors, maturation markers, and proliferation marker, we identified NK cell maturation program as mBM5+mBM8, mBM2+mBM3+ mBM6 and mBM0, by which immature NK cells should go through to gain optimal effector function, according to this model, CSF3R△NK/NK mice contained more NK cells belonging to the terminally mature mBM0 than CSF3RWT/WT mice. “Cell Killing” and “leukocyte mediated cytotoxicity” pathway was enriched in CSF3R△NK/NK mice, indicating enhanced activation state of NK cells. In conclusion, our results uncover a potent checkpoint in NK cells protecting against tumors, suggesting a promising approach of targeting G-CSFR for NK cell-based immunotherapies.

Tumour-associated macrophages as a potential target to improve natural killer cell-based immunotherapies.

Adoptive transfer of natural killer (NK) cells has been proposed as a novel immunotherapy for malignant tumours resistant to current therapeutic modalities. Several clinical studies have demonstrated that the NK cell-infusion is well tolerated without severe side effects and shows promising results in haematological malignancies. However, patients with malignant solid tumours do not show significant responses to this therapy. Such disappointing results largely arise from the inefficient delivery of infused NK cells and the impairment of their functions in the tumour microenvironment (TME). Tumour-associated macrophages (TAMs) are the most abundant stromal cells in the TME of most solid tumours, and a high TAM density correlates with poor prognosis of cancer patients. Although our knowledge of the interactions between TAMs and NK cells is limited, many studies have indicated that TAMs suppress NK cell cytotoxicity against cancer cells. Therefore, blockade of TAM functions can be an attractive strategy to improve NK cell-based immunotherapies. On the other hand, macrophages are reported to activate NK cells under certain circumstances. This essay presents our current knowledge about mechanisms by which macrophages regulate NK cell functions and discusses possible therapeutic approaches to block macrophage-mediated NK cell suppression.

NKG2A gene variant predicts outcome of immunotherapy in AML and modulates the repertoire and function of NK cells

BackgroundThe natural killer (NK) complex (NKC) harbors multiple genes such as KLRC1 (encoding NKG2A) and KLRK1 (encoding NKG2D) that are central to regulation of NK cell function. We aimed at...

The Important Roles of Natural Killer Cells in Liver Fibrosis.

Liver fibrosis accompanies the development of various chronic liver diseases and promotes their progression. It is characterized by the abnormal accumulation of extracellular matrix proteins (ECM) and impaired ECM degradation. Activated hepatic stellate cells (HSCs) are the major cellular source of ECM-producing myofibroblasts. If liver fibrosis is uncontrolled, it may lead to cirrhosis and even liver cancer, primarily hepatocellular carcinoma (HCC). Natural killer (NK) cells are a key component of innate immunity and have miscellaneous roles in liver health and disease. Accumulating evidence shows that NK cells play dual roles in the development and progression of liver fibrosis, including profibrotic and anti-fibrotic functions. Regulating NK cells can suppress the activation of HSCs and improve their cytotoxicity against activated HSCs or myofibroblasts to reverse liver fibrosis. Cells such as regulatory T cells (Tregs) and molecules such as prostaglandin E receptor 3 (EP3) can regulate the cytotoxic function of NK cells. In addition, treatments such as alcohol dehydrogenase 3 (ADH3) inhibitors, microRNAs, natural killer group 2, member D (NKG2D) activators, and natural products can enhance NK cell function to inhibit liver fibrosis. In this review, we summarized the cellular and molecular factors that affect the interaction of NK cells with HSCs, as well as the treatments that regulate NK cell function against liver fibrosis. Despite a lot of information about NK cells and their interaction with HSCs, our current knowledge is still insufficient to explain the complex crosstalk between these cells and hepatocytes, liver sinusoidal endothelial cells, Kupffer cells, B cells, and T cells, as well as thrombocytes, regarding the development and progression of liver fibrosis.

Differential regulation of natural killer cells by tumor necrosis factor receptors 1 and 2

Abstract Tumor necrosis factor (TNF) is a key cytokine across homeostasis, health, and disease. However, the role of TNF is often dichotomous in that it is critical for protective anti-microbial and anti-tumour responses, yet it is also a major player in immune dysfunction and immune-related pathology. Surprisingly, while the effects of TNF on myeloid responses are well studied, how TNF impacts lymphocyte responses is yet to be elucidated. This is particularly the case for natural killer (NK) cells, innate lymphoid cells which play a key role in immune protection against both cancer and infection. To address this knowledge gap, we have generated novel transgenic mouse models which lack the receptors for TNF (TNFR1 and/or TNFR2) specifically on NK cells, allowing us to precisely dissect how TNF directly regulates NK cell function and survival, along with the relative importance of each receptor. Using single cell RNA sequencing among other techniques, we have discovered TNF regulates expression of co-inhibitory receptors on NK cells, including Tim3 and TIGIT, through both TNFR1 and TNFR2. In models of infection and cancer we have found that TNFR1 plays an inhibitory role through depletion of NK cells, leading to increased disease burden. Conversely, TNFR2 plays a protective role through maintenance of optimal NK function and cytokine production, promoting disease control. This ongoing work establishes the importance of TNF in the regulation of NK cell function, which could have significant clinical implications.

The mechanobiology of NK cells- 'Forcing NK to Sense' target cells.

Natural killer (NK) cells are innate immune lymphocytes that recognize and kill cancer and infected cells, which makes them unique 'off-the-shelf' candidates for a new generation of immunotherapies. Biomechanical forces in homeostasis and pathophysiology accrue additional immune regulation for NK immune responses. Indeed, cellular and tissue biomechanics impact NK receptor clustering, cytoskeleton remodeling, NK transmigration through endothelial cells, nuclear mechanics, and even NK-dendritic cell interaction, offering a plethora of unexplored yet important dynamic regulation for NK immunotherapy. Such events are made more complex by the heterogeneity of human NK cells. A significant question remains on whether and how biochemical and biomechanical cues collaborate for NK cell mechanotransduction, a process whereby mechanical force is sensed, transduced, and translated to downstream mechanical and biochemical signalling. Herein, we review recent advances in understanding how NK cells perceive and mechanotransduce biophysical cues. We focus on how the cellular cytoskeleton crosstalk regulates NK cell function while bearing in mind the heterogeneity of NK cells, the direct and indirect mechanical cues for NK anti-tumor activity, and finally, engineering advances that are of translational relevance to NK cell biology at the systems level.

Metabolic regulation of NK cell function: implications for immunotherapy.

Natural killer (NK) cells are innate immune lymphocytes capable of rapidly responding to tumors and infection without prior sensitization. There is increasing interest and success in harnessing NK cell function for the treatment of disease, in particular cancers. NK cell activation is dependent on integration of signals through cytokine and germline-encoded activating and inhibitory receptors. The availability of metabolic fuels and pathways is required for NK effector functions including proliferation, killing, and production of interferon gamma (IFN-γ). An understanding of NK cell immunometabolism is thus essential for developing immunotherapy approaches that will allow for optimal effector functions in patients. Studies in mice and humans have demonstrated stimulation-dependent metabolic changes that are required for NK cell function. Here we review the most recent findings in NK cell immunometabolism relevant to disease models and translation to therapy of patients.

Phospho-proteomics reveals that RSK signaling is required for proliferation of natural killer cells stimulated with IL-2 or IL-15

Natural killer (NK) cells are cytotoxic lymphocytes that play a critical role in the innate immune system. Although cytokine signaling is crucial for the development, expansion, and cytotoxicity of NK cells, the signaling pathways stimulated by cytokines are not well understood. Here, we sought to compare the early signaling dynamics induced by the cytokines interleukin (IL)-2 and IL-15 using liquid chromatography-mass spectrometry (LC-MS)-based phospho-proteomics. Following stimulation of the immortalized NK cell line NK-92 with IL-2 or IL-15 for 5, 10, 15, or 30 min, we identified 8,692 phospho-peptides from 3,023 proteins. Comparing the kinetic profiles of 3,619 fully quantified phospho-peptides, we found that IL-2 and IL-15 induced highly similar signaling in NK-92 cells. Among the IL-2/IL-15-regulated phospho-peptides were both well-known signaling events like the JAK/STAT pathway and novel signaling events with potential functional significance including LCP1 pSer5, STMN1 pSer25, CHEK1 pSer286, STIM1 pSer608, and VDAC1 pSer104. Using bioinformatic approaches, we sought to identify kinases regulated by IL-2/IL-15 stimulation and found that the p90 ribosomal S6 kinase (p90RSK) family was activated by both cytokines. Using pharmacological inhibitors, we then discovered that RSK signaling is required for IL-2 and IL-15-induced proliferation in NK-92 cells. Taken together, our analysis represents the first phospho-proteomic characterization of cytokine signaling in NK cells and increases our understanding of how cytokine signaling regulates NK cell function.

Inhibition of O-GlcNAcylation Decreases the Cytotoxic Function of Natural Killer Cells.

Natural killer (NK) cells mediate killing of malignant and virus-infected cells, a property that is explored as a cell therapy approach in the clinic. Various cell intrinsic and extrinsic factors affect NK cell cytotoxic function, and an improved understanding of the mechanism regulating NK cell function is necessary to accomplish better success with NK cell therapeutics. Here, we explored the role of O-GlcNAcylation, a previously unexplored molecular mechanism regulating NK cell function. O-GlcNAcylation is a post-translational modification mediated by O-GlcNAc transferase (OGT) that adds the monosaccharide N-acetylglucosamine to serine and threonine residues on intracellular proteins and O-GlcNAcase (OGA) that removes the sugar. We found that stimulation of NK cells with the cytokines interleukin-2 (IL-2) and IL-15 results in enhanced O-GlcNAcylation of several cellular proteins. Chemical inhibition of O-GlcNAcylation using OSMI-1 was associated with a decreased expression of NK cell receptors (NKG2D, NKG2A, NKp44), cytokines [tumor necrosis factor (TNF)-α, interferon (IFN-γ)], granulysin, soluble Fas ligand, perforin, and granzyme B in NK cells. Importantly, inhibition of O-GlcNAcylation inhibited NK cell cytotoxicity against cancer cells. However, increases in O-GlcNAcylation following OGA inhibition using an OGA inhibitor or shRNA-mediated suppression did not alter NK cell cytotoxicity. Finally, we found that NK cells pretreated with OSMI-1 to inhibit O-GlcNAcylation showed compromised cytotoxic activity against tumor cells in vivo in a lymphoma xenograft mouse model. Overall, this study provides the seminal insight into the role of O-GlcNAcylation in regulating NK cell cytotoxic function.

Extracellular matrix proteins regulate NK cell function in peripheral tissues.

Natural killer (NK) cells reject major histocompatibility complex class I (MHC-I)–deficient bone marrow through direct cytotoxicity but not solid organ transplants devoid of MHC-I. Here, we demonstrate an immediate switch in NK cell function upon exit from the circulation, characterized by a shift from direct cytotoxicity to chemokine/cytokine production. In the skin transplant paradigm, combining an NK cell–specific activating ligand, m157, with missing self MHC-I resulted in complete graft rejection, which was dependent on NK cells as potential helpers and T cells as effectors. Extracellular matrix proteins, collagen I, collagen III, and elastin, blocked NK cell cytotoxicity and promoted their chemokine/cytokine production. NK cell cytotoxicity against MHC-I–deficient melanoma in the skin was markedly increased by blocking tumor collagen deposition. MHC-I down-regulation occurred in solid human cancers but not leukemias, which could be directly targeted by circulating cytotoxic NK cells. Our findings uncover a fundamental mechanism that restricts direct NK cell cytotoxicity in peripheral tissues.

Natural Killer Cell-Mediated Immunotherapy for Leukemia.

Simple SummaryConventional therapies such as chemotherapy and radiation in leukemia increase infection susceptibility, adverse side effects and immune cell inactivation. Natural killer (NK) cells are the first line of defense against cancer and are critical in the recognition and cytolysis of rapidly dividing and abnormal cell populations. In this review, we describe NK cells and NK cell receptors, functional impairment of NK cells in leukemia, NK cell immunotherapies currently under investigation including monoclonal antibodies (mAbs), adoptive transfer, chimeric antigen receptor-NKs (CAR-NKs), bi-specific/tri-specific killer engagers (BiKEs/TriKEs) and potential targets of NK cell-mediated immunotherapy for leukemia in the future.Leukemia is a malignancy of the bone marrow and blood resulting from the abnormal differentiation of hematopoietic stem cells (HSCs). There are four main types of leukemia including acute myeloid leukemia (AML), acute lymphoblastic leukemia (ALL), chronic myeloid leukemia (CML), and chronic lymphocytic leukemia (CLL). While chemotherapy and radiation have been conventional forms of treatment for leukemia, these therapies increase infection susceptibility, adverse side effects and immune cell inactivation. Immunotherapies are becoming promising treatment options for leukemia, with natural killer (NK) cell-mediated therapy providing a specific direction of interest. The role of NK cells is critical for cancer cell elimination as these immune cells are the first line of defense against cancer proliferation and are involved in both recognition and cytolysis of rapidly dividing and abnormal cell populations. NK cells possess various activating and inhibitory receptors, which regulate NK cell function, signaling either inhibition and continued surveillance, or activation and subsequent cytotoxic activity. In this review, we describe NK cells and NK cell receptors, functional impairment of NK cells in leukemia, NK cell immunotherapies currently under investigation, including monoclonal antibodies (mAbs), adoptive transfer, chimeric antigen receptor-NKs (CAR-NKs), bi-specific/tri-specific killer engagers (BiKEs/TriKEs) and future potential targets of NK cell-based immunotherapy for leukemia.

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

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

NK Cells in a Tug-of-War With Cancer: The Roles of Transcription Factors and Cytoskeleton.

Natural killer (NK) cells are innate immune cells which play a key role in shaping the immune response against cancer. Initially hailed for their potential to recognise and eliminate tumour cells, their application has been greatly hindered by the immunosuppressive tumour microenvironment (TME) which suppresses NK functions (e.g., cytotoxicity). This dysfunctional state that is accompanied by phenotypic changes such as upregulation of inhibitory receptors and downregulation of activating receptors, forms the basis of what many researchers have referred to as ‘exhausted’ NK cells. However, there is no consensus on whether these phenotypes are sufficient to define an exhausted state of the NK cell. While recent advances in checkpoint inhibition appear to show promise in early-stage pre-clinical studies, much remains to be fully explored and understood in the context of the TME. The TME is where the NK cells are subjected to interaction with various cell types and soluble factors, which could exert an inhibitory effect on NK cytotoxicity. In this review, we provide an overview of the general markers of NK cell exhaustion viz, the surface activating and inhibitory receptors. We also highlight the potential role of T-box transcription factors in characterising such a dysfunctional state and discuss the often-overlooked mechanism of cell cytoskeletal dynamics in regulating NK cell function. These aspects may further contribute to NK exhaustion or NK revival in cancer and may open new avenues to explore cancer treatment strategies.

Metastasis-associated macrophages constrain antitumor capability of natural killer cells in the metastatic site at least partially by membrane bound transforming growth factor β

BackgroundMetastatic breast cancer is a leading cause of cancer-related death in women worldwide. Infusion of natural killer (NK) cells is an emerging immunotherapy for such malignant tumors, although elimination of...

Polarized mitochondria as guardians of NK cell fitness.

Distinct metabolic demands accompany lymphocyte differentiation into short-lived effector and long-lived memory cells. How bioenergetics processes are structured in innate natural killer (NK) cells remains unclear. We demonstrate that circulating human CD56Dim (NKDim) cells have fused mitochondria and enhanced metabolism compared with CD56Br (NKBr) cells. Upon activation, these 2 subsets showed a dichotomous response, with further mitochondrial potentiation in NKBr cells vs paradoxical mitochondrial fission and depolarization in NKDim cells. The latter effect impaired interferon-γ production, but rescue was possible by inhibiting mitochondrial fragmentation, implicating mitochondrial polarization as a central regulator of NK cell function. NKDim cells are heterogeneous, and mitochondrial polarization was associated with enhanced survival and function in mature NKDim cells, including memory-like human cytomegalovirus-dependent CD57+NKG2C+ subsets. In contrast, patients with genetic defects in mitochondrial fusion had a deficiency in adaptive NK cells, which had poor survival in culture. These results support mitochondrial polarization as a central regulator of mature NK cell fitness.

PD-1 Expression on NK Cells in Malaria-Exposed Individuals Is Associated with Diminished Natural Cytotoxicity and Enhanced Antibody-Dependent Cellular Cytotoxicity.

Natural killer (NK) cells are key effector cells of innate resistance capable of destroying tumors and virus-infected cells through cytotoxicity and rapid cytokine production. The control of NK cell responses is complex and only partially understood. PD-1 is an inhibitory receptor that regulates T cell function, but a role for PD-1 in regulating NK cell function is only beginning to emerge. Here, we investigated PD-1 expression on NK cells in children and adults in Mali in a longitudinal analysis before, during, and after infection with Plasmodium falciparum malaria. We found that NK cells transiently upregulate PD-1 expression and interleukin-6 (IL-6) production in some individuals during acute febrile malaria. Furthermore, the percentage of PD-1 expressing NK cells increases with age and cumulative malaria exposure. Consistent with this, NK cells of malaria-naive adults upregulated PD-1 following P. falciparum stimulation in vitro Additionally, functional in vitro studies revealed that PD-1 expression on NK cells is associated with diminished natural cytotoxicity but enhanced antibody-dependent cellular cytotoxicity (ADCC). These data indicate that PD-1+ NK cells expand in the context of chronic immune activation and suggest that PD-1 may contribute to skewing NK cells toward enhanced ADCC during infections such as malaria.

Tumor Microenvironment-Associated Extracellular Matrix Components Regulate NK Cell Function.

The tumor microenvironment (TME) is composed of multiple infiltrating host cells (e.g., endothelial cells, fibroblasts, lymphocytes, and myeloid cells), extracellular matrix, and various secreted or cell membrane-presented molecules. Group 1 innate lymphoid cells (ILCs), which includes natural killer (NK) cells and ILC1, contribute to protecting the host against cancer and infection. Both subsets are able to quickly produce cytokines such as interferon gamma (IFN-γ), chemokines, and other growth factors in response to activating signals. However, the TME provides many molecules that can prevent the potential effector function of these cells, thereby protecting the tumor. For example, TME-derived tumor growth factor (TGF)-β and associated members of the superfamily downregulate NK cell cytotoxicity, cytokine secretion, metabolism, proliferation, and induce effector NK cells to upregulate ILC1-like characteristics. In concert, a family of carbohydrate-binding proteins called galectins, which can be produced by different cells composing the TME, can downregulate NK cell function. Matrix metalloproteinase (MMP) and a disintegrin and metalloproteinase (ADAM) are also enzymes that can remodel the extracellular matrix and shred receptors from the tumor cell surface, impairing the activation of NK cells and leading to less effective effector functions. Gaining a better understanding of the characteristics of the TME and its associated factors, such as infiltrating cells and extracellular matrix, could lead to tailoring of new personalized immunotherapy approaches. This review provides an overview of our current knowledge on the impact of the TME and extracellular matrix-associated components on differentiation, impairment, and function of NK cells.

Mirc11 Disrupts Inflammatory but Not Cytotoxic Responses of NK Cells.

Natural killer (NK) cells generate proinflammatory cytokines that are required to contain infections and tumor growth. However, the posttranscriptional mechanisms that regulate NK cell functions are not fully understood. Here, we define the role of the microRNA cluster known as Mirc11 (which includes miRNA-23a, miRNA-24a, and miRNA-27a) in NK cell-mediated proinflammatory responses. Absence of Mirc11 did not alter the development or the antitumor cytotoxicity of NK cells. However, loss of Mirc11 reduced generation of proinflammatory factors in vitro and interferon-γ-dependent clearance of Listeria monocytogenes or B16F10 melanoma in vivo by NK cells. These functional changes resulted from Mirc11 silencing ubiquitin modifiers A20, Cbl-b, and Itch, allowing TRAF6-dependent activation of NF-κB and AP-1. Lack of Mirc11 caused increased translation of A20, Cbl-b, and Itch proteins, resulting in deubiquitylation of scaffolding K63 and addition of degradative K48 moieties on TRAF6. Collectively, our results describe a function of Mirc11 that regulates generation of proinflammatory cytokines from effector lymphocytes.