The Notch ligands Jagged2, Delta1, and Delta4 induce differentiation and expansion of functional human NK cells from CD34+ cord blood hematopoietic progenitor cells

Deciphering the localization and trajectory of human natural killer cell development

Innate immune cells represent the first line of cellular immunity, comprised of both circulating and tissue-resident natural killer cells and innate lymphoid cells. These innate lymphocytes arise from a common CD34+ progenitor that differentiates into mature natural killer cells and innate lymphoid cells. The successive stages in natural killer cell maturation are characterized by increased lineage restriction and changes to phenotype and function. Mechanisms of human natural killer cell development have not been fully elucidated, especially the role of signals that drive the spatial localization and maturation of natural killer cells. Cytokines, extracellular matrix components, and chemokines provide maturation signals and influence the trafficking of natural killer cell progenitors to peripheral sites of differentiation. Here we present the latest advances in our understanding of natural killer and innate lymphoid cell development in peripheral sites, including secondary lymphoid tissues (i.e. tonsil). Recent work in the field has provided a model for the spatial distribution of natural killer cell and innate lymphoid cell developmental intermediates in tissue and generated further insights into the developmental niche. In support of this model, future studies using multifaceted approaches seek to fully map the developmental trajectory of human natural killer cells and innate lymphoid cells in secondary lymphoid tissues.

Enhancing cord blood stem cell-derived NK cell growth and differentiation through hyperosmosis

BACKGROUND

Natural killer (NK) cells hold great promise in treating diverse hematopoietic and solid tumors. Despite their availability from peripheral blood and cord blood, stem cell-derived NK cells offer an 'off-the-shelf' solution. Hematopoietic stem and progenitor cells (HSPCs) derived from cord blood pose no risk to the newborn or mother and are virtually ideal sources for NK cell differentiation.

METHODS

We developed a modified protocol to differentiate HSPCs to NK cells under serum-free conditions using defined factors. The HSPC-derived NK (HSC-NK) cells could be expanded in a K562 feeder cell-dependent manner. Furthermore, using lentivirus transduction, chimeric antigen receptor (CAR)-modified HSPCs could be differentiated into NK cells, leading to the establishment of CAR-NK cells.

RESULTS

The efficiency of NK cell differentiation from HSPCs was increased through the simple modulation of osmotic pressure by the addition of sodium chloride or glucose. Furthermore, the hyperosmosis-primed HSC-NK cells exhibited enhanced proliferation capacity and maintained normal functional characteristics, including transcriptome and antitumor efficacy. The optimized protocol yielded approximately 1.8 million NK cells from a single CD34-positive cell within a 28-day cycle, which signifies more than a ten-fold increase in efficiency relative to the conventional methods. This optimized protocol was also suitable for generating CAR-NK cells with high yields compared to standard conditions.

CONCLUSIONS

The results of this study establish high osmotic pressure as a simple yet powerful adjustment that significantly enhances the efficiency and functionality of HSC-NK cells, including CAR-NK cells. This optimized protocol could lead to cost-effective, high-yield NK cell therapies, potentially revolutionizing cancer immunotherapy strategies.

The Notch signaling pathway: a potential target for cancer immunotherapy

Dysregulation of the Notch signaling pathway, which is highly conserved across species, can drive aberrant epigenetic modification, transcription, and translation. Defective gene regulation caused by dysregulated Notch signaling often affects networks controlling oncogenesis and tumor progression. Meanwhile, Notch signaling can modulate immune cells involved in anti- or pro-tumor responses and tumor immunogenicity. A comprehensive understanding of these processes can help with designing new drugs that target Notch signaling, thereby enhancing the effects of cancer immunotherapy. Here, we provide an up-to-date and comprehensive overview of how Notch signaling intrinsically regulates immune cells and how alterations in Notch signaling in tumor cells or stromal cells extrinsically regulate immune responses in the tumor microenvironment (TME). We also discuss the potential role of Notch signaling in tumor immunity mediated by gut microbiota. Finally, we propose strategies for targeting Notch signaling in cancer immunotherapy. These include oncolytic virotherapy combined with inhibition of Notch signaling, nanoparticles (NPs) loaded with Notch signaling regulators to specifically target tumor-associated macrophages (TAMs) to repolarize their functions and remodel the TME, combining specific and efficient inhibitors or activators of Notch signaling with immune checkpoint blockers (ICBs) for synergistic anti-tumor therapy, and implementing a customized and effective synNotch circuit system to enhance safety of chimeric antigen receptor (CAR) immune cells. Collectively, this review aims to summarize how Notch signaling intrinsically and extrinsically shapes immune responses to improve immunotherapy.

The Notch Signaling Pathway Contributes to Angiogenesis and Tumor Immunity in Breast Cancer

Breast cancer in women is the first leading tumor in terms of incidence worldwide. Some subtypes of BC lack distinct molecular targets and exhibit therapeutic resistance; these patients have a poor prognosis. Thus, the search for new molecular targets is an ongoing challenge for BC therapy. The Notch signaling pathway is found in both vertebrates and invertebrates, and it is a highly conserved in the evolution of the species, controlling cellular fates such as death, proliferation, and differentiation. Numerous studies have shown that improper activation of Notch signaling may lead to excessive cell proliferation and cancer, with tumor-promoting and tumor-suppressive effects in various carcinomas. Thus, inhibitors of Notch signaling are actively being investigated for the treatment of various tumors. The role of Notch signaling in BC has been widely studied in recent years. There is a growing body of evidence suggesting that Notch signaling has a pro-oncogenic role in BC, and the tumor-promoting effect is largely a result of the diverse nature of tumor immunity. Immunological abnormality is also a factor involved in the pathogenesis of BC, suggesting that Notch signaling could be a target for BC immunotherapies. Furthermore, angiogenesis is essential for BC growth and metastasis, and the Notch signaling pathway has been implicated in angiogenesis, so studying the role of Notch signaling in BC angiogenesis will provide new prospects for the treatment of BC. We summarize the potential roles of the current Notch signaling pathway and its inhibitors in BC angiogenesis and the immune response in this review and describe the pharmacological targets of Notch signaling in BC, which may serve as a theoretical foundation for future research into exploring this pathway for novel BC therapies.

The Immunomodulatory Role of Hypoxic Tumor-Derived Extracellular Vesicles

Simple Summary

Hypoxia, a characteristic of many cancer types, can suppress the antitumor effector functions of the adaptive and innate immune system. Tumor-cell-derived extracellular vesicles, which function as a mechanism of communication between tumor cells and immune cells, are also affected by hypoxia, and may drive immunosuppression. The aim of this review is to summarize the current knowledge on hypoxic cancer-cell-derived extracellular vesicles in immunosuppression, and to provide an overview of enriched factors (i.e., miRNA and proteins) in hypoxic tumor-derived EVs and their role in immunomodulation. This complete overview may indicate relevant directions for future research into the role of hypoxia in immunosuppression during cancer.

Abstract

Tumor-associated immune cells frequently display tumor-supportive phenotypes. These phenotypes, induced by the tumor microenvironment (TME), are described for both the adaptive and the innate arms of the immune system. Furthermore, they occur at all stages of immune cell development, up to effector function. One major factor that contributes to the immunosuppressive nature of the TME is hypoxia. In addition to directly inhibiting immune cell function, hypoxia affects intercellular crosstalk between tumor cells and immune cells. Extracellular vesicles (EVs) play an important role in this intercellular crosstalk, and changes in both the number and content of hypoxic cancer-cell-derived EVs are linked to the transfer of hypoxia tolerance. Here, we review the current knowledge about the role of these hypoxic cancer-cell-derived EVs in immunosuppression. In addition, we provide an overview of hypoxia-induced factors (i.e., miRNA and proteins) in tumor-derived EVs, and their role in immunomodulation.

Quantifying Human Natural Killer Cell Migration by Imaging and Image Analysis

Migration is an important function for natural killer cells. Cell motility has implications in development, tissue infiltration, and cytotoxicity, and measuring the properties of natural killer (NK) cell migration using in vitro assays can be highly informative. Many researchers have an interest in studying properties of NK cell migration in the context of genetic mutation, disease, or in specific tissues and microenvironments. Motility assays can also provide information on the localization of proteins during different phases of cell migration. These assays can be performed on different surfaces for migration or coupled with chemoattractants and/or target cells to test functional outcomes or characterize cell migration speeds and phenotypes. NK cells undergo migration during differentiation in tissue, and these conditions can be modeled by culturing NK cells on a confluent bed of stromal cells on glass and imaging cell migration. Alternatively, fibronectin- or ICAM-1-coated surfaces promote NK cell migration and can be used as substrates. Here, we will describe techniques for the experimental setup and analysis of NK cell motility assays by confocal microscopy or in-incubator imaging using commercially available systems. Finally, we describe open-source software for analyzing cell migration using manual tracking or automated approaches and discuss considerations for the implementation of each of these methods.

Notch signaling defects in NK cells in patients with cancer

Altered expressions of proto-oncogenes have been reported during normal lymphocytes mitogenesis and in T and B lymphocytes in patients with autoimmune diseases. We have recently demonstrated a significantly decreased expression of c-kit and c-Myc in NK cells isolated from patients with cancer, which might be related to the functional deficiency of NK cells in the tumor environment. Here, focusing on the regulatory mechanisms of this new clinical phenomenon, we determined expression of c-Myc, Notch1, Notch2, p-53, Cdk6, Rb and phosphorylated Rb in NK cells isolated from the healthy donors and cancer patients. The results of our study revealed a significant down-regulation of expression of Notch receptors and up-regulation of Cdk6 expression in NK cells in cancer, while no significant changes in the expression of p53 and Rb proteins were seen. These data revealed novel signaling pathways altered in NK cells in the tumor environment and support further investigation of the origin of deregulated expression of proto-oncogenes in NK cells patients with different types of cancer.

Notch Regulates Innate Lymphoid Cell Plasticity during Human NK Cell Development

Human NK cells develop in tonsils through discrete NK cell developmental intermediates (NKDIs), yet the mechanistic regulation of this process is unclear. We demonstrate that Notch activation in human tonsil-derived stage 3 (CD34^-CD117⁺CD94^-NKp80^-) and 4A (CD34^-CD117^+/-CD94⁺NKp80^-) NKDIs promoted non-NK innate lymphoid cell differentiation at the expense of NK cell differentiation. In contrast, stage 4B (CD34^-CD117^+/-CD94⁺NKp80⁺) NKDIs were NK cell lineage committed despite Notch activation. Interestingly, whereas NK cell functional maturation from stage 3 and 4A NKDIs was independent of Notch activation, the latter was required for high NKp80 expression and a stage 4B-like phenotype by the NKDI-derived NK cells. The Notch-dependent effects required simultaneous engagement with OP9 stromal cells and were also stage-specific, with NOTCH1 and NOTCH2 receptors regulating stage 3 NKDIs and NOTCH1 primarily regulating stage 4A NKDIs. These data establish stage-specific and stromal-dependent roles for Notch in regulating human NK cell developmental plasticity and maturation.

Transcriptional Regulation of Natural Killer Cell Development and Functions

Natural killer (NK) cells are the major lymphocyte subset of the innate immune system. Their ability to mediate anti-tumor cytotoxicity and produce cytokines is well-established. However, the molecular mechanisms associated with the development of human or murine NK cells are not fully understood. Knowledge is being gained about the environmental cues, the receptors that sense the cues, signaling pathways, and the transcriptional programs responsible for the development of NK cells. Specifically, a complex network of transcription factors (TFs) following microenvironmental stimuli coordinate the development and maturation of NK cells. Multiple TFs are involved in the development of NK cells in a stage-specific manner. In this review, we summarize the recent advances in the understandings of TFs involved in the regulation of NK cell development, maturation, and effector function, in the aspects of their mechanisms, potential targets, and functions.

Generation of cell-derived matrices that support human NK cell migration and differentiation

Human NK cells are effectors of the innate immune system that originate from hematopoietic precursors in the bone marrow. While stromal cell lines that support NK cell development from hematopoietic precursors are often used to generate mature NK cells from lymphoid precursors in vitro, the nature of contributing factors of these stromal cells to the generation of functionally mature NK cells has been poorly described. Previous studies have shown that developing NK cells adhere to, and migrate on, developmentally supportive stroma. Here, we describe the generation of cell-derived matrices (CDMs) from a commonly used murine fetal liver stromal cell line. These CDMs are derived directly from the same EL08.1D2 stromal cell line known to support NK cell differentiation and contain ECM structural components fibronectin and collagen. We demonstrate that CDMs support NK cell adhesion and migration with similar properties as intact cells. Further, we show that CDMs support NK cell maturation from lymphoid precursors in vitro, albeit with reduced cell survival compared to intact cell-based differentiation. Together, these results describe a cell-free system that supports NK cell development and that can serve as a useful model for studying the nature of the biochemical interactions between NK cell developmental intermediates and developmentally supportive substrates.

Pharmacological targeting of natural killer cells for cancer immunotherapy

Natural killer (NK) cells are innate lymphocytes that rapidly respond to cancer cells without prior sensitization or restriction to the cognate antigen in comparison with tumor antigen-specific T cells. Recent advances in understanding NK-cell biology have elucidated the molecular mechanisms underlying the differentiation and maturation of NK cells, in addition to the control of their effector functions by investigating the receptors and ligands involved in the recognition of cancer cells by NK cells. Such clarification of NK-cell recognition of cancer cells also revealed the mechanism by which cancer cells potentially evade NK-cell-dependent immune surveillance. Furthermore, the recent clinical results of T-cell-targeted cancer immunotherapy have increased the expectations for new immunotherapies by targeting NK cells. However, the potential use of NK cells in cancer immunotherapy is not fully understood. In this review, we discuss the current evidence and future potential of pharmacological targeting of NK cells in cancer immunotherapy.

From stem cell to immune effector: how adhesion, migration, and polarity shape T-cell and natural killer cell lymphocyte development in vitro and in vivo

Lymphocyte development is a complex and coordinated pathway originating from pluripotent stem cells during embryogenesis and continuing even as matured lymphocytes are primed and educated in adult tissue. Hematopoietic stem cells develop in a specialized niche that includes extracellular matrix and supporting stromal and endothelial cells that both maintain stem cell pluripotency and enable the generation of differentiated cells. Cues for lymphocyte development include changes in integrin-dependent cell motility and adhesion which ultimately help to determine cell fate. The capacity of lymphocytes to adhere and migrate is important for modulating these developmental signals both by regulating the cues that the cell receives from the local microenvironment as well as facilitating the localization of precursors to tissue niches throughout the body. Here we consider how changing migratory and adhesive phenotypes contribute to human natural killer (NK)- and T-cell development as they undergo development from precursors to mature, circulating cells and how our understanding of this process is informed by in vitro models of T- and NK cell generation.

MicroRNA regulation of natural killer cell development and function in leukemia

MicroRNAs (miRNAs) are now recognized as important regulators of all cellular processes, including immune function and cancer survival. These evolutionary preserved, single-stranded, non-coding RNA molecules mediate important functional effects primarily through post-transcriptional regulation of protein expression. MiRNAs are known to mediate multiple oncogenic pathways in tumor cells, both tumor promoting and tumor suppressing. In addition to a direct tumor cell effect, miRNAs have also been shown to play a critical role in immune cell development, function and survival. Here we expand on previous reports to evaluate miRNA regulation in natural killer (NK) cells primarily in humans and focus on their influence on NK cell development and function in the setting of hematologic malignancies. In addition, we highlight the most recent miRNA discoveries in hematologic malignancies and discuss areas of future exploration relevant to the translational field of innate immunology and miRNA-based therapeutic intervention.

Bronchial Epithelial Cells Promote the Differentiation of Th2 Lymphocytes in Airway Microenvironment through Jagged/Notch-1 Signaling after RSV Infection

BACKGROUND

The aim of this study was to investigate the role of Notch-1 signaling through Notch-1 ligands on bronchial epithelial cells (BECs) in regulating the development of T helper 2 (Th2) lymphocytes after RSV infection.

METHODS

Firstly, we analyzed the expression of cytokines and Notch-1 ligands in BECs by using real-time PCR. Then, RSV-infected BECs were co-cultured with CD4+ T cells in a transwell chamber for 48 h, and differentiation of T cells in the lower chamber was determined using flow cytometry and real-time PCR. JAG1 siRNA was then used to determine the effects of Jagged/Notch-1 signaling on the differentiation of Th2. An RSV-infected mouse model was also used to analyze the secretion of Th differentiation-associated cytokines in serum and lung tissues using ELISA, the histopathological changes using HE staining, and the expression of JAG1 and JAG2 in BECs.

RESULTS

The results showed that RSV promoted the expression of Th2-type cytokines and Jagged-1 and inhibited the expression of Jagged-2 in normal BECs. RSV-infected BECs induced Th2 differentiation. In addition, JAG1 downregulation inhibited the differentiation of Th2 and promoted differentiation of Th1. In the RSV-infected mouse model, the RSV titer, inflammation decreased with time. IL-4 and IL-17 increased on day 28 and 60, while IFNγ increased on day 7 and 28. Moreover, the expression of Jagged-1 increased and that of Jagged-2 decreased in BECs, which was consistent with IL-4 production in lung tissues.

CONCLUSION

Our data showed that BECs had the potential to promote the differentiation of Th2 lymphocytes through Jagged-1/Notch-1 signaling.

Noncoding RNA in NK cells

Noncoding RNAs (ncRNA) are important regulators that modulate cell proliferation, apoptosis, the cell cycle, and DNA methylation. NK cells mediate the immune response via the secretion of various cytokines and are important innate immune cells in the human immune system. Recent studies have found that ncRNA plays an important role in NK cell development and function. With recent advances in bioinformatics and next-generation sequencing, novel ncRNAs have been identified, allowing us to more fully appreciate its functions in NK cell biology. In this review, we summarize and discuss the latest studies on the functions and regulatory mechanisms of long noncoding RNA (lncRNA) and microRNA in NK cells from the viewpoint of epigenetic mechanisms to help us clearly understand ncRNA in NK cells.

Dynamical Analysis of the Regulatory Network Controlling Natural Killer Cells Differentiation

Many disease fighting strategies have focused on the generation of NK cells, since they constitute the main immune barrier against cancer and intracellular pathogens such as viruses. Therefore, a predictive model for the development of NK cells would constitute a useful tool to test several hypotheses regarding the production of these cells during both physiological and pathological conditions. Here, we present a boolean network model that reproduces experimental results reported on the literature regarding the progressive stages of the development of NK cells in wild-type and mutant backgrounds. The model allows for the simulation of different conditions, including extracellular micro-environment as well as the simulation of genetic alterations. It also describes how NK cell differentiation depends on a molecular regulatory network that controls the specification of lymphoid lineages, such as T and B cells, which share a common progenitor with NKs. Furthermore, the study shows that the structure of the regulatory network strongly determines the stability of the expression patterns against perturbations.

OP9 Feeder Cells Are Superior to M2-10B4 Cells for the Generation of Mature and Functional Natural Killer Cells from Umbilical Cord Hematopoietic Progenitors

Adoptive natural killer (NK) cell therapy relies on the acquisition of large numbers of mature and functional NK cells. An option for future immunotherapy treatments is to use large amounts of NK cells derived and differentiated from umbilical cord blood (UCB) CD34⁺ hematopoietic stem cells (HSCs), mainly because UCB is one of the most accessible HSC sources. In our study, we compared the potential of two stromal cell lines, OP9 and M2-10B4, for in vitro generation of mature and functional CD56⁺ NK cells from UCB CD34⁺ HSC. We generated higher number of CD56⁺ NK cells in the presence of the OP9 cell line than when they were generated in the presence of M2-10B4 cells. Furthermore, higher frequency of CD56⁺ NK cells was achieved earlier when cultures were performed with the OP9 cells than with the M2-10B4 cells. Additionally, we studied in detail the maturation stages of CD56⁺ NK cells during the in vitro differentiation process. Our data show that by using both stromal cell lines, CD34⁺ HSC in vitro differentiated into the terminal stages 4–5 of maturation resembled the in vivo differentiation pattern of human NK cells. Higher frequencies of more mature NK cells were reached earlier by using OP9 cell line than M2-10B4 cells. Alternatively, we observed that our in vitro NK cells expressed similar levels of granzyme B and perforin, and there were no significant differences between cultures performed in the presence of OP9 cell line or M2-10B4 cell line. Likewise, degranulation and cytotoxic activity against K562 target cells were very similar in both culture conditions. The results presented here provide an optimal strategy to generate high numbers of mature and functional NK cells in vitro, and point toward the use of the OP9 stromal cell line to accelerate the culture procedure to obtain them. Furthermore, this method could establish the basis for the generation of mature NK cells ready for cancer immunotherapy.

Mechanistic roles of autophagy in hematopoietic differentiation

Autophagy is increasingly recognized for its active role in development and differentiation. In particular, its role in the differentiation of hematopoietic cells has been extensively studied, likely because blood cells are accessible, easy to identify and purify, and their progenitor tree is well defined. This review aims to discuss the mechanisms by which autophagy impacts on differentiation, using hematopoietic cell types as examples. Autophagy's roles include the remodeling during terminal differentiation, the maintenance of a long-lived cell type, and the regulation of the balance between self-renewal and quiescence in stem-like cells. We discuss and compare the mechanistic roles of autophagy, such as prevention of apoptosis, supply of energy metabolites and metabolic adaption, and selective degradation of organelles and of regulatory factors.

Withaferin A induces cell death and differentiation in multiple myeloma cancer stem cells

Multiple myeloma (MM) remains an incurable malignancy despite the development of novel therapeutics. This is believed to be due to a subset of rare chemotherapy-resistant cancer stem cells (CSCs). Differentiation therapy represents one strategy aimed at reducing the stemness of CSCs. The anticancer effect of withaferin A (WFA) was studied in MM-CSCs and RPMI 8226 MM tumoral plasma cells (RPMIs). WFA exhibited growth inhibitory effects in both MM-CSCs and RPMIs, with IC₅₀ values of 649 and 224 nM, respectively. WFA also induced a G₂ cell cycle arrest, as well as cell death and apoptosis. Although, WFA did not exhibit a direct anti-migratory effect, a remarkable morphological change was observed in MM-CSCs in response to WFA treatment. Using qPCR gene expression analyses, WFA caused a reduction in stemness markers, and a promotion of differentiation markers in MM-CSCs. These results warrant further investigation of WFA in relevant MM animal models.

Manufacturing Natural Killer Cells as Medicinal Products

Natural Killer (NK) cells are innate lymphoid cells (ILC) with cytotoxic and regulatory properties. Their functions are tightly regulated by an array of inhibitory and activating receptors, and their mechanisms of activation strongly differ from antigen recognition in the context of human leukocyte antigen presentation as needed for T-cell activation. NK cells thus offer unique opportunities for new and improved therapeutic manipulation, either in vivo or in vitro, in a variety of human diseases, including cancers. NK cell activity can possibly be modulated in vivo through direct or indirect actions exerted by small molecules or monoclonal antibodies. NK cells can also be adoptively transferred following more or less substantial modifications through cell and gene manufacturing, in order to empower them with new or improved functions and ensure their controlled persistence and activity in the recipient. In the present review, we will focus on the technological and regulatory challenges of NK cell manufacturing and discuss conditions in which these innovative cellular therapies can be brought to the clinic.

Notch signaling at later stages of NK cell development enhances KIR expression and functional maturation

The Notch signaling pathway plays a substantial role in human NK cell development. However, the role of Notch on killer Ig-like receptor (KIR) upregulation and acquisition of effector function has not been explored. To evaluate how Notch influences terminal differentiation, cord blood-derived NK cells or sorted peripheral blood NK cells were cultured with IL-15 for 7 d with inhibitory or activating Notch signals. Inhibition of Notch signaling significantly decreased KIR expression, whereas activation enhanced it. Overexpression of activated Notch on cord blood-derived NK cells resulted in a 2-fold increase in KIR expression, indicating that Notch signaling plays a direct, cell-intrinsic role in KIR regulation. Moreover, Notch-mediated KIR expression on NK cells is regulated through cis inhibition by delta-like ligand 1. Notch signaling also enhances CD16 upregulation that precedes KIR expression. Concomitant with the upregulation of KIR and CD16, Notch signaling induces increased cytolytic effector capacity and cytokine secretion, even in posttransplant samples in which NK cell function is inherently defective. Given these attributes of Notch signaling, we propose that Notch agonists may enhance NK cell maturation and tumor killing in a posttransplant setting.

Improving the outcome of leukemia by natural killer cell-based immunotherapeutic strategies

Blurring the boundary between innate and adaptive immune system, natural killer (NK) cells are widely recognized as potent anti-leukemia mediators. Alloreactive donor NK cells have been shown to improve the outcome of allogeneic stem-cell transplantation for leukemia. In addition, in vivo transfer of NK cells may soon reveal an important therapeutic tool for leukemia, if tolerance to NK-mediated anti-leukemia effects is overcome. This will require, at a minimum, the ex vivo generation of a clinically safe NK cell product containing adequate numbers of NK cells with robust anti-leukemia potential. Ideally, ex vivo generated NK cells should also have similar anti-leukemia potential in different patients, and be easy to obtain for convenient clinical scale-up. Moreover, optimal clinical protocols for NK therapy in leukemia and other cancers are still lacking. These and other issues are being currently addressed by multiple research groups. This review will first describe current laboratory NK cell expansion and differentiation techniques by separately addressing different NK cell sources. Subsequently, it will address the mechanisms known to be responsible for NK cell alloreactivity, as well as their clinical impact in the hematopoietic stem cells transplantation setting. Finally, it will briefly provide insight on past NK-based clinical trials.

Antigen presenting cell-mediated expansion of human umbilical cord blood yields log-scale expansion of natural killer cells with anti-myeloma activity

Natural killer (NK) cells are important mediators of anti-tumor immunity and are active against several hematologic malignancies, including multiple myeloma (MM). Umbilical cord blood (CB) is a promising source of allogeneic NK cells but large scale ex vivo expansion is required for generation of clinically relevant CB-derived NK (CB-NK) cell doses. Here we describe a novel strategy for expanding NK cells from cryopreserved CB units using artificial antigen presenting feeder cells (aAPC) in a gas permeable culture system. After 14 days, mean fold expansion of CB-NK cells was 1848-fold from fresh and 2389-fold from cryopreserved CB with >95% purity for NK cells (CD56⁺/CD3⁻) and less than 1% CD3⁺ cells. Though surface expression of some cytotoxicity receptors was decreased, aAPC-expanded CB-NK cells exhibited a phenotype similar to CB-NK cells expanded with IL-2 alone with respect to various inhibitory receptors, NKG2C and CD94 and maintained strong expression of transcription factors Eomesodermin and T-bet. Furthermore, CB-NK cells formed functional immune synapses with and demonstrated cytotoxicity against various MM targets. Finally, aAPC-expanded CB-NK cells showed significant in vivo activity against MM in a xenogenic mouse model. Our findings introduce a clinically applicable strategy for the generation of highly functional CB-NK cells which can be used to eradicate MM.

Dual analysis of the murine cytomegalovirus and host cell transcriptomes reveal new aspects of the virus-host cell interface

Major gaps in our knowledge of pathogen genes and how these gene products interact with host gene products to cause disease represent a major obstacle to progress in vaccine and antiviral drug development for the herpesviruses. To begin to bridge these gaps, we conducted a dual analysis of Murine Cytomegalovirus (MCMV) and host cell transcriptomes during lytic infection. We analyzed the MCMV transcriptome during lytic infection using both classical cDNA cloning and sequencing of viral transcripts and next generation sequencing of transcripts (RNA-Seq). We also investigated the host transcriptome using RNA-Seq combined with differential gene expression analysis, biological pathway analysis, and gene ontology analysis. We identify numerous novel spliced and unspliced transcripts of MCMV. Unexpectedly, the most abundantly transcribed viral genes are of unknown function. We found that the most abundant viral transcript, recently identified as a noncoding RNA regulating cellular microRNAs, also codes for a novel protein. To our knowledge, this is the first viral transcript that functions both as a noncoding RNA and an mRNA. We also report that lytic infection elicits a profound cellular response in fibroblasts. Highly upregulated and induced host genes included those involved in inflammation and immunity, but also many unexpected transcription factors and host genes related to development and differentiation. Many top downregulated and repressed genes are associated with functions whose roles in infection are obscure, including host long intergenic noncoding RNAs, antisense RNAs or small nucleolar RNAs. Correspondingly, many differentially expressed genes cluster in biological pathways that may shed new light on cytomegalovirus pathogenesis. Together, these findings provide new insights into the molecular warfare at the virus-host interface and suggest new areas of research to advance the understanding and treatment of cytomegalovirus-associated diseases.

Location and cellular stages of natural killer cell development

The identification of distinct tissue-specific natural killer (NK) cell populations that apparently mature from local precursor populations has brought new insight into the diversity and developmental regulation of this important lymphoid subset. NK cells provide a necessary link between the early (innate) and late (adaptive) immune responses to infection. Gaining a better understanding of the processes that govern NK cell development should allow us to harness better NK cell functions in multiple clinical settings, as well as to gain further insight into how these cells undergo malignant transformation. In this review, we summarize recent advances in understanding sites and cellular stages of NK cell development in humans and mice.

MicroRNA regulation of natural killer cells

Natural killer (NK) cells are innate immune lymphocytes critical for host defense against viral infection and surveillance against malignant transformation. MicroRNAs (miRNAs) are a family of small, non-coding RNAs that regulate a wide variety of cellular processes. Recent advances have highlighted the importance of miRNA-mediated post-transcriptional regulation in NK cell development, maturation, and function. This review focuses on several facets of this regulatory mechanism in NK cells: (1) the expressed NK cell miRNA transcriptome; (2) the impact of total miRNA deficiency on NK cells; (3) the role of specific miRNAs regulating NK cell development, survival, and maturation; (4) the intrinsic role of miRNAs regulating NK cell function, including cytokine production, proliferation, and cytotoxicity; and (5) the role of NK cell miRNAs in disease. Currently our knowledge of how miRNAs regulate NK cell biology is limited, and thus we also explore key open questions in the field, as well as approaches and techniques to ascertain the role of individual miRNAs as important molecular regulators.

Delta-like ligand (DLL)1 expression in early mouse decidua and its localization to uterine natural killer cells

Uterine vascular changes, critical for pregnancy success, occur at each implant site during endometrial decidualization. Mesometrial decidualization recruits high numbers of angiogenic, uterine Natural Killer (uNK) cells that trigger midpregnancy spiral arterial remodeling. We postulated that uNK cells contribute to early decidual angiogenesis as endothelial-cell extrinsic sources of Delta-like ligand 1 (DLL1), a molecule that induces endothelial tip cell differentiation and orthogonal vascular growth in other tissues. Virgin uteri expressed Dll1 mesometrially and anti-mesometrially and relative expression increased in both anatomic regions as pregnancy progressed. Analyses of transcripts from gd10.5 uNK cells flow sorted on the basis of expression of Dolichos biflorus agglutinin (DBA) lectin revealed that DBA+ but not DBA- uNK cells expressed Dll1. Immunostaining at gd4.5 found DLL1-expressing cells rare. At gd6.5, DBA+ uNK cells at all stages of maturation expressed DLL1. By gd10.5, DLL1 immunoreactivity was strongly expressed by some but not all DBA+ uNK cells and more weakly by DBA- cells. DLL1+ cells were mesometrially stratified and concentrated within central decidua basalis. Our data suggest that uNK cells have the potential to induce endothelial tip cell differentiation and to promote non-planar vascular growth within early decidua basalis.

Natural killer cell regulation by microRNAs in health and disease

Natural killer (NK) cells are innate immune lymphocytes that are critical for normal host defense against infections and mediate antitumor immune responses. MicroRNAs (miRNAs) are a family of small, noncoding RNAs that posttranscriptionally regulate the majority of cellular processes and pathways. Our understanding of how miRNAs regulate NK cells biology is limited, but recent studies have provided novel insight into their expression by NK cells, and how they contribute to the regulation of NK cell development, maturation, survival, and effector function. Here, we review the expression of miRNAs by NK cells, their contribution to cell intrinsic and extrinsic control of NK cell development and effector response, and their dysregulation in NK cell malignancies.

Generation of natural killer cells from hematopoietic stem cells in vitro for immunotherapy

Natural killer (NK) cells are part of the innate immune system and are an alluring option for immunotherapy due to their ability to kill infected cells or cancer cells without prior sensitization. Throughout the past 20 years, different groups have been able to reproduce NK cell development in vitro, and NK cell ontogeny studies have provided the basis for the establishment of protocols to produce NK cells in vitro for immunotherapy. Here, we briefly discuss NK cell development and NK cell immunotherapy approaches. We review the factors needed for NK cell differentiation in vitro, which stem cell sources have been used, published protocols, challenges and future directions for Good Manufacturing Practice protocols.

Production of cytotoxic, KIR-negative NK cells from CD34+ cord blood cells with the use of Notch signaling

The use of natural killer (NK) cells as cell therapy against acute leukemia is an active area of investigation. The optimal source of cytotoxic NK cells for therapeutic use is presently unknown. With funds from the National Blood Foundation, the author's lab has developed in vitro culture systems that use the Notch receptor ligand Delta4 for the differentiation and expansion of functional NK cells from CD34+ cord blood hematopoietic progenitor cells. These Notch-induced NK (N-NK) cells display a predominantly immature, CD56(bright) surface phenotype, with expression of activating receptors important for leukemia cell recognition and killing, but with an absence of inhibitory receptors that bind major histocompatibility complex (MHC) class I, making them free of restriction by self-MHC. They are capable of directly killing hematopoietic tumor cell lines and primary leukemia cells in vitro. Thus, cytotoxic, HLA-independent N-NK cells may represent a novel cell therapy for hematopoietic malignancy.

Cutting edge: microRNA-181 promotes human NK cell development by regulating Notch signaling

MicroRNAs (miRs) have recently been identified as important regulators of gene expression at the posttranscriptional level. Although it has clearly been established that miRs influence the ontogeny of several immune cell lineages, the role of individual miRs during NK cell development has not been described. In this study, we show that miR-181 expression levels have a profound impact on the development of human NK cells from CD34(+) hematopoietic progenitor cells and IFN-γ production in primary CD56(+) NK cells. We also demonstrate that nemo-like kinase (NLK), an inhibitor of Notch signaling, is a target of miR-181 in NK cells, and knockdown of NLK mirrors the developmental effect of miR-181 overexpression. We conclude that miR-181 promotes NK cell development, at least in part, through the suppression of NLK, providing an important link between miRs and Notch signaling.

Notch ligand delta-like 4 regulates development and pathogenesis of allergic airway responses by modulating IL-2 production and Th2 immunity

Activation of the canonical Notch pathways has been implicated in Th cell differentiation, but the role of specific Notch ligands in Th2-mediated allergic airway responses has not been completely elucidated. In this study, we show that delta-like ligand 4 (Dll4) was upregulated on dendritic cells in response to cockroach allergen. Blocking Dll4 in vivo during either the primary or secondary response enhanced allergen-induced pathogenic consequences including airway hyperresponsiveness and mucus production via increased Th2 cytokines. In vitro assays demonstrated that Dll4 regulates IL-2 in T cells from established Th2 responses as well as during primary stimulation. Notably, Dll4 blockade during the primary, but not the secondary, response increased IL-2 levels in lung and lymph node of allergic mice. The in vivo neutralization of Dll4 was associated with increased expansion and decreased apoptosis during the primary allergen sensitization. Moreover, Dll4-mediated Notch activation of T cells during primary stimulation in vitro increased apoptosis during the contraction/resting phase of the response, which could be rescued by exogenous IL-2. Consistent with the role for Dll4-mediated IL-2 regulation in overall T cell function, the frequency of IL-4-producing cells was also significantly altered by Dll4 both in vivo and in vitro. These data demonstrate a regulatory role of Dll4 both in initial Th2 differentiation and in Th2 cytokine production in established allergic responses.