Membrane-bound IL-21 promotes sustained ex vivo proliferation of human natural killer cells

Innovative Strategies to Improve the Clinical Application of NK Cell-Based Immunotherapy

Natural killer cells constitute a part of the innate immune system that mediates an effective immune response towards virus-infected and malignant cells. In recent years, research has focused on exploring and advancing NK cells as an active immunotherapy platform. Despite major advances, there are several key challenges that need to be addressed for the effective translation of NK cell research to clinical applications. This review highlights some of these challenges and the innovative strategies being developed to overcome them, including in vitro expansion, in vivo persistence, infiltration to the tumor site, and prevention of exhaustion.

Challenges to the broad application of allogeneic natural killer cell immunotherapy of cancer

Natural killer (NK) cells are innate immune cells that recognize malignant cells through a wide array of germline-encoded receptors. Triggering of activating receptors results in cytotoxicity and broad immune system activation. The former is achieved through release of cytotoxic granules and presentation of death receptor ligands, while the latter is mediated by inflammatory cytokines, such as interferon-γ and tumor necrosis factor α. Early success with ex vivo activation of NK cells and adoptive transfer suggest they are a safe therapeutic with promising responses in advanced hematologic malignancies. In particular, adoptive NK cell therapies can serve as a 'bridge' to potentially curative allogeneic stem cell transplantation. In addition, strategies are being developed that expand large numbers of cells from limited starting material and mature NK cells from precursors. Together, these make 'off-the-shelf' NK cells possible to treat a wide range of cancers. Research efforts have focused on creating a range of tools that increase targeting of therapeutic NK cells toward cancer-from therapeutic antibodies that drive antibody-dependent cellular cytotoxicity, to chimeric antigen receptors. As these novel therapies start to show promise in clinical trials, the field is rapidly moving toward addressing other challenges that limit NK cell therapeutics and the goal to treat solid tumors. This review describes the state of therapeutic NK cell targeting of tumors; discusses the challenges that need to be addressed before NK cells can be applied as a wide-ranging treatment for cancer; and points to some of the innovations that are being developed to surmount these challenges. Suppressive cells in the tumor microenvironment pose a direct threat to therapeutic NK cells, through presentation of inhibitory ligands and secretion of suppressive cytokines and metabolites. The nutrient- and oxygen-starved conditions under which NK cells must function necessitate an understanding of therapeutic NK cell metabolism that is still emerging. Prior to these challenges, NK cells must find their way into and persist in the tumor itself. Finally, the desirability of a 'single-shot' NK cell treatment and the problems and benefits of a short-lived rejection-prone NK cellular product are discussed.

CHMP2A regulates tumor sensitivity to natural killer cell-mediated cytotoxicity

Natural killer (NK) cells are known to mediate killing of various cancer types, but tumor cells can develop resistance mechanisms to escape NK cell-mediated killing. Here, we use a "two cell type" whole genome CRISPR-Cas9 screening system to discover key regulators of tumor sensitivity and resistance to NK cell-mediated cytotoxicity in human glioblastoma stem cells (GSC). We identify CHMP2A as a regulator of GSC resistance to NK cell-mediated cytotoxicity and we confirm these findings in a head and neck squamous cells carcinoma (HNSCC) model. We show that deletion of CHMP2A activates NF-κB in tumor cells to mediate increased chemokine secretion that promotes NK cell migration towards tumor cells. In the HNSCC model we demonstrate that CHMP2A mediates tumor resistance to NK cells via secretion of extracellular vesicles (EVs) that express MICA/B and TRAIL. These secreted ligands induce apoptosis of NK cells to inhibit their antitumor activity. To confirm these in vitro studies, we demonstrate that deletion of CHMP2A in CAL27 HNSCC cells leads to increased NK cell-mediated killing in a xenograft immunodeficient mouse model. These findings illustrate a mechanism of tumor immune escape through EVs secretion and identify inhibition of CHMP2A and related targets as opportunities to improve NK cell-mediated immunotherapy.

CRISPR Gene Editing of Human Primary NK and T Cells for Cancer Immunotherapy

Antitumor activity of immune cells such as T cells and NK cells has made them auspicious therapeutic regimens for adaptive cancer immunotherapy. Enhancing their cytotoxic effects against malignancies and overcoming their suppression in tumor microenvironment (TME) may improve their efficacy to treat cancers. Clustered, regularly interspaced short palindromic repeats (CRISPR) genome editing has become one of the most popular tools to enhance immune cell antitumor activity. In this review we highlight applications and practicability of CRISPR/Cas9 gene editing and engineering strategies for cancer immunotherapy. In addition, we have reviewed several approaches to study CRISPR off-target effects.

Advances in NK cell production

Immunotherapy based on natural killer (NK) cells is a promising approach for treating a variety of cancers. Unlike T cells, NK cells recognize target cells via a major histocompatibility complex (MHC)-independent mechanism and, without being sensitized, kill the cells directly. Several strategies for obtaining large quantities of NK cells with high purity and high cytotoxicity have been developed. These strategies include the use of cytokine-antibody fusions, feeder cells or membrane particles to stimulate the proliferation of NK cells and enhance their cytotoxicity. Various materials, including peripheral blood mononuclear cells (PBMCs), umbilical cord blood (UCB), induced pluripotent stem cells (iPSCs) and NK cell lines, have been used as sources to generate NK cells for immunotherapy. Moreover, genetic modification technologies to improve the proliferation of NK cells have also been developed to enhance the functions of NK cells. Here, we summarize the recent advances in expansion strategies with or without genetic manipulation of NK cells derived from various cellular sources. We also discuss the closed, automated and GMP-controlled large-scale expansion systems used for NK cells and possible future NK cell-based immunotherapy products.

iPSC-Derived Natural Killer Cell Therapies - Expansion and Targeting

Treatment of cancer with allogeneic natural killer (NK) cell therapies has seen rapid development, especially use against hematologic malignancies. Clinical trials of NK cell-based adoptive transfer to treat relapsed or refractory malignancies have used peripheral blood, umbilical cord blood and pluripotent stem cell-derived NK cells, with each approach undergoing continued clinical development. Improving the potency of these therapies relies on genetic modifications to improve tumor targeting and to enhance expansion and persistence of the NK cells. Induced pluripotent stem cell (iPSC)-derived NK cells allow for routine targeted introduction of genetic modifications and expansion of the resulting NK cells derived from a clonal starting cell population. In this review, we discuss and summarize recent important advances in the development of new iPSC-derived NK cell therapies, with a focus on improved targeting of cancer. We then discuss improvements in methods to expand iPSC-derived NK cells and how persistence of iPSC-NK cells can be enhanced. Finally, we describe how these advances may combine in future NK cell-based therapy products for the treatment of both hematologic malignancies and solid tumors.

Differential effects on natural killer cell production by membrane-bound cytokine stimulations

Robust manufacturing production of natural killer (NK) cells has been challenging in allogeneic NK cell-based therapy. Here, we compared the impact of cytokines on NK cell expansion by developing recombinant K562 feeder cell lines expressing membrane-bound cytokines, mIL15, mIL21, and 41BBL, individually or in combination. We found that 41BBL played a dominant role in promoting up to 500,000-fold of NK cell expansion after a 21-day culture process without inducing exhaustion. However, 41BBL stimulation reduced the overall cytotoxic activity of NK cells when combined with mIL15 and mIL21. Additionally, long-term stimulation with mIL15 and mIL21, but not 41BBL, increased CD56 expression and CD56bright population, which is unexpectedly correlated with the NK cell cytotoxicity. By conducting single-cell sequencing, we identified distinct subpopulations of NK cells induced by different cytokines, including an adaptive-like CD56brightCD16-CD49a+ subset induced by mIL15. Through gene expression analysis, we found that cytokines modulated signaling pathways and target genes involved in cell cycle, senescence, self-renewal, migration, and maturation, in a different manner. Together, our study demonstrated cytokine signal pathways play different roles in NK cell expansion and differentiation, which shed light on NK cell process design to improve productivity and product quality. This article is protected by copyright. All rights reserved.

T cell receptor engineering of primary NK cells to therapeutically target tumors and tumor immune evasion

BACKGROUND

T cell receptor (TCR)-engineered cells can be powerful tools in the treatment of malignancies. However, tumor resistance by Human Leukocyte antigen (HLA) class I downregulation can negatively impact the success of any TCR-mediated cell therapy. Allogeneic natural killer (NK) cells have demonstrated efficacy and safety against malignancies without inducing graft-versus-host-disease, highlighting the feasibility for an 'off the shelf' cellular therapeutic. Furthermore, primary NK cells can target tumors using a broad array of intrinsic activation mechanisms. In this study, we combined the antitumor effector functions of NK cells with TCR engineering (NK-TCR), creating a novel therapeutic strategy to avoid TCR-associated immune resistance.

METHODS

BOB1, is a transcription factor highly expressed in all healthy and malignant B cell lineages, including multiple myeloma (MM). Expression of an HLA-B*07:02 restricted BOB1-specifc TCR in peripheral blood-derived NK cells was achieved following a two-step retroviral transduction protocol. NK-TCR was then compared with TCR-negative NK cells and CD8-T cells expressing the same TCR for effector function against HLA-B*07:02+ B-cell derived lymphoblastoid cell lines (B-LCL), B-cell acute lymphoblastic leukemia and MM cell lines in vitro and in vivo.

RESULTS

Firstly, TCR could be reproducibly expressed in NK cells isolated from the peripheral blood of multiple healthy donors generating pure NK-TCR cell products. Secondly, NK-TCR demonstrated antigen-specific effector functions against malignancies which were previously resistant to NK-mediated lysis and enhanced NK efficacy in vivo using a preclinical xenograft model of MM. Moreover, antigen-specific cytotoxicity and cytokine production of NK-TCR was comparable to CD8 T cells expressing the same TCR. Finally, in a model of HLA-class I loss, tumor cells with B2M KO were lysed by NK-TCR in an NK-mediated manner but were resistant to T-cell based killing.

CONCLUSION

NK-TCR cell therapy enhances NK cell efficacy against tumors through additional TCR-mediated lysis. Furthermore, the dual efficacy of NK-TCR permits the specific targeting of tumors and the associated TCR-associated immune resistance, making NK-TCR a unique cellular therapeutic.

The Future of Natural Killer Cell Immunotherapy for B Cell Non-Hodgkin Lymphoma (B Cell NHL)

Natural killer (NK) cells have played a critical—if largely unrecognized or ignored—role in the treatment of B cell non-Hodgkin lymphoma (NHL) since the introduction of CD20-directed immunotherapy with rituximab as a cornerstone of therapy over 25 years ago. Engagement with NK cells leading to lysis of NHL targets through antibody-dependent cellular cytotoxicity (ADCC) is a critical component of rituximab’s mechanism of action. Despite this important role, the only aspect of B cell NHL therapy that has been adopted as standard therapy that even indirectly augments or restores NK cell function is the introduction of obinutuzumab, a CD20 antibody with enhanced ability to engage with NK cells. However, over the last 5 years, adoptive immunotherapy with effector lymphocytes of B cell NHL has experienced tremendous growth, with five different CAR T cell products now licensed by the FDA, four of which target CD19 and have approved indications for some subtype of B cell NHL—axicabtagene ciloleucel, brexucabtagene autoleucel, lisocabtagene maraleucel, and tisagenlecleucel. These T cell-based immunotherapies essentially mimic the recognition, activation pathway, and cytotoxic machinery of a CD19 antibody engaging NK cells and lymphoma targets. Despite their efficacy, these T cell-based immunotherapies have been difficult to implement because they require 4–6 weeks of manufacture, are costly, and have significant toxicities. This renewed interest in the potential of cellular immunity—and the manufacturing, supply chain, and administration logistics that have been addressed with these new agents—have ignited a new wave of enthusiasm for NK cell-directed therapies in NHL. With high safety profiles and proven anti-lymphoma efficacy, one or more new NK cell-directed modalities are certain to be introduced into the standard toolbox of NHL therapy within the next few years, be it function-enhancing cytokine muteins, multi-domain NK cell engagers, or adoptive therapy with expanded or genetically modified NK cells.

Feeder-Cell-Free and Serum-Free Expansion of Natural Killer Cells Using Cloudz Microspheres, G-Rex6M, and Human Platelet Lysate

The versatility of natural killer cells has ignited growing interest in their therapeutic use for cancer and other immunotherapy treatments. However, NK cells compose a small portion of peripheral blood mononuclear cells (5%–20% of PBMCs) and clinical doses require billions of cells. Manufacturing suitable doses of NK cells remains a major challenge for NK immunotherapy. The current standard for expanding NK cells relies on feeder cells and fetal bovine serum to achieve large expansion, but both encounter regulatory concerns. We developed NK Cloudz, a dissolvable polymer-based microsphere platform, as an alternative to a feeder cell approach to expand NK cells. We demonstrated that a combination of NK Cloudz, a G-Rex6M culture vessel, and GMP Human Platelet Lysate expanded NK cells 387 ± 100-fold in 10 days from a PBMC starting population. The NK purity, viability, and cytotoxicity were similar to both a feeder cell protocol and an FBS-based protocol. Additionally, we found no significant differences between FBS and GMP Human Platelet Lysate and concluded that platelet lysate is a good xeno-free alternative to FBS for NK expansion. Overall, we demonstrated a feeder-cell-free and FBS-free protocol that leverages NK Cloudz as a promising step toward a commercial GMP manufacturing method to expand NK cells for therapeutic use.

3D-organoid culture supports differentiation of human CAR+ iPSCs into highly functional CAR T cells

Unlimited generation of chimeric antigen receptor (CAR) T cells from human-induced pluripotent stem cells (iPSCs) is an attractive approach for "off-the-shelf" CAR T cell immunotherapy. Approaches to efficiently differentiate iPSCs into canonical αβ T cell lineages, while maintaining CAR expression and functionality, however, have been challenging. We report that iPSCs reprogramed from CD62L⁺ naive and memory T cells followed by CD19-CAR engineering and 3D-organoid system differentiation confers products with conventional CD8αβ-positive CAR T cell characteristics. Expanded iPSC CD19-CAR T cells showed comparable antigen-specific activation, degranulation, cytotoxicity, and cytokine secretion compared with conventional CD19-CAR T cells and maintained homogeneous expression of the TCR derived from the initial clone. iPSC CD19-CAR T cells also mediated potent antitumor activity in vivo, prolonging survival of mice with CD19⁺ human tumor xenografts. Our study establishes feasible methodologies to generate highly functional CAR T cells from iPSCs to support the development of "off-the-shelf" manufacturing strategies.

Progression-Free Survival of a Patient with Advanced Hepatocellular Carcinoma Treated with Adoptive Cell Therapy Using Natural Killer Cells: A Case Report

Adoptive cell therapy (ACT) is a promising treatment that is considered safe and efficient. Natural killer (NK) cells play an important role in the innate immune system and destroy target cells such as tumor cells without prior sensitization. Here, we report a 59-year-old man with advanced diffuse hepatocellular carcinoma (HCC) who underwent 17 courses of NK cell treatment from March 2017 to July 2018. Although he presented with progressive disease, his hydrothorax and ascites decreased, and his state of mind, appetite and quality of life were markedly improved after treatment versus at admission. To date, his survival time is >48 months. Here, we provide evidence that NK cell adoptive therapy has no adverse effects, enhances immune function, and improves the quality of life of patients with HCC.

NK cells in the brain: implications for brain tumor development and therapy

Natural killer (NK) cells are innate lymphoid cells with robust antitumor functions rendering them promising therapeutic tools against malignancies. Despite constituting a minor fraction of the immune cells infiltrating tumors in the brain, insights into their role in central nervous system (CNS) pathophysiology are emerging. The challenges posed by a profoundly immunosuppressive microenvironment as well as by tumor resistance mechanisms necessitate exploring avenues to enhance the therapeutic potential of NK cells in both primary and metastatic brain malignancies. In this review, we summarize the role of NK cells in the pathogenesis of tumors in the brain and discuss the avenues investigated to harness their anticancer effects against primary and metastatic CNS tumors, including sources of therapeutic NK cells, combinations with other treatments, and novel engineering approaches for augmenting their cytotoxicity. We also highlight relevant preclinical evidence and clinical trials of NK cell-based therapies.

Engineered NK Cells Against Cancer and Their Potential Applications Beyond

Cell therapy is an innovative therapeutic concept where viable cells are implanted, infused, or grafted into a patient to treat impaired or malignant tissues. The term was first introduced circa the 19th century and has since resulted in multiple breakthroughs in different fields of medicine, such as neurology, cardiology, and oncology. Lately, cell and gene therapy are merging to provide cell products with additional or enhanced properties. In this context, adoptive transfer of genetically modified cytotoxic lymphocytes has emerged as a novel treatment option for cancer patients. To this day, five cell therapy products have been FDA approved, four of which for CD19-positive malignancies and one for B-cell maturation antigen (BCMA)-positive malignancies. These are personalized immunotherapies where patient T cells are engineered to express chimeric antigen receptors (CARs) with the aim to redirect the cells against tumor-specific antigens. CAR-T cell therapies show impressive objective response rates in clinical trials that, in certain instances, may reach up to 80%. However, the life-threatening side effects associated with T cell toxicity and the manufacturing difficulties of developing personalized therapies hamper their widespread use. Recent literature suggests that Natural Killer (NK) cells, may provide a safer alternative and an 'off-the-shelf' treatment option thanks to their potent antitumor properties and relatively short lifespan. Here, we will discuss the potential of NK cells in CAR-based therapies focusing on the applications of CAR-NK cells in cancer therapy and beyond.

Feeder Cells at the Interface of Natural Killer Cell Activation, Expansion and Gene Editing

Genome engineered natural killer (NK) cell therapies are emerging as a promising cancer immunotherapy platform with potential advantages and remaining uncertainties. Feeder cells induce activation and proliferation of NK cells via cell surface receptor-ligand interactions, supported by cytokines. Feeder cell expanded NK cell products have supported several NK cell adoptive transfer clinical trials over the past decade. Genome engineered NK cell therapies, including CAR-NK cells, seek to combine innate and alloreactive NK cell anti-tumor activity with antigen specific targeting or additional modifications aimed at improving NK cell persistence, homing or effector function. The profound activating and expansion stimulus provided by feeder cells is integral to current applications of clinical-scale genome engineering approaches in donor-derived, primary NK cells. Herein we explore the complex interactions that exist between feeder cells and both viral and emerging non-viral genome editing technologies in NK cell engineering. We focus on two established clinical-grade feeder systems; Epstein-Barr virus transformed lymphoblastoid cell lines and genetically engineered K562.mbIL21.4-1BBL feeder cells.

Glucocorticoids and natural killer cells: A suppressive relationship

Glucocorticoids exert their pharmacological actions by mimicking and amplifying the function of the endogenous glucocorticoid system's canonical physiological stress response. They affect the immune system at the levels of inflammation and adaptive and innate immunity. These effects are the basis for therapeutic use of glucocorticoids. Innate immunity is the body's first line of defense against disease conditions. It is relatively nonspecific and, among its mediators, natural killer(NK) cells link innate and acquired immunity. NK cell numbers are altered in patients with auto immune diseases, and research suggests that interactions between glucocorticoids and natural killer cells arecritical for successful glucocorticoid therapy. The aim of this review is to summarize these interactions while highlighting the latest and most important developments in this field. Production and release in theblood of endogenous glucocorticoids are strictly regulated by the hypothalamus-pituitary-adrenal axis. Aself-regulatory mechanism prevents excessive plasma levels of these hormones. However, exogenousstimuli such as stress, inflammation, infections, cancer, and autoimmune disease can trigger thehypothalamus-pituitary-adrenal axis response and lead to excessive systemic release of glucocorticoids.Thus, stress stimuli, such as sleep deprivation, intense exercise, depression, viral infections, andcancer, can result in release of glucocorticoids and associated immunosuppressant effects. Among theseeffects are decreases in the numbers and activities of NK cells in inflammatory and autoimmune diseases(e.g., giant cell arteritis, polymyalgia rheumatica, and familial hypogammaglobulinemia).

Natural Killer (NK) and CAR-NK Cell Expansion Method using Membrane Bound-IL-21-Modified B Cell Line

Chimeric antigen receptor (CAR)-modified immune cell therapy has become an emerging treatment for cancers and infectious diseases. NK-based immunotherapy, particularly CAR-NK cell, is one of the most promising 'off-the-shelf' development without severe life-threatening toxicity. However, the bottleneck for developing a successful CAR-NK therapy is achieving sufficient numbers of non-exhaustive, long-lived, 'off-the-shelf' CAR-NK cells from a third party. Here, we developed a new CAR-NK expansion method using an Epstein-Barr virus- (EBV) transformed B cell line expressing a genetically modified membrane form of interleukin-21 (IL-21). In this protocol, step-by-step procedures are provided to expand NK and CAR-NK cells from cord blood and peripheral blood, as well as solid organ tissues. This work will significantly enhance the clinical development of CAR-NK immunotherapy.

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

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

A Hot Topic: Cancer Immunotherapy and Natural Killer Cells

Despite significant progress in recent years, the therapeutic approach of the multiple different forms of human cancer often remains a challenge. Besides the well-established cancer surgery, radiotherapy and chemotherapy, immunotherapeutic strategies gain more and more attention, and some of them have already been successfully introduced into the clinic. Among these, immunotherapy based on natural killer (NK) cells is considered as one of the most promising options. In the present review, we will expose the different possibilities NK cells offer in this context, compare data about the theoretical background and mechanism(s) of action, report some results of clinical trials and identify several very recent trends. The pharmaceutical industry is quite interested in NK cell immunotherapy, which will benefit the speed of progress in the field.

Cellular Therapy Advances in Chronic Lymphocytic Leukemia and Richter's Syndrome

Over the past 10 years, there have been great treatment advances for chronic lymphocytic leukemia (CLL) with the development of small molecule inhibitors. However, there remains an area of unmet need for patients who progress on novel therapies. The development of cellular therapies in CLL has been hindered by CLL induced immunosuppression. Fortunately, recent progress in various methods in immunomodulation may help overcome this limitation in CLL. These advances have spurred ongoing interest in the development of cellular therapies for CLL, including chimeric antigen receptor (CAR) T cell therapies, bi-specific antibodies, and use of natural killer cells. These novel treatment modalities may hold promise for patients with refractory, and potentially transformed disease. Here, we discuss the development of CAR-T cell therapy in CLL and the impact of combining CAR-T and small molecule inhibitors on treatment outcomes, the evolving role of bi-specific antibodies and natural killer cells, and comment on the use of cellular therapies for Richter's syndrome.

Production of human CAR-NK cells with lentiviral vectors and functional assessment in vitro

Although natural killer (NK) cells have become a promising immune effector cell for chimeric antigen receptor (CAR)-based therapy, generating human CAR-NK cells with high transgene efficiency has been challenging. In this protocol, we describe how to generate CAR-NK cells with transduction efficiencies >15% from healthy donor ex vivo expanded NK cells using third generation lentiviral vectors (LVs). We also show how to assess CAR-NK cell anti-tumor function in vitro using a flow cytometry-based killing assay.

For complete details on the use and execution of this protocol, please refer to Portillo et al. (2021).

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PBMC isolation and expansion of human NK cells from healthy donors

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Production of third generation lentiviral vectors for NK cell transduction

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A protocol for the generation of CAR-modified NK cells from human expanded NK cells

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A flow cytometry-based assay to assess CAR-NK cell cytotoxicity in vitro

Increased Susceptibility of the CD57- NK Cells Expressing KIR2DL2/3 and NKG2C to iCasp9 Gene Retroviral Transduction and the Relationships with Proliferative Potential, Activation Degree, and Death Induction Response

Nowadays, the use of genetically modified NK cells is a promising strategy for cancer immunotherapy. The additional insertion of genes capable of inducing cell suicide allows for the timely elimination of the modified NK cells. Different subsets of the heterogenic NK cell population may differ in proliferative potential, in susceptibility to genetic viral transduction, and to the subsequent induction of cell death. The CD57⁻NKG2C⁺ NK cells are of special interest as potential candidates for therapeutic usage due to their high proliferative potential and certain features of adaptive NK cells. In this study, CD57⁻ NK cell subsets differing in KIR2DL2/3 and NKG2C expression were transduced with the iCasp9 suicide gene. The highest transduction efficacy was observed in the KIR2DL2/3⁺NKG2C⁺ NK cell subset, which demonstrated an increased proliferative potential with prolonged cultivation. The increased transduction efficiency of the cell cultures was associated with the higher expression level of the HLA-DR activation marker. Among the iCasp9-transduced subsets, KIR2DL2/3⁺ cells had the weakest response to the apoptosis induction by the chemical inductor of dimerization (CID). Thus, KIR2DL2/3⁺NKG2C⁺ NK cells showed an increased susceptibility to the iCasp9 retroviral transduction, which was associated with higher proliferative potential and activation status. However, the complete elimination of these cells with CID is impeded.

Current Perspectives on "Off-The-Shelf" Allogeneic NK and CAR-NK Cell Therapies

Natural killer cells (NK cells) are the first line of the innate immune defense system, primarily located in peripheral circulation and lymphoid tissues. They kill virally infected and malignant cells through a balancing play of inhibitory and stimulatory receptors. In pre-clinical investigational studies, NK cells show promising anti-tumor effects and are used in adoptive transfer of activated and expanded cells, ex-vivo. NK cells express co-stimulatory molecules that are attractive targets for the immunotherapy of cancers. Recent clinical trials are investigating the use of CAR-NK for different cancers to determine the efficiency. Herein, we review NK cell therapy approaches (NK cell preparation from tissue sources, ways of expansion ex-vivo for "off-the-shelf" allogeneic cell-doses for therapies, and how different vector delivery systems are used to engineer NK cells with CARs) for cancer immunotherapy.

Defining the AHR-regulated transcriptome in NK cells reveals gene expression programs relevant to development and function

AHR directly regulates a wide range of genes in NK cells, including those involved in cell signaling, oxidative stress, and metabolism.

Knowing of the repertoire of genes regulated by AHR may help us better understand NK-cell dysfunction mediated by AHR ligands in cancer.

The aryl hydrocarbon receptor (AHR) is a ligand-activated transcription factor that regulates cellular processes in cancer and immunity, including innate immune cell development and effector function. However, the transcriptional repertoire through which AHR mediates these effects remains largely unexplored. To elucidate the transcriptional elements directly regulated by AHR in natural killer (NK) cells, we performed RNA and chromatin immunoprecipitation sequencing on NK cells exposed to AHR agonist or antagonist. We show that mature peripheral blood NK cells lack AHR, but its expression is induced by Stat3 during interleukin-21–driven activation and proliferation, coincident with increased NCAM1 (CD56) expression resulting in a CD56^bright phenotype. Compared with control conditions, NK cells expanded in the presence of the AHR antagonist, StemRegenin-1, were unaffected in proliferation or cytotoxicity, had no increase in NCAM1 transcription, and maintained the CD56^dim phenotype. However, it showed altered expression of 1004 genes including those strongly associated with signaling pathways. In contrast, NK cells expanded in the presence of the AHR agonist, kynurenine, showed decreased cytotoxicity and altered expression of 97 genes including those strongly associated with oxidative stress and cellular metabolism. By overlaying these differentially expressed genes with AHR chromatin binding, we identified 160 genes directly regulated by AHR, including hallmark AHR targets AHRR and CYP1B1 and known regulators of phenotype, development, metabolism, and function such as NCAM1, KIT, NQO1, and TXN. In summary, we define the AHR transcriptome in NK cells, propose a model of AHR and Stat3 coregulation, and identify potential pathways that may be targeted to overcome AHR-mediated immune suppression.

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

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

Horses for Courses in the Era of CARs: Advancing CAR T and CAR NK Cell Therapies

The adoptive transfer of allogeneic CAR NK cells holds great promise as an anticancer modality due to the relative ease of manufacturing and genetic modification of NK cells, which translates into affordable pricing. Compared to the pronounced efficacy of CAR T cell therapy in the treatment of B cell malignancies, rigorous clinical and preclinical assessment of the antitumor properties of CAR NK cells has been lagging behind. In this brief review, we summarize the biological features of NK cells that may help define the therapeutic niche of CAR NK cells as well as create more potent NK cell-based anticancer products. In addition, we compare T cells and NK cells as the carriers of CARs using the data of single-cell transcriptomic analysis.

The Biological Role and Therapeutic Potential of NK Cells in Hematological and Solid Tumors

NK cells are an attractive target for cancer immunotherapy due to their potent antitumor activity. The main advantage of using NK cells as cytotoxic effectors over T cells is a reduced risk of graft versus host disease. At present, several variants of NK-cell-based therapies are undergoing clinical trials and show considerable effectiveness for hematological tumors. In these types of cancers, the immune cells themselves often undergo malignant transformation, which determines the features of the disease. In contrast, the current use of NK cells as therapeutic agents for the treatment of solid tumors is much less promising. Most studies are at the stage of preclinical investigation, but few progress to clinical trials. Low efficiency of NK cell migration and functional activity in the tumor environment are currently considered the major barriers to NK cell anti-tumor therapies. Various therapeutic combinations, genetic engineering methods, alternative sources for obtaining NK cells, and other techniques are aiming at the development of promising NK cell anticancer therapies, regardless of tumorigenesis. In this review, we compare the role of NK cells in the pathogenesis of hematological and solid tumors and discuss current prospects of NK-cell-based therapy for hematological and solid tumors.

NK cell-based therapies for HIV infection: Investigating current advances and future possibilities

NK cells are well-known for their antiviral functions. Also, their role in HIV has been well established, with rapid responses elicited during early HIV infection. Most immune cells including CD4⁺ T cells, monocytes, Mϕs, and dendritic cells are readily infected by HIV. Recent evidence from multiple studies has suggested that similar to these cells, in chronic conditions like HIV, NK cells also undergo functional exhaustion with impaired cytotoxicity, altered cytokine production, and impaired ADCC. NK-based immunotherapy aims to successfully restore, boost, and modify their activity as has been already demonstrated in the field of cancer immunotherapy. The utilization of NK cell-based strategies for the eradication of HIV from the body provides many advantages over classical ART. The literature search consisted of manually selecting the most relevant studies from databases including PubMed, Embase, Google Scholar, and ClinicalTrial.gov. Some of the treatments currently under consideration are CAR-NK cell therapy, facilitating ADCC, TLR agonists, bNAbs, and BiKEs/TriKEs, blocking inhibitory NK receptors during infection, IL-15 and IL-15 superagonists (eg: ALT-803), and so on. This review aims to discuss the NK cell-based therapies currently under experimentation against HIV infection and finally highlight the challenges associated with NK cell-based immunotherapies.

Comparative Immunogenomics of Canine Natural Killer Cells as Immunotherapy Target

Natural killer (NK) cells are key effectors of the innate immune system, but major differences between human and murine NK cells have impeded translation. Outbred dogs offer an important link for studies of NK biology and immunotherapy. We analyzed gene expression of putative NK populations from healthy dogs and dogs with naturally-occurring cancers examining differential gene expression across multiple conditions, including steady-state, in vitro activation with cytokines and co-culture, and in vivo activation with inhaled IL-15 in dogs receiving IL-15 immunotherapy. We also compared dog, mouse and human CD3-NKp46+ NK cells using a novel orthologous transcriptome. Distinct transcriptional profiles between NK populations exist between conditions and in vitro versus in vivo treatments. In cross-species analysis, canine NK cells were globally more similar to human NK cells than mice. These data define canine NK cell gene expression under multiple conditions and across species, filling an important gap in translational NK studies.

New Orders to an Old Soldier: Optimizing NK Cells for Adoptive Immunotherapy in Hematology

NK (Natural Killer) cell-mediated adoptive immunotherapy has gained attention in hematology due to the progressing knowledge of NK cell receptor structure, biology and function. Today, challenges related to NK cell expansion and persistence in vivo as well as low cytotoxicity have been mostly overcome by pioneering trials that focused on harnessing NK cell functions. Recent technological advancements in gene delivery, gene editing and chimeric antigen receptors (CARs) have made it possible to generate genetically modified NK cells that enhance the anti-tumor efficacy and represent suitable “off-the-shelf” products with fewer side effects. In this review, we highlight recent advances in NK cell biology along with current approaches for potentiating NK cell proliferation and activity, redirecting NK cells using CARs and optimizing the procedure to manufacture clinical-grade NK and CAR NK cells for adoptive immunotherapy.

Adoptive immunotherapy with double-bright (CD56bright /CD16bright ) expanded natural killer cells in patients with relapsed or refractory acute myeloid leukaemia: a proof-of-concept study

Patients with acute myeloid leukaemia (AML) have a five-year survival rate of 28·7%. Natural killer (NK)-cell have anti-leukaemic activity. Here, we report on a series of 13 patients with high-risk R/R AML, treated with repeated infusions of double-bright (CD56^bright /CD16^bright ) expanded NK cells at an academic centre in Brazil. NK cells from HLA-haploidentical donors were expanded using K562 feeder cells, modified to express membrane-bound interleukin-21. Patients received FLAG, after which cryopreserved NK cells were thawed and infused thrice weekly for six infusions in three dose cohorts (10⁶ -10⁷ cells/kg/infusion). Primary objectives were safety and feasibility. Secondary endpoints included overall response (OR) and complete response (CR) rates at 28-30 days after the first infusion. Patients received a median of five prior lines of therapy, seven with intermediate or adverse cytogenetics, three with concurrent central nervous system (CNS) leukaemia, and one with concurrent CNS mycetoma. No dose-limiting toxicities, infusion-related fever, or cytokine release syndrome were observed. An OR of 78·6% and CR of 50·0% were observed, including responses in three patients with CNS disease and clearance of a CNS mycetoma. Multiple infusions of expanded, cryopreserved NK cells were safely administered after intensive chemotherapy in high-risk patients with R/R AML and demonstrated encouraging outcomes.

Chimeric Antigen Receptor-Engineered Natural Killer (CAR NK) Cells in Cancer Treatment; Recent Advances and Future Prospects

Natural Killer (NK) cells are critical members of the innate immunity lymphocytes and have a critical role in host defense against malignant cells. Adoptive cell therapy (ACT) using chimeric antigen receptor (CAR) redirects the specificity of the immune cell against a target-specific antigen. ACT has recently created an outstanding opportunity for cancer treatment. Unlike CAR-armored T cells which hadnsome shortcomings as the CAR-receiving construct, Major histocompatibility complex (MHC)-independency, shorter lifespan, the potential to produce an off-the-shelf immune product, and potent anti-tumor properties of the NK cells has introduced NK cells as a potent alternative target for expression of CAR. Here, we aim to provide an updated overview on the current improvements in CAR NK design and immunobiology and describe the potential of CAR-modified NK cells as an alternative “off-the-shelf” carrier of CAR. We also provide lists for the sources of NK cells in the process of CAR NK cell production, different methods for transduction of the CAR genetic sequence to NK cells, the differences between CAR T and CAR NK, and CAR NK-targeted tumor antigens in current studies. Additionally, we provide data on recently published preclinical and clinical studies of CAR NK therapy and a list of finished and ongoing clinical trials. For achieving CAR NK products with higher efficacy and safety, we discuss current challenges in transduction and expansion of CAR NK cells, CAR NK therapy side effects, and challenges that limit the optimal efficacy of CAR NK cells and recommend possible solutions to enhance the persistence, function, safety, and efficacy of CAR NK cells with a special focus on solid tumors.

Unleashing the power of NK cells in anticancer immunotherapy

Due to their physiological role in removing damaged cells, natural killer (NK) cells represent ideal candidates for cellular immunotherapy in the treatment of cancer. Thereby, the cytotoxicity of NK cells is regulated by signals on both, the NK cells as well as the targeted tumor cells, and the interplay and balance of these signals determine the killing capacity of NK cells. One promising avenue in cancer treatment is therefore the combination of NK cell therapy with agents that either help to increase the killing capacity of NK cells or sensitize tumor cells to an NK cell-mediated attack. In this mini-review, we present different strategies that can be explored to unleash the potential of NK cell immunotherapy. In particular, we summarize how modulation of apoptosis signaling within tumor cells can be exploited to sensitize tumor cells to NK cell-mediated cytotoxicity.

Hijacking TYRO3 from Tumor Cells via Trogocytosis Enhances NK-Cell Effector Functions and Proliferation

Trogocytosis is a fast, cell-cell contact-dependent uptake of membrane patches and associated molecules by one cell from another. Here, we report our investigation of trogocytosis of TYRO3, a cell membrane protein, from tumor target cells to natural killer (NK) cells and the associated functional consequences for NK cells. We found that although NK cells did not express endogenous TYRO3 on the cell surface, activated NK cells rapidly acquired TYRO3 from tumor cells via trogocytosis in vitro and in vivo. NK cells that acquired TYRO3, which we termed TYRO3⁺ NK cells, had significantly enhanced cytotoxicity and IFNγ production as well as higher expression of some activated surface markers compared with TYRO3^- NK cells. Furthermore, the activation status of NK cells and TYRO3 expression levels on donor cells, either endogenous or ectopic, positively correlated with trogocytosis levels. When the antigen-presenting cell (APC) K562 leukemia cell line, a feeder cell line to expand NK cells, overexpressed TYRO3, TYRO3 was transferred to NK cells via trogocytosis, which improved NK-cell proliferation ex vivo. This provides a strategy to manufacture NK cells or their engineered counterparts, such as chimeric antigen receptor NK cells, for the treatment of cancer or infectious diseases.

Decrease post-transplant relapse using donor-derived expanded NK-cells

In this phase I/II clinical trial, we investigated the safety and efficacy of high doses of mb-IL21 ex vivo expanded donor-derived NK cells to decrease relapse in 25 patients with myeloid malignancies receiving haploidentical stem-cell transplantation (HSCT). Three doses of donor NK cells (1 × 10⁵-1 × 10⁸ cells/kg/dose) were administered on days -2, +7, and +28. Results were compared with an independent contemporaneously treated case-matched cohort of 160 patients from the CIBMTR database.After a median follow-up of 24 months, the 2-year relapse rate was 4% vs. 38% (p = 0.014), and disease-free survival (DFS) was 66% vs. 44% (p = 0.1) in the cases and controls, respectively. Only one relapse occurred in the study group, in a patient with the high level of donor-specific anti-HLA antibodies (DSA) presented before transplantation. The 2-year relapse and DFS in patients without DSA was 0% vs. 40% and 72% vs. 44%, respectively with HR for DFS in controls of 2.64 (p = 0.029). NK cells in recipient blood were increased at day +30 in a dose-dependent manner compared with historical controls, and had a proliferating, mature, highly cytotoxic, NKG2C+/KIR+ phenotype.Administration of donor-derived expanded NK cells after haploidentical transplantation was safe, associated with NK cell-dominant immune reconstitution early post-transplant, preserved T-cell reconstitution, and improved relapse and DFS. TRIAL REGISTRATION: NCT01904136 ( https://clinicaltrials.gov/ct2/show/NCT01904136 ).

Expansion of cytotoxic natural killer cells in multiple myeloma patients using K562 cells expressing OX40 ligand and membrane-bound IL-18 and IL-21

BACKGROUND

Natural killer (NK) cell-based immunotherapy is a promising treatment approach for multiple myeloma (MM), but obtaining a sufficient number of activated NK cells remains challenging. Here, we report an improved method to generate ex vivo expanded NK (eNK) cells from MM patients based on genetic engineering of K562 cells to express OX40 ligand and membrane-bound (mb) IL-18 and IL-21.

METHODS

K562-OX40L-mbIL-18/-21 cells were generated by transducing K562-OX40L cells with a lentiviral vector encoding mbIL-18 and mbIL-21, and these were used as feeder cells to expand NK cells from peripheral blood mononuclear cells of healthy donors (HDs) and MM patients in the presence of IL-2/IL-15. Purity, expansion rate, receptor expression, and functions of eNK cells were determined over four weeks of culture.

RESULTS

NK cell expansion was enhanced by short exposure of soluble IL-18 and IL-21 with K562-OX40L cells. Co-culture of NK cells with K562-OX40L-mbIL-18/-21 cells resulted in remarkable expansion of NK cells from HDs (9,860-fold) and MM patients (4,929-fold) over the 28-day culture period. Moreover, eNK cells showed increased expression of major activation markers and enhanced cytotoxicity towards target K562, U266, and RPMI8226 cells.

CONCLUSIONS

Our data suggest that genetically engineered K562 cells expressing OX40L, mbIL-18, and mbIL-21 improve the expansion of NK cells, increase activation signals, and enhance their cytolytic activity towards MM cells.

BCL7B is a potential novel diagnosis and prognosis biomarker for sarcomas using bioinformatics analysis

BCL7B plays a potential role in the progression of various cancers, while its role in sarcomas is unknown. We aimed to evaluate BCL7B's diagnostic and prognostic value, and potential BCL7B-related mechanisms in sarcomas based on The Cancer Genome Atlas (TCGA) database. We collected patients with sarcoma from TCGA. Wilcoxon rank sum test was used to compare the expression of BCL7B in sarcoma samples with different clinical-pathologic features. Univariate Cox regression analysis and multivariate Cox regression analysis were used to evaluate prognosis factors for sarcoma. Gene set enrichment analysis (GSEA) was conducted to elucidate the significant functions and pathways associated with BCL7B. BCL7B was a potential biomarker for distinguishing normal and tumor tissues with the analysis of ROC curve (AUC = 0.588). Low BCL7B expression was significantly correlated with tumor multifocal (OR = 0.39 for yes vs no), larger residual tumor (OR = 0.40 for R1,R2 vs RO), male gender (OR = 0.48 for male vs female) and White race (OR = 0.29 for White vs Asian, Black or African American). High BCL7B expression was correlated with leiomyosarcoma histological type (OR = 6.08 for leiomyosarcoma vs dedifferentiated liposarcoma, pleomorphic sarcoma). Univariate and multivariate Cox regression analysis showed that low BCL7B expression was independently associated with poor overall survival (P = .008). GSEA showed that GPCR (G protein-coupled receptors) ligand binding, secreted factors, class A1 rhodopsin-like receptors, extracellular matrix organization, core matrisome, Fc epsilon receptor I mediated NF-κB activation, and WNT signaling pathway were differentially enriched in BCL7B low expression phenotype (|NES| > 1, adjusted P value <.05, and FDR value <0.25). BCL7B may play an important role in sarcoma progression and may be a potential biomarker for prognosis and diagnosis in sarcomas.

Differentiation of natural killer cells from induced pluripotent stem cells under defined, serum- and feeder-free conditions

BACKGROUND AIMS

Traditionally, natural killer (NK) cells are sourced from the peripheral blood of donors-a laborious and highly donor-specific process. Processes for generating NK cells from induced pluripotent stem cells (iPSCs) have demonstrated that it is possible to successfully generate renewable alloreactive NK cells that are not only functional in vivo but can also be genetically engineered for enhanced function. However, poor standardization and cumbersome differentiation procedures suggest that further improvements in the control of the differentiation process are necessary.

METHODS

Here the authors evaluated the potential of differentiating NK cells from centrally authenticated iPSCs under entirely chemically defined and serum-free conditions as well as their immunotherapeutic potential, after expansion in feeder-free media, against solid tumors targets. To address limitations of current differentiation approaches, the authors did not utilize feeder or stromal cell layers, TrypLE adaptation or peripheral blood during the differentiation process. The authors also evaluated the feasibility of utilizing centrally authenticated iPSC lines, thus circumventing protocol- and donor-induced variability associated with reprogramming approaches, and characterized these iPSC-NK cells in terms of cytotoxicity, cytokine production and degranulation potential against solid tumor cell lines and patient-derived targets.

RESULTS

Differentiation of iPSCs generated NK cells that were predominantly CD56⁺/CD16⁺/CD3^- and expressed NK activation markers NKG2D, NKp30, NKp44, NKp46 and DNAM-1. These iPSC-NK cells mediated effector functions, including cytotoxicity, degranulation and IFN-γ production, in response to solid tumor targets, including patient-derived cancer cells, and could be cryopreserved and expanded in culture.

CONCLUSIONS

The ability to produce NK cells under defined conditions and the functional responses elicited by these iPSC-NK cells suggest that they could represent promising effectors in clinical adoptive transfer settings as a renewable source of donor-independent NK cells for immunotherapy of solid tumors.

Combinatorial immunotherapy of N-803 (IL-15 superagonist) and dinutuximab with ex vivo expanded natural killer cells significantly enhances in vitro cytotoxicity against GD2+ pediatric solid tumors and in vivo survival of xenografted immunodeficient NSG mice

Background

Children with recurrent and/or metastatic osteosarcoma (OS), neuroblastoma (NB) and glioblastoma multiforme (GBM) have a dismal event-free survival (<25%). The majority of these solid tumors highly express GD2. Dinutuximab, an anti-GD2 monoclonal antibody, significantly improved event-free survival in children with GD2⁺ NB post autologous stem cell transplantation and enhanced natural killer (NK) cell-mediated antibody-dependent cell cytotoxicity. Thus, approaches to increase NK cell number and activity, improve persistence and trafficking, and enhance tumor targeting may further improve the clinical benefit of dinutuximab. N-803 is a superagonist of an interleukin-15 (IL-15) variant bound to an IL-15 receptor alpha Su-Fc fusion with enhanced biological activity.

Methods

The anti-tumor combinatorial effects of N-803, dinutuximab and ex vivo expanded peripheral blood NK cells (exPBNK) were performed in vitro using cytoxicity assays against GD2⁺ OS, NB and GBM cells. Perforin and interferon (IFN)-γ levels were measured by ELISA assays. Multiple cytokines/chemokines/growth factors released were measured by multiplex assays. Human OS, GBM or NB xenografted NOD/SCID/IL2rγnull (NSG) mice were used to investigate the anti-tumor combinatorial effects in vivo.

Results

N-803 increased the viability and proliferation of exPBNK. The increased viability and proliferation are associated with increased phosphorylation of Stat3, Stat5, AKT, p38MAPK and the expression of NK activating receptors. The combination of dinutuximab and N-803 significantly enhanced in vitro cytotoxicity of exPBNK with enhanced perforin and IFN-γ release against OS, GBM and NB. The combination of exPBNK+N-803+dinutuximab significantly reduced the secretion of tumor necrosis factor-related apoptosis-inducing ligand (TRAIL), platelet-derived growth factor-BB (PDGF-BB), and stem cell growth factor beta (SCGF-β) from OS or GBM tumor cells. Furthermore, OS or GBM significantly inhibited the secretion of regulated on activation, normal T cell expressed and presumably secreted (RANTES) and stromal cell-derived factor-1 alpha (SDF-1α) from exPBNK cells (p<0.001) but significantly enhanced monokine induced by gamma interferon (MIG) secretion from exPBNK cells (p<0.001). N-803 combined with dinutuximab and exPBNK cells significantly extended the survival of OS, GBM or NB xenografted NSG mice.

Conclusions

Our results provide the rationale for the development of a clinical trial of N-803 in combination with dinutuximab and ex vivo exPBNK cells in patients with recurrent or metastatic GD2⁺ solid tumors.

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

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

Expanded natural killer cells augment the antimyeloma effect of daratumumab, bortezomib, and dexamethasone in a mouse model

The use of natural killer (NK) cells is a promising and safe immunotherapeutic approach in the field of cancer immunotherapy. However, combination treatments are required to enhance the effector functions and therapeutic efficacy of NK cells. In this study, we investigated the potential of daratumumab (Dara), bortezomib, and dexamethasone (Dvd) to augment the antitumor effects of NK cells in a multiple myeloma (MM) xenograft mouse model. NK cells were expanded and activated using the K562-OX40 ligand and membrane-bound IL-18 and IL-21 in the presence of IL-2 and IL-15 from peripheral blood mononuclear cells from MM patients. A human MM xenograft model was established using human RPMI8226-RFP-FLuc cells in NOD/SCID IL-2Rγ^null (NSG) mice. Tumor-bearing mice were divided into six treatment groups: no treatment, expanded NK cells (eNKs), Dara, Dara + eNKs, Dvd, and Dvd + eNKs. Dvd treatment strongly enhanced the cytotoxicity of eNKs by upregulating expression of NK cell activation ligands, downregulating expression of NK cell inhibitory ligands, and promoting antibody-dependent cellular cytotoxicity. The combination of eNKs with Dvd significantly prolonged mouse survival and reduced the tumor burden and serum M-protein level. Furthermore, Dvd pretreatment significantly increased eNK persistence and homing to MM sites. Our findings suggest that Dvd treatment potentiates the antimyeloma effects of NK cells expanded and activated ex vivo by modulating immune responses in MM-bearing mice.

Oncolytic parainfluenza virus combines with NK cells to mediate killing of infected and non-infected lung cancer cells within 3D spheroids: role of type I and type III interferon signaling

BACKGROUND

There is intense interest in developing novel oncolytic viruses, which can be used in cancer therapies along with immune cells such as natural killer (NK) cells. We have previously developed a particle-based method for in vitro expansion of highly cytotoxic human NK cells (PM21-NK cells). Here, we have tested the hypothesis that oncolytic parainfluenza virus 5 (P/V virus) can combine with PM21-NK cells for targeted killing of lung cancer cells.

METHODS

PM21-NK cells were assayed for killing of P/V virus-infected A549, H1299 and Calu-1 lung cancer cells in two-dimensional (2D) and three-dimensional (3D) cultures using flow cytometry, luminescence and kinetic imaging-based methods. Blocking antibodies were used to evaluate NK cell activating receptors involved in PM21-NK cell killing of infected target cells. Media transfer experiments tested soluble factors that increase PM21-NK cell killing of both P/V virus-infected and uninfected tumor cells.

RESULTS

In 2D cultures, PM21-NK cells efficiently killed P/V virus-infected cancer cells compared with non-infected cells, through involvement of the viral glycoprotein and NK cell receptors NKp30, NKp46 and NKG2D. In 3D spheroid cultures, P/V virus infection was restricted to the outer layer of the spheroid. However, PM21-NK cells were able to more efficiently kill both the outer layer of infected cells in the spheroid and progressing further to kill the uninfected interior cells. Media transfer experiments demonstrated that P/V virus infection produced both type I and type III interferons, which decreased cell growth, which contributed to a reduction in the overall number of uninfected tumor cells in conjunction with PM21-NK cells. Across five cancer cell lines, the contribution of P/V virus infection on PM21-NK cell killing of target cells correlated with interferon induction.

CONCLUSION

Our data support the potential of combining oncolytic parainfluenza virus with PM21-NK cell adoptive therapy against lung cancer.

Optimizing NK Cell-Based Immunotherapy in Myeloid Leukemia: Abrogating an Immunosuppressive Microenvironment

Natural killer (NK) cells are prominent cytotoxic and cytokine-producing components of the innate immune system representing crucial effector cells in cancer immunotherapy. Presently, various NK cell-based immunotherapies have contributed to the substantial improvement in the reconstitution of NK cells against advanced-staged and high-risk AML. Various NK cell sources, including haploidentical NK cells, adaptive NK cells, umbilical cord blood NK cells, stem cell-derived NK cells, chimeric antigen receptor NK cells, cytokine-induced memory-like NK cells, and NK cell lines have been identified. Devising innovative approaches to improve the generation of therapeutic NK cells from the aforementioned sources is likely to enhance NK cell expansion and activation, stimulate ex vivo and in vivo persistence of NK cells and improve conventional treatment response of myeloid leukemia. The tumor-promoting properties of the tumor microenvironment and downmodulation of NK cellular metabolic activity in solid tumors and hematological malignancies constitute a significant impediment in enhancing the anti-tumor effects of NK cells. In this review, we discuss the current NK cell sources, highlight ongoing interventions in enhancing NK cell function, and outline novel strategies to circumvent immunosuppressive factors in the tumor microenvironment to improve the efficacy of NK cell-based immunotherapy and expand their future success in treating myeloid leukemia.

Telomerase Reverse Transcriptase Increases Proliferation and Lifespan of Human NK Cells without Immortalization

NK cells are the first line of defense against viruses and malignant cells, and their natural functionality makes these cells a promising candidate for cancer cell therapy. The genetic modifications of NK cells, allowing them to overcome some of their inherent limitations, such as low proliferative potential, can enable their use as a therapeutic product. We demonstrate that hTERT-engineered NK cell cultures maintain a high percentage of cells in the S/G2 phase for an extended time after transduction, while the life span of NK cells is measurably extended. Bulk and clonal NK cell cultures pre-activated in vitro with IL-2 and K562-mbIL21 feeder cells can be transduced with hTERT more efficiently compared with the cells activated with IL-2 alone. Overexpressed hTERT was functionally active in transduced NK cells, which displayed upregulated expression of the activation marker HLA-DR, and decreased expression of the maturation marker CD57 and activating receptor NKp46. Larger numbers of KIR2DL2/3+ cells in hTERT-engineered populations may indicate that NK cells with this phenotype are more susceptible to transduction. The hTERT-modified NK cells demonstrated a high natural cytotoxic response towards K562 cells and stably expressed Ki67, a proliferation marker. Overall, our data show that ectopic hTERT expression in NK cells enhances their activation and proliferation, extends in vitro life span, and can be a useful tool in developing NK-based cancer cell therapies.

Adoptive Natural Killer Cell Immunotherapy for Canine Osteosarcoma

Osteosarcoma is the most common primary bone tumor in both humans and dogs. It is a highly metastatic cancer and therapy has not improved significantly since the inclusion of adjuvant chemotherapy into disease treatment strategies. Osteosarcoma is an immunogenic tumor, and thus development of immunotherapies for its treatment, especially treatment of microscopic pulmonary metastases might improve outcomes. NK cells are lymphocytes of the innate immune system and can recognize a variety of stressed cells, including cancer cells, in the absence of major histocompatibility complex (MHC)-restricted receptor ligand interactions. NK cells have a role in controlling tumor progression and metastasis and are important mediators of different therapeutic interventions. The core hypothesis of adoptive natural killer (NK) cell therapy is there exists a natural defect in innate immunity (a combination of cancer-induced reduction in NK cell numbers and immunosuppressive mechanisms resulting in suppressed function) that can be restored by adoptive transfer of NK cells. Here, we review the rationale for adoptive NK cell immunotherapy, NK cell biology, TGFβ and the immunosuppressive microenvironment in osteosarcoma, manufacturing of ex vivo expanded NK cells for the dog and provide perspective on the present and future clinical applications of adoptive NK cell immunotherapy in spontaneous osteosarcoma and other cancers in the dog.

Metabolic flexibility determines human NK cell functional fate in the tumor microenvironment

NK cells are central to anti-tumor immunity and recently showed efficacy for treating hematologic malignancies. However, their dysfunction in the hostile tumor microenvironment remains a pivotal barrier for cancer immunotherapies against solid tumors. Using cancer patient samples and proteomics, we found that human NK cell dysfunction in the tumor microenvironment is due to suppression of glucose metabolism via lipid peroxidation-associated oxidative stress. Activation of the Nrf2 antioxidant pathway restored NK cell metabolism and function and resulted in greater anti-tumor activity in vivo. Strikingly, expanded NK cells reprogrammed with complete metabolic substrate flexibility not only sustained metabolic fitness but paradoxically augmented their tumor killing in the tumor microenvironment and in response to nutrient deprivation. Our results uncover that metabolic flexibility enables a cytotoxic immune cell to exploit the metabolic hostility of tumors for their advantage, addressing a critical hurdle for cancer immunotherapy.

Expanded human NK cells armed with CAR uncouple potent anti-tumor activity from off-tumor toxicity against solid tumors

Despite the remarkable success of chimeric antigen receptor (CAR)-T cells against hematologic malignancies, severe off-tumor effects have constrained their use against solid tumors. Recently, CAR-engineered natural killer (NK) cells have emerged as an effective and safe alternative. Here, we demonstrate that HER2 CAR-expression in NK cells from healthy donors and patients with breast cancer potently enhances their anti-tumor functions against various HER2-expressing cancer cells, regardless of MHC class I expression. Moreover, HER2 CAR-NK cells exert higher cytotoxicity than donor-matched HER2 CAR-T cells against tumor targets. Importantly, unlike CAR-T cells, HER2 CAR-NK cells do not elicit enhanced cytotoxicity or inflammatory cytokine production against non-malignant human lung epithelial cells with basal HER2 expression. Further, HER2 CAR-NK cells maintain high cytotoxic function in the presence of immunosuppressive factors enriched in solid tumors. These results show that CAR-NK cells may be a highly potent and safe source of immunotherapy in the context of solid tumors.

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Primary HER2 CAR-NK cells from patients with cancer have potent anti-tumor functions

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HER2 CAR-NK cells have a higher tumor killing capacity than HER2 CAR-T cells

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HER2 CAR-NK cells are not overly activated against HER2+ lung epithelial cells

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CAR-NK cells can overcome inhibition by the immunosuppressive factors TGF-β and PGE2

Reduced frequency of cytotoxic CD56dim CD16+ NK cells leads to impaired antibody-dependent degranulation in EBV-positive classical Hodgkin lymphoma

Around 30–50% of classical Hodgkin lymphoma (cHL) cases in immunocompetent individuals from industrialized countries are associated with the B-lymphotropic Epstein-Barr virus (EBV). Although natural killer (NK) cells exhibit anti-viral and anti-tumoral functions, virtually nothing is known about quantitative and qualitative differences in NK cells in patients with EBV+ cHL vs. EBV- cHL. Here, we prospectively investigated 36 cHL patients without known immune suppression or overt immunodeficiency at diagnosis. All 10 EBV+ cHL patients and 25 out 26 EBV- cHL were seropositive for EBV antibodies, and EBV+ cHL patients presented with higher plasma EBV DNA levels compared to EBV- cHL patients. We show that the CD56^dim CD16⁺ NK cell subset was decreased in frequency in EBV+ cHL patients compared to EBV- cHL patients. This quantitative deficiency translates into an impaired CD56^dim NK cell mediated degranulation toward rituximab-coated HLA class 1 negative lymphoblastoid cells in EBV+ compared to EBV- cHL patients. We finally observed a trend to a decrease in the rituximab-associated degranulation and ADCC of in vitro expanded NK cells of EBV+ cHL compared to healthy controls. Our findings may impact on the design of adjunctive treatment targeting antibody-dependent cellular cytotoxicity in EBV+ cHL.