A tri-specific killer engager against mesothelin targets NK cells towards lung cancer

New treatments are required to enhance current therapies for lung cancer. Mesothelin is a surface protein overexpressed in non-small cell lung cancer (NSCLC) that shows promise as an immunotherapeutic target in phase I clinical trials. However, the immunosuppressive environment in NSCLC may limit efficacy of these therapies. We applied time-of-flight mass cytometry to examine the state of circulating mononuclear cells in fourteen patients undergoing treatment for unresectable lung cancer. Six patients had earlier stage NSCLC (I-IVA) and eight had highly advanced NSCLC (IVB). The advanced NSCLC patients relapsed with greater frequency than the earlier stage patients. Before treatment, patients with very advanced NSCLC had a greater proportion of CD14- myeloid cells than patients with earlier NSCLC. These patients also had fewer circulating natural killer (NK) cells bearing an Fc receptor, CD16, which is crucial to antibody-dependent cellular cytotoxicity. We designed a high affinity tri-specific killer engager (TriKE®) to enhance NK cytotoxicity against mesothelin+ targets in this environment. The TriKE consisted of CD16 and mesothelin binding elements linked together by IL-15. TriKE enhanced proliferation of lung cancer patient NK cells in vitro. Lung cancer lines are refractory to NK cell killing, but the TriKE enhanced cytotoxicity and cytokine production by patient NK cells when challenged with tumor. Importantly, TriKE triggered NK cell responses from patients at all stages of disease and treatment, suggesting TriKE can enhance current therapies. These pre-clinical studies suggest mesothelin-targeted TriKE has the potential to overcome the immunosuppressive environment of NSCLC to treat disease.

Adaptive single-KIR+NKG2C+ NK cells expanded from select superdonors show potent missing-self reactivity and efficiently control HLA-mismatched acute myeloid leukemia

BACKGROUND

Natural killer (NK) cells hold great promise as a source for allogeneic cell therapy against hematological malignancies, including acute myeloid leukemia (AML). Current treatments are hampered by variability in NK cell subset responses, a limitation which could be circumvented by specific expansion of highly potent single killer immunoglobulin-like receptor (KIR)⁺NKG2C⁺ adaptive NK cells to maximize missing-self reactivity.

METHODS

We developed a GMP-compliant protocol to expand adaptive NK cells from cryopreserved cells derived from select third-party superdonors, that is, donors harboring large adaptive NK cell subsets with desired KIR specificities at baseline. We studied the adaptive state of the cell product (ADAPT-NK) by flow cytometry and mass cytometry as well as cellular indexing of transcriptomes and epitopes by sequencing (CITE-Seq). We investigated the functional responses of ADAPT-NK cells against a wide range of tumor target cell lines and primary AML samples using flow cytometry and IncuCyte as well as in a mouse model of AML.

RESULTS

ADAPT-NK cells were >90% pure with a homogeneous expression of a single self-HLA specific KIR and expanded a median of 470-fold. The ADAPT-NK cells largely retained their adaptive transcriptional signature with activation of effector programs without signs of exhaustion. ADAPT-NK cells showed high degranulation capacity and efficient killing of HLA-C/KIR mismatched tumor cell lines as well as primary leukemic blasts from AML patients. Finally, the expanded adaptive NK cells had preserved robust antibody-dependent cellular cytotoxicity potential and combination of ADAPT-NK cells with an anti-CD16/IL-15/anti-CD33 tri-specific engager led to near-complete killing of resistant CD45^dim blast subtypes.

CONCLUSIONS

These preclinical data demonstrate the feasibility of off-the-shelf therapy with a non-engineered, yet highly specific, NK cell population with full missing-self recognition capability.

TEM8 Tri-specific Killer Engager binds both tumor and tumor stroma to specifically engage natural killer cell anti-tumor activity

BACKGROUND

The tumor microenvironment contains stromal cells, including endothelial cells and fibroblasts, that aid tumor growth and impair immune cell function. Many solid tumors remain difficult to cure because of tumor-promoting stromal cells, but current therapies targeting tumor stromal cells are constrained by modest efficacy and toxicities. TEM8 is a surface antigen selectively upregulated on tumor and tumor stromal cells, endothelial cells and fibroblasts that may be targeted with specific natural killer (NK) cell engagement.

METHODS

A Tri-specific Killer Engager (TriKE) against TEM8-'cam1615TEM8'-was generated using a mammalian expression system. Its function on NK cells was assessed by evaluation of degranulation, inflammatory cytokine production, and killing against tumor and stroma cell lines in standard co-culture and spheroid assays. cam1615TEM8-mediated proliferation and STAT5 phosphorylation in NK cells was tested and compared with T cells by flow cytometry. NK cell proliferation, tumor infiltration, and tumor and tumor-endothelium killing by cam1615TEM8 and interleukin-15 (IL-15) were assessed in NOD scid gamma (NSG) mice.

RESULTS

cam1615TEM8 selectively stimulates NK cell degranulation and inflammatory cytokine production against TEM8-expressing tumor and stromal cell lines. The increased activation translated to superior NK cell killing of TEM8-expressing tumor spheroids. cam1615TEM8 selectively stimulated NK cell but not T cell proliferation in vitro and enhanced NK cell proliferation, survival, and tumor infiltration in vivo. Finally, cam1615TEM8 stimulated NK cell killing of tumor and tumor endothelial cells in vivo.

CONCLUSIONS

Our findings indicate that the cam1615TEM8 TriKE is a novel anti-tumor, anti-stroma, and anti-angiogenic cancer therapy for patients with solid tumors. This multifunctional molecule works by selectively targeting and activating NK cells by costimulation with IL-15, and then targeting that activity to TEM8+ tumor cells and TEM8+ tumor stroma.

Balanced engagement of activating and inhibitory receptors mitigates human NK cell exhaustion

Natural killer (NK) cell exhaustion is caused by chronic exposure to activating stimuli during viral infection, tumorigenesis, and prolonged cytokine treatment. Evidence suggests that exhaustion may play a role in disease progression, however relative to T cell exhaustion, the mechanisms underlying NK cell exhaustion and methods of reversing it are poorly understood. Here, we describe a novel in vitro model of exhaustion that employs plate-bound agonists of the NK cell activating receptors NKp46 and NKG2D to induce canonical exhaustion phenotypes. In this model, prolonged activation results in downregulation of activating receptors, upregulation of checkpoint markers, decreased cytokine production and cytotoxicity in vitro, defects in glycolytic metabolism, and decreased persistence, function, and tumor control in vivo. Furthermore, we discover a beneficial effect of NK cell inhibitory receptor signaling during exhaustion. By simultaneously engaging the inhibitory receptor NKG2A during activation in our model, cytokine production and cytotoxicity defects can be mitigated, suggesting that balancing positive and negative signals integrated by effector NK cells can be beneficial for anti-tumor immunity. Together, these data uncover some of the mechanisms underlying NK cell exhaustion in humans and establish our novel in vitro model as a valuable tool for studying the processes regulating exhaustion.

Abstract 2878: Mediating NK cell function against solid tumors, via targeting of tumor stroma, using a TEM8-targeting Tri-specific Killer Engager (TriKE®)

Immunotherapies for solid tumors need to overcome barriers within the solid tumor microenvironment (TME), including stromal cells, cancer-associated fibroblasts, endothelial cells, pericytes, and immune cells. These can comprise a significant portion of the tumor mass in many common carcinomas and contribute to immune cell dysfunction within the tumor. Stromal cells support cancer cells through several mechanisms and can promote metastasis. Tumor vasculature supplies cancer cells with nutrients and oxygen necessary for tumor growth and dissemination. Thus, targeting these components of cancer can enhance tumor rejection directly and increase sensitization of surviving tumors to immune infiltration and chemotherapeutic treatments through weakening of the tumor architecture. While there are current antiangiogenic therapies being tested clinically, they have associated toxicities in normal angiogenic processes, limiting clinical efficacy. Tumor Endothelial Marker 8 (TEM8, encoded by the ANTXR1 gene) is a highly conserved integrin-like adhesion molecule that was discovered on the endothelium of colorectal cancer, and subsequent studies identified its expression on multiple stromal cells—endothelial cells, fibroblasts, and pericytes—in the tumor microenvironment of diverse human cancer types. Little to no expression has been demonstrated in normal human stroma, indicating that this would be a good target for immunotherapy. Using a mammalian expression system, we designed and expressed a TEM8 targeting TriKE (cam1615TEM8) consisting of a humanized anti-CD16 single domain antibody, a wild-type IL-15 moiety, and an anti-TEM8 scFv. cam1615TEM8 induces NK cell degranulation and cytokine production against TEM8+ tumor and stromal cell lines (endothelial cells and fibroblasts). Using TEM8- cancer lines and a TEM8-CRISPR knockout version of A549 lung cancer lines, we show that cam1615TEM8 only activates NK cells in the presence of tumor antigen. cam1615TEM8 also preferentially stimulates TEM8+ tumor spheroid killing. Moreover, the camelid anti-CD16 nanobody selectively enhances signaling by the IL-15 moiety to NK cells, specifically promoting NK cell survival and proliferation in vitro and in vivo. In an in vivo xenogeneic mouse model, containing human NK cells and tumor, cam1615TEM8-treated mice had enhanced NK cell tumor infiltration, significantly decreased tumor growth, and enhanced survival when compared to IL-15 treated mice. Since TEM8 is highly conserved, and the scFv within the TriKE is reactive to mouse TEM8, we were able to show reduced tumor endothelial density in the tumors of mice treated with cam1615TEM8. Given the findings of this study cam1615TEM8 could be leveraged in several clinical settings by inducing NK cell specific targeting of the tumor itself and/or the tumor endothelium and stroma.

Citation Format: Martin Felices, Michael Kaminski, Peter Hinderlie, Rachel Hopps, Laura Bendzick, Melissa Geller, Jeffrey S. Miller. Mediating NK cell function against solid tumors, via targeting of tumor stroma, using a TEM8-targeting Tri-specific Killer Engager (TriKE®) [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 2878.

iPSC-derived NK cells maintain high cytotoxicity and enhance in vivo tumor control in concert with T cells and anti-PD-1 therapy

The development of immunotherapeutic monoclonal antibodies targeting checkpoint inhibitory receptors, such as programmed cell death 1 (PD-1), or their ligands, such as PD-L1, has transformed the oncology landscape. However, durable tumor regression is limited to a minority of patients. Therefore, combining immunotherapies with those targeting checkpoint inhibitory receptors is a promising strategy to bolster antitumor responses and improve response rates. Natural killer (NK) cells have the potential to augment checkpoint inhibition therapies, such as PD-L1/PD-1 blockade, because NK cells mediate both direct tumor lysis and T cell activation and recruitment. However, sourcing donor-derived NK cells for adoptive cell therapy has been limited by both cell number and quality. Thus, we developed a robust and efficient manufacturing system for the differentiation and expansion of high-quality NK cells derived from induced pluripotent stem cells (iPSCs). iPSC-derived NK (iNK) cells produced inflammatory cytokines and exerted strong cytotoxicity against an array of hematologic and solid tumors. Furthermore, we showed that iNK cells recruit T cells and cooperate with T cells and anti-PD-1 antibody, further enhancing inflammatory cytokine production and tumor lysis. Because the iNK cell derivation process uses a renewable starting material and enables the manufacturing of large numbers of doses from a single manufacture, iNK cells represent an "off-the-shelf" source of cells for immunotherapy with the capacity to target tumors and engage the adaptive arm of the immune system to make a "cold" tumor "hot" by promoting the influx of activated T cells to augment checkpoint inhibitor therapies.

Evaluation of adaptive NK cells in ovarian cancer patients with cytomegalovirus (CMV) reactivation and systemic inflammation

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Background: Cytomegalovirus (CMV) is a common infection associated with increased inflammation (c-reactive protein (CRP) upon reactivation during immunosuppression. CMV infection has been associated with a subset of NK cells (adaptive) that are long-lived, have enhanced cytotoxicity, and thought to contribute to cancer control. Previous evaluation of a retrospective study showed CMV+CRP+ patients had significantly worse RFS and OS compared to CMV+ CRP− patients who had the longest OS. These findings suggest CMV may be immunomodulatory and, without immunosuppressive effects of inflammation, may be protective. We are further evaluating for the presence of adaptive NK cells in the patients to evaluate if these populations of cells are drivers for the changes in outcomes. Methods: Serum and ascites (22 samples each) collected in a prospective study at the time of surgery for HGSOC were evaluated for CMV and inflammation. CMV status and systemic inflammation were measured by immunoassay for CMV immunoglobulin G (IgG), dPCR for CMV DNA and C-reactive protein (CRP). Samples were categorized as reactive or non-reactive for CMV and positive or negative for CRP (≤10, > 10 mg/L). Adaptive NK cell percentages were analyzed using GraphPad Prims 8 and p-values ≤ 0.05 were considered statistically significant. Proteomic techniques to quantify adaptive NK cells, differences in NK cell maturation and cytotoxicity are in process for an additional 80 samples. Results: CMV reactive patients showed increased percentages of adaptive NK cells (NKG2C+CD57+) in the blood and peritoneal cavity compared to CMV negative patients. There is a trend in the presence of adaptive NK cells in patient samples that are CMV reactive and CRP positive compared to CMV nonreactive and CRP positive. Conclusions: Preliminary analysis shows a trend in presence of adaptive NK cells in both the blood and peritoneal cavity of these patients but analysis is ongoing.

A Genetically Engineered Primary Human Natural Killer Cell Platform for Cancer Immunotherapy

Enhancing natural killer (NK) cell cytotoxicity by blocking inhibitory signaling could lead to improved NK-based cancer immunotherapy. Thus, we have developed a highly efficient method for editing the genome of human NK cells using CRISPR/Cas9 to knock out inhibitory signaling molecules. Our method efficiently edits up to 90% of primary peripheral blood NK cells. As a proof-of-principle we demonstrate highly efficient knockout of ADAM17 and PDCD1, genes that have a functional impact on NK cells, and demonstrate that these gene-edited NK cells have significantly improved activity, cytokine production, and cancer cell cytotoxicity. Furthermore, we were able to expand cells to clinically relevant numbers, without loss of activity. We also demonstrate that our CRISPR/Cas9 method can be used for efficient knockin of genes by delivering homologous recombination template DNA using recombinant adeno-associated virus serotype 6 (rAAV6). Our platform represents a feasible method for generating engineered primary NK cells as a universal therapeutic for cancer immunotherapy.

Synergistic activity between IL-15 signaling and checkpoint blockade drives enhanced NK cell expansion and tumor control in ovarian cancer

Survival in ovarian cancer patients has not improved in the past 40 years, stressing a need for new lines of therapy. NK cell immunotherapy in ovarian cancer has not been extensively explored due to limited data showing defective NK cell function in these patients. Our previous work shows that an IL-15 super-agonist (NANT N-803 (formerly ALT-803)) can bypass some of the deficiencies. However, we show here that though N-803 enhances NK cell activation, it also induces NK PD-1 expression and inflammatory cytokines secreted by the NK cells induce PD-L1 expression on ovarian tumors. To bypass this negative feedback we combined N-803 with an anti-PD-L1 antibody (Avelumab) and show a potent increase in NK cell activation and long-term real-time in vitro tumor killing. Furthermore, combined N-803/Avelumab induces robust killing of ovarian cancer tumor spheroids, not seen with individual treatments. To evaluate the benefits of this combined treatment in vivo we tested them in a xenogeneic model of ovarian cancer containing human ovarian cancer cells (MA148lucs or OVCAR8lucs) and human NK cells. Our data clearly shows reduced tumor burden, by bioluminescent imaging, and potently increased NK cell expansion with the combined treatment when compared to individual treatments. Since Avelumab is capable of driving antibody dependent cell-mediated cytotoxicity (ADCC) we wanted to evaluate the impact of checkpoint signals in the synergy excluding ADCC using an anti-PD-1 antibody (Pembrolizumab). Combination of N-803 with Pembrolizumab yielded similar tumor control and NK cell expansion in the in vivo model, indicating that the synergy lies in checkpoint signals and IL-15 signaling, and not just in amplification of ADCC via N-803.

Cytokine-induced memory-like natural killer cells have enhanced function, proliferation, and in vivo expansion against ovarian cancer cells

OBJECTIVE

Natural killer (NK) cells are lymphocytes well suited for adoptive immunotherapy. Attempts with adoptive NK cell immunotherapy against ovarian cancer have proven unsuccessful, with the main limitations including failure to expand and diminished effector function. We investigated if incubation of NK cells with interleukin (IL)-12, IL-15, and IL-18 for 16h could produce cytokine-induced memory-like (CIML) NK cells capable of enhanced function against ovarian cancer.

METHODS

NK cells were preactivated briefly with IL-12, IL-15, and IL-18, rested, then placed against ovarian cancer targets to assess phenotype and function via flow cytometry. Real-time NK-cell-mediated tumor-killing was evaluated. Using ascites cells and cell-free ascites fluid, NK cell proliferation and function within the immunosuppressive microenvironment was evaluated in vitro. Finally, CIML NK cells were injected intraperitoneal (IP) into an in vivo xenogeneic mouse model of ovarian cancer.

RESULTS

CIML NK cells demonstrate enhanced cytokine (IFN-γ) production and NK-cell-mediated killing of ovarian cancer. NK cells treated overnight with cytokines led to robust activation characterized by temporal shedding of CD16, induction of CD25, and enhanced proliferation. CIML NK cells proliferate more with enhanced effector function compared to controls in an immunosuppressive microenvironment. Finally, human CIML NK cells exhibited potent antitumor effects within a xenogeneic mouse model of ovarian cancer.

CONCLUSIONS

CIML NK cells have enhanced functionality and persistence against ovarian cancer in vitro and in vivo, even when exposed to ascites fluid. These findings provide a strategy for NK cell-based immunotherapy to circumvent the immunosuppressive nature of ovarian cancer.

Continuous treatment with IL-15 exhausts human NK cells via a metabolic defect

NK cell-based immunotherapies have been gaining traction in the clinic for treatment of cancer. IL-15 is currently being used in number of clinical trials to improve NK cell expansion and function. The objective of this study is to evaluate the effect of repetitive IL-15 exposure on NK cells. An in vitro model in which human NK cells are continuously (on on on) or intermittently (on off on) treated with IL-15 was used to explore this question. After treatment, cells were evaluated for proliferation, survival, cell cycle gene expression, function, and metabolic processes. Our data indicate that continuous treatment of NK cells with IL-15 resulted in decreased viability and a cell cycle arrest gene expression pattern. This was associated with diminished signaling, decreased function both in vitro and in vivo, and reduced tumor control. NK cells continuously treated with IL-15 also displayed a reduced mitochondrial respiration profile when compared with NK cells treated intermittently with IL-15. This profile was characterized by a decrease in the spare respiratory capacity that was dependent on fatty acid oxidation (FAO). Limiting the strength of IL-15 signaling via utilization of an mTOR inhibitor rescued NK cell functionality in the group continuously treated with IL-15. The findings presented here show that human NK cells continuously treated with IL-15 undergo a process consistent with exhaustion that is accompanied by a reduction in FAO. These findings should inform IL-15-dosing strategies in NK cell cancer immunotherapeutic settings.

IL-15 super-agonist (ALT-803) enhances natural killer (NK) cell function against ovarian cancer

OBJECTIVE

Natural killer (NK) cells represent a powerful immunotherapeutic target as they lyse tumors directly, do not require differentiation, and can elicit potent inflammatory responses. The objective of these studies was to use an IL-15 super-agonist complex, ALT-803 (Altor BioScience Corporation), to enhance the function of both normal and ovarian cancer patient derived NK cells by increasing cytotoxicity and cytokine production.

METHODS

NK cell function from normal donor peripheral blood mononuclear cells (PBMCs) and ovarian cancer patient ascites was assessed using flow cytometry and chromium release assays ±ALT-803 stimulation. To evaluate the ability of ALT-803 to enhance NK cell function in vivo against ovarian cancer, we used a MA148-luc ovarian cancer NOD scid gamma (NSG) xenogeneic mouse model with transferred human NK cells.

RESULTS

ALT-803 potently enhanced functionality of NK cells against all ovarian cancer cell lines with significant increases seen in CD107a, IFNγ and TNFα expression depending on target cell line. Function was also rescued in NK cells derived from ovarian cancer patient ascites. Finally, only animals treated with intraperitoneal ALT-803 displayed an NK dependent significant decrease in tumor.

CONCLUSIONS

ALT-803 enhances NK cell cytotoxicity against ovarian cancer in vitro and in vivo and is able to rescue functionality of NK cells derived from ovarian cancer patient ascites. These findings suggest that ALT-803 has the potential to enhance NK cell-based immunotherapeutic approaches for the treatment of ovarian cancer.

Mouse Xenograft Model for Intraperitoneal Administration of NK Cell Immunotherapy for Ovarian Cancer

Natural killer (NK) cells are an attractive cell population for immunotherapy. Adoptive transfer of NK cells has been tested in multiple clinical trials including acute myeloid leukemia (AML) and ovarian cancer, although limitations do exist especially for treatment of solid tumors. In order to overcome these limitations, mouse xenograft models are needed for evaluation of various NK cell populations, as well as routes of NK cell administration. Here, we describe the methods used for the establishment of an intraperitoneal (ip) ovarian cancer mouse xenograft model with ip delivery of NK cells. This model has been successfully employed with multiple ovarian cell lines and could be applied to other tumor models where the tumor's primary location is in the peritoneal cavity. It is also compatible with multiple routes of NK cell administration. Bioluminescent imaging for monitoring tumor formation and response provides for easy visualization of NK cell tumor inhibition. This xenograft model is superior to other models because the tumor is implanted into the same physiological space where ovarian cancer is found, which allows for improved mimicking of actual disease.

Induced Pluripotent Stem Cell-Derived Natural Killer Cells for Treatment of Ovarian Cancer

Natural killer (NK) cells can provide effective immunotherapy for ovarian cancer. Here, we evaluated the ability of NK cells isolated from peripheral blood (PB) and NK cells derived from induced pluripotent stem cell (iPSC) to mediate killing of ovarian cancer cells in a mouse xenograft model. A mouse xenograft model was used to evaluate the intraperitoneal delivery of three different NK cell populations: iPSC-derived NK cells, PB-NK cells that had been activated and expanded in long-term culture, and overnight activated PB-NK cells that were isolated through CD3/CD19 depletion of PB B and T cells. Bioluminescent imaging was used to monitor tumor burden of luciferase expressing tumor lines. Tumors were allowed to establish prior to administering NK cells via intraperitoneal injection. These studies demonstrate a single dose of any of the three NK cell populations significantly reduced tumor burden. When mice were given three doses of either iPSC-NK cells or expanded PB-NK cells, the median survival improved from 73 days in mice untreated to 98 and 97 days for treated mice, respectively. From these studies, we conclude iPSC-derived NK cells mediate antiovarian cancer killing at least as well as PB-NK cells, making these cells a viable resource for immunotherapy for ovarian cancer. Due to their ability to be easily differentiated into NK cells and their long-term expansion potential, iPSCs can be used to produce large numbers of well-defined NK cells that can be banked and used to treat a large number of patients including treatment with multiple doses if necessary.

Expression of chimeric receptor CD4ζ by natural killer cells derived from human pluripotent stem cells improves in vitro activity but does not enhance suppression of HIV infection in vivo

Cell-based immunotherapy has been gaining interest as an improved means to treat human immunodeficiency virus (HIV)/AIDS. Human embryonic stem cells (hESCs) and induced pluripotent stem cells (iPSCs) could become a potential resource. Our previous studies have shown hESC and iPSC-derived natural killer (NK) cells can inhibit HIV-infected targets in vitro. Here, we advance those studies by expressing a HIV chimeric receptor combining the extracellular portion of CD4 to the CD3ζ intracellular signaling chain. We hypothesized that expression of this CD4ζ receptor would more efficiently direct hESC- and iPSC-derived NK cells to target HIV-infected cells. In vitro studies showed the CD4ζ expressing hESC- and iPSC-NK cells inhibited HIV replication in CD4+ T-cells more efficiently than their unmodified counterparts. We then evaluated CD4ζ expressing hESC (CD4ζ-hESC)- and iPSC-NK cells in vivo anti-HIV activity using a humanized mouse model. We demonstrated significant suppression of HIV replication in mice treated with both CD4ζ-modified and -unmodified hESC-/iPSC-NK cells compared with control mice. However, we did not observe significantly increased efficacy of CD4ζ expression in suppression of HIV infection. These studies indicate that hESC/iPSC-based immunotherapy can be used as a unique resource to target HIV/AIDS.

Clinical-scale derivation of natural killer cells from human pluripotent stem cells for cancer therapy

Adoptive transfer of antitumor lymphocytes has gained intense interest in the field of cancer therapeutics over the past two decades. Human natural killer (NK) cells are a promising source of lymphocytes for anticancer immunotherapy. NK cells are part of the innate immune system and exhibit potent antitumor activity without need for human leukocyte antigen matching and without prior antigen exposure. Moreover, the derivation of NK cells from pluripotent stem cells could provide an unlimited source of lymphocytes for off-the-shelf therapy. To date, most studies on hematopoietic cell development from human embryonic stem cells (hESCs) and induced pluripotent stem cells (iPSCs) have used incompletely defined conditions and been on a limited scale. Here, we have used a two-stage culture system to efficiently produce NK cells from hESCs and iPSCs in the absence of cell sorting and without need for xenogeneic stromal cells. This novel combination of embryoid body formation using defined conditions and membrane-bound interleukin 21-expressing artificial antigen-presenting cells allows production of mature and functional NK cells from several different hESC and iPSC lines. Although different hESC and iPSC lines had varying efficiencies in hematopoietic development, all cell lines tested could produce functional NK cells. These methods can be used to generate enough cytotoxic NK cells to treat a single patient from fewer than 250,000 input hESCs/iPSCs. Additionally, this strategy provides a genetically amenable platform to study normal NK cell development and education in vitro.