Results of a phase I trial with Haploidentical mbIL-21 ex vivo expanded NK cells for patients with multiply relapsed and refractory AML

Natural killer (NK)-cells have potent anti-tumor effects, yet it remains unclear if they are effective for patients with relapsed acute myeloid leukemia (AML). In a phase I clinical trial, we treated 12 patients (median age 60 years) with refractory AML (median 5 lines of prior therapy, median bone marrow blast count of 47%) with fludarabine/cytarabine followed by 6 infusions of NK-cells expanded from haploidentical donors using K562 feeder cells expressing membrane-bound IL21 and 4-1BBL. Patients received 106-107/kg/dose. No toxicity or graft-versus-host disease (GVHD) was observed and MTD was not reached. Seven patients (58.3%) responded and achieved a complete remission (CR) with/without count recovery. Median time to best response was 48 days. Five responding patients proceeded to a haploidentical transplant from the same donor. After a median follow-up of 52 months, 1-year overall survival (OS) for the entire group was 41.7%, better for patients who responded with CR/CRi (57.14%), and for patients who responded and underwent transplantation (60%). Persistence and expansion of donor-derived NK-cells were identified in patients' blood, and serum IFNγ levels rose concurrently with NK cell infusions. A higher count-functional inhibitory KIR was associated with higher likelihood of achieving CR/CRi. In conclusion, we observed a significant response to ex vivo expanded NK-cell administration in refractory AML patients without adverse effects.

Trabectedin Enhances Oncolytic Virotherapy by Reducing Barriers to Virus Spread and Cytotoxic Immunity in Preclinical Pediatric Bone Sarcoma

We previously reported that the DNA alkylator and transcriptional-blocking chemotherapeutic agent trabectedin enhances oncolytic herpes simplex viroimmunotherapy in human sarcoma xenograft models, though the mechanism remained to be elucidated. Here we report trabectedin disrupts the intrinsic cellular anti-viral response which increases viral transcript spread throughout the human tumor cells. We also extended our synergy findings to syngeneic murine sarcoma models, which are poorly susceptible to virus infection. In the absence of robust virus replication, we found trabectedin enhanced viroimmunotherapy efficacy by reducing immunosuppressive macrophages and stimulating granzyme expression in infiltrating T and NK cells to cause immune-mediated tumor regressions. Thus, trabectedin enhances both the direct virus-mediated killing of tumor cells and the viral-induced activation of cytotoxic effector lymphocytes to cause tumor regressions across models. Our data provide a strong rationale for clinical translation as both mechanisms should be simultaneously active in human patients.

Single-cell functional genomics reveals determinants of sensitivity and resistance to natural killer cells in blood cancers

Cancer cells can evade natural killer (NK) cell activity, thereby limiting anti-tumor immunity. To reveal genetic determinants of susceptibility to NK cell activity, we examined interacting NK cells and blood cancer cells using single-cell and genome-scale functional genomics screens. Interaction of NK and cancer cells induced distinct activation and type I interferon (IFN) states in both cell types depending on the cancer cell lineage and molecular phenotype, ranging from more sensitive myeloid to less sensitive B-lymphoid cancers. CRISPR screens in cancer cells uncovered genes regulating sensitivity and resistance to NK cell-mediated killing, including adhesion-related glycoproteins, protein fucosylation genes, and transcriptional regulators, in addition to confirming the importance of antigen presentation and death receptor signaling pathways. CRISPR screens with a single-cell transcriptomic readout provided insight into underlying mechanisms, including regulation of IFN-γ signaling in cancer cells and NK cell activation states. Our findings highlight the diversity of mechanisms influencing NK cell susceptibility across different cancers and provide a resource for NK cell-based therapies.

Knockout of the inhibitory receptor TIGIT enhances the antitumor response of ex vivo expanded NK cells and prevents fratricide with therapeutic Fc-active TIGIT antibodies

BACKGROUND

Inhibitory receptor T-cell Immunoreceptor with Ig and ITIM domains (TIGIT) expressed by Natural Killer (NK) and T cells regulates cancer immunity and has been touted as the next frontier in the development of cancer immunotherapeutics. Although early results of anti-TIGIT and its combinations with antiprogrammed death-ligand 1 were highly exciting, results from an interim analysis of phase III trials are disappointing. With mixed results, there is a need to understand the effects of therapeutic anti-TIGIT on the TIGIT+ immune cells to support its clinical use. Most of the TIGIT antibodies in development have an Fc-active domain, which binds to Fc receptors on effector cells. In mouse models, Fc-active anti-TIGIT induced superior immunity, while Fc receptor engagement was required for its efficacy. NK-cell depletion compromised the antitumor immunity of anti-TIGIT indicating the essential role of NK cells in the efficacy of anti-TIGIT. Since NK cells express TIGIT and Fc-receptor CD16, Fc-active anti-TIGIT may deplete NK cells via fratricide, which has not been studied.

METHODS

CRISPR-Cas9-based TIGIT knockout (KO) was performed in expanded NK cells. Phenotypic and transcriptomic properties of TIGIT KO and wild-type (WT) NK cells were compared with flow cytometry, CyTOF, and RNA sequencing. The effect of TIGIT KO on NK-cell cytotoxicity was determined by calcein-AM release and live cell imaging-based cytotoxicity assays. The metabolic properties of TIGIT KO and WT NK cells were compared with a Seahorse analyzer. The effect of the Fc-component of anti-TIGIT on NK-cell fratricide was determined by co-culturing WT and TIGIT KO NK cells with Fc-active and Fc-inactive anti-TIGIT.

RESULTS

TIGIT KO increased the cytotoxicity of NK cells against multiple cancer cell lines including spheroids. TIGIT KO NK cells upregulated mTOR complex 1 (mTORC1) signaling and had better metabolic fitness with an increased basal glycolytic rate when co-cultured with cancer cells compared with WT NK cells. Importantly, TIGIT KO prevented NK-cell fratricide when combined with Fc-active anti-TIGIT.

CONCLUSIONS

TIGIT KO in ex vivo expanded NK cells increased their cytotoxicity and metabolic fitness and prevented NK-cell fratricide when combined with Fc-active anti-TIGIT antibodies. These fratricide-resistant TIGIT KO NK cells have therapeutic potential alone or in combination with Fc-active anti-TIGIT antibodies to enhance their efficacy.

Opportunities and challenges of combining adoptive cellular therapy with oncolytic virotherapy

The use of oncolytic viruses (OVs) and adoptive cell therapies (ACT) have independently emerged as promising approaches for cancer immunotherapy. More recently, the combination of such agents to obtain a synergistic anticancer effect has gained attention, particularly in solid tumors, where immune-suppressive barriers of the microenvironment remain a challenge for desirable therapeutic efficacy. While adoptive cell monotherapies may be restricted by an immunologically cold or suppressive tumor microenvironment (TME), OVs can serve to prime the TME by eliciting a wave of cancer-specific immunogenic cell death and inducing enhanced antitumor immunity. While OV/ACT synergy is an attractive approach, immune-suppressive barriers remain, and methods should be considered to optimize approaches for such combination therapy. In this review, we summarize current approaches that aim to overcome these barriers to enable optimal synergistic antitumor effects.

Deletion of Glycogen Synthase Kinase 3 Beta Reprograms NK Cell Metabolism

Loss of cytotoxicity and defective metabolism are linked to glycogen synthase kinase 3 beta (GSK3β) overexpression in natural killer (NK) cells from patients with acute myeloid leukemia or from healthy donors after expansion ex vivo with IL-15. Drug inhibition of GSK3β in these NK cells improves their maturation and cytotoxic activity, but the mechanisms of GSK3β-mediated dysfunction have not been well studied. Here, we show that expansion of NK cells with feeder cells expressing membrane-bound IL-21 maintained normal GSK3β levels, allowing us to study GSK3β function using CRISPR gene editing. We deleted GSK3B and expanded paired-donor knockout and wild-type (WT) NK cells and then assessed transcriptional and functional alterations induced by loss of GSK3β. Surprisingly, our data showed that deletion of GSK3B did not alter cytotoxicity, cytokine production, or maturation (as determined by CD57 expression). However, GSK3B-KO cells demonstrated significant changes in expression of genes related to rRNA processing, cell proliferation, and metabolic function, suggesting possible metabolic reprogramming. Next, we found that key genes downregulated in GSK3B-KO NK cells were upregulated in GSK3β-overexpressing NK cells from AML patients, confirming this correlation in a clinical setting. Lastly, we measured cellular energetics and observed that GSK3B-KO NK cells exhibited 150% higher spare respiratory capacity, a marker of metabolic fitness. These findings suggest a role for GSK3β in regulating NK cell metabolism.

Pediatric versus adult high grade glioma: Immunotherapeutic and genomic considerations

High grade gliomas are identified as malignant central nervous tumors that spread rapidly and have a universally poor prognosis. Historically high grade gliomas in the pediatric population have been treated similarly to adult high grade gliomas. For the first time, the most recent classification of central nervous system tumors by World Health Organization has divided adult from pediatric type diffuse high grade gliomas, underscoring the biologic differences between these tumors in different age groups. The objective of our review is to compare high grade gliomas in the adult versus pediatric patient populations, highlighting similarities and differences in epidemiology, etiology, pathogenesis and therapeutic approaches. High grade gliomas in adults versus children have varying clinical presentations, molecular biology background, and response to chemotherapy, as well as unique molecular targets. However, increasing evidence show that they both respond to recently developed immunotherapies. This review summarizes the distinctions and commonalities between the two in disease pathogenesis and response to therapeutic interventions with a focus on immunotherapy.

Cerebral organoids containing an AUTS2 missense variant model microcephaly

Variants in the AUTS2 gene are associated with a broad spectrum of neurological conditions characterized by intellectual disability, microcephaly, and congenital brain malformations. Here, we use a human cerebral organoid model to investigate the pathophysiology of a heterozygous de novo missense AUTS2 variant identified in a patient with multiple neurological impairments including primary microcephaly and profound intellectual disability. Proband cerebral organoids exhibit reduced growth, deficits in neural progenitor cell (NPC) proliferation and disrupted NPC polarity within ventricular zone-like regions compared to control cerebral organoids. We used CRISPR-Cas9-mediated gene editing to correct this variant and demonstrate rescue of impaired organoid growth and NPC proliferative deficits. Single-cell RNA sequencing revealed a marked reduction of G1/S transition gene expression and alterations in WNT-β-catenin signalling within proband NPCs, uncovering a novel role for AUTS2 in NPCs during human cortical development. Collectively, these results underscore the value of cerebral organoids to investigate molecular mechanisms underlying AUTS2 syndrome.

Optimization and validation of CAR transduction into human primary NK cells using CRISPR and AAV

Human primary natural killer (NK) cells are being widely advanced for cancer immunotherapy. However, methods for gene editing of these cells have suffered low transduction rates, high cell death, and loss of transgene expression after expansion. Here, we developed a highly efficient method for site-specific gene insertion in NK cells using CRISPR (Cas9/RNP) and AAVs. We compared AAV vectors designed to mediate gene insertion by different DNA repair mechanisms, homology arm lengths, and virus concentrations. We then validated the method for site-directed gene insertion of CD33-specific CARs into primary human NK cells. CAR transduction was efficient, its expression remained stable after expansion, and it improved efficacy against AML targets.

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.

Assessment of Beta-2 Microglobulin Gene Edited Airway Epithelial Stem Cells as a treatment for Sulfur Mustard Inhalation

Respiratory system damage is the primary cause of mortality in individuals who are exposed to vesicating agents including sulfur mustard (SM). Despite these devastating health complications, there are no fielded therapeutics that are specific for such injuries. Previous studies reported that SM inhalation depleted the tracheobronchial airway epithelial stem cell (TSC) pool and supported the hypothesis, TSC replacement will restore airway epithelial integrity and improve health outcomes for SM-exposed individuals. TSC express Major Histocompatibility Complex (MHC-I) transplantation antigens which increases the chance that allogeneic TSC will be rejected by the patient’s immune system. However, previous studies reported that Beta-2 microglobulin (B2M) knockout cells lacked cell surface MHC-I and suggested that B2M knockout TSC would be tolerated as an allogeneic graft. This study used a Cas9 ribonucleoprotein (RNP) to generate B2M-knockout TSC, which are termed Universal Donor Stem Cells (UDSC). Whole genome sequencing identified few off-target modifications and demonstrated the specificity of the RNP approach. Functional assays demonstrated that UDSC retained their ability to self-renew and undergo multilineage differentiation. A preclinical model of SM inhalation was used to test UDSC efficacy and identify any treatment-associated adverse events. Adult male Sprague-Dawley rats were administered an inhaled dose of 0.8 mg/kg SM vapor which is the inhaled LD₅₀ on day 28 post-challenge. On recovery day 2, vehicle or allogeneic Fisher rat UDSC were delivered intravenously (n = 30/group). Clinical parameters were recorded daily, and planned euthanasia occurred on post-challenge days 7, 14, and 28. The vehicle and UDSC treatment groups exhibited similar outcomes including survival and a lack of adverse events. These studies establish a baseline which can be used to further develop UDSC as a treatment for SM-induced airway disease.

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.

NKG2D-CAR-transduced natural killer cells efficiently target multiple myeloma

CAR-T-cell therapy against MM currently shows promising results, but usually with serious toxicities. CAR-NK cells may exert less toxicity when redirected against resistant myeloma cells. CARs can be designed through the use of receptors, such as NKG2D, which recognizes a wide range of ligands to provide broad target specificity. Here, we test this approach by analyzing the antitumor activity of activated and expanded NK cells (NKAE) and CD45RA- T cells from MM patients that were engineered to express an NKG2D-based CAR. NKAE cells were cultured with irradiated Clone9.mbIL21 cells. Then, cells were transduced with an NKG2D-4-1BB-CD3z-CAR. CAR-NKAE cells exhibited no evidence of genetic abnormalities. Although memory T cells were more stably transduced, CAR-NKAE cells exhibited greater in vitro cytotoxicity against MM cells, while showing minimal activity against healthy cells. In vivo, CAR-NKAE cells mediated highly efficient abrogation of MM growth, and 25% of the treated mice remained disease free. Overall, these results demonstrate that it is feasible to modify autologous NKAE cells from MM patients to safely express a NKG2D-CAR. Additionally, autologous CAR-NKAE cells display enhanced antimyeloma activity demonstrating that they could be an effective strategy against MM supporting the development of NKG2D-CAR-NK-cell therapy for MM.

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 ).

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.

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.

Evaluation of membrane bound IL-21 expanded natural killer cells for chronic lymphocytic leukemia therapy

Chronic lymphocytic leukemia (CLL) is the most prevalent adult leukemia and remains incurable despite recent therapeutic advances. Natural killer (NK) cells have potent anti-cancer effects, but efforts to use NK cell therapy in CLL have been limited by poor NK cell growth and anti-leukemia activity. We sought to determine if stimulating NK cells ex vivo with K562-based feeder cells expressing membrane-bound IL-21 (mbIL-21) (Denman et al., 2012) could overcome the limitations of prior techniques to create an effective therapy for CLL.

Our data demonstrate that healthy donor-derived mbIL-21 expanded NK cells have increased antibody-dependent cellular cytotoxicity (ADCC) and direct cytotoxicity (DC; without targeting antibody) against CLL cell lines. This technique can also overcome CLL-induced NK suppression – CLL patient-derived NK cells expanded equally and were as potent as normal donor-derived NKs, including against both allogeneic and autologous CLL tumor cells. CLL tumor cells are not susceptible to DC but are very vulnerable to ADCC with anti-CD20 antibodies (rituximab or obinutuzumab). The lack of direct cytotoxicity of tumor cells was correlated to low NK:CLL quantitative conjugate formation, suggesting a lack of tumor target recognition.

Blocking antibodies to FasL, TNFα, and TRAIL show that only TRAIL contributes modestly to anti-CLL tumor cytotoxicity, while application of folimycin demonstrates that perforin/granzyme release is the major mechanism of cytotoxicity. In vivo, treatment with expanded NK cells plus obinutuzumab significantly prolongs survival in the OSU-CLL human xenograft model. Based on these data, we are planning a clinical trial of mbIL-21 expanded NK cells plus obinutuzumab in CLL patients.

Pharmacologic inhibition of lysine-specific demethylase 1 as a therapeutic and immune-sensitization strategy in pediatric high-grade glioma

BACKGROUND

Diffuse midline gliomas (DMG), including brainstem diffuse intrinsic pontine glioma (DIPG), are incurable pediatric high-grade gliomas (pHGG). Mutations in the H3 histone tail (H3.1/3.3-K27M) are a feature of DIPG, rendering them therapeutically sensitive to small-molecule inhibition of chromatin modifiers. Pharmacological inhibition of lysine-specific demethylase 1 (LSD1) is clinically relevant but has not been carefully investigated in pHGG or DIPG.

METHODS

Patient-derived DIPG cell lines, orthotopic mouse models, and pHGG datasets were used to evaluate effects of LSD1 inhibitors on cytotoxicity and immune gene expression. Immune cell cytotoxicity was assessed in DIPG cells pretreated with LSD1 inhibitors, and informatics platforms were used to determine immune infiltration of pHGG.

RESULTS

Selective cytotoxicity and an immunogenic gene signature were established in DIPG cell lines using clinically relevant LSD1 inhibitors. Pediatric HGG patient sequencing data demonstrated survival benefit of this LSD1-dependent gene signature. Pretreatment of DIPG with these inhibitors increased lysis by natural killer (NK) cells. Catalytic LSD1 inhibitors induced tumor regression and augmented NK cell infusion in vivo to reduce tumor burden. CIBERSORT analysis of patient data confirmed NK infiltration is beneficial to patient survival, while CD8 T cells are negatively prognostic. Catalytic LSD1 inhibitors are nonperturbing to NK cells, while scaffolding LSD1 inhibitors are toxic to NK cells and do not induce the gene signature in DIPG cells.

CONCLUSIONS

LSD1 inhibition using catalytic inhibitors is selectively cytotoxic and promotes an immune gene signature that increases NK cell killing in vitro and in vivo, representing a therapeutic opportunity for pHGG.

KEY POINTS

1. LSD1 inhibition using several clinically relevant compounds is selectively cytotoxic in DIPG and shows in vivo efficacy as a single agent.2. An LSD1-controlled gene signature predicts survival in pHGG patients and is seen in neural tissue from LSD1 inhibitor-treated mice.3. LSD1 inhibition enhances NK cell cytotoxicity against DIPG in vivo and in vitro with correlative genetic biomarkers.

Phase I study of intraventricular infusions of autologous ex vivo expanded NK cells in children with recurrent medulloblastoma and ependymoma

BACKGROUND

Recurrent pediatric medulloblastoma and ependymoma have a grim prognosis. We report a first-in-human, phase I study of intraventricular infusions of ex vivo expanded autologous natural killer (NK) cells in these tumors, with correlative studies.

METHODS

Twelve patients were enrolled, 9 received protocol therapy up to 3 infusions weekly, in escalating doses from 3 × 106 to 3 × 108 NK cells/m2/infusion, for up to 3 cycles. Cerebrospinal fluid (CSF) was obtained for cellular profile, persistence, and phenotypic analysis of NK cells. Radiomic characterization on pretreatment MRI scans was performed in 7 patients, to develop a non-invasive imaging-based signature.

RESULTS

Primary objectives of NK cell harvest, expansion, release, and safety of 112 intraventricular infusions of NK cells were achieved in all 9 patients. There were no dose-limiting toxicities. All patients showed progressive disease (PD), except 1 patient showed stable disease for one month at end of study follow-up. Another patient had transient radiographic response of the intraventricular tumor after 5 infusions of NK cell before progressing to PD. At higher dose levels, NK cells increased in the CSF during treatment with repetitive infusions (mean 11.6-fold). Frequent infusions of NK cells resulted in CSF pleocytosis. Radiomic signatures were profiled in 7 patients, evaluating ability to predict upfront radiographic changes, although they did not attain statistical significance.

CONCLUSIONS

This study demonstrated feasibility of production and safety of intraventricular infusions of autologous NK cells. These findings support further investigation of locoregional NK cell infusions in children with brain malignancies.

Natural killer cell therapy for hematologic malignancies: successes, challenges, and the future

The adoptive transfer of natural killer (NK) cells is an emerging therapy in the field of immuno-oncology. In the last 3 decades, NK cells have been utilized to harness the anti-tumor immune response in a wide range of malignancies, most notably with early evidence of efficacy in hematologic malignancies. NK cells are dysfunctional in patients with hematologic malignancies, and their number and function are further impaired by chemotherapy, radiation, and immunosuppressants used in initial therapy and hematopoietic stem cell transplantation. Restoring this innate immune deficit may lead to improved therapeutic outcomes. NK cell adoptive transfer has proven to be a safe in these settings, even in the setting of HLA mismatch, and a deeper understanding of NK cell biology and optimized expansion techniques have improved scalability and therapeutic efficacy. Here, we review the use of NK cell therapy in hematologic malignancies and discuss strategies to further improve the efficacy of NK cells against these diseases.

Genetic and epigenetic modification of human primary NK cells for enhanced antitumor activity

Cancer immunotherapy using genetically modified immune cells such as those expressing chimeric antigen receptors has shown dramatic outcomes in patients with refractory and relapsed malignancies. Natural killer (NK) cells as a member of the innate immune system, possessing both anticancer (cytotoxic) and proinflammatory (cytokine) responses to cancers and rare off-target toxicities have great potential for a wide range of cancer therapeutic settings. Therefore, improving NK cell antitumor activity through genetic modification is of high interest in the field of cancer immunotherapy. However, gene manipulation in primary NK cells has been challenging because of broad resistance to many genetic modification methods that work well in T cells. Here we review recent successful approaches for genetic and epigenetic modification of NK cells including epigenetic remodeling, transposons, mRNA-mediated gene delivery, lentiviruses, and CRISPR gene targeting.

Scaffolding LSD1 Inhibitors Impair NK Cell Metabolism and Cytotoxic Function Through Depletion of Glutathione

Cell therapies such as chimeric-antigen receptor (CAR) T-cells and NK cells are cutting-edge methods for treating cancer and other diseases. There is high interest in optimizing drug treatment regimens to best work together with emerging cell therapies, such as targeting epigenetic enzymes to stimulate recognition of tumor cells by immune cells. Herein, we uncover new mechanisms of the histone demethylase LSD1, and various inhibitors targeting unique domains of LSD1, in the function of NK cells grown for cell therapy. Catalytic inhibitors (tranylcypromine and the structural derivatives GSK LSD1 and RN-1) can irreversibly block the demethylase activity of LSD1, while scaffolding inhibitors (SP-2509 and clinical successor SP-2577, also known as seclidemstat) disrupt epigenetic complexes that include LSD1. Relevant combinations of LSD1 inhibitors with cell therapy infusions and immune checkpoint blockade have shown efficacy in pre-clinical solid tumor models, reinforcing a need to understand how these drugs would impact T- and NK cells. We find that scaffolding LSD1 inhibitors potently reduce oxidative phosphorylation and glycolysis of NK cells, and higher doses induce mitochondrial reactive oxygen species and depletion of the antioxidant glutathione. These effects are unique to scaffolding inhibitors compared to catalytic, to NK cells compared to T-cells, and importantly, can fully ablate the lytic capacity of NK cells. Supplementation with biologically achievable levels of glutathione rescues NK cell cytolytic function but not NK cell metabolism. Our results suggest glutathione supplementation may reverse NK cell activity suppression in patients treated with seclidemstat.

Histone Deacetylase Inhibitors and IL21 Cooperate to Reprogram Human Effector CD8+ T Cells to Memory T Cells

Clinical response rates after adoptive cell therapy (ACT) are highly correlated with in vivo persistence of the infused T cells. However, antigen-specific T cells found in tumor sites are often well-differentiated effector cells with limited persistence. Central memory CD8+ T cells, capable of self-renewal, represent desirable ACT products. We report here that exposure to a histone deacetylase inhibitor (HDACi) and IL21 could reprogram differentiated human CD8+ T cells into central memory-like T cells. Dedifferentiation of CD8+ T cells was initiated by increased H3 acetylation and chromatin accessibility at the CD28 promoter region. This led to IL21-mediated pSTAT3 binding to the CD28 region, and subsequent upregulation of surface CD28 and CD62L (markers of central memory T cells). The reprogrammed cells exhibited enhanced proliferation in response to both IL2 and IL15, and a stable memory-associated transcriptional signature (increased Lef1 and Tcf7). Our findings support the application of IL21 and HDACi for the in vitro generation of highly persistent T-cell populations that can augment the efficacy of adoptively transferred T cells.

Fc-engineered anti-CD33 monoclonal antibody potentiates cytotoxicity of membrane-bound interleukin-21 expanded natural killer cells in acute myeloid leukemia

BACKGROUND

Qualitative and quantitative defects in natural killer (NK) cells have been noted in patients with acute myeloid leukemia (AML), providing rationale for infusion of donor-derived NK cells. We previously showed that decitabine enhances expression of NKG2D ligands in AML with additive cytotoxicity when NK cells and Fc (fragment crystallizable region)-engineered CD33 monoclonal antibody (CD33mAb) was used. We conducted a phase 1 study evaluating decitabine and haploidentical NK cells in relapsed AML. Using patient samples from this study, we evaluated whether ex vivo donor-derived expanded NK cells with or without CD33mAb was effective in decitabine-treated AML.

METHODS

Bone marrow aspirates were collected from patients at pre- and post-NK cell infusion. NK cells from healthy donors were expanded for 14 days using irradiated K562 feeder cells displaying membrane-bound IL-21 (mbIL-21). Patient samples were used to test in vitro activity of mbIL-21 NK cells ± CD33m Ab-dependent cellular cytotoxicity (ADCC) and AML patient derived xenograft (PDX) mice were developed to test in vivo activity.

RESULTS

Upon incubation with primary AML blasts, mbIL-21 NK cells showed variable donor-dependent intra-cellular interferon-γ production, which increased with CD33mAb-coated AML. ADCC assays revealed mbIL-21 NK cells effectively lysed primary AML blasts with higher activity on CD33mAb-coated AML. Importantly, CD33mAb-dependent enhanced cytotoxicity by mbIL-21 NK cells was maintained in AML cells from patients even 24 days post-decitabine treatment. In vivo infusion of mbIL-21 NK cells in AML PDX mice, treated with CD33mAb, reduced the tumor burden.

DISCUSSION

These data show the therapeutic utility of mbIL-21 NK cells that can be further potentiated by addition of CD33mAb in AML.

Blood and tissue biomarker analysis in dogs with osteosarcoma treated with palliative radiation and intra-tumoral autologous natural killer cell transfer

We have previously reported radiation-induced sensitization of canine osteosarcoma (OSA) to natural killer (NK) therapy, including results from a first-in-dog clinical trial. Here, we report correlative analyses of blood and tissue specimens for signals of immune activation in trial subjects. Among 10 dogs treated with palliative radiotherapy (RT) and intra-tumoral adoptive NK transfer, we performed ELISA on serum cytokines, flow cytometry for immune phenotype of PBMCs, and PCR on tumor tissue for immune-related gene expression. We then queried The Cancer Genome Atlas (TCGA) to evaluate the association of cytotoxic/immune-related gene expression with human sarcoma survival. Updated survival analysis revealed five 6-month survivors, including one dog who lived 17.9 months. Using feeder line co-culture for NK expansion, we observed maximal activation of dog NK cells on day 17-19 post isolation with near 100% expression of granzyme B and NKp46 and high cytotoxic function in the injected NK product. Among dogs on trial, we observed a trend for higher baseline serum IL-6 to predict worse lung metastasis-free and overall survival (P = 0.08). PCR analysis revealed low absolute gene expression of CD3, CD8, and NKG2D in untreated OSA. Among treated dogs, there was marked heterogeneity in the expression of immune-related genes pre- and post-treatment, but increases in CD3 and CD8 gene expression were higher among dogs that lived > 6 months compared to those who did not. Analysis of the TCGA confirmed significant differences in survival among human sarcoma patients with high and low expression of genes associated with greater immune activation and cytotoxicity (CD3e, CD8a, IFN-γ, perforin, and CD122/IL-2 receptor beta). Updated results from a first-in-dog clinical trial of palliative RT and autologous NK cell immunotherapy for OSA illustrate the translational relevance of companion dogs for novel cancer therapies. Similar to human studies, analyses of immune markers from canine serum, PBMCs, and tumor tissue are feasible and provide insight into potential biomarkers of response and resistance.

Efficient and Robust NK-Cell Transduction With Baboon Envelope Pseudotyped Lentivector

NK-cell resistance to transduction is a major technical hurdle for developing NK-cell immunotherapy. By using Baboon envelope pseudotyped lentiviral vectors (BaEV-LVs) encoding eGFP, we obtained a transduction rate of 23.0 ± 6.6% (mean ± SD) in freshly-isolated human NK-cells (FI-NK) and 83.4 ± 10.1% (mean ± SD) in NK-cells obtained from the NK-cell Activation and Expansion System (NKAES), with a sustained transgene expression for at least 21 days. BaEV-LVs outperformed Vesicular Stomatitis Virus type-G (VSV-G)-, RD114- and Measles Virus (MV)- pseudotyped LVs (p < 0.0001). mRNA expression of both BaEV receptors, ASCT1 and ASCT2, was detected in FI-NK and NKAES, with higher expression in NKAES. Transduction with BaEV-LVs encoding for CAR-CD22 resulted in robust CAR-expression on 38.3 ± 23.8% (mean ± SD) of NKAES cells, leading to specific killing of NK-resistant pre-B-ALL-RS4;11 cell line. Using a larger vector encoding a dual CD19/CD22-CAR, we were able to transduce and re-expand dual-CAR-expressing NKAES, even with lower viral titer. These dual-CAR-NK efficiently killed both CD19KO- and CD22KO-RS4;11 cells. Our results suggest that BaEV-LVs may efficiently enable NK-cell biological studies and translation of NK-cell-based immunotherapy to the clinic.

The role of AhR in transcriptional regulation of immune cell development and function

The aryl hydrocarbon receptor (AhR) is a ligand-activated transcriptional factor (TF) that is a member of the Per-Arnt-Sim family of proteins. AhR regulates diverse processes, including malignant transformation, hematopoietic cell development, and fate determination of immune cell lineages. Moreover, AhR forms a crucial link between innate and adaptive arms of the immune system. Malignant cells frequently evolve multiple mechanisms for suppressing tumor-specific responses, including the induction of suppressive pathways involving AhR and its metabolic byproducts in the tumor microenvironment that promote immune evasion and tumor progression. Thus, interest is high in further defining the role of AhR in carcinogenesis and immune development and regulation, particularly regarding the therapeutic interventions that unleash immune responses to cancer cells. Here, we provide an overview of the role of AhR in the regulation of innate and adaptive immune response and discuss the implications of targeting this pathway to augment the immune response in cancer patients.

Immunotherapies for pediatric cancer: current landscape and future perspectives

The advent of immunotherapy has revolutionized how we manage and treat cancer. While the majority of immunotherapy-related studies performed to date have focused on adult malignancies, a handful of these therapies have also recently found success within the pediatric space. In this review, we examine the immunotherapeutic agents that have achieved the approval of the US Food and Drug Administration for treating childhood cancers, highlighting their development, mechanisms of action, and the lessons learned from the seminal clinical trials that ultimately led to their approval. We also shine a spotlight on several emerging immunotherapeutic modalities that we believe are poised to have a positive impact on the treatment of pediatric malignancies in the near future.

Membrane bound IL-21 based NK cell feeder cells drive robust expansion and metabolic activation of NK cells

NK cell adoptive therapy is a promising cancer therapeutic approach, but there are significant challenges that limiting its feasibility and clinical efficacy. One difficulty is the paucity of clinical grade manufacturing platforms to support the large scale expansion of highly active NK cells. We created an NK cell feeder cell line termed 'NKF' through overexpressing membrane bound IL-21 that is capable of inducing robust and sustained proliferation (>10,000-fold expansion at 5 weeks) of highly cytotoxic NK cells. The expanded NK cells exhibit increased cytotoxic function against a panel of blood cancer and solid tumor cells as compared to IL-2-activated non-expanded NK cells. The NKF-expanded NK cells also demonstrate efficacy in mouse models of human sarcoma and T cell leukemia. Mechanistic studies revealed that membrane-bound IL-21 leads to an activation of a STAT3/c-Myc pathway and increased NK cell metabolism with a shift towards aerobic glycolysis. The NKF feeder cell line is a promising new platform that enables the large scale proliferation of highly active NK cells in support of large scale third party NK cell clinical studies that have been recently intiatied. These results also provide mechanistic insights into how membrane-bound IL-21 regulates NK cell expansion.

Expression of carcinoma, apoptosis, and cell-death-related genes are determinants for sensitivity of pediatric cancer cell lines to lysis by natural killer cells

Natural killer (NK) cells have potential utility in pediatric cancer immunotherapy for their ability to lyse diverse tumor targets, lack of dependence on mutation-associated tumor antigens, and for their relative safety demonstrated so far in clinical trials. Here, we evaluate the cytotoxic potential of expanded NK cells against a well-characterized panel of pediatric cancer cell lines representing Ewing sarcoma, rhabdomyosarcoma, neuroblastoma, lymphoma, leukemia, and brain tumors. We correlate their sensitivity NK cell lysis with tumor phenotypic, transcriptomic, and genetic determinants, and correlate known immunogenetic determinants with donor NK cell potency. Although ligand expression on cell lines stratified according to hematologic versus nonhematologic cancer types, the sensitivity to NK cell lysis varied widely and did not correlate with cancer type, expression of individual activating or inhibitory ligands, gene-expression clusters of NK cell ligands, disease status (newly diagnosed or relapsed), or MYCN amplification. Rather, sensitivity to NK cell-mediated lysis was associated with a novel 96-gene cluster of predominantly carcinoma-, apoptosis-, and cell death-related pathways, and with functional p53 status. NK cell potency was strongly associated with activating KIR gene content, but not with KIR/KIR-ligand mismatch. This study suggests that adoptive immunotherapy with expanded NK cells has the potential for a wide range of pediatric cancers, identifies potential biomarkers of efficacy and response, and establishes a foundation for using this cell line panel for the preclinical evaluation of immunotherapies.

Intravenous Bone Marrow Mononuclear Cells for Acute Ischemic Stroke: Safety, Feasibility, and Effect Size from a Phase I Clinical Trial

Cellular therapy is a promising investigational modality to enhance poststroke recovery. We conducted a single-arm, phase I clinical trial to determine the safety and feasibility of intravenous (IV) administration of autologous bone marrow mononuclear cells (MNCs) after acute ischemic stroke (AIS). Patients with moderate severity of AIS underwent bone marrow harvest followed by IV reinfusion of MNCs within 24-72 hours of onset. A target dose of 10 million cells per kilogram was chosen based on preclinical data. Patients were followed up daily during hospitalization and at 1, 3, 6, 12, and 24 months for incidence of adverse events using laboratory, clinical (12 months), and radiological (24 months) parameters. The trial was powered to detect severe adverse events (SAEs) with incidences of at least 10% and planned to enroll 30 patients. Primary outcomes were study-related SAEs and the proportion of patients successfully completing study intervention. A propensity score-based matched control group was used for the estimation of effect size (ES) for day-90 modified Rankin score (mRS). There were no study-related SAEs and, based on a futility analysis, enrolment was stopped after 25 patients. All patients successfully completed study intervention and most received the target dose. Secondary analysis estimated the ES to be a reduction of 1 point (95% confidence interval: 0.33-1.67) in median day-90 mRS for treated patients as compared with the matched control group. Bone marrow harvest and infusion of MNCs is safe and feasible in patients with AIS. The estimated ES is helpful in designing future randomized controlled trials. Stem Cells 2019;37:1481-1491.

Immunotherapeutic Challenges for Pediatric Cancers

Solid tumors contain a mixture of malignant cells and non-malignant infiltrating cells that often create a chronic inflammatory and immunosuppressive microenvironment that restricts immunotherapeutic approaches. Although childhood and adult cancers share some similarities related to microenvironmental changes, pediatric cancers are unique, and adult cancer practices may not be wholly applicable to our pediatric patients. This review highlights the differences in tumorigenesis, viral infection, and immunologic response between children and adults that need to be considered when trying to apply experiences from experimental therapies in adult cancer patients to pediatric cancers.

Abstract A065: Genome-scale CRISPR screens identify essential genes for tumor sensitivity to NK cells

Harnessing natural killer (NK) cells to attack tumors could improve immune-based cancer treatment strategies. However, mechanisms regulating sensitivity or resistance of cancer cells to the effector function of NK cells are incompletely understood. Here, we performed genome-scale CRISPR-Cas9 loss-of-function screens in human cancer cells to discover genes that influence susceptibility to primary human NK cells. To screen for genes essential for the interaction between NK cells and cancer cells, we infected human cancer cells expressing Cas9 with a genome-scale lentiviral guide RNA library. The resulting pool of knockout cells was exposed to NK cells expanded from peripheral blood of healthy donors. Enriched and depleted knockout clones were detected by next-generation sequencing of the integrated sgRNA cassettes, enabling identification of genes conferring resistance or susceptibility to NK cell-mediated lysis. The screens were performed in cell lines from diverse cancer types, including chronic myeloid leukemia (CML), B cell acute lymphoblastic leukemia, diffuse large B-cell lymphoma (DLBCL), and multiple myeloma. We recovered several known mechanisms of NK cell/cancer cell interactions, demonstrating feasibility of the screening approach. Loss of genes encoding components of the MHC class I complex (B2M, HLA-A, HLA-C, HLA-E) sensitized multiple cancer cell lines to NK cell-mediated lysis. This is consistent with missing-self recognition as a fundamental mechanism of NK cell activation. Furthermore, knockout of IFN-JAK-STAT signaling mediators led to increased tumor cell lysis, suggesting that MHC class I induction in response to NK cell-derived IFN gamma enables NK cell evasion by tumor cells. We also identified genes essential for effective NK cell-mediated lysis. NCR3LG1, encoding the B7-H6 ligand for the NKp30 activating NK cell receptor, was essential for NK cell lysis of CML cells. In contrast, knockout of apoptotic mediators and TRAIL pathway components conferred resistance to NK cell cytotoxicity in DLBCL cells, indicating heterogeneity in NK cell/cancer cell interactions between cancer types. Our data support a view that distinct mechanisms regulate sensitivity to NK cell cytotoxicity in different cancers. Importantly, our results indicate that loss-of-function mutations in the antigen-presenting machinery and the IFN-JAK-STAT pathway sensitize tumors to NK cell effector function. As alterations in these genes are associated with resistance to T-cell immunotherapies such as PD-1 blockade, NK cell-based therapies could be employed to overcome resistance in these patients. In summary, we suggest that systematic identification of mechanisms governing tumor immune susceptibility has the potential to uncover novel immunotherapy targets.

Citation Format: Olli Dufva, Jay Klievink, Khalid Saeed, Matti Kankainen, Mette Ilander, Tiiina Hannunen, Sonja Lagström, Pekka Ellonen, Dean A Lee, Satu Mustjoki. Genome-scale CRISPR screens identify essential genes for tumor sensitivity to NK cells [abstract]. In: Proceedings of the Fourth CRI-CIMT-EATI-AACR International Cancer Immunotherapy Conference: Translating Science into Survival; Sept 30-Oct 3, 2018; New York, NY. Philadelphia (PA): AACR; Cancer Immunol Res 2019;7(2 Suppl):Abstract nr A065.

Analysis of NK cell clones obtained using interleukin-2 and gene-modified K562 cells revealed the ability of "senescent" NK cells to lose CD57 expression and start expressing NKG2A

In this work, we analyzed the phenotype and growth of human NK cell clones obtained by the stimulation of individual NK cells with IL-2 and gene-modified K562 feeder cells expressing membrane-bound IL-21 (K562-mbIL21). We generated clones from NK cells at distinct differentiation and activation stages, determined by CD56, CD57 and HLA-DR expression levels. Less differentiated CD56^bright NK cell subsets showed higher cloning efficiency compared with more differentiated CD56^dim subsets, especially with the CD57^bright subset. However, clones from the CD56^dimCD57^– subset lived longer on average than other subsets. Moreover, several clones with the highest cell numbers were derived from CD56^dimCD57^–HLA-DR⁻cells. Most of the clones including those derived from more differentiated CD56^dimCD57^+/–NKG2A^– NK cells showed a less-differentiated NKG2A⁺ phenotype. Also, CD57^– cells were frequently observed in clones derived from CD57⁺ NK cells suggesting the loss of CD57 during the cloning process. On the other hand, KIR surface expression once detected for a clone never disappeared entirely, confirming irreversibility of the KIR expression. In summary, we have demonstrated that in specific conditions terminally differentiated CD57⁺ human NK cells are able to acquire the CD57^– phenotype that was previously not observed and, thus, was considered impossible.

Education-dependent activation of glycolysis promotes the cytolytic potency of licensed human natural killer cells

BACKGROUND

The mechanism by which natural killer (NK) cell education results in licensed NK cells with heightened effector function against missing self-targets is not known.

OBJECTIVE

We sought to identify potential mechanisms of enhanced function in licensed human NK cells.

METHODS

We used expanded human NK cells from killer immunoglobulin-like receptor (KIR)/HLA-genotyped donors sorted for single-KIR⁺ cells to generate pure populations of licensed and unlicensed NK cells. We performed proteomic and gene expression analysis of these cells before and after receptor cross-linking and performed functional and metabolic analysis before and after interference with selected metabolic pathways. We verified key findings using freshly isolated and sorted NK cells from peripheral blood.

RESULTS

We confirmed that licensed human NK cells are greater in number in peripheral blood and proliferate more in vitro than unlicensed NK cells. Using high-throughput protein analysis, we found that unstimulated licensed NK cells have increased expression of the glycolytic enzyme pyruvate kinase muscle isozyme M2 and after KIR cross-linking have increased phosphorylation of the metabolic modulators p38-α and 5' adenosine monophosphate-activated protein kinase α. After cytokine expansion and activation, unlicensed NK cells depended solely on mitochondrial respiration for cytolytic function, whereas licensed NK cells demonstrated metabolic reprogramming toward glycolysis and mitochondrial-dependent glutaminolysis, leading to accumulation of glycolytic metabolites and depletion of glutamate. As such, blocking both glycolysis and mitochondrial-dependent respiration was required to suppress the cytotoxicity of licensed NK cells.

CONCLUSIONS

Collectively, our data support an arming model of education in which enhanced glycolysis in licensed NK cells supports proliferative and cytotoxic capacity.

Abstract 2556: Expanded ovarian cancer patient NK cells represent a novel, cytotoxic phenotype and reduce autologous tumor in a patient-derived xenograft ovarian cancer model

Introduction: Ex vivo expanded NK cells are emerging as a promising cancer immunotherapy and have recently shown clinical effectiveness in treating hematological malignancies. NK cell therapy has encountered challenges against solid tumors, such as ovarian cancer, due to the immunosuppressive tumor environment which inhibits NK cell function. In addition, autologous NK cell therapy has been limited due to the diminished function of cancer patient NK cells and inhibition by self-MHC. In the present study, we assessed whether expansion of ovarian cancer patient NK cells overcomes limitations of autologous NK cell therapy against high grade serous ovarian cancer (HGSOC).

Experimental Procedures: NK cells were expanded ex vivo from peripheral blood (PB) and ascites of HGSOC patients or PB of healthy donors using K562-mb-IL-21 feeder cell expansion. We compared expanded and unexpanded NK cell cytotoxicity against ovarian cancer cells in vitro. Given recent evidence that CD56brightCD16- NK cells have greater anti-tumor potential than CD56dimCD16+ NK cells, we assessed relative expression of CD56 and CD16 on expanded NK cells. To study autologous NK cell therapy, we established a translational patient-derived xenograft (PDX) model of ovarian cancer. We adoptively transferred expanded ovarian cancer patient PB- and ascites-NK cells into cell-line xenograft and autologous PDX ovarian cancer models. Tumor burden, ascites progression, and survival of xenograft mice were assessed.

Results: We report that expanded NK cells express a novel CD56bright/brightCD16+ phenotype and have greater in vitro cytotoxicity than unexpanded NK cells against ovarian cancer cells. Adoptive transfer of expanded ovarian cancer patient PB- and ascites-NK cells reduced tumor burden of well-established ovarian cancer in cell-line xenograft mice to levels comparable to no tumor controls. Furthermore, expanded NK cells improved median survival by 3.4-5.2 times compared to untreated xenograft mice. Importantly, expanded ovarian cancer patient NK cells exerted a therapeutic effect in autologous PDX mice: expanded NK cells delayed ascites progression and inhibited development of peritoneal tumors.

Conclusions: Our results support an emerging concept that CD56bright NK cells have greater anti-tumor capacities than CD56dim NK cells. The therapeutic effects of expanded ovarian cancer patient NK cells on tumor burden and survival indicate that expansion converts immunosuppressed cancer patient NK cells to a cytotoxic subset that remains highly functional in an autologous tumor environment. The effectiveness of expanded ascites-NK cells identifies tumor-associated NK cells as a potential NK cell source for therapy. This study indicates that expanded autologous NK cells may be a promising therapy for ovarian cancer and other solid tumors.

Citation Format: Sophie M. Poznanski, Tina Nham, Marianne V. Chew, Amanda J. Lee, Isabella Y. Fan, Dean A. Lee, Hal Hirte, Ali A. Ashkar. Expanded ovarian cancer patient NK cells represent a novel, cytotoxic phenotype and reduce autologous tumor in a patient-derived xenograft ovarian cancer model [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 2556.

Generation of Knock-out Primary and Expanded Human NK Cells Using Cas9 Ribonucleoproteins

CRISPR/Cas9 technology is accelerating genome engineering in many cell types, but so far, gene delivery and stable gene modification have been challenging in primary NK cells. For example, transgene delivery using lentiviral or retroviral transduction resulted in a limited yield of genetically-engineered NK cells due to substantial procedure-associated NK cell apoptosis. We describe here a DNA-free method for genome editing of human primary and expanded NK cells using Cas9 ribonucleoprotein complexes (Cas9/RNPs). This method allowed efficient knockout of the TGFBR2 and HPRT1 genes in NK cells. RT-PCR data showed a significant decrease in gene expression level, and a cytotoxicity assay of a representative cell product suggested that the RNP-modified NK cells became less sensitive to TGFβ. Genetically modified cells could be expanded post-electroporation by stimulation with irradiated mbIL21-expressing feeder cells.

Correction: Inhibiting TGF-beta signaling preserves the function of highly activated, in vitro expanded natural killer cells in AML and colon cancer models

[This corrects the article DOI: 10.1371/journal.pone.0191358.].

Aggressive natural killer-cell leukemia mutational landscape and drug profiling highlight JAK-STAT signaling as therapeutic target

Aggressive natural killer-cell (NK-cell) leukemia (ANKL) is an extremely aggressive malignancy with dismal prognosis and lack of targeted therapies. Here, we elucidate the molecular pathogenesis of ANKL using a combination of genomic and drug sensitivity profiling. We study 14 ANKL patients using whole-exome sequencing (WES) and identify mutations in STAT3 (21%) and RAS-MAPK pathway genes (21%) as well as in DDX3X (29%) and epigenetic modifiers (50%). Additional alterations include JAK-STAT copy gains and tyrosine phosphatase mutations, which we show recurrent also in extranodal NK/T-cell lymphoma, nasal type (NKTCL) through integration of public genomic data. Drug sensitivity profiling further demonstrates the role of the JAK-STAT pathway in the pathogenesis of NK-cell malignancies, identifying NK cells to be highly sensitive to JAK and BCL2 inhibition compared to other hematopoietic cell lineages. Our results provide insight into ANKL genetics and a framework for application of targeted therapies in NK-cell malignancies.

Aggressive natural killer-cell leukemia (ANKL) has few targeted therapies. Here ANKL patients are reported to harbor STAT3, RAS-MAPK pathway, DDX3X and epigenetic modifier mutations; and drug sensitivity profiling uncovers the importance of the JAK-STAT pathway, revealing potential ANKL therapeutic targets.

Ex vivo-expanded NK cells from blood and ascites of ovarian cancer patients are cytotoxic against autologous primary ovarian cancer cells

Ovarian cancer (OC) is the leading cause of gynecological cancer-related death in North America. Most ovarian cancer patients (OCPs) experience disease recurrence after first-line surgery and chemotherapy; thus, there is a need for novel second-line treatments to improve the prognosis of OC. Although peripheral blood-derived NK cells are known for their ability to spontaneously lyse tumour cells without prior sensitization, ascites-derived NK cells (ascites-NK cells) isolated from OCPs exhibit inhibitory phenotypes, impaired cytotoxicity and may play a pro-tumourigenic role in cancer progression. Therefore, it is of interest to improve the cytotoxic effector function of impaired OCP ascites-NK cells at the tumour environment. We investigated the efficacy of using an artificial APC-based ex vivo expansion technique to generate cytotoxic, expanded NK cells from previously impaired OCP ascites-NK cells, for use in an autologous model of NK cell immunotherapy. We are the first to obtain a log-scale expansion of OCP ascites-NK cells that upregulate the surface expression of activating receptors NKG2D, NKp30, NKp44, produce robust amounts of anti-tumour cytokines in the presence of OC cells and mediate direct tumour cytotoxicity against ascites-derived, primary OC cells obtained from autologous patients. Our findings demonstrate that it is possible to generate cytotoxic OCP ascites-NK cells from previously impaired OCP ascites-NK cells, which presents a promising immunotherapeutic target for the second-line treatment of OC. Future work should focus on evaluating the in vivo efficacy of autologous NK cell immunotherapy through the intraperitoneal delivery of NK cell expansion factors to a preclinical xenograft mouse model of human OC.

Inhibiting TGF-beta signaling preserves the function of highly activated, in vitro expanded natural killer cells in AML and colon cancer models

Natural killer cells harnessed from healthy individuals can be expanded ex vivo using various platforms to produce large doses for adoptive transfer into cancer patients. During such expansion, NK cells are increasingly activated and more efficient at killing cancer cells. Adoptive transfer however introduces these activated cells into a highly immunosuppressive tumor microenvironment mediated in part by excessive transforming growth factor beta (TGF-beta) from both cancer cells and their surrounding stroma. This microenvironment ultimately limits the clinical efficacy of NK cell therapy. In this study, we examined the use of a TGF-beta receptor kinase inhibitor, LY2157299, in preserving the cytotoxic function of ex vivo expanded, highly activated NK cells following sustained exposure to pathologic levels of TGF-beta in vitro and in a liver metastases model of colon cancer. Using myeloid leukemia and colon cancer cell lines, we show that the TGF-beta driven impairment of NK cell cytotoxicity is mitigated by LY2157299. We demonstrate this effect using quantitative cytotoxicity assays as well as by showing a preserved activated phenotype with high NKG2D/CD16 expression and enhanced cytokine production. In a mouse liver metastases model of colon cancer, we observed significantly improved eradication of liver metastases in mice treated with adoptive NK cells combined with LY2157299 compared with mice receiving NK cells or TGF beta inhibition alone. We propose that the therapeutic efficacy of adoptive NK cell therapy clinically will be markedly enhanced by complementary approaches targeting TGF-beta signaling in vivo.

Radiotherapy enhances natural killer cell cytotoxicity and localization in pre-clinical canine sarcomas and first-in-dog clinical trial

BACKGROUND

We have previously shown that radiotherapy (RT) augments natural killer (NK) functions in pre-clinical models of human and mouse cancers, including sarcomas. Since dogs are an excellent outbred model for immunotherapy studies, we sought to assess RT plus local autologous NK transfer in canine sarcomas.

METHODS

Dog NK cells (CD5^dim, NKp46+) were isolated from PBMCs and expanded with irradiated K562-C9-mIL21 feeder cells and 100 IU/mL recombinant human IL-2. NK homing and cytotoxicity ± RT were evaluated using canine osteosarcoma tumor lines and dog patient-derived xenografts (PDX). In a first-in-dog clinical trial for spontaneous osteosarcoma, we evaluated RT and intra-tumoral autologous NK transfer.

RESULTS

After 14 days, mean NK expansion and yield were 19.0-fold (±8.6) and 258.9(±76.1) ×10⁶ cells, respectively. Post-RT, NK cytotoxicity increased in a dose-dependent fashion in vitro reaching ~ 80% at effector:target ratios of ≥10:1 (P < 0.001). In dog PDX models, allogeneic NK cells were cytotoxic in ex vivo killing assays and produced significant PDX tumor growth delay (P < 0.01) in vivo. After focal RT and intravenous NK transfer, we also observed significantly increased NK homing to tumors in vivo. Of 10 dogs with spontaneous osteosarcoma treated with focal RT and autologous NK transfer, 5 remain metastasis-free at the 6-month primary endpoint with resolution of suspicious pulmonary nodules in one patient. We also observed increased activation of circulating NK cells after treatment and persistence of labelled NK cells in vivo.

CONCLUSIONS

NK cell homing and cytotoxicity are increased following RT in canine models of sarcoma. Results from a first-in-dog clinical trial are promising, including possible abscopal effects.

Ex vivo expanded natural killer cells from breast cancer patients and healthy donors are highly cytotoxic against breast cancer cell lines and patient-derived tumours

BACKGROUND

Natural killer (NK) cells play a critical role in cancer immunosurveillance. Recent developments in NK cell ex-vivo expansion makes it possible to generate millions of activated NK cells from a small volume of peripheral blood. We tested the functionality of ex vivo expanded NK cells in vitro against breast cancer cell lines and in vivo using a xenograft mouse model. The study aim was to assess functionality and phenotype of expanded NK cells from breast cancer patients against breast cancer cell lines and autologous primary tumours.

METHODS

We used a well-established NK cell co-culture system to expand NK cells ex vivo from healthy donors and breast cancer patients and examined their surface marker expression. Moreover, we tested the ability of expanded NK cells to lyse the triple negative breast cancer and HER2-positive breast cancer cell lines MDA-MB-231 and MDA-MB-453, respectively. We also tested their ability to prevent tumour growth in vivo using a xenograft mouse model. Finally, we tested the cytotoxicity of expanded NK cells against autologous and allogeneic primary breast cancer tumours in vitro.

RESULTS

After 3 weeks of culture we observed over 1000-fold expansion of NK cells isolated from either breast cancer patients or healthy donors. We also showed that the phenotype of expanded NK cells is comparable between those from healthy donors and cancer patients. Moreover, our results confirm the ability of ex vivo expanded NK cells to lyse tumour cell lines in vitro. While the cell lines examined had differential sensitivity to NK cell killing we found this was correlated with level of major histocompatibility complex (MHC) class I expression. In our in vivo model, NK cells prevented tumour establishment and growth in immunocompromised mice. Finally, we showed that NK cells expanded from the peripheral blood of breast cancer patients show high cytotoxicity against allogeneic and autologous patient-derived tumour cells in vitro.

CONCLUSION

NK cells from breast cancer patients can be expanded similarly to those from healthy donors, have a high cytotoxic ability against breast cancer cell lines and patient-derived tumour cells, and can be compatible with current cancer treatments to restore NK cell function in cancer patients.