Natural Killer Cell Line NK-92 Research Articles

Abstract LB069: Repurposing anti-mesothelin CAR-NK immunotherapy against colorectal cancer

Abstract Colorectal cancer (CRC) is the third most common cancer worldwide, with highly variable prognosis and response to treatment. A large subset of patients does not respond to standard treatments or develops resistance. As an alternative, adoptive immunotherapy based on chimeric antigen receptor (CAR)-transduced immune cells has been proposed, however with significant adverse events. We therefore evaluated alternative CAR targets already tested in other tumour types, and employed the natural killer cell line NK-92 for CAR transduction because of its more favourable toxicity profile. As an alternative antigen, we considered mesothelin (MSLN), the most represented in CAR-based clinical studies for solid tumours. MSLN RNA expression was analysed in large series of CRC patient-derived xenografts (PDXs, n=500), cell lines (n=150) and tumours (n=640), to evaluate its distribution and to identify MSLN-overexpressing models. NK-92 cells were transduced with anti-MSLN CAR, and subsequently sorted and cloned. Activity of CAR-NK-92 cells against target-expressing ovarian and CRC cells was assessed in vitro and in vivo. Statistical significance of efficacy was evaluated by t-test. The large-scale expression analysis highlighted that about 10% of CRCs overexpress MSLN at levels comparable to those of ovarian cancer, a typical target of MSLN-CAR-based therapy. Intriguingly, MSLN overexpression is more frequent in the CRIS-B poor prognosis subtype and KRAS/BRAF-mutant CRC. Lentiviral transduction of NK-92 cells with the MSLN-CAR, followed by sorting and cloning, led to the identification of one clone, NK-92cl45, stably expressing the CAR and retaining the NK phenotype. As expected, the clone demonstrated significant in vitro and in vivo activity against ovarian cancer cells. When repurposed against models of CRC expressing high MSLN levels, it displayed comparable efficacy, both in vitro and in vivo. Specificity of NK-92cl45 was confirmed by the absence of activity on control models with low or absent MSLN. Our results provide preclinical evidence that a subset of colorectal cancers expressing high mesothelin levels can be effectively targeted by MSLN-CAR-based immunotherapy. The potential therapeutic impact of these findings is enhanced by the fact that frequently MSLN-overexpressing CRCs display worse prognosis and resistance to standard care. Citation Format: Erica Torchiaro, Marco Cortese, Alice D'Andrea, Consalvo Petti, Enzo Medico. Repurposing anti-mesothelin CAR-NK immunotherapy against colorectal cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 2 (Late-Breaking, Clinical Trial, and Invited Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(7_Suppl):Abstract nr LB069.

Abstract 3998: Preclinical efficacy of a synthetic Notch-based combinatorial immunotherapy against colorectal cancer with HER2 amplification

Abstract HER2 amplification occurs in about 5% of colorectal cancers (CRC) and is only partially associated with clinical response to combined HER2/EGFR targeted treatment. An alternative approach, based on Adoptive Cell Therapy (ACT) using T cells engineered with anti-HER2 Chimeric Antigen Receptor (CAR), proved toxic due to "on-target off-tumor" activity. Therefore, we developed a combinatorial ACT strategy to safely target HER2 amplification in CRC using a synNotch-based artificial regulatory network. A synthetic Notch receptor was employed in which the extracellular domain is an anti-HER2 scFv and the intracellular domain contains the GAL4VP64 artificial transcription factor. Engagement of the HER2-synNotch by overexpressed HER2 on the surface of target cells induces GAL4VP64 cleavage and translocation to the nucleus, where it drives expression of a CAR under a GAL4-responsive promoter. In this way, only cells co-expressing both HER2 and the CAR target are killed. Carcinoembryonic antigen (CEA) was selected as a colon-specific CAR target: CEA expression is indeed restricted to the digestive tract and is increased in CRC. The natural killer cell line NK-92 was chosen as effector to be engineered. NK-92 cells transduced with HER2-synNotch and inducible CEA-CAR lentiviral vectors were subsequently sorted in the OFF and ON state to select those with the higher CAR induction after synNotch engagement. Subsequently, cloning of sorted cells led to identification of an optimally responsive clone (clone 5F), in terms of specificity and amplitude of CAR induction. The 5F clone demonstrated significant activity in vitro and in vivo specifically against HER2amp CRC models, with no effects on cells with physiological HER2 levels. In vitro, the 5F clone displayed selective cytotoxicity against HER2amp/CEA+ CRC cells, with minimal killing activity against HER2amp/CEA- cells, or HER2norm/CEA+ cells. Additional assays on 3D organoids highlighted better recruitment and infiltration by the 5F clone respect to NK-92 WT cells, only in HER2amp models. In vivo, NK-92.5F significantly impaired tumor growth in two different HER2amp CRC models, with no effect on HER2norm CRC cells. To further improve survival, tumor penetration and in vivo efficacy of the NK-92.5F clone, a more complex system was built, in which HER2 synNotch engagement drives expression of both the CEA-CAR and IL2. 5F-IL2 cells displayed further increased cytotoxicity in vitro. In vivo, 5F-IL2 cells drastically increased survival of mice carrying HER2amp CRC xenografts with respect to the parental 5F clone. The observed selective therapeutic efficacy both in vitro and in vivo of this innovative HER2 synNotch/CEA-CAR system, and its future evolutions, opens perspectives for possible clinical applications in cases of HER2amp CRC resistant or partially responsive to HER2/EGFR blockade. Citation Format: Marco Cortese, Erica Torchiaro, Alice D'Andrea, Consalvo Petti, Federica Invrea, Letizia Franco, Chiara Donini, Valeria Leuci, Simonetta M. Leto, Valentina Vurchio, Francesca Cottino, Claudio Isella, Sabrina Arena, Elisa Vigna, Andrea Bertotti, Livio Trusolino, Dario Sangiolo, Enzo Medico. Preclinical efficacy of a synthetic Notch-based combinatorial immunotherapy against colorectal cancer with HER2 amplification [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 3998.

Successful expansion and cryopreservation of human natural killer cell line NK-92 for clinical manufacturing.

Natural killer (NK) cells have recently shown renewed promise as therapeutic cells for use in treating hematologic cancer indications. Despite this promise, NK cell manufacturing workflows remain largely manual, open, and disconnected, and depend on feeders, as well as outdated unit operations or processes, often utilizing research-grade reagents. Successful scale-up of NK cells critically depends on the availability and performance of nutrient-rich expansion media and cryopreservation conditions that are conducive to high cell viability and recovery post-thaw. In this paper we used Cytiva hardware and media to expand the NK92 cell line in a model process that is suitable for GMP and clinical manufacturing of NK cells. We tested a range of cryopreservation factors including cooling rate, a range of DMSO-containing and DMSO-free cryoprotectants, ice nucleation, and cell density. Higher post-thaw recovery was seen in cryobags over cryovials cooled in identical conditions, and cooling rates of 1°C/min or 2°C/min optimal for cryopreservation in DMSO-containing and DMSO-free cryoprotectants respectively. Higher cell densities of 5x107 cells/ml gave higher post-thaw viability than those cryopreserved at either 1x106 or 5x106 cells/ml. This enabled us to automate, close and connect unit operations within the workflow while demonstrating superior expansion and cryopreservation of NK92 cells. Cellular outputs and performance were conducive to clinical dosing regimens, serving as a proof-of-concept for future clinical and commercial manufacturing.

SETDB1 Suppresses Interferon Responses and NK Cell-Mediated Immunosurveillance Specifically in Monocytic AML

Acute myeloid leukemia (AML) with monocytic differentiation (monocytic AML) responds poorly to current treatments, including venetoclax-based therapy. To identify novel therapeutic targets in monocytic AML, we conducted in vivo and in vitro CRISPR/Cas9 library screens using a pooled sgRNA library targeting epigenetic regulators with a mouse monocytic AML model driven by SETBP1 and ASXL1 mutations (cSAM: combined expression of SETBP1 and ASXL1 Mutations). We ranked all the epigenetic genes according to the in vivo specific essentiality, and selected several candidates which were more depleted in mice rather than in cell cultures. The top-ranked gene was Setdb1, which encodes a histone H3 lysine 9 (H3K9) methyltransferase. In addition, several H3K9 trimethylation (H3K9me3) regulators, ATF7IP and TRIM33, were also more important in vivo than in vitro in our screens. ATF7IP is a cofactor of SETDB1 to enhance its enzymatic activity. TRIM33 is also involved in H3K9me3 modification. These data suggest the critical role of the SETDB1-ATF7IP-TRIM33 H3K9 methyltransferase complex in the development of AML in vivo. To validate the results of our screenings and to investigate the role of immune cells in our transplantation assay, we next transplanted control and Setdb1-knockout (KO) cSAM cells into three types of mice with different immune systems: the immunocompetent C57BL/6 mice, the immunodeficient NSG mice lacking T, B and natural killer (NK) cells, and the C57BL/6J- Rag2-/- mice lacking mature T and B cells but possessing NK cells. Although Setdb1 depletion did not inhibit the growth of cSAM cells in NSG mice, it showed the strong growth-inhibitory effect in C57BL/6 mice and Rag2-/- mice (Fig 1A). Since both C57BL/6 mice and Rag2-/- mice have NK cells, these data suggest that SETDB1 promotes leukemogenesis by suppressing NK cell-mediated cytotoxicity in vivo. Mechanistically, loss of Setdb1 induced upregulation of NKG2D ligands, interferon-stimulated genes (ISGs), and endogenous retrovirus (ERV) sequences through H3K9me3 reduction, thereby rendering cSAM cells more susceptible to NK cell-mediated cytotoxicity. Setdb1 depletion also induced myeloid maturation of cSAM cells towards macrophages and downregulation of major histocompatibility complex class I (MHC-I), which contributed to the increased susceptibility of Setdb1-depleted cSAM cells to NK cell-mediated cytotoxicity. Next, we investigated whether SETDB1 inactivation also sensitizes human AML cells to NK cells using the co-culture assay with an IL-2 dependent NK cell line NK-92. Loss of SETDB1 rendered monocytic AML cell lines, NOMO-1, THP-1, OCI-AML3, U937, and NB4, more susceptible to NK-92 cell-mediated cytotoxicity. SETDB1 depletion also induced overactivation of interferon signaling and intrinsic apoptosis in these monocytic AML cells. In contrast, non-monocytic AML cells, such as K562, TF-1, and Kasumi-1, were not sensitive to SETDB1 depletion. SETDB1 depletion neither increased the susceptibility to NK cell-mediated cytotoxicity nor induced apoptosis in non-monocytic AML cells. Subsequent analyses revealed that SETDB1 depletion reduced H3K9me3 at the monocyte-specific enhancer regions with ERV sequences to upregulate NK cell-activating ligands and ISGs. Because the “ERV enhancers” are active only in monocyte lineage, SETDB1 is essential specifically in monocytic AML. Finally, we identified MNDA and its mouse counterpart Ifi203 as biomarkers to predict the sensitivity of each AML to SETDB1 depletion. MNDA is one of the ISGs and is involved in myeloid cell differentiation. Human monocytic AML cells that are dependent on SETDB1 expressed higher MNDA at both RNA and protein levels compared to other subtypes of AML. We also found that Ifi203-high mouse AML cells transformed by MLL-AF9 were sensitive to Setdb1 depletion, whereas Setdb1 was dispensable in Ifi203-low mouse AML cells transformed by RUNX1-RUNX1T1. In summary, our findings reveal the critical and selective role of SETDB1 in monocytic AML. SETDB1 mediates H3K9me3 at the monocyte-specific ERV enhancers to repress the expression of NK cell-activating ligands and ISGs, thereby suppressing immunogenicity and apoptosis in monocytic AML (Fig 1B). SETDB1 as well as its binding partners could be promising therapeutic targets to treat monocytic AMLs that are relatively resistant to the current standard therapies.

Reovirus infection of tumor cells reduces the expression of NKG2D ligands, leading to impaired NK-cell cytotoxicity and functionality.

In recent years, reoviruses have been of major interest in immunotherapy because of their oncolytic properties. Preclinical and clinical trials, in which reovirus was used for the treatment of melanoma and glioblastoma, have paved the way for future clinical use of reovirus. However, little is known about how reovirus infection affects the tumor microenvironment and immune response towards infected tumor cells. Studies have shown that reovirus can directly stimulate natural killer (NK) cells, but how reovirus affects cellular ligands on tumor cells, which are ultimately key to tumor recognition and elimination by NK cells, has not been investigated. We tested how reovirus infection affects the binding of the NK Group-2 member D (NKG2D) receptor, which is a dominant mediator of NK cell anti-tumor activity. Using models of human-derived melanoma and glioblastoma tumors, we demonstrated that NKG2D ligands are downregulated in tumor cells post-reovirus-infection due to the impaired translation of these ligands in reovirus-infected cells. Moreover, we showed that downregulation of NKG2D ligands significantly impaired the binding of NKG2D to infected tumor cells. We further demonstrated that reduced recognition of NKG2D ligands significantly alters NK cell anti-tumor cytotoxicity in human primary NK cells and in the NK cell line NK-92. Thus, this study provides novel insights into reovirus-host interactions and could lead to the development of novel reovirus-based therapeutics that enhance the anti-tumor immune response.

ErbB2 (HER2)-CAR-NK-92 cells for enhanced immunotherapy of metastatic fusion-driven alveolar rhabdomyosarcoma.

Metastatic rhabdomyosarcoma (RMS) is a challenging tumor entity that evades conventional treatments and endogenous antitumor immune responses, highlighting the need for novel therapeutic strategies. Applying chimeric antigen receptor (CAR) technology to natural killer (NK) cells may offer safe, effective, and affordable therapies that enhance cancer immune surveillance. Here, we assess the efficacy of clinically usable CAR-engineered NK cell line NK-92/5.28.z against ErbB2-positive RMS in vitro and in a metastatic xenograft mouse model. Our results show that NK-92/5.28.z cells effectively kill RMS cells in vitro and significantly prolong survival and inhibit tumor progression in mice. The persistence of NK-92/5.28.z cells at tumor sites demonstrates efficient antitumor response, which could help overcome current obstacles in the treatment of solid tumors. These findings encourage further development of NK-92/5.28.z cells as off-the-shelf immunotherapy for the treatment of metastatic RMS.

Dysregulation of natural killer cells’ receptor expression and cytotoxic function by hydroxychloroquine

Abstract Background and Aim: Natural killer (NK) cells are crucial players of the innate immune system, especially in the fight against tumors and infections. Besides, NK cells are known to contribute in inflammatory processes associated with multiple diseases. The drug hydroxychloroquine (HCQ) has been repurposed to be used for the treatment of malaria, autoimmune diseases, and COVID-19 infection. However, its direct mechanism of action on NK cells remains unknown. In this study, we aimed to examine the effects of HCQ on NK cell activity and function. Materials and Methods: The human NK cell line NK92 was cultured and treated with HCQ at 1, 5, and 10 μM for 24 and 48 hours. Then, NK92 cell viability, NKG2D and CD107a expression, as well as NK92 cell cytotoxicity were assessed. Also, IFN-γ production was measured by ELISA after HCQ treatment. Statistical analysis was performed where p<0.05 was considered statistically significant. Results: Upon treatment with different concentrations of HCQ for 48 hours, NK92 cell viability significantly decreased in a dose-dependent manner, with the lowest viability noted at 10 μM of HCQ. Additionally, NKG2D and CD107a expression were significantly reduced upon treatment with 5 and 10 μM of HCQ. Similarly, the cytotoxicity of NK92 cells against K562 cells was reduced at both 5:1 and 10:1, effector to target (E: T) cell ratios, when 10 μM HCQ was used. In contrast, IFN-γ levels were significantly increased upon the treatment with 1, 5, and 10 μM HCQ. Conclusion: This study highlights the effect of HCQ on activating receptor expression, cytotoxicity, and IFN-γ production of NK cells. Despite being an immunomodulatory drug, more studies are needed to further understand HCQ’s effects on NK cells and perhaps other effector cells. None

Abstract LB091: Design, characterization and preclinical validation of a combinatorial CAR-based immunotherapy against colorectal cancer with HER2 amplification

Abstract Adoptive immunotherapy based on chimeric antigen receptor (CAR)-T cells has led to successful treatment of some hematological malignancies, but it remains extremely challenging for solid tumors, mostly because of “on-target off-tumor” toxicity, as observed in the case of anti-HER2 CAR-T treatment of colorectal cancer (CRC) with HER2 amplification. To enable adoptive immunotherapy against HER2-amplified CRC, we therefore considered a combinatorial strategy based on the synNotch-based artificial regulatory network. A synthetic Notch receptor was employed in which the extracellular domain is an anti-HER2 scFv and the intracellular domain contains the GAL4-VP64 artificial transcription factor. Engagement of the anti-HER2 domain by target cells drives GAL4-VP64 cleavage and translocation to the nucleus, where it drives expression of a CAR under a GAL4-responsive promoter. In this way, only cells co-expressing both HER2 and the CAR target are killed. As a CRC-specific CAR target we selected CEA, product of the CEACAM5 gene. CEA expression is restricted to the digestive tract and is increased in cancer. For the generation of HER2-synNotch CEA-CAR effectors, we chose the natural killer cell line NK-92 and transduced it with two lentiviral vectors, encoding respectively the HER2 synNotch and the second-generation anti-CEA CAR with CD28 costimulatory domain. Transduced cells were repeatedly sorted in the ON and OFF state to select those with the best CAR induction after synNotch engagement; cloning of sorted cells led to identification of an optimally responsive clone (clone 5F), showing no basal CEA-CAR expression and massive induction in the presence of HER2-overexpressing cancer cells. In vitro, the 5F clone displayed selective cytotoxicity against HER2++/CEA++ CRC cells, with minimal killing activity against HER2++/CEA- breast cancer cells, or against CRC cells expressing CEA but without HER2 amplification. In vitro 3D models highlighted better recruitment and infiltration by NK-92 clone 5F respect to NK-92 WT cells, only of HER2++ organoids. In vivo, the clone 5F significantly impaired tumor growth in two different HER2++ CRC models. The observed selective efficacy both in vitro and in vivo of the HER2-synNotch/CEA-CAR approach opens a perspective for possible clinical applications in cases of HER2-amplified CRC displaying primary or secondary resistance to HER2/EGFR blockade. Citation Format: Marco Cortese, Erica Torchiaro, Federica Invrea, Consalvo Petti, Alice D'Andrea, Sabrina Arena, Enzo Medico. Design, characterization and preclinical validation of a combinatorial CAR-based immunotherapy against colorectal cancer with HER2 amplification [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 2 (Clinical Trials and Late-Breaking Research); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(8_Suppl):Abstract nr LB091.

Efficient Redirection of NK Cells by Genetic Modification with Chemokine Receptors CCR4 and CCR2B

Natural killer (NK) cells are a subset of lymphocytes that offer great potential for cancer immunotherapy due to their natural anti-tumor activity and the possibility to safely transplant cells from healthy donors to patients in a clinical setting. However, the efficacy of cell-based immunotherapies using both T and NK cells is often limited by a poor infiltration of immune cells into solid tumors. Importantly, regulatory immune cell subsets are frequently recruited to tumor sites. In this study, we overexpressed two chemokine receptors, CCR4 and CCR2B, that are naturally found on T regulatory cells and tumor-resident monocytes, respectively, on NK cells. Using the NK cell line NK-92 as well as primary NK cells from peripheral blood, we show that genetically engineered NK cells can be efficiently redirected using chemokine receptors from different immune cell lineages and migrate towards chemokines such as CCL22 or CCL2, without impairing the natural effector functions. This approach has the potential to enhance the therapeutic effect of immunotherapies in solid tumors by directing genetically engineered donor NK cells to tumor sites. As a future therapeutic option, the natural anti-tumor activity of NK cells at the tumor sites can be increased by co-expression of chemokine receptors with chimeric antigen receptors (CAR) or T cell receptors (TCR) on NK cells can be performed in the future.

Na+/H+-exchanger 1 enhances antitumor activity of engineered NK-92 natural killer cells.

Adoptive cell transfer (ACT) immunotherapy has remarkable efficacy against some hematological malignancies. However, its efficacy in solid tumors is limited by the adverse tumor microenvironment (TME) conditions, most notably that acidity inhibits T and natural killer (NK) cell mTOR complex 1 (mTORC1) activity and impairs cytotoxicity. In several reported studies, systemic buffering of tumor acidity enhanced the efficacy of immune checkpoint inhibitors. Paradoxically, we found in a c-Myc-driven hepatocellular carcinoma model that systemic buffering increased tumor mTORC1 activity, negating inhibition of tumor growth by anti-PD1 treatment. Therefore, in this proof-of-concept study, we tested the metabolic engineering of immune effector cells to mitigate the inhibitory effect of tumor acidity while avoiding side effects associated with systemic buffering. We first overexpressed an activated RHEB in the human NK cell line NK-92, thereby rescuing acid-blunted mTORC1 activity and enhancing cytolytic activity. Then, to directly mitigate the effect of acidity, we ectopically expressed acid extruder proteins. Whereas ectopic expression of carbonic anhydrase IX (CA9) moderately increased mTORC1 activity, it did not enhance effector function. In contrast, overexpressing a constitutively active Na+/H+-exchanger 1 (NHE1; SLC9A1) in NK-92 did not elevate mTORC1 but enhanced degranulation, target engagement, in vitro cytotoxicity, and in vivo antitumor activity. Our findings suggest the feasibility of overcoming the inhibitory effect of the TME by metabolically engineering immune effector cells, which can enhance ACT for better efficacy against solid tumors.

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

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

Abstract 3147: Natural killer cells mediate tumor-inhibitory functions of USP6 in Ewing sarcoma

Abstract INTRODUCTION: Understanding how Natural Killer (NK) cell activity is regulated by cancer cells is critical for developing NK-cell based immunotherapies. Our studies show that the deubiquitinating enzyme ubiquitin-specific protease-6 (USP6) can induce an immune-stimulatory hot tumor microenvironment in Ewing sarcoma (ES), the 2nd most common pediatric bone cancer. High USP6 expression in ES is associated with significantly improved overall and progression-free survival. We found that USP6 expression in ES cells inhibits xenograft growth in nude mice, but not NSG mice, implicating a role for the innate immune system, particularly cytotoxic NK cells. Notably, USP6 expression enhanced intra-tumoral abundance, activation, and proliferative capacity of NK cells. In vitro cytotoxicity assays confirm that USP6 can directly augment the ability of ES cells to activate NK cells. Based on these observations, we hypothesize that NK cells are essential for USP6-mediated tumor suppression and seek to determine the mechanism by which their cytolytic function is activated by USP6. METHOD: We used ES cell lines A673 and RD-ES expressing USP6 in a doxycycline (dox)-inducible manner, the immortalized human NK cell line NK-92, and primary human and mouse NK cells. Athymic nude or RAG2-/- mice were xenografted subcutaneously with ES cell lines and fed dox-infused water to induce USP6. Immune cell abundance and activation were monitored both in tumors and peripheral blood by flow cytometry. For in vivo depletion of NK cells, 300ug of anti-NK1.1 (PK136) ab was injected i.p. into RAG2-/- mice one day prior to ES xenografting, then once weekly thereafter. RESULTS: USP6 induces in ES cells the surface expression of multiple NK activating ligands, as well as receptors for the apoptotic factor TRAIL (DR5) and Type I/II interferons (IFNAR1 and IFNGR1), both in vitro and in vivo. This leads to enhanced NK activation and renders ES cells hypersensitive to NK-mediated cytotoxicity. IFNy released by activated NK cells feeds back on the USP6-expressing ES cells, inducing synergistic expression of multiple IFNy-inducible genes, including chemokines CXCL9/10 (chemoattractants for NK cells) and ICAM-1 (essential for immunological synapse formation between NK cells and their targets). A potent feed forward loop for NK activation/ES cell killing is thus generated. Concordantly, in RAG2-/- mice, USP6 induces increased intratumoral infiltration and activation of NK cells, and also, strikingly, systemic activation of NK cells. Depletion of NK cells using anti-NK1.1(PK136) completely abrogates USP6-mediated inhibition of ES xenograft growth. CONCLUSION: NK cells are essential for mediating the tumor inhibitory functions of USP6 in ES. We posit that USP6’s ability to activate NK cells both intratumorally and systemically underlies its association with improved ES patient prognosis, which we seek to exploit for therapeutic benefit in future studies. Citation Format: Kanika Jain, Ian C. Henrich, Laura Nicole Quick, Robert A. Young, Margaret M. Chou. Natural killer cells mediate tumor-inhibitory functions of USP6 in Ewing sarcoma [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 3147.

Examination of IgG Fc Receptor CD16A and CD64 Expression by Canine Leukocytes and Their ADCC Activity in Engineered NK Cells.

Human natural killer (NK) cells can target tumor cells in an antigen-specific manner by the recognition of cell bound antibodies. This process induces antibody-dependent cell-mediated cytotoxicity (ADCC) and is exclusively mediated by the low affinity IgG Fc receptor CD16A (FcγRIIIA). Exploiting ADCC by NK cells is a major area of emphasis for advancing cancer immunotherapies. CD64 (FcγRI) is the only high affinity IgG FcR and it binds to the same IgG isotypes as CD16A, but it is not expressed by human NK cells. We have generated engineered human NK cells expressing recombinant CD64 with the goal of increasing their ADCC potency. Preclinical testing of this approach is essential for establishing efficacy and safety of the engineered NK cells. The dog provides particular advantages as a model, which includes spontaneous development of cancer in the setting of an intact and outbred immune system. To advance this immunotherapy model, we cloned canine CD16A and CD64 and generated specific mAbs. We report here for the first time the expression patterns of these FcγRs on dog peripheral blood leukocytes. CD64 was expressed by neutrophils and monocytes, but not lymphocytes, while canine CD16A was expressed at high levels by a subset of monocytes and lymphocytes. These expression patterns are similar to that of human leukocytes. Based on phenotypic characteristics, the CD16A+ lymphocytes consisted of T cells (CD3+ CD8+ CD5dim α/β TCR+) and NK cells (CD3− CD5− CD94+), but not B cells. Interestingly, the majority of canine CD16A+ lymphocytes were from the T cell population. Like human CD16A, canine CD16A was downregulated by a disintegrin and metalloproteinase 17 (ADAM17) upon leukocyte activation, revealing a conserved means of regulation. We also directly demonstrate that both canine CD16A and CD64 can induce ADCC when expressed in the NK cell line NK-92. These findings pave the way to engineering canine NK cells or T cells with high affinity recombinant canine CD64 to maximize ADCC and to test their safety and efficacy to benefit both humans and dogs.

Senolytics in a Model of Alzheimer's Disease

The therapeutic effects of senescent cell killing with senolytics in neurodegeneration mouse models poise this strategy as an intervention candidate for Alzheimer’s Disease (AD). However, it is unclear whether senolytic therapies for AD are translatable to human cells. To determine whether senolytics could be a viable therapeutic for AD, we have treated long-term mixed human neuron/astrocyte primary cultures with amyloid beta oligomers (ABO), which we have shown to induce a phenotype consistent with senescence in neurons. Fifteen days after ABO treatment, we administered Navitoclax (Nav) and the natural killer cell-line NK92, which are known to selectively kill senescent cells in the periphery. Following treatment, we assessed senescence markers in our cultures as well as senescent cell killing selectivity through cleaved Caspase 3 quantification. Our preliminary data show that Nav (8, 4, and 0.5uM) kills both control and ABO treated cells. NK92 cells (10 to 1 effector to target ratio) also kill some control cells, suggesting there is not a clear cut mechanism by which NK92 cells can distinguish senescent from non-senescent neurons or astrocytes. Although analysis of selective killing is ongoing, off-target killing indicates that we need more refined senolytic strategies to implement their safe human use.

Selective Cytotoxicity of Single and Dual Anti-CD19 and Anti-CD138 Chimeric Antigen Receptor-Natural Killer Cells against Hematologic Malignancies.

Natural killer (NK) cells are part of the first line of defense that rapidly respond to malignant transformed cells. Chimeric antigen receptor- (CAR-) engineered NK cells, although are still at the preliminary stage, have been shown to be alternative to CAR-T cells, mainly due to the absence of graft-versus-host disease and safer clinical profile. Allogeneic human NK cell line NK-92 cells, equipped by CAR, are being developed for clinical applications. Herein, we designed third-generation CARs, optimized the production protocol, and generated CAR-NK-92 cells, targeting CD19 and/or CD138 antigens that employ CD28, 4-1BB, and CD3ζ signaling, with >80% CAR expression, designated as CD19-NK-92, CD138-NK-92, and dual-NK-92 cells. The generated CAR-NK-92 cells displayed high and selective cytotoxicity toward various corresponding leukemia, lymphoma, and multiple myeloma cell lines in vitro. Multitargeting approach using a mixture of CD19-NK-92 and CD138-NK-92 cells was also evaluated at various ratios to test the idea of personalized formulation to match the patients' antigen expression profile. Our data indicate that increasing the ratio of CD19-NK-92 to CD138-NK-92 could improve NK cytotoxicity in leukemia cells with a relatively higher expression of CD19 over CD138, supporting the personalized proof of concept. This information represents the basis for further in vivo studies and future progress to clinical trials.

Human IL-15 Inhibits NK Cells Specific for Human NK-92 Cells

Recent studies have indicated that natural killer (NK) cells present in peripheral blood mononuclear cells (PBMCs) might be responsible for the somewhat poor outcome of clinical trials conducted with the NK cell line NK-92, as well as chimeric antigen receptor-modified NK-92 cells against leukemias and lymphomas. These NK cells and how their cytotoxic profiles can be altered by some common gamma chain receptor-dependent cytokines or by removal of CD4+ cells have been addressed herein. A time-resolved fluorometric assay using 2.2':6'.2"-terpyridine-6.6"-dicarboxylic acid-labeled NK-92 or K562 as target cells was used for measuring the cytotoxic activity of cytokine-treated PBMCs and purified NK cells. Pre-incubation with 25 ng/ml interleukin 12 (IL-12), IL-15 or IL-21 for 72 h increased NK cell activity against K562 cells by more than 90% (1:25 target:effector ratio), whereas the corresponding NK cell activity against NK-92 cells was reduced by 15.9±0.1% by IL-12 and 50.6±2.9% by IL-15 compared to cells treated with medium alone. IL-7, on the other hand, increased NK activity against K562 to a much smaller extent (10.4±0.4%) and inhibited NK-92 cell lysis by 15.2±0.3%. Interestingly, similar amounts of IL-2 potentiated NK cell activity against both K562 and NK-92 cells by 50.9±0.5% and 14.3±0.9%, respectively. Purification of NK cells with magnetic beads demonstrated that NK cells indeed were responsible for the observed cytotoxic activity against both NK-92 cells (58.5±9.10%, 1:100 target:effector ratio) and K562 cells (81.6±9.57%, 1:100 target:effector ratio). Elimination of CD4+ cells from PBMCs did not alter the NK activity profile. This study highlights a problem that might arise with immune-based NK-92 and chimeric antigen receptor-transduced NK-92 cell therapies and pinpoints the need for evaluating new NK-like cell lines.

Targeting T-Cell Malignancies with Chimeric Antigen Receptors Using Two Structurally Different Antigen Binding Domains Against CD5

Patients with relapsed T-cell acute lymphoblastic leukemia (T-ALL) have extremely poor survival when treated with chemotherapy alone. Allogeneic hematopoietic stem cell transplantation (HSCT) offers a chance of cure for these patients, but attaining clinical remission in order to undergo HSCT remains the biggest therapeutic challenge. Chimeric antigen receptor (CAR) T-cell therapy has been used with great success in relapsed/refractory B-ALL patients. The same approach, however, is difficult in targeting T-cell disease given the lack of a T-lymphoblast specific surface antigen. The use of natural killer (NK) cells as the effector cell provides a potential solution. We are testing two different CAR structures directed against CD5, a pan T-cell marker; one consisting of a more traditional immunoglobulin (Ig) based single chain variable fragment (scFv), while the other comprising of a variable lymphocyte receptor (VLR) as the antigen recognition domain. VLRs are single chain crescent shaped proteins that represent the functional unit of the adaptive immune system in jawless vertebrates. Our previous work has shown that a VLR can be used as an alternative for CAR-based antigen recognition. Here, we directly compare a VLR to its scFv counterpart in a CAR setting. The single chain structure of a VLR allows for the rapid creation of novel CARs, compared to the corresponding use of a scFv-CAR, in which the variable heavy and light sequences need further engineering for adapting to CAR technologies. Thus, our hypothesis was that natural killer cells engineered to express an anti-CD5 CAR can specifically be used to target T-cell malignancies, with the VLR-CAR being equal or superior to scFv-based cassettes. We constructed two second generation CARs using the VLR or scFv sequence targeting CD5 as our antigen recognition domain. Both CD5-CAR constructs showed similar activity when tested in CD5-positive Jurkat cells. For our cytotoxicity studies, we used the IL-2 dependent natural killer cell line NK-92. To generate uniform populations of CAR-expressing NK cells we transduced NK-92 cells with a dual lentiviral construct expressing the CD5-CAR and green fluorescent protein (GFP), and then selected for the positively transduced cells using flow sorting for GFP. In vitro cytotoxicity studies showed significantly increased killing using the CD5-CAR expressing NK-92 cells compared to unmodified NK-92 cells (p<0.05), for both VLR and scFv modified cells. We then tested the two CD5-CARs in a T-cell leukemia mouse model. NOD scid gamma (NSG) mice were intravenously injected with luciferase expressing Jurkat leukemia cells to establish the T-cell leukemia xenograft model. Four doses of NK-92 cells were injected over a two week period starting on day 7 post-tumor injection. Bioluminescence imaging was used to monitor tumor burden. The CD5-scFv-CAR NK-92 treated mice group had a significant survival advantage over the other groups (p<0.01). Interestingly, the CD5-VLR-CAR NK-92 treated mice did not have a significant advantage over naïve NK-92 or saline treated groups. Given the superior in vivo cytotoxicity demonstrated in our studies, we plan to use the CD5-scFV-CAR going forward as we transition to primary cells. Overall, these studies provide the foundation to move these studies into preclinical testing as a treatment for relapsed T-ALL. DisclosuresNo relevant conflicts of interest to declare.

Impact of phytochemicals and plant extracts on viability and proliferation of NK cell line NK-92 - a closer look at immunomodulatory properties of goji berries extract in human colon cancer cells.

Due to the fact that lymphocytes NK (natural killer cells) are the first line of defence of the body against cancer, one of the goals of modern immunotherapy is the enhancement of their natural activities for the effective recognition, detection, and elimination of cancer cells. The aim of the study was to evaluate the influence of selected phytochemicals (curcumin and resveratrol) and plant extracts (chlorella and goji berries) on NK cells viability and proliferation, as well as cytotoxic activity against colon cancer - one of the most common cancer worldwide. The impact of phytochemicals, viability and proliferation of plant extracts on NK cells was examined in NK-92 cells using both LDH and MTT assays. The immunomodulatory properties of selected compounds were tested against human colon cancer cell line LS180 using the MTT test. Extracts of chlorella and goji berries significantly increased NK cell proliferation, while curcumin and resveratrol did not affect this process. Curcumin, as well as extracts of chlorella and goji berries, did not impact NK viability, while resveratrol significantly increased it. LDH test revealed the cytotoxic effect of chlorella extract and curcumin in NK-92 cell cultures. On the contrary, goji berries extract significantly decreased LDH level, while resveratrol did not affect the integrity of NK cell membranes. Studies conducted in co-cultures NK cells, also directly eliminated colon cancer cells. Performed studies revealed immunomodulatory properties of goji berries extract, which improved viability and proliferation of NK cells, and above all, significantly increased their ability to recognize and eliminate colon cancer cells.

Sialylation of Human Natural Killer (NK) Cells is Regulated by IL-2.

Sialic acids are terminal sugars on the cell surface that are found on all cell types including immune cells like natural killer (NK) cells. The attachment of sialic acids to different glycan structures is catalyzed by sialyltransferases in the Golgi. However, the expression pattern of sialyltransferases in NK cells and their expression after activation has not yet been analyzed. Therefore, the present study determines which sialyltransferases are expressed in human NK cells and if activation with IL-2 changes the sialylation of NK cells. The expression of sialyltransferases was analyzed in the three human NK cell lines NK-92, NKL, KHYG-1 and primary NK cells. NK-92 cells were cultured in the absence or presence of IL-2, and changes in the sialyltransferase expression were measured by qPCR. Furthermore, specific sialylation was investigated by flow cytometry. In addition, polySia and NCAM were measured by Western blot analyses. IL-2 leads to a reduced expression of ST8SIA1, ST6GAL1 and ST3GAL1. α-2,3-Sialylation remained unchanged, while α-2,6-sialylation was increased after IL-2 stimulation. Moreover, an increase in the amount of NCAM and polySia was observed in IL-2-activated NK cells, whereas GD3 ganglioside was decreased. In this study, all sialyltransferases that were expressed in NK cells could be identified. IL-2 regulates the expression of some sialyltransferases and leads to changes in the sialylation of NK cells.

\u201cUniCAR\u201d-modified off-the-shelf NK-92 cells for targeting of GD2-expressing tumour cells

Antigen-specific redirection of immune effector cells with chimeric antigen receptors (CARs) demonstrated high therapeutic potential for targeting cancers of different origins. Beside CAR-T cells, natural killer (NK) cells represent promising alternative effectors that can be combined with CAR technology. Unlike T cells, primary NK cells and the NK cell line NK-92 can be applied as allogeneic off-the-shelf products with a reduced risk of toxicities. We previously established a modular universal CAR (UniCAR) platform which consists of UniCAR-expressing immune cells that cannot recognize target antigens directly but are redirected by a tumour-specific target module (TM). The TM contains an antigen-binding moiety fused to a peptide epitope which is recognized by the UniCAR molecule, thereby allowing an on/off switch of CAR activity, and facilitating flexible targeting of various tumour antigens depending on the presence and specificity of the TM. Here, we provide proof of concept that it is feasible to generate a universal off-the-shelf cellular therapeutic based on UniCAR NK-92 cells targeted to tumours expressing the disialoganglioside GD2 by GD2-specific TMs that are either based on an antibody-derived single-chain fragment variable (scFv) or an IgG4 backbone. Redirected UniCAR NK-92 cells induced specific killing of GD2-expressing cells in vitro and in vivo, associated with enhanced production of interferon-γ. Analysis of radiolabelled proteins demonstrated that the IgG4-based format increased the in vivo half-life of the TM markedly in comparison to the scFv-based molecule. In summary, UniCAR NK-92 cells represent a universal off-the-shelf platform that is highly effective and flexible, allowing the use of different TM formats for specific tumour targeting.