synNotch-programmed iPSC-derived NK cells usurp TIGIT and CD73 activities for glioblastoma therapy.

Severe heterogeneity within glioblastoma has spurred the notion that disrupting the interplay between multiple elements on immunosuppression is at the core of meaningful anti-tumor responses. T cell immunoreceptor with Ig and ITIM domains (TIGIT) and its glioblastoma-associated antigen, CD155, form a highly immunosuppressive axis in glioblastoma and other solid tumors, yet targeting of TIGIT, a functionally heterogeneous receptor on tumor-infiltrating immune cells, has largely been ineffective as monotherapy, suggesting that disruption of its inhibitory network might be necessary for measurable responses. It is within this context that we show that the usurpation of the TIGIT - CD155 axis via engineered synNotch-mediated activation of induced pluripotent stem cell-derived natural killer (NK) cells promotes transcription factor-mediated activation of a downstream signaling cascade that results in the controlled, localized blockade of CD73 to disrupt purinergic activity otherwise resulting in the production and accumulation of immunosuppressive extracellular adenosine. Such "decoy" receptor engages CD155 binding to TIGIT, but tilts inhibitory TIGIT/CD155 interactions toward activation via downstream synNotch signaling. Usurping activities of TIGIT and CD73 promotes the function of adoptively transferred NK cells into intracranial patient-derived models of glioblastoma and enhances their natural cytolytic functions against this tumor to result in complete tumor eradication. In addition, targeting both receptors, in turn, reprograms the glioblastoma microenvironment via the recruitment of T cells and the downregulation of M2 macrophages. This study demonstrates that TIGIT/CD155 and CD73 are targetable receptor partners in glioblastoma. Our data show that synNotch-engineered pluripotent stem cell-derived NK cells are not only effective mediators of anti-glioblastoma responses within the setting of CD73 and TIGIT/CD155 co-targeting, but represent a powerful allogeneic treatment option for this tumor.

TIGIT contributes to the regulation of 4-1BB and does not define NK cell dysfunction in glioblastoma.

TIGIT is a receptor on human natural killer (NK) cells. Here, we report that TIGIT does not spontaneously induce inhibition of NK cells in glioblastoma (GBM), but rather acts as a decoy-like receptor, by usurping binding partners and regulating expression of NK activating ligands and receptors. Our data show that in GBM patients, one of the underpinnings of unresponsiveness to TIGIT blockade is that by targeting TIGIT, NK cells do not lose an inhibitory signal, but gains the potential for new interactions with other, shared, TIGIT ligands. Therefore, TIGIT does not define NK cell dysfunction in GBM. Further, in GBM, TIGIT+ NK cells are hyperfunctional. In addition, we discovered that 4-1BB correlates with TIGIT expression, the agonism of which contributes to TIGIT immunotherapy. Overall, our data suggest that in GBM, TIGIT acts as a regulator of a complex network, and provide new clues about its use as an immunotherapeutic target.

Engineered natural killer cells impede the immunometabolic CD73-adenosine axis in solid tumors.

Immunometabolic reprogramming due to adenosine produced by CD73 (encoded by the 5'-ectonucleotidase gene NT5E) is a recognized immunosuppressive mechanism contributing to immune evasion in solid tumors. Adenosine is not only known to contribute to tumor progression, but it has specific roles in driving dysfunction of immune cells, including natural killer (NK) cells. Here, we engineered human NK cells to directly target the CD73-adenosine axis by blocking the enzymatic activity of CD73. In doing so, the engineered NK cells not only impaired adenosinergic metabolism driven by the hypoxic uptake of ATP by cancer cells in a model of non-small-cell lung cancer, but also mediated killing of tumor cells due to the specific recognition of overexpressed CD73. This resulted in a 'single agent' immunotherapy that combines antibody specificity, blockade of purinergic signaling, and killing of targets mediated by NK cells. We also showed that CD73-targeted NK cells are potent in vivo and result in tumor arrest, while promoting NK cell infiltration into CD73+ tumors and enhancing intratumoral activation.

Functional expression of CD73 on human natural killer cells.

The production of adenosine by CD73 on cancer cells in the tumor microenvironment is a recognized immunosuppressive mechanism contributing to immune evasion in many solid tumors. While NK cells have been purported to overexpress CD73 under certain conditions, this phenomenon has remained elusive and unclear. We have found that while NK cells are able to upregulate expression of CD73 on their surface when exposed to CD73+ cancer cells, this upregulation is not universal, nor is it often substantial. Rather, our data point to the extent of CD73 expression on NK cells to be both cancer-specific and environmentally-driven, and largely limited in intensity. We found that NK cell overexpression of CD73 responds to the level of CD73 on cancer cells and is enhanced in hypoxia. Interestingly, human CD73+ NK cells appear hyperfunctional in vitro compared to CD73- NK cells, suggesting that CD73 expression could be a bystander of NK cell activation. In addition, glioblastoma patient data show that tumor-infiltrating NK cells express CD73 variably, depending on donor, and present lower expression of CD16, alongside patient-specific changes in CEACAM1, CXCR3 and TIM-3, suggesting some functional changes in NK cell responses associated with expression of CD73 on NK cells in vivo. Taken together, our study is the first to show that while NK cells are largely resistant to the upregulation of CD73, CD73 expression is inducible on NK cells in response to CD73 on cancer cells, and these cells are associated with distinct functional signatures.

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

BACKGROUND AIMS: Traditionally, natural killer (NK) cells are sourced from the peripheral blood of donors-a laborious and highly donor-specific process. Processes for generating NK cells from induced pluripotent stem cells (iPSCs) have demonstrated that it is possible to successfully generate renewable alloreactive NK cells that are not only functional in vivo but can also be genetically engineered for enhanced function. However, poor standardization and cumbersome differentiation procedures suggest that further improvements in the control of the differentiation process are necessary. METHODS: Here the authors evaluated the potential of differentiating NK cells from centrally authenticated iPSCs under entirely chemically defined and serum-free conditions as well as their immunotherapeutic potential, after expansion in feeder-free media, against solid tumors targets. To address limitations of current differentiation approaches, the authors did not utilize feeder or stromal cell layers, TrypLE adaptation or peripheral blood during the differentiation process. The authors also evaluated the feasibility of utilizing centrally authenticated iPSC lines, thus circumventing protocol- and donor-induced variability associated with reprogramming approaches, and characterized these iPSC-NK cells in terms of cytotoxicity, cytokine production and degranulation potential against solid tumor cell lines and patient-derived targets. RESULTS: Differentiation of iPSCs generated NK cells that were predominantly CD56+/CD16+/CD3- and expressed NK activation markers NKG2D, NKp30, NKp44, NKp46 and DNAM-1. These iPSC-NK cells mediated effector functions, including cytotoxicity, degranulation and IFN-γ production, in response to solid tumor targets, including patient-derived cancer cells, and could be cryopreserved and expanded in culture. CONCLUSIONS: The ability to produce NK cells under defined conditions and the functional responses elicited by these iPSC-NK cells suggest that they could represent promising effectors in clinical adoptive transfer settings as a renewable source of donor-independent NK cells for immunotherapy of solid tumors.

CD155 immunoregulation as a target for natural killer cell immunotherapy in glioblastoma.

Natural killer (NK) cells are powerful immune effectors, modulating their anti-tumor function through a balance activating and inhibitor ligands on their cell surface. Though still emerging, cancer immunotherapies utilizing NK cells are proving promising as a modality for the treatment of a number of solid tumors, including glioblastoma (GBM) and other gliomas, but are often limited due to complex immunosuppression associated with the GBM tumor microenvironment which includes overexpression of inhibitory receptors on GBM cells. CD155, or poliovirus receptor (PVR), has recently emerged as a pro-tumorigenic antigen, overexpressed on GBM and contributing to increased GBM migration and aggressiveness. CD155 has also been established as an immunomodulatory receptor, able to both activate NK cells through interactions with CD226 (DNAM-1) and CD96 and inhibit them through interaction with TIGIT. However, NK cell TIGIT expression has been shown to be upregulated in cancer, establishing CD155 as a predominantly inhibitory receptor within the context of GBM and other solid tumors, and rendering it of interest as a potential target for antigen-specific NK cell-based immunotherapy. This review will explore the function of CD155 within GBM as it relates to tumor migration and NK cell immunoregulation, as well as pre-clinical and clinical targeting of CD155/TIGIT and the potential that this pathway holds for the development of emerging NK cell-based immunotherapies.

Natural Killer Cells as Allogeneic Effectors in Adoptive Cancer Immunotherapy.

Natural killer (NK) cells are attractive within adoptive transfer settings in cancer immunotherapy due to their potential for allogeneic use; their alloreactivity is enhanced under conditions of killer immunoglobulin-like receptor (KIR) mismatch with human leukocyte antigen (HLA) ligands on cancer cells. In addition to this, NK cells are platforms for genetic modification, and proliferate in vivo for a shorter time relative to T cells, limiting off-target activation. Current clinical studies have demonstrated the safety and efficacy of allogeneic NK cell adoptive transfer therapies as a means for treatment of hematologic malignancies and, to a lesser extent, solid tumors. However, challenges associated with sourcing allogeneic NK cells have given rise to controversy over the contribution of NK cells to graft-versus-host disease (GvHD). Specifically, blood-derived NK cell infusions contain contaminating T cells, whose activation with NK-stimulating cytokines has been known to lead to heightened release of proinflammatory cytokines and trigger the onset of GvHD in vivo. NK cells sourced from cell lines and stem cells lack contaminating T cells, but can also lack many phenotypic characteristics of mature NK cells. Here, we discuss the available published evidence for the varying roles of NK cells in GvHD and, more broadly, their use in allogeneic adoptive transfer settings to treat various cancers.

Purinergic targeting enhances immunotherapy of CD73+ solid tumors with piggyBac-engineered chimeric antigen receptor natural killer cells.

BACKGROUND: The anti-tumor immunity of natural killer (NK) cells can be paralyzed by the CD73-induced generation of immunosuppressive adenosine from precursor ATP within the hypoxic microenvironment of solid tumors. In an effort to redirect purinergic immunosuppression of NK cell anti-tumor function, we showed, for the first time, that immunometabolic combination treatment with NKG2D-engineered CAR-NK cells alongside blockade of CD73 ectonucleotidase activity can result in significant anti-tumor responses in vivo. METHODS: NK cells were engineered non-virally with NKG2D.CAR-presenting vectors based on the piggyBac transposon system with DAP10 and CD3ζ co-signaling domains. The anti-tumor immunity of NKG2D.CAR.NK cells in combination with CD73 targeting was evaluated against multiple solid tumor targets in vitro and humanized mouse xenografts in immunodeficient tumor-bearing mice in vivo. Intratumoral migration was evaluated via immunohistochemical staining, while degranulation capacity and IFN-γ production of NK cells were measured in response to solid tumor targets. RESULTS: Our results showed that CD73 blockade can mediate effective purinergic reprogramming and enhance anti-tumor cytotoxicity both in vitro and in vivo by enhancing the killing ability of CAR-engineered NK cells against CD73+ solid tumor targets via mechanisms that might imply alleviation from adenosinergic immunometabolic suppression. CD73 blockade improved the intratumoral homing of CD56+ CAR-NK cells in vivo. These engineered NK cells showed synergistic therapeutic efficacy in combination with CD73 targeting against CD73+ human lung cancer xenograft models. Interestingly, CD73 blockade could inhibit tumor growth in vivo independently of adaptive immune cells, innate immunity or NK cell-mediated ADCC. CONCLUSIONS: Immunotherapies targeting the adenosinergic signaling cascade, which act by neutralizing CD73 ectoenzymatic activity, had thus far not been evaluated in humanized tumor models, nor had the implication of innate immunity been investigated. Taken together, our pre-clinical efficacy data demonstrate, for the first time, the potential of targeting CD73 to modulate purinergic signaling and enhance adoptive NK cell immunotherapy via mechanisms that could implicate autocrine tumor control as well as by mediating adenosinergic signaling.

Tumor Microenvironment-Induced Immunometabolic Reprogramming of Natural Killer Cells.

Energy metabolism is key to the promotion of tumor growth, development, and metastasis. At the same time, cellular metabolism also mediates immune cell survival, proliferation and cytotoxic responses within the tumor microenvironment. The ability of natural killer cells to eradicate tumors relies on their ability to functionally persist for the duration of their anti-tumor effector activity. However, a tumor's altered metabolic requirements lead to compromised functional responses of cytokine-activated natural killer cells, which result in decreased effectiveness of adoptive cell-based immunotherapies. Tumors exert these immunosuppressive effects through a number of mechanisms, a key driver of which is hypoxia. Hypoxia also fuels the generation of adenosine from the cancer-associated ectoenzymes CD39 and CD73. Adenosine's immunosuppression manifests in decreased proliferation and impaired anti-tumor function, with adenosinergic signaling emerging as an immunometabolic checkpoint blockade target. Understanding such immunometabolic suppression is critical in directing the engineering of a new generation of natural killer cell-based immunotherapies that have the ability to more effectively target difficult-to-treat solid tumors.

Adenosinergic Signaling Alters Natural Killer Cell Functional Responses.

Adenosine is a potent immunosuppressive purine metabolite contributing to the pathogenesis of solid tumors. Extracellular adenosine signals on tumor-infiltrating NK cells to inhibit their proliferation, maturation, and cytotoxic function. Cytokine priming imparts upon NK cells distinct activation statuses, which modulate NK anti-tumor immunity and responses to purinergic metabolism. Here, for the first time, we investigated human NK cell responses to adenosinergic signaling in the context of distinct cytokine priming programs. NK cells were shown to be hyper-responsive to adenosine when primed with IL-12 and IL-15 compared to IL-2, exhibiting enhanced IFN-γ expression from CD56bright and CD56dim subsets while modulating the expression of activation marker NKG2D. These responses resulted in signaling that was dependent on mTOR. Adenosine induced upregulation of transcriptional signatures for genes involved in immune responses while downregulating cellular metabolism and other protein synthesis functions that correlate to inhibited oxidative phosphorylation and glycolysis. Overall, our findings show that adenosine acts on specific cellular pathways rather than inducing a broad inhibition of NK cell functions. These responses are dependent on cytokine priming signatures and are important in designing therapeutic interventions that can reprogram NK cell immunometabolism for improved immunotherapies of solid tumors.