TGF beta secreted by B16 melanoma antagonizes cancer gene immunotherapy bystander effect

Transdermal nanolipoplex simultaneously inhibits subcutaneous melanoma growth and suppresses systemically metastatic melanoma by activating host immunity

Benefit for clinical melanoma treatments, the transdermal neoadjuvant therapy could reduce surgery region and increase immunotherapy efficacy. Using lipoplex (Lipo-PEG-PEI-complex, LPPC) encapsulated doxorubicin (DOX) and carrying CpG oligodeoxynucleotide; the transdermally administered nano-liposomal drug complex (LPPC-DOX-CpG) would have high cytotoxicity and immunostimulatory activity to suppress systemic metastasis of melanoma. LPPC-DOX-CpG dramatically suppressed subcutaneous melanoma growth by inducing tumor cell apoptosis and recruiting immune cells into the tumor area. Animal studies further showed that the colonization and growth of spontaneously metastatic melanoma cells in the liver and lung were suppressed by transdermal LPPC-DOX-CpG. Furthermore, NGS analysis revealed IFN-γ and NF-κB pathways were triggered to recruit and activate the antigen-presenting-cells and effecter cells, which could activate the anti-tumor responses as the major mechanism responsible for the therapeutic effect of LPPC-DOX-CpG. Finally, we have successfully proved transdermal LPPC-DOX-CpG as a promising penetrative carrier to activate systemic anti-tumor immunity against subcutaneous and metastatic tumor.

Progression of melanoma is suppressed by targeting all transforming growth factor‑β isoforms with an Fc chimeric receptor

Melanoma is an aggressive type of cancer originating from the skin that arises from neoplastic changes in melanocytes. Transforming growth factor-β (TGF-β) is a pleiotropic cytokine and is known to contribute to melanoma progression by inducing the epithelial-mesenchymal transition (EMT) program and creating an environment that favors tumor progression. There are three TGF-β isoforms, TGF-β1, TGF-β2 and TGF-β3, all of which engage in pro-tumorigenic activities by activating SMAD signaling pathways. All TGF-β isoforms activate signaling pathways by binding to their TGF-β type I (TβRI) and type II (TβRII) receptors. Thus, effective targeting of all TGF-β isoforms is of great importance. In the present study, chimeric proteins comprising the extracellular domains of TβRI and/or TβRII fused with the Fc portion of human immunoglobulin (IgG) were validated in the melanoma context. The Fc chimeric receptor comprising both TβRI and TβRII (TβRI-TβRII-Fc) effectively trapped all TGF-β isoforms. Conversely, TβRII-Fc chimeric receptor, that comprises TβRII only, was able to interact with TGF-β1 and TGF-β3 isoforms, but not with TGF-β2, which is a poor prognostic factor for melanoma patients. Accordingly, it was revealed that TβRI-TβRII-Fc chimeric receptor suppressed the EMT program in melanoma cells in vitro induced by any of the three TGF-β isoforms, as revealed by decreased expression of mesenchymal markers. Conversely, TβRII-Fc chimeric receptor inhibited the EMT program induced by TGF-β1 and TGF-β3. In addition, it was established that tumor growth in subcutaneous mouse melanoma was inhibited by TβRI-TβRII-Fc chimeric receptor indicating that Fc chimeric receptor could be applied to modify the tumor microenvironment (TME) of melanoma. Therefore, designing of Fc chimeric receptors targeting TGF-β signals that affect various components of the TME may result in the development of effective anti-melanoma agents.

Targeting NK Cells to Enhance Melanoma Response to Immunotherapies

Natural killer (NK) cells are a key component of an innate immune system. They are important not only in initiating, but also in augmenting adaptive immune responses. NK cell activation is mediated by a carefully orchestrated balance between the signals from inhibitory and activating NK cell receptors. NK cells are potent producers of proinflammatory cytokines and are also able to elicit strong antitumor responses through secretion of perforin and granzyme B. Tumors can develop many mechanisms to evade NK cell antitumor responses, such as upregulating ligands for inhibitory receptors, secreting anti-inflammatory cytokines and recruiting immunosuppressive cells. Enhancing NK cell responses will likely augment the effectiveness of immunotherapies, and strategies to accomplish this are currently being evaluated in clinical trials. A comprehensive understanding of NK cell biology will likely provide additional opportunities to further leverage the antitumor effects of NK cells. In this review, we therefore sought to highlight NK cell biology, tumor evasion of NK cells and clinical trials that target NK cells.

Cyano Enone-Bearing Triterpenoid Soloxolone Methyl Inhibits Epithelial-Mesenchymal Transition of Human Lung Adenocarcinoma Cells In Vitro and Metastasis of Murine Melanoma In Vivo

Introduction of α-cyano α,β-unsaturated carbonyl moiety into natural cyclic compounds markedly improves their bioactivities, including inhibitory potential against tumor growth and metastasis. Previously, we showed that cyano enone-bearing derivatives of 18βH-glycyrrhetinic (GA) and deoxycholic acids displayed marked cytotoxicity in different tumor cell lines. Moreover, GA derivative soloxolone methyl (SM) was found to induce ER stress and apoptosis in tumor cells in vitro and inhibit growth of carcinoma Krebs-2 in vivo. In this work, we studied the effects of these compounds used in non-toxic dosage on the processes associated with metastatic potential of tumor cells. Performed screening revealed SM as a hit compound, which inhibits motility of murine melanoma B16 and human lung adenocarcinoma A549 cells and significantly suppresses colony formation of A549 cells. Further study showed that SM effectively blocked transforming growth factor β (TGF-β)-induced epithelial-mesenchymal transition (EMT) of A549 cells: namely, inhibited TGF-β-stimulated motility and invasion of tumor cells as well as loss of their epithelial characteristics, such as, an acquisition of spindle-like phenotype, up- and down-regulation of mesenchymal (vimentin, fibronectin) and epithelial (E-cadherin, zona occludens-1 (ZO-1)) markers, respectively. Network pharmacology analysis with subsequent verification by molecular modeling revealed that matrix metalloproteinases MMP-2/-9 and c-Jun N-terminal protein kinase 1 (JNK1) can be considered as hypothetical primary targets of SM, mediating its marked anti-EMT activity. The inhibitory effect of SM on EMT revealed in vitro was further confirmed in a metastatic model of murine B16 melanoma: SM was found to effectively block metastatic dissemination of melanoma B16 cells in vivo, increase expression of E-cadherin and suppress expression of MMP-9 in lung metastatic foci. Altogether, our data provided valuable information for a better understanding of the antitumor activity of cyano enone-bearing semisynthetic compounds and revealed SM as a promising anti-metastatic drug candidate.

IL-2 and Anti-TGF-β Promote NK Cell Reconstitution and Anti-tumor Effects after Syngeneic Hematopoietic Stem Cell Transplantation

Simple Summary

Hematopoietic stem cell transplantation (HSCT) causes early immune deficiency and susceptibility to both opportunistic infections and cancer relapse. In this study, using a mouse model where donor cells can be tracked over time, we have observed that the combination of IL-2 (a cytokine which activates the immune system) combined with the blockade of TGF-β (a cytokine which suppresses the immune system) increased immune recovery and resulted in greater anti-tumor efficacy. The combination of IL-2 and anti-TGF-β accelerated NK cell and myeloid cell reconstitution after HSCT.

Abstract

The failure of autologous hematopoietic stem cell transplantation (HSCT) has been associated with a profound immunodeficiency that follows shortly after treatment, which renders patients susceptible to opportunistic infections and/or cancer relapse. Thus, given the additional immunosuppressive pathways involved in immune evasion in cancer, strategies that induce a faster reconstitution of key immune effector cells are needed. Natural killer (NK) cells mediate potent anti-tumor effector functions and are the first immune cells to repopulate after HSCT. TGF-β is a potent immunosuppressive cytokine that can impede both the development and function of immune cells. Here, we evaluated the use of an immunotherapeutic regimen that combines low dose of IL-2, an NK cell stimulatory signal, with TGF-β neutralization, in order to accelerate NK cell reconstitution following congenic HSCT in mice by providing stimulatory signals yet also abrogating inhibitory ones. This therapy led to a marked expansion of NK cells and accelerated NK cell maturation. Following HSCT, mature NK cells from the treated recipients displayed an activated phenotype and enhanced anti-tumor responses both in vitro and in vivo. No overt toxicities or adverse effects were observed in the treated recipients. However, these stimulatory effects on NK cell recovery were predicated upon continuous treatment as cessation of treatment led to return to baseline levels and to no improvement of overall immune recovery when assessed at later time-points, indicating strict regulatory control of the NK cell compartment. Overall, this study still demonstrates that therapies that combine positive and negative signals can be plausible strategies to accelerate NK cell reconstitution following HSCT and augment anti-tumor efficacy.

Dexamethasone induced apoptosis of A549 cells via the TGF-β1/Smad2 pathway

Lung cancers are the most commonly diagnosed malignant tumors, and are one of the leading causes of morbidity and mortality worldwide. Dexamethasone (DEX) serves an important function in the regulation of lung cancer cell proliferation; however, the mechanisms involved still remain unknown. In the present study, the effects of DEX on A549 cell proliferation and apoptosis were examined, in addition to the potential downstream regulatory mechanisms underlying these effects. A549 cells were treated with different concentrations of DEX at 12, 24 and 48 h time points, followed by the addition of SB431542, an inhibitor of the TGF-β1 receptor, to block the TGF-β1 signaling pathway. Cell proliferation was analyzed using a 3-(4,5-diethylthiazol-2-yl)-5-(3-carboxymethoxyphenyl)-2-(4-sulfophenyl)-2H-tetrazolium, inner salt. The apoptosis rate was measured by Hoechst 33342 and Annexin V/propidium iodide staining and the expression of transforming growth factor (TGF)-β1, Smad family member 2 (Smad2) and caspase-3 were assessed by western blot. The results from the present study demonstrated that the proliferation of A549 cells decreased and the apoptosis rate significantly increased following DEX treatment (P<0.05). Furthermore, the expression of TGF-β1, Smad2 and caspase-3 were significantly increased following DEX stimulation (P<0.05), the effects of which were abrogated by the addition of the TGF-β1 receptor inhibitor, SB431542 (P<0.05). DEX-induced apoptosis in A549 cells, and this effect was abrogated by SB431542, an inhibitor of TGF-β1 receptor signaling, which indicated that the TGF-β1/Smad2 pathway may be associated with this process and SB431542 may function as an antitumor drug in the future.

Stimulation of Natural Killer Cell-Mediated Tumor Immunity by an IL15/TGFβ-Neutralizing Fusion Protein

The clinical efficacy of immune cytokines used for cancer therapy is hampered by elements of the immunosuppressive tumor microenvironment such as TGFβ. Here we demonstrate that FIST15, a recombinant chimeric protein composed of the T-cell-stimulatory cytokine IL15, the sushi domain of IL15Rα and a TGFβ ligand trap, can overcome immunosuppressive TGFβ to effectively stimulate the proliferation and activation of natural killer (NK) and CD8⁺ T cells with potent antitumor properties. FIST15-treated NK and CD8⁺ T cells produced more IFNγ and TNFα compared with treatment with IL15 and a commercially available TGFβ receptor-Fc fusion protein (sTβRII) in the presence of TGFβ. Murine B16 melanoma cells, which overproduce TGFβ, were lysed by FIST15-treated NK cells in vitro at doses approximately 10-fold lower than NK cells treated with IL15 and sTβRII. Melanoma cells transduced to express FIST15 failed to establish tumors in vivo in immunocompetent murine hosts and could only form tumors in beige mice lacking NK cells. Mice injected with the same cells were also protected from subsequent challenge by unmodified B16 melanoma cells. Finally, mice with pre-established B16 melanoma tumors responded to FIST15 treatment more strongly compared with tumors treated with control cytokines. Taken together, our results offer a preclinical proof of concept for the use of FIST15 as a new class of biological therapeutics that can coordinately neutralize the effects of immunosuppressive TGFβ in the tumor microenvironment while empowering tumor immunity. Cancer Res; 76(19); 5683-95. ©2016 AACR.

Targeting miR-23a in CD8+ cytotoxic T lymphocytes prevents tumor-dependent immunosuppression

CD8(+) cytotoxic T lymphocytes (CTLs) have potent antitumor activity and therefore are leading candidates for use in tumor immunotherapy. The application of CTLs for clinical use has been limited by the susceptibility of ex vivo-expanded CTLs to become dysfunctional in response to immunosuppressive microenvironments. Here, we developed a microRNA-targeting (miRNA-targeting) approach that augments CTL cytotoxicity and preserves immunocompetence. Specifically, we screened for miRNAs that modulate cytotoxicity and identified miR-23a as a strong functional repressor of the transcription factor BLIMP-1, which promotes CTL cytotoxicity and effector cell differentiation. In a cohort of advanced lung cancer patients, miR-23a was upregulated in tumor-infiltrating CTLs, and expression correlated with impaired antitumor potential of patient CTLs. We determined that tumor-derived TGF-β directly suppresses CTL immune function by elevating miR-23a and downregulating BLIMP-1. Functional blocking of miR-23a in human CTLs enhanced granzyme B expression, and in mice with established tumors, immunotherapy with just a small number of tumor-specific CTLs in which miR-23a was inhibited robustly hindered tumor progression. Together, our findings provide a miRNA-based strategy that subverts the immunosuppression of CTLs that is often observed during adoptive cell transfer tumor immunotherapy and identify a TGF-β-mediated tumor immune-evasion pathway.

Increased antitumor effects using IL-2 with anti-TGF-β reveals competition between mouse NK and CD8 T cells

Because of increasing interest in the removal of immunosuppressive pathways in cancer, the combination of IL-2 with Abs to neutralize TGF-β, a potent immunosuppressive cytokine, was assessed. Combination immunotherapy resulted in significantly greater antitumor effects. These were correlated with significant increases in the numbers and functionality of NK cells, NK cell progenitors, and activated CD8 T cells, resulting in the observed antitumor effects. Combination immunotherapy also was accompanied by lesser toxicities than was IL-2 therapy alone. Additionally, we observed a dual competition between NK cells and activated CD8 T cells such that, after immunotherapy, the depletion of either effector population resulted in the increased total expansion of the other population and compensatory antitumor effects. This study demonstrates the efficacy of this combination immunotherapeutic regimen as a promising cancer therapy and illustrates the existence of potent competitive regulatory pathways between NK cells and CD8 T cells in response to systemic activation.

Role of the complement system in NK cell-mediated antitumor T-cell responses

The role of the complement system in oncogenesis and tumor progression remains poorly understood. We have recently demonstrated that the induction of a tumor-specific CD8⁺ T-cell response is improved upon transient inhibition of the complement system, which is coupled to an increased availability of natural killer cells. The complement system may therefore turn out to constitute a promising target for the development of novel anticancer therapeutics.

Prostate apoptosis response-4 mediates TGF-β-induced epithelial-to-mesenchymal transition

A growing body of evidence supports that the epithelial-to-mesenchymal transition (EMT), which occurs during cancer development and progression, has a crucial role in metastasis by enhancing the motility of tumor cells. Transforming growth factor-β (TGF-β) is known to induce EMT in a number of cancer cell types; however, the mechanism underlying this transition process is not fully understood. In this study we have demonstrated that TGF-β upregulates the expression of tumor suppressor protein Par-4 (prostate apoptosis response-4) concomitant with the induction of EMT. Mechanistic investigations revealed that exogenous treatment with each TGF-β isoform upregulates Par-4 mRNA and protein levels in parallel levels of phosphorylated Smad2 and IκB-α increase. Disruption of TGF-β signaling by using ALK5 inhibitor, neutralizing TGF-β antibody or phosphoinositide 3-kinase inhibitor reduces endogenous Par-4 levels, suggesting that both Smad and NF-κB pathways are involved in TGF-β-mediated Par-4 upregulation. NF-κB-binding sites in Par-4 promoter have previously been reported; however, using chromatin immunoprecipitation assay we showed that Par-4 promoter region also contains Smad4-binding site. Furthermore, TGF-β promotes nuclear localization of Par-4. Prolonged TGF-β3 treatment disrupts epithelial cell morphology, promotes cell motility and induces upregulation of Snail, vimentin, zinc-finger E-box binding homeobox 1 and N-Cadherin and downregulation of Claudin-1 and E-Cadherin. Forced expression of Par-4, results in the upregulation of vimentin and Snail expression together with increase in cell migration. In contrast, small interfering RNA-mediated silencing of Par-4 expression results in decrease of vimentin and Snail expression and prevents TGF-β-induced EMT. We have also uncovered a role of X-linked inhibitor of apoptosis protein in the regulation of endogenous Par-4 levels through inhibition of caspase-mediated cleavage. In conclusion, our findings suggest that Par-4 is a novel and essential downstream target of TGF-β signaling and acts as an important factor during TGF-β-induced EMT.

Modulation of tumor immunity by soluble and membrane-bound molecules at the immunological synapse

To circumvent pathology caused by infectious microbes and tumor growth, the host immune system must constantly clear harmful microorganisms and potentially malignant transformed cells. This task is accomplished in part by T-cells, which can directly kill infected or tumorigenic cells. A crucial event determining the recognition and elimination of detrimental cells is antigen recognition by the T cell receptor (TCR) expressed on the surface of T cells. Upon binding of the TCR to cognate peptide-MHC complexes presented on the surface of antigen presenting cells (APCs), a specialized supramolecular structure known as the immunological synapse (IS) assembles at the T cell-APC interface. Such a structure involves massive redistribution of membrane proteins, including TCR/pMHC complexes, modulatory receptor pairs, and adhesion molecules. Furthermore, assembly of the immunological synapse leads to intracellular events that modulate and define the magnitude and characteristics of the T cell response. Here, we discuss recent literature on the regulation and assembly of IS and the mechanisms evolved by tumors to modulate its function to escape T cell cytotoxicity, as well as novel strategies targeting the IS for therapy.

Inhibition of TGF-β signaling in genetically engineered tumor antigen-reactive T cells significantly enhances tumor treatment efficacy

Transforming growth factor β (TGF-β) is a cytokine with complex biological functions that may involve tumor promotion or tumor suppression. It has been reported that multiple types of tumors secrete TGF-β, which can inhibit tumor-specific cellular immunity and may represent a major obstacle to the success of tumor immunotherapy. In this study, we sought to enhance tumor immunotherapy using genetically modified antigen-specific T cells by interfering with TGF-β signaling. We constructed three γ-retroviral vectors, one that expressed TGF-β-dominant-negative receptor II (DNRII) or two that secreted soluble TGF-β receptors: soluble TGF-β receptor II (sRII) and the sRII fused with mouse IgG Fc domain (sRIIFc). We demonstrated that T cells genetically modified with these viral vectors were resistant to exogenous TGF-β-induced smad-2 phosphorylation in vitro. The functionality of antigen-specific T cells engineered to resist TGF-β signaling was further evaluated in vivo using the B16 melanoma tumor model. Antigen-specific CD8+ T cells (pmel-1) or CD4+ T cells (tyrosinase-related protein-1) expressing DNRII dramatically improved tumor treatment efficacy. There was no enhancement in the B16 tumor treatment using cells secreting soluble receptors. Our data support the potential application of the blockade of TGF-β signaling in tumor-specific T cells for cancer immunotherapy.

T cell receptor (TCR)-transgenic CD8 lymphocytes rendered insensitive to transforming growth factor beta (TGFβ) signaling mediate superior tumor regression in an animal model of adoptive cell therapy

Tumor antigen-reactive T cells must enter into an immunosuppressive tumor microenvironment, continue to produce cytokine and deliver apoptotic death signals to affect tumor regression. Many tumors produce transforming growth factor beta (TGFβ), which inhibits T cell activation, proliferation and cytotoxicity. In a murine model of adoptive cell therapy, we demonstrate that transgenic Pmel-1 CD8 T cells, rendered insensitive to TGFβ by transduction with a TGFβ dominant negative receptor II (DN), were more effective in mediating regression of established B16 melanoma. Smaller numbers of DN Pmel-1 T cells effectively mediated tumor regression and retained the ability to produce interferon-γ in the tumor microenvironment. These results support efforts to incorporate this DN receptor in clinical trials of adoptive cell therapy for cancer.

A MCP1 fusokine with CCR2-specific tumoricidal activity

Background

The CCL2 chemokine is involved in promoting cancer angiogenesis, proliferation and metastasis by malignancies that express CCR2 receptor. Thus the CCL2/CCR2 axis is an attractive molecular target for anticancer drug development.

Methods

We have generated a novel fusion protein using GMCSF and an N-terminal truncated version of MCP1/CCL2 (6-76) [hereafter GMME1] and investigated its utility as a CCR2-specific tumoricidal agent.

Results

We found that distinct to full length CCL2 or its N-truncated derivative (CCL2 5-76), GMME1 bound to CCR2 on mouse lymphoma EG7, human multiple myeloma cell line U266, or murine and human medulloblastoma cell lines, and led to their death by apoptosis. We demonstrated that GMME1 specifically blocked CCR2-associated STAT3 phosphorylation and up-regulated pro-apoptotic BAX. Furthermore, GMME1 significantly inhibited EG7 tumor growth in C57BL/6 mice, and induced apoptosis of primary myeloma cells from patients.

Conclusion

Our data demonstrate that GMME1 is a fusokine with a potent, CCR2 receptor-mediated pro-apoptotic effect on tumor cells and could be exploited as a novel biological therapy for CCR2⁺ malignancies including lymphoid and central nervous system malignancies.

Induction of monocyte chemoattractant protein-1 and interleukin-10 by TGFbeta1 in melanoma enhances tumor infiltration and immunosuppression

Melanoma progression is associated with the expression of different growth factors, cytokines, and chemokines. Because TGFβ1 is a pleiotropic cytokine involved not only in physiologic processes but also in cancer development, we analyzed in A375 human melanoma cells, the effect of TGFβ1 on monocyte chemoattractant protein-1 (MCP-1) and interleukin-10 (IL-10) expression, two known factors responsible for melanoma progression. TGFβ1 increased the expression of MCP-1 and IL-10 in A375 cells, an effect mediated by the cross-talk between Smad, PI3K (phosphoinositide 3-kinase)/AKT, and BRAF-MAPK (mitogen activated protein kinase) signaling pathways. Supernatants from TGFβ1-treated A375 cells enhanced MCP-1-dependent migration of monocytes, which, in turn, expressed high levels of TGF,β1, bFGF, and VEGF mRNA. Moreover, these supernatants also inhibited functional properties of dendritic cells through IL-10-dependent mechanisms. When using in vitro, the TGFβ1-blocking peptide P144, TGFβ1-dependent Smad3 phosphorylation, and expression of MCP-1 and IL-10 were inhibited. In vivo, treatment of A375 tumor-bearing athymic mice with P144 significantly reduced tumor growth, associated with a lower macrophage infiltrate and decreased intratumor MCP-1 and VEGF levels, as well as angiogenesis. Finally, in C57BL/6 mice with B16-OVA melanoma tumors, when administered with immunotherapy, P144 decreased tumor growth and intratumor IL-10 levels, linked to enhanced activation of dendritic cells and natural killer cells, as well as anti-OVA T-cell responses. These results show new effects of TGFβ1 on melanoma cells, which promote tumor progression and immunosuppression, strongly reinforcing the relevance of this cytokine as a molecular target in melanoma.

The human ortholog of granulocyte macrophage colony-stimulating factor and interleukin-2 fusion protein induces potent ex vivo natural killer cell activation and maturation

Natural killer (NK) cells are appealing cellular pharmaceuticals for cancer therapy because of their innate ability to recognize and kill tumor cells. Therefore, the development of methods that can enhance the potency in their anticancer effect would be desirable. We have previously shown that a murine granulocyte macrophage colony-stimulating factor (GM-CSF)/interleukin 2 (IL-2) fusion protein displays novel antitumor properties in vivo compared with both cytokines in combination due to recruitment of NK cells. In the present work, we have found that human ortholog of the GM-CSF/IL-2 fusion protein (a.k.a. hGIFT2) induces robust NK cell activation ex vivo with significant secretion of RANTES and a 37-fold increase in IFNgamma production when compared with either IL-2 or GM-CSF single cytokine treatment or their combination. Moreover, hGIFT2 upregulates the expression of NK cell activating receptors NKp44, NKp46, and DNAM-1 (CD226), as well as CD69, CD107a, and IL-2Rbeta expression. In addition, hGIFT2 promotes NK cell maturation, based on the downregulation of CD117 expression and upregulation of CD11b. This phenotype correlates with significantly greater cytotoxicity against tumor cells. At the molecular level, hGIFT2 leads to a potent activation of Janus-activated kinases (JAK) downstream of both IL-2 and GM-CSF receptors (JAK1 and JAK2, respectively) and consequently leads to a hyperphosphorylation of signal transducers and activators of transcription (STAT)1, STAT3, and STAT5. In conclusion, hGIFT2 fusokine possesses unique biochemical properties distinct from IL-2 and GM-CSF, constitutes a novel and potent tool for ex vivo NK cell activation and maturation, and may be of use for cancer cell immunotherapy.