The Role of CD137 and Its Ligand in Chronic Lymphocytic Leukemia (CLL)

Blood ◽  
2008 ◽  
Vol 112 (11) ◽  
pp. 3130-3130
Author(s):  
Tina Baessler ◽  
Corina Buechele ◽  
Matthias Krusch ◽  
Benjamin J Schmiedel ◽  
Lothar Kanz ◽  
...  
Keyword(s):  
Nk Cells ◽  
Tumor Immunity ◽  
Nk Cell ◽  
Cell Subset ◽  
Surrogate Marker ◽  
Lymphocytic Leukemia ◽  
Cellular Cytotoxicity ◽  
Antibody Dependent Cellular Cytotoxicity ◽  
Cell Reactivity

Abstract Tumor immunosurveillance is dependent on the reciprocal interaction between tumor cells and anti-tumor immunity mediated e.g. by NK cells. This has led to the concept of tumor immunoediting, which incorporates the multitude of mechanisms underlying this dual tumor- and immune-sculpting interaction. Various members of the TNF/TNFR family modulate differentiation, proliferation, activation, and death of both tumor and immune effector cells. Very recently the TNFR family member CD137 has been shown to be induced on NK cells by Fc receptor triggering indicating that not only the Fab region but also the Fc part of a given antibody may be responsible for effects attributed to CD137 modulation (Lin et al., Blood2008, 112: 699). Thus we here studied the role of human CD137 and its cognate counterpart, the CD137 ligand (CD137L) in the interaction of CLL with NK cells. High levels of CD137L expression were detected on B-CLL cells in all investigated patients (n=40). Incubation of CLL cells in the presence of an immobilized CD137-Ig fusionprotein significantly induced the release of the immunoregulatory cytokine TNF demonstrating that CLL-expressed CD137L was capable to transduce bidirectional signals. Furthermore, we found that NK cells of CLL patients displayed substantial CD137 expression. While being absent on resting NK cells, CD137 expression was upregulated on the CD56dimCD16+ but not the CD56brightCD16− NK cell subset of healthy donors upon activation e.g. with IL-2 or IL-15. In addition, CD137 was also induced on NK cells after incubation in supernatants of PBMC of CLL patients. Surprisingly, disruption of CD137-CD137L interaction in cocultures of allogenic NK cells with patient CLL cells by blocking CD137 antibody caused a significant increase in NK cell cytotoxicity. The observed inhibitory effect of CD137L on NK cell reactivity was confirmed in cytotoxicity assays using CD137L-transfectants with mock-transfectants as control. Furthermore, blocking CD137-CD137L interaction also substantially enhanced Rituximab-induced antibody dependent cellular cytotoxicity in an allogenic setting. Importantly, CD137 blockade also substantially enhanced CD107a expression as a surrogate marker for granule mobilization on autologous NK cells within PBMC of B-CLL patients, and this effect was observed both in the absence and more pronounced in the presence of Rituximab. Thus, expression of functional CD137L by CLL cells impairs anti-tumor immunity by diminishing both direct and antibody-dependent cellular cytotoxicity of allogenic and autologous NK cells. Modulation of the CD137-CD137L system might therefore be a suitable therapeutic approach in strategies like antibody therapy which rely on a sufficient NK cell anti-tumor response.

Glucocorticoid-Induced TNFR-Related Protein (GITR) Ligand Mediates Tumor Immunoediting in Chronic Lymphocytic Leukemia and Impairs Direct and Rituximab-Induced NK Cell Anti-Leukemia Reactivity.

Blood ◽  
2009 ◽  
Vol 114 (22) ◽  
pp. 4403-4403
Author(s):  
Corina Buechele ◽  
Tina Baessler ◽  
Benjamin J Schmiedel ◽  
Lothar Kanz ◽  
Helmut R Salih
Keyword(s):  
Chronic Lymphocytic Leukemia ◽  
Nk Cells ◽  
Tumor Immunity ◽  
Nk Cell ◽  
Conflicts Of Interest ◽  
Inhibitory Effect ◽  
Lymphocytic Leukemia ◽  
Cell Reactivity ◽  
Immune Effector ◽  
Ifn Γ

Abstract Abstract 4403 Members of the TNF/TNF receptor (TNFR) family of proteins govern differentiation, proliferation, activation, and death of both tumor and immune effector cells and thus play an important role in tumor immunoediting, the reciprocal interaction of tumor cells and anti-tumor immunity. Activation of the TNFR family member GITR has recently been shown to stimulate T cell-mediated anti-tumor immunity in mice. However, available data suggest that GITR mediates different effects in mice and men, and may impair anti-tumor immunity of human NK cells. Here we studied the expression and function of GITR ligand (GITRL) in patients with chronic lymphocytic leukemia (CLL) and the consequences of GITR-GITRL interaction for NK cell reactivity against CLL cells. Substantial GITRL expression was detected on primary B-CLL cells in 38 of 48 (79%) investigated patients. Upon interaction with its cognate receptor, GITRL induced the release of immunoregulatory cytokines like TNF by the leukemia cells, which demonstrated that CLL-expressed GITRL is functional and capable to transduce bidirectional signals. Moreover, disruption of GITR-GITRL interaction in cultures of allogenic NK cells with patient CLL cells by addition of blocking antibody caused a significant increase in NK cell granule mobilization, cytotoxicity and IFN-γ production. The inhibitory effect of tumor-expressed GITRL on the reactivity of human NK cells was also confirmed in cocultures of C1R lymphoma cells transfected to express GITRL with mock transfectants serving as control. In addition, blocking GITR-GITRL interaction also considerably augmented both antibody-dependent cellular cytotoxicity (ADCC) and antibody-induced IFN-γ production of NK cells in cultures with allogenic CLL cells upon Rituximab exposure. Of note, GITR blockade also significantly enhanced anti-leukemia reactivity of autologous NK cells among PBMC of B-CLL patients, and this reinforcement of NK cell effector functions was observed both regarding the direct and, more pronounced, Rituximab-induced anti-leukemia reactivity (both n=10, p<0.01, Student's T test). Thus, expression of functional GITRL by CLL cells potently influences tumor immunoediting and impairs anti-tumor immunity by diminishing both direct and Rituximab-dependent anti-leukemia reactivity of NK cells. Modulation of the GITR-GITRL system might therefore serve to enhance the efficacy of therapeutic approaches in CLL which, like Rituximab-induced ADCC or stem cell transplantation, rely on a sufficient NK cell anti-tumor response. Disclosures: No relevant conflicts of interest to declare.

scholarly journals LIR‐1 educates expanded human NK cells and defines a unique antitumor NK cell subset with potent antibody‐dependent cellular cytotoxicity

2021 ◽  
Vol 10 (10) ◽  
Author(s):  
Caroline Leijonhufvud ◽  
Robert Reger ◽  
Filip Segerberg ◽  
Jakob Theorell ◽  
Heinrich Schlums ◽  
...  
Keyword(s):  
Nk Cells ◽  
Nk Cell ◽  
Cell Subset ◽  
Cellular Cytotoxicity ◽  
Antibody Dependent Cellular Cytotoxicity

Fc-Engineered NKG2D-IgG1 Fusion Proteins Target Leukemia Cells for Antibody-Dependent Cellular Cytotoxicity (ADCC) of NK Cells

Blood ◽  
2011 ◽  
Vol 118 (21) ◽  
pp. 1537-1537 ◽  
Author(s):  
Julia Hilpert ◽  
Katrin Baltz-Ghahremanpour ◽  
Benjamin J Schmiedel ◽  
Lothar Kanz ◽  
Gundram Jung ◽  
...  
Keyword(s):  
Nk Cells ◽  
Fusion Proteins ◽  
Nk Cell ◽  
Conflicts Of Interest ◽  
Leukemia Cell ◽  
Leukemic Cells ◽  
Leukemia Cells ◽  
Target Cells ◽  
Cellular Cytotoxicity ◽  
Antibody Dependent Cellular Cytotoxicity

Abstract Abstract 1537 The capability of anti-tumor antibodies to recruit Fc-receptor (FcR) bearing effector cells like NK cells, a feature considered critical for therapeutic success, can be markedly improved by modifications of the human IgG1 part. At present, Fc-engineered antibodies targeting leukemia cells are yet not available. The various ligands of the NK cell-activating immunoreceptor NKG2D (NKG2DL) are generally absent on healthy cells but upregulated on malignant cells of various origins including leukemia. We aimed to take advantage of the tumor-restricted expression of NKG2DL by using them as target-antigens for Fc-optimized NKG2D-IgG1 fusion proteins targeting leukemia cells for antibody-dependent cellular cytotoxicity (ADCC) and IFN-g production of NK cells. NKG2D-IgG1 fusion proteins with distinct modifications in their Fc portion were generated as previously described (Lazar 2006; Armour 1999). Compared to wildtype NKG2D-Fc (NKG2D-Fc-WT), the mutants (S239D/I332E and E233P/L234V/L235A/DG236/A327G/A330S) displayed highly enhanced (NKG2D-Fc-ADCC) and abrogated (NKG2D-Fc-KO) affinity to the NK cell FcgRIIIa receptor but comparable binding to NKG2DL-expressing target cells. Functional analyses with allogenic NK cells and leukemia cell lines as well as primary leukemic cells of AML and CLL patients revealed that NKG2D-Fc-KO significantly (p<0.05, Mann-Whitney U test) reduced NK cytotoxicity and IFN-g production (about 20% and 30% reduction, respectively), which can be attributed to blockade of NKG2DL-mediated activating signals. Treatment with NKG2D-Fc-WT significantly (p<0.05, Mann-Whitney U test) enhanced NK reactivity (about 20% and 100% increase in cytotoxicity and cytokine production, respectively). The effects observed upon treatment with NKG2D-Fc-ADCC by far exceeded that of NKG2D-Fc-WT resulting in at least doubled NK ADCC and IFN-g production compared to NKG2D-Fc-WT. When applied in combination with Rituximab in analyses with CLL cells, a clear additive effect resulting in a more than four-fold increase of ADCC and FcgRIIIa-induced IFN-g production was observed. The NKG2D-Fc fusion proteins did not induce NK reactivity against healthy blood cells, which is in line with the tumor-restricted expression of NKG2DL. Of note, treatment with NKG2D-Fc-ADCC also significantly (p<0.05, Mann-Whitney U test) enhanced reactivity (up to 70% increase) of NK cells against NKG2DL-positive AML and CLL cells among patient PBMC in an autologous setting. Together, our results demonstrate that Fc-engineered NKG2D-Fc-ADCC fusion proteins can effectively target NKG2DL-expressing leukemia cells for NK anti-tumor reactivity. In line with the hierarchically organized potential of the various activating receptors governing NK reactivity and due to their highly increased affinity to the FcgRIIIa receptor, NKG2D-Fc-ADCC potently enhances NK anti-leukemia reactivity despite the inevitable reduction of activating signals upon binding to NKG2DL. Due to the tumor-restricted expression of NKG2DL, Fc-modified NKG2D-Ig may thus constitute an attractive means for immunotherapy of leukemia. Disclosures: No relevant conflicts of interest to declare.

Different NK cell–activating receptors preferentially recruit Rab27a or Munc13-4 to perforin-containing granules for cytotoxicity

Blood ◽  
2009 ◽  
Vol 114 (19) ◽  
pp. 4117-4127 ◽  
Author(s):  
Stephanie M. Wood ◽  
Marie Meeths ◽  
Samuel C. C. Chiang ◽  
Anne Grete Bechensteen ◽  
Jaap J. Boelens ◽  
...  
Keyword(s):  
Nk Cells ◽  
Nk Cell ◽  
Reciprocal Relationship ◽  
Target Cells ◽  
Cellular Cytotoxicity ◽  
Antibody Dependent Cellular Cytotoxicity ◽  
Loss Of Function ◽  
Lytic Granules ◽  
Molecular Events ◽  
Cell Release

Abstract The autosomal recessive immunodeficiencies Griscelli syndrome type 2 (GS2) and familial hemophagocytic lymphohistiocytosis type 3 (FHL3) are associated with loss-of-function mutations in RAB27A (encoding Rab27a) and UNC13D (encoding Munc13-4). Munc13-4 deficiency abrogates NK-cell release of perforin-containing lytic granules induced by signals for natural and antibody-dependent cellular cytotoxicity. We demonstrate here that these signals fail to induce degranulation in resting NK cells from Rab27a-deficient patients. In resting NK cells from healthy subjects, endogenous Rab27a and Munc13-4 do not colocalize extensively with perforin. However, phorbol 12-myristate 13-acetate and ionomycin stimulation or conjugation to susceptible target cells induced myosin-dependent colocalization of Rab27a and Munc13-4 with perforin. Unexpectedly, individual engagement of receptors leukocyte functional antigen-1, NKG2D, or 2B4 induced colocalization of Rab27a, but not Munc13-4, with perforin. Conversely, engagement of antibody-dependent cellular cytotoxicity receptor CD16 induced colocalization of Munc13-4, but not Rab27a, with perforin. Furthermore, colocalization of Munc13-4 with perforin was Rab27a-dependent. In conclusion, Rab27a or Munc13-4 recruitment to lytic granules is preferentially regulated by different receptor signals, demonstrating that individual target cell ligands regulate discrete molecular events for lytic granule maturation. The data suggest Rab27a facilitates degranulation at an early step yet highlight a reciprocal relationship between Munc13-4 and Rab27a for degranulation.

scholarly journals Intrinsic Resistance of Chronic Lymphocytic Leukemia Cells to NK Cell-Mediated Lysis Can Be Overcome In Vitro by Pharmacological Inhibition of Cdc42-Induced Actin Cytoskeleton Remodeling

2021 ◽  
Vol 12 ◽  
Author(s):  
Hannah Wurzer ◽  
Liza Filali ◽  
Céline Hoffmann ◽  
Max Krecke ◽  
Andrea Michela Biolato ◽  
...  
Keyword(s):  
Chronic Lymphocytic Leukemia ◽  
Actin Cytoskeleton ◽  
Nk Cells ◽  
Nk Cell ◽  
Granzyme B ◽  
Lymphocytic Leukemia ◽  
Cell Cytotoxicity ◽  
Cytoskeleton Remodeling ◽  
Nk Cell Cytotoxicity

Natural killer (NK) cells are innate effector lymphocytes with strong antitumor effects against hematologic malignancies such as chronic lymphocytic leukemia (CLL). However, NK cells fail to control CLL progression on the long term. For effective lysis of their targets, NK cells use a specific cell-cell interface, known as the immunological synapse (IS), whose assembly and effector function critically rely on dynamic cytoskeletal changes in NK cells. Here we explored the role of CLL cell actin cytoskeleton during NK cell attack. We found that CLL cells can undergo fast actin cytoskeleton remodeling which is characterized by a NK cell contact-induced accumulation of actin filaments at the IS. Such polarization of the actin cytoskeleton was strongly associated with resistance against NK cell-mediated cytotoxicity and reduced amounts of the cell-death inducing molecule granzyme B in target CLL cells. Selective pharmacological targeting of the key actin regulator Cdc42 abrogated the capacity of CLL cells to reorganize their actin cytoskeleton during NK cell attack, increased levels of transferred granzyme B and restored CLL cell susceptibility to NK cell cytotoxicity. This resistance mechanism was confirmed in primary CLL cells from patients. In addition, pharmacological inhibition of actin dynamics in combination with blocking antibodies increased conjugation frequency and improved CLL cell elimination by NK cells. Together our results highlight the critical role of CLL cell actin cytoskeleton in driving resistance against NK cell cytotoxicity and provide new potential therapeutic point of intervention to target CLL immune escape.

The FLT3-Inhibitors Midostaurin, Sunitinib, Sorafenib, and TKI258 Differentially Affect NK Cell-Mediated Immunesurveillance of Acute Myeloid Leukemia.

Blood ◽  
2009 ◽  
Vol 114 (22) ◽  
pp. 3785-3785
Author(s):  
Julia Salih ◽  
Lothar Kanz ◽  
Helmut R Salih ◽  
Matthias Krusch
Keyword(s):  
Nk Cells ◽  
Myeloid Leukemia ◽  
Nk Cell ◽  
Immune Surveillance ◽  
Leukemia Cells ◽  
Target Cells ◽  
Cell Reactivity ◽  
Flt3 Inhibitors ◽  
Ifn Γ

Abstract Abstract 3785 Poster Board III-721 FLT3 is a receptor tyrosine kinase with an important role in hematopoietic progenitor cell survival and proliferation. The discovery of internal tandem duplication mutations (ITD) in FLT3 was a major breakthrough in understanding the role of abnormally activated FLT3 in myeloid transformation. Between 15% and 34% of AML patients show FLT3-ITD mutations, and thus the inhibition of FLT3 in combination with chemotherapeutic agents may be a promising stragety in the treatment of Acute Myeloid Leukemia (AML). Several protein kinase inhibitors (PKI) targeting FLT3 like e.g. Midostaurin, Sunitinib, Sorafenib, and TKI258 are currently under preclinical and/or clinical evaluation (http://clinicaltrials.gov/ct2/results?term=AML+and+FLT3). Since those PKI, besides targeting their eponymous enzyme FLT3, also inhibit signaling via other molecules they may impair the effector function of various components of anti-tumor immunity. NK cells as part of the innate immune system play an important role in the immune surveillance of tumors due to their ability to directly kill target cells and to shape adaptive immune responses by secreting cytokines like IFN-γ. Clinical evidence for the particularly important role of NK cells in leukemia has recently been provided by studies of haploidentical stem cell transplantation (Ruggeri et al., Science 2002). We report here that CD107a expression as a surrogate marker for degranulation of NK cells within PBMC is inhibited by pharmacological concentrations of Sorafenib (10μg/ml) and Midostaurin (2μg/ml), but not by Sunitinib (200ng/ml) and TKI258 (125ng/ml). In line, pharmacological concentrations of Sunitinib and TKI258 did not affect NK cell cytotoxicity and IFN-γ production in cocultures with leukemia cells. Sorafenib and Midostaurin caused a clear concentration-dependent inhibition of NK cell cytokine production in response to target cells both in resting and in IL-2 activated state (92% and 66%, respectively at plasma peak levels). Furthermore, pharmacological concentrations of Sorafenib and Midostaurin also reduced lysis of leukemia cells by NK cells (54% and 58%, respectively, E:T ratio 10:1) and thus generally compromised NK cell reactivity. Analysis of NK cell signaling revealed that Sorafenib, but not Midostaurin decreased phosphorylation of PI3K and ERK which are important regulators of NK cell reactivity. Thus, Midostaurin inhibits yet undefined signaling events which are crucial for NK effector functions, but are independent of the “classical” PI3K – Rac – PAK – MEK – ERK pathway and are presently under study. Moreover, in light of the important role of NK cells in the immune surveillance of leukemia and the differential influence of clinically used FLT3-inhibitors on NK cell functions our data indicate that the choice and dosing of the most suitable compound in the treatment of AML requires further characterization and careful consideration. Disclosures: No relevant conflicts of interest to declare.

Fc-Engineered RANK-Fc Fusion Proteins for Neutralization of Soluble RANKL and Induction of Antibody-Dependent Cellular Cytotoxicity (ADCC) Against Multiple Myeloma

Blood ◽  
2010 ◽  
Vol 116 (21) ◽  
pp. 3039-3039
Author(s):  
Benjamin J Schmiedel ◽  
Carolin Scheible ◽  
Tina Baessler ◽  
Constantin M Wende ◽  
Stefan Wirths ◽  
...  
Keyword(s):  
Multiple Myeloma ◽  
Nk Cells ◽  
Fusion Proteins ◽  
Nk Cell ◽  
Conflicts Of Interest ◽  
Soluble Form ◽  
Target Cells ◽  
Published Data ◽  
Cellular Cytotoxicity ◽  
Antibody Dependent Cellular Cytotoxicity

Abstract Abstract 3039 Bone resorption is commonly associated with aging, but also with certain cancers. Recent studies identified Receptor Activator of NF-κB (RANK) ligand (RANKL) and its receptors RANK and osteoprotegerin as key regulators of bone remodelling. Multiple myeloma (MM) disrupts the balance within this molecule system towards osteoclastogenesis and bone destruction. Neutralization of RANKL by the monoclonal antibody Denosumab (AMG162) is presently being evaluated for treatment of both non-malignant and malignant osteolysis. We found, in line with previously published data, that primary MM cells (9 of 10) express substantial levels of RANKL at the cell surface and that MM cells directly release RANKL in soluble form (sRANKL). Next we evaluated the possibility to combine neutralization of sRANKL with targeting of MM cells for antibody-dependent cellular cytotoxicity (ADCC) of NK cells utilizing RANK-Ig fusion proteins with modified Fc portions. Compared to wildtype RANK-Fc, our mutants (S239D/I332E and E233P/L234V/L235A/DG236/A327G/A330S) displayed highly enhanced (RANK-Fc-ADCC) and abrogated (RANK-Fc-KO) affinity, respectively, to the NK cell FcγRIIIa, but comparable capacity to neutralize RANKL in binding competition and osteoclast formation assays. Analyses with RANKL transfectants and RANKL-negative controls confirmed the high and lacking potential of the RANK-Fc-ADCC and the RANK-Fc-KO to induce NK ADCC, respectively, and ascertained that the RANK-Fc-ADCC specifically induced NK cell lysis of RANKL-expressing but not RANKL-negative target cells. Most notably, in cultures of NK cells with RANKL-expressing primary MM cells RANK-Fc-ADCC potently enhanced NK cell degranulation, cytokine release and MM cells lysis due to enhanced NK reactivity. Thus, our Fc-engineered RANK-Fc-ADCC fusion protein may both neutralize detrimental effects of sRANKL and enhance NK anti-tumor reactivity by targeting RANKL-expressing malignant cells thereby constituting an attractive immunotherapeutic means for treatment of MM. Disclosures: No relevant conflicts of interest to declare.

scholarly journals Intratumor Regulatory Noncytotoxic NK Cells in Patients with Hepatocellular Carcinoma

Cells ◽  
2021 ◽  
Vol 10 (3) ◽  
pp. 614
Author(s):  
Alessandra Zecca ◽  
Valeria Barili ◽  
Danila Rizzo ◽  
Andrea Olivani ◽  
Elisabetta Biasini ◽  
...  
Keyword(s):  
Hepatocellular Carcinoma ◽  
Nk Cells ◽  
Nk Cell ◽  
Functional Characterization ◽  
Cell Subset ◽  
Cytotoxic Potential ◽  
Tnf Α ◽  
Oncogenic Function

Previous studies support the role of natural killer (NK) cells in controlling hepatocellular carcinoma (HCC) progression. However, ambiguity remains about the multiplicity and the role of different NK cell subsets, as a pro-oncogenic function has been suggested. We performed phenotypic and functional characterization of NK cells infiltrating HCC, with the corresponding nontumorous tissue and liver from patients undergoing liver resection for colorectal liver metastasis used as controls. We identified a reduced number of NK cells in tumors with higher frequency of CD56BRIGHTCD16− NK cells associated with higher expression of NKG2A, NKp44, and NKp30 and downregulation of NKG2D. Liver-resident (CXCR6+) NK cells were reduced in the tumors where T-bethiEomeslo expression was predominant. HCCs showed higher expression of CD49a with particular enrichment in CD49a+Eomes+ NK cells, a subset typically represented in the decidua and playing a proangiogenic function. Functional analysis showed reduced TNF-α production along with impaired cytotoxic capacity that was inversely related to CXCR6−, T-bethiEomeslo, and CD49a+Eomes+ NK cells. In conclusion, we identified a subset of NK cells infiltrating HCC, including non-liver-resident cells that coexpressed CD49a and Eomes and showed reduced cytotoxic potential. This NK cell subset likely plays a regulatory role in proangiogenic function.

scholarly journals Involvement of NFAT Transcription Factors in NK Cell Reactivity

Blood ◽  
2016 ◽  
Vol 128 (22) ◽  
pp. 1344-1344 ◽  
Author(s):  
Kathrin Rothfelder ◽  
Melanie Märklin ◽  
Julia Wild ◽  
Daniela Dörfel ◽  
Lothar Kanz ◽  
...  
Keyword(s):  
Transcription Factors ◽  
Nk Cells ◽  
Nk Cell ◽  
Inhibitory Effect ◽  
Target Cells ◽  
Cell Reactivity ◽  
Tumor Immunosurveillance ◽  
Metastatic Burden ◽  
And Function

Abstract NK cells are lymphoid components of innate immunity and play an important role in tumor immunosurveillance. One of the major transcriptional regulators in lymphoid cells is NFAT (Nuclear Factor of Activated T Cells), as highlighted by its important role in T and B cell development and function. With regard to NK cells, available data indicate that NFAT is dispensable for development. However, several lines of evidence including the observation that the immunosuppressive drugs cyclosporin A and tacrolimus, which mediate their effects through inhibition of calcineurin and consecutively NFAT, influence NK reactivity implicate a role of this family of transcription factors in NK cell reactivity and function. Here we employed different genetic mouse models on the C57BL/6 background to directly study the functional role of NFAT in NK cells. We found that except for NFAT3 mRNA and protein of all family members (NFAT 1, 2, 4 and 5) was expressed in resting NK cells of wild type (WT) mice with NFAT1, 2 and 4 being most abundantly detectable. When we employed NK cells with knockout (KO) of NFAT 1, 2, and 4 in comparative in vitro analyses, we surprisingly found that lack of NFAT resulted in enhanced NK cell activation, degranulation and release of immunomodulatory cytokines like IFN-γ after co-culture with YAC-1 target cells as well as increased production of granzyme B and perforin after cytokine activation. The inhibitory effect of NFAT on NK cell effector function was further confirmed in vivo by employing WT and germ line NFAT KO animals in the syngeneic B16 melanoma model, which revealed a significantly reduced metastatic burden in NFAT KO mice. Depletion of NK cells in this model system in turn resulted in increased metastasis, however, with WT animals displaying significantly higher metastatic burden compared to NFAT KO mice. As this pointed to the fact that NFAT influences metastasis via both NK-dependent and independent mechanisms, we further generated mice with a NK cell-specific (conditional Ncr1-Cre dependent) NFAT2 KO. When these animals were employed again in analyses of B16 lung metastasis, comparative analyses with WT animals confirmed the inhibitory effect of NFAT on NK tumor immunosurveillance. Taken together, these results provide the first direct evidence for the functional involvement of NFAT in NK cell antitumor reactivity and, in contrast to T and B cells, identify NFAT as a negative regulator of NK cell function. Disclosures No relevant conflicts of interest to declare.

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