Cell-mediated Tumor Surveillance Research Articles

XAF1 is secreted from stressed tumor cells to activate T cell-mediated tumor surveillance via Lck-ERK signaling

X-linked inhibitor of apoptosis-associated factor 1 (XAF1) is a stress-inducible tumor suppressor that is commonly inactivated in multiple types of human malignancies. Nevertheless, the molecular basis for the XAF1-mediated tumor suppression remains largely undefined. Here, we report that XAF1 is secreted from cells under various cytotoxic stress conditions and activates T cell-mediated tumor surveillance. In cancer cells exposed to interferon −γ, tumor necrosis factor −α, and etoposide, XAF1 is elevated and actively secreted through the unconventional endo-lysosomal trafficking pathway and the zinc finger 4 domain of XAF1 plays an essential for this secretion. Secreted XAF1 is internalized into nearby T cells through clathrin-mediated endocytosis and stimulates proliferation, migration, and tumor infiltration of T cells. Internalized XAF1 activates RAF-MEK-ERK signaling through the direct interaction with and phosphorylation of lymphocyte-specific protein tyrosine kinase. In response to interferon −γ injection, Xaf1+/+ tumors display significantly higher regression rate and T cell infiltration compared to Xaf1−/− tumors while Xaf1−/− tumors are markedly reduced by injection of recombinant Xaf1. XAF1 expression is associated with overall survival in T cell-enriched cancer patients and also correlates with prognosis in T cell-based immunotherapies. Together, our study identifies XAF1 as a novel secretory immune-modulatory tumor suppressor, illuminating the mechanistic consequence of its inactivation in tumorigenesis.

STAT1 Isoforms Differentially Regulate NK Cell Maturation and Anti-tumor Activity.

Natural killer (NK) cells are important components of the innate immune defense against infections and cancers. Signal transducer and activator of transcription 1 (STAT1) is a transcription factor that is essential for NK cell maturation and NK cell-dependent tumor surveillance. Two alternatively spliced isoforms of STAT1 exist: a full-length STAT1α and a C-terminally truncated STAT1β isoform. Aberrant splicing is frequently observed in cancer cells and several anti-cancer drugs interfere with the cellular splicing machinery. To investigate whether NK cell-mediated tumor surveillance is affected by a switch in STAT1 splicing, we made use of knock-in mice expressing either only the STAT1α (Stat1α/α) or the STAT1β (Stat1β/β) isoform. NK cells from Stat1α/α mice matured normally and controlled transplanted tumor cells as efficiently as NK cells from wild-type mice. In contrast, NK cells from Stat1β/β mice showed impaired maturation and effector functions, albeit less severe than NK cells from mice that completely lack STAT1 (Stat1–/–). Mechanistically, we show that NK cell maturation requires the presence of STAT1α in the niche rather than in NK cells themselves and that NK cell maturation depends on IFNγ signaling under homeostatic conditions. The impaired NK cell maturation in Stat1β/β mice was paralleled by decreased IL-15 receptor alpha (IL-15Rα) surface levels on dendritic cells, macrophages and monocytes. Treatment of Stat1β/β mice with exogenous IL-15/IL-15Rα complexes rescued NK cell maturation but not their effector functions. Collectively, our findings provide evidence that STAT1 isoforms are not functionally redundant in regulating NK cell activity and that the absence of STAT1α severely impairs, but does not abolish, NK cell-dependent tumor surveillance.

Exploration of the Role of Tumor Suppressor Genes Foxo1 and PTEN in the Tumorigenesis of Mouse Natural Killer-Cell Lymphoma

To explore whether tumor suppressor gene Foxo1 and PTEN play a critical role in the tumorigenesis of mouse natural killer-cell lymphoma. NKp46-iCre mice were crossed with mice carrying floxed Foxo1 alleles (Foxo1fl/fl) as well as floxed PTEN alleles (PTENfl/fl) to generate mice in which Foxo1 and PTEN in NK cells were knock-out, referred as Foxo1△NKPTEN△NK. The growth and development of the mice and tumor formation were observed. The flow cytometry was used to detect the percentages of NK cells in main lymphatic organs. B16F10 metanoma model of tumor metastasis was utilized to investigate NK cell-mediated tumor surveillance in vivo after NK cells special deletion of Foxol and PTEN. The mouse model with NK cell-special Foxo1 and PTEN double knockout was established. Compared with control group (Foxo1fl/flPTENfl/fl mice), Foxo1△NKPTEN△NK mice were born alive and appeared to be healthy over a period of 46 weeks. No spontaneous tumor formation was observed at this stage. There were no significant differences in NK cell percentages of gated lymphocytes from various organs including blood, bone marrow, peripheral lymph node and spleen between Foxo1△NKPTEN△NK mice and Foxo1fl/flPTENfl/fl mice [PB: 4.76%±0.46% vs 4.17%±0.64% (P＞0.05, n=8); BM: 1.13%±0.23% vs 1.31%±0.10% (P＞0.05, n=8) ; LN: 0.50%±0.10% vs 0.85%±0.20% (P＞0.05, n=8); SP: 4.41%±0.65% vs 3.50%±0.24% (P＞0.05, n=8)]. B16F10 melanoma metastasis model of tumor was established, No differences in median survival time were observed in the 2 types of mice (P＞0.05, n=13). The simultaneous deletion of the Foxo1 and PTEN genes may not plays significant role in the tumorigenesis of mouse natural killer-cell lymphoma and NK cell-mediated tumor surveillance in vivo.

Abnormal Expression of c-Myc Oncogene in NK Cells in Patients with Cancer.

Natural killer (NK) cells have received a lot of attention in recent years for the roles they play in immunity and particularly in antitumor immune responses. Although defects in NK cell functions are recognized as important mechanisms for immune evasion of malignant cells, molecular pathways regulating NK cell dysfunction and exhaustion in cancer are largely unknown. Here we tested whether the c-myc proto-oncogene, known to promote cell proliferation, growth, differentiation, and apoptosis by regulating the expression of numerous target genes, may be involved in the mechanism of NK cell abnormalities in patients with lung and gastric cancer. Analysis of c-myc mRNA and protein expression in peripheral blood NK cells, mitogen-activated protein kinase (MAPK) activity, cell cycle, and cell longevity revealed a significantly decreased expression of c-myc mRNA and protein and mitotic arrest of NK cells in different phases of cell cycle. In addition, a significant decrease of NK cell death was also detected. These data allow the suggestion that defects of NK cell-mediated tumor surveillance may be associated with disturbed c-myc expression in NK cells in cancer patients. A better understanding of the mechanisms of NK cell dysfunction in cancer will help in the NK cell-mediated therapeutic eradication of primary and metastatic cancer cells and prolong patient survival.

Loss of JAK1 Drives Innate Immune Deficiency.

The Janus kinase—signal transducers and activators of transcription (JAK-STAT) signaling pathway is critical in tuning immune responses and its dysregulation is tightly associated with cancer and immune disorders. Disruption of interleukin (IL)-15/STAT5 signaling pathway due to the loss of IL-15 receptor chains, JAK3 or STAT5 leads to immune deficiencies with natural killer (NK) cell abnormalities. JAK1, together with JAK3 transmits signals downstream of IL-15, but the exact contribution of JAK1 to NK cell biology remains to be elucidated. To study the consequences of JAK1 deficiency in NK cells, we generated mice with conditional deletion of JAK1 in NKp46+ cells (Jak1fl/flNcr1Cre). We show here that deletion of NK cell-intrinsic JAK1 significantly reduced NK cell numbers in the bone marrow and impaired their development. In line, we observed almost a complete loss of NK cells in the spleen, blood, and liver, proving a crucial role of JAK1 in peripheral NK cells. In line, Jak1fl/+Ncr1Cre mice showed significantly impaired NK cell-mediated tumor surveillance. Our data suggest that JAK2 is not able to compensate for the loss of JAK1 in NK cells. Importantly, conditional deletion of JAK2 in NKp46+ cells had no effect on peripheral NK cells revealing that NK cell-intrinsic JAK2 is dispensable for NK cell survival. In summary, we identified that loss of JAK1 in NK cells drives innate immune deficiency, whereas JAK2 deficiency leaves NK cell numbers and maturation unaltered. We thus propose that in contrast to currently used JAK1/JAK2 inhibitors, the use of JAK2-specific inhibitors would be advantageous for the patients by leaving NK cells intact.

Loss of CXCR4 in Myeloid Cells Enhances Antitumor Immunity and Reduces Melanoma Growth through NK Cell and FASL Mechanisms.

The chemokine receptor, CXCR4, is involved in cancer growth, invasion, and metastasis. Several promising CXCR4 antagonists have been shown to halt tumor metastasis in preclinical studies, and clinical trials evaluating the effectiveness of these agents in patients with cancer are ongoing. However, the impact of targeting CXCR4 specifically on immune cells is not clear. Here, we demonstrate that genetic deletion of CXCR4 in myeloid cells (CXCR4MyeΔ/Δ) enhances the antitumor immune response, resulting in significantly reduced melanoma tumor growth. Moreover, CXCR4MyeΔ/Δ mice exhibited slowed tumor progression compared with CXCR4WT mice in an inducible melanocyte BrafV600E/Pten -/- mouse model. The percentage of Fas ligand (FasL)-expressing myeloid cells was reduced in CXCR4MyeΔ/Δ mice as compared with myeloid cells from CXCR4WT mice. In contrast, there was an increased percentage of natural killer (NK) cells expressing FasL in tumors growing in CXCR4MyeΔ/Δ mice. NK cells from CXCR4MyeΔ/Δ mice also exhibited increased tumor cell killing capacity in vivo, based on clearance of NK-sensitive Yac-1 cells. NK cell-mediated killing of Yac-1 cells occurred in a FasL-dependent manner, which was partially dependent upon the presence of CXCR4MyeΔ/Δ neutrophils. Furthermore, enhanced NK cell activity in CXCR4MyeΔ/Δ mice was also associated with increased production of IL18 by specific leukocyte subpopulations. These data suggest that CXCR4-mediated signals from myeloid cells suppress NK cell-mediated tumor surveillance and thereby enhance tumor growth. Systemic delivery of a peptide antagonist of CXCR4 to tumor-bearing CXCR4WT mice resulted in enhanced NK-cell activation and reduced tumor growth, supporting potential clinical implications for CXCR4 antagonism in some cancers. Cancer Immunol Res; 6(10); 1186-98. ©2018 AACR.

Primary immunodeficiencies and hematological malignancies

Primary immunodeficiency disease (PID) is characterized by an impaired immune system along with recurrent and severe and/or opportunistic infections; these infections are frequently associated with malignancies and autoimmune disorders. Dysregulation of the adaptive immune system leads to an increased risk of malignancies. Various mechanisms contribute to increased tumor susceptibility in patients with PIDs, which are as follows: defective cell-mediated tumor surveillance, defective apoptosis, specific susceptibility to carcinogens, decreased pathogen clearance and over-active inflammatory responses, defects in cytokinesis, impaired control of virus-infected cells, defects in cell cycle control, and impaired cellular response to genotoxic agents. Moreover, some malignancies might arise owing to germline mutations in PID-causative genes. Here, we describe the close association between PIDs and malignancies, particularly hematopoietic malignancies.

In vivo tumor surveillance by NK cells requires TYK2 but not TYK2 kinase activity

Tyrosine kinase 2 (TYK2) is a Janus kinase (JAK) that is crucially involved in inflammation, carcinogenesis and defense against infection. The cytotoxic activity of natural killer (NK) cells in TYK2-deficient (Tyk2 −/−) mice is severely reduced, although the underlying mechanisms are largely unknown. Using Tyk2 −/− mice and mice expressing a kinase-inactive version of TYK2 (Tyk2 K923E ), we show that NK cell function is partly independent of the enzymatic activity of TYK2. Tyk2 −/− and Tyk2 K923E NK cells develop normally in the bone marrow, but the maturation of splenic Tyk2 −/− NK cells (and to a lesser extent of Tyk2 K923E NK cells) is impaired. In contrast, the production of interferon γ (IFNγ) in response to interleukin 12 (IL-12) or to stimulation through NK cell-activating receptors strictly depends on the presence of enzymatically active TYK2. The cytotoxic activity of Tyk2 K923E NK cells against a range of target cells in vitro is higher than that of Tyk2 −/− NK cells. Consistently, Tyk2 K923E mice control the growth of NK cell-targeted tumors significantly better than TYK2-deficient mice, showing the physiological relevance of the finding. Inhibitors of TYK2's kinase activity are being developed for the treatment of inflammatory diseases and cancers, but their effects on tumor immune surveillance have not been investigated. Our finding that TYK2 has kinase-independent functions in vivo suggests that such inhibitors will leave NK cell mediated tumor surveillance largely intact and that they will be suitable for use in cancer therapy.

The Coding Genome of Nodal Marginal Zone Lymphoma Reveals Recurrent Molecular Alterations of PTPRD and Other Jak/Stat Signaling Genes

Background. Nodal marginal zone lymphoma (NMZL) is one of the few B-cell tumors still remaining orphan of cancer gene lesions. By combining whole exome sequencing (WES), deep sequencing of tumor-related genes, high resolution SNP array and RNAseq, here we aim at characterizing the coding genome of NMZL and at disclosing the pathways that are molecularly deregulated in this lymphoma.Methods. The study was based on 35 NMZL (tumor representation >70%) with a diagnosis confirmed by: i) pathological revision of lymph node histology; and ii) lack of clinico-radiological evidence of extranodal or splenic disease either at diagnosis or during follow-up. Consistent with NMZL, the cases investigated: i) lacked CD5, CD10 and cyclin D1 expression, 7q deletion, t(11;14), t(14;18), t(11;18) and t(1;14) translocations; and ii) recurrently harbored +3 (14%), +12 (14%) and preferential usage of the IGHV4-34 gene (17%). WES (HiSeq 2500, Illumina; mean coverage per sample: 38x-114x) and high density SNP array (Cytoscan HD, Affymetrix) of tumor/normal DNA pairs from 18 discovery NMZL identified 557 non-synonymous somatic mutations (average: 30.9/case) affecting 504 genes and 61 copy number abnormalities (CNA) (average 3.4/case). To further characterize mutation recurrence, the 504 discovered genes were investigated in an independent validation panel of 17 NMZL by targeted sequencing of tumor/normal DNA pairs (MiSeq; target region: 1.6 Mb; mean coverage per sample: 171x-386x). The 17 validation NMZL were also assessed for CNA by high density SNP arrays. RNAseq of 11 discovery NMZL did not identify any recurrent gene fusion. Results. By compiling the results of WES and high resolution SNP array, 39 genes were recurrently affected in >3/35 (9%) NMZL by mutations (n=30 genes) or focal CNA (n=9 genes). Among these, MLL2 (34%), PTPRD (20%) and NOTCH2 (20%) were most frequently mutated. Overall, recurrently mutated genes pointed to the molecular deregulation of specific programs in NMZL, namely JAK/STAT, NOTCH, NF-κB and toll-like receptor (TLR) signaling, cell cycle, chromatin remodeling/transcriptional regulation and immune escape (Fig. 1A). JAK/STAT signaling was targeted by mutually exclusive lesions in 43% of NMZL, and the protein tyrosine phosphatase receptor delta (PTPRD) tumor suppressor was the most frequently affected gene of this system in 20% of NMZL (Fig. 1B-E). PTPRD inhibits JAK/STAT signaling through the dephosphorylation of active p-STAT3. PTPRD lesions in NMZL were represented by somatic mutations that truncated or modified the tyrosine phosphatase domain, as well as deletions of the entire gene locus, including focal and biallelic losses (Fig. 1B-C). Interrogation of institutional and public genomic datasets revealed that PTPRD mutations are specific for NMZL, being rare or absent in other mature B-cell tumors, including splenic marginal zone lymphoma (Fig. 1D). Other JAK/STAT signaling genes affected in NMZL were JAK2, CXCR4 (6%), PTPN2, JAK3, STAT2, SH2B3 and CUL3 (3%) (Fig. 1E). NF-kB signaling was altered in 54% of NMZL by lesions of TNFAIP3 (14%), BCL10, REL (11%), CARD11 (9%), TRAF3 and BIRC3 (6%). NOTCH signaling was targeted in 40% of NMZL by mutations that alternatively involved NOTCH2 (20%), SPEN (11%), RBPJL (6%), FBXW7, DTX1, ITCH and MAML2 (3%). TLR signaling was targeted in 17% of NMZL, including mutations of MYD88 (9%), IRAK1BP1, PELI2 and SEMP6 (3%). Several cell cycle genes were molecularly deregulated in 43% of NMZL, including CDKN2A, PARK2, PARKG (9%), CDC16, CDCA2 (6%), CCNA1, CCNT2, CDK5, CDK13, CDK20, BTG2, HECA and PLK2 (3%). Most (71%) NMZL harbored genetic lesions affecting epigenetic modifiers (MLL2: 34%; CREBBP: 9%; EP300: 6%; TRRAP: 6%), histones (20%) or transcriptional co-repressors (TBL1XR1: 14%; ARID1A: 14%; RCOR1: 11%; NCOR2: 9%, ARID1B: 9%). Finally, the TNFRSF14 and FAS genes, involved in T cell-mediated tumor surveillance, were disrupted by mutations and/or deletions in 17% and 14% NMZL, respectively.Conclusions. A number of actionable cellular programs are molecularly deregulated in NMZL, including JAK/STAT, NOTCH, NF-κB and TLR signaling, cell cycle and chromatin remodeling. PTPRD lesions are among the most recurrent alterations in NMZL and appear to be specific for this lymphoma type across mature B-cell tumors. [Display omitted] DisclosuresNo relevant conflicts of interest to declare.

Fas ligand–mediated immune surveillance by T cells is essential for the control of spontaneous B cell lymphomas

Loss of function of the tumor suppressor gene PRDM1 (also known as BLIMP1) or deregulated expression of the oncogene BCL6 occurs in a large proportion of diffuse large B cell lymphoma (DLBCL) cases. However, targeted mutation of either gene in mice leads to only slow and infrequent development of malignant lymphoma, and despite frequent mutation of BCL6 in activated B cells of healthy individuals, lymphoma development is rare. Here we show that T cells prevent the development of overt lymphoma in mice caused by Blimp1 deficiency or overexpression of Bcl6 in the B cell lineage. Impairment of T cell control results in rapid development of DLBCL-like disease, which can be eradicated by polyclonal CD8(+) T cells in a T cell receptor-, CD28- and Fas ligand-dependent manner. Thus, malignant transformation of mature B cells requires mutations that impair intrinsic differentiation processes and permit escape from T cell-mediated tumor surveillance.

Loss of STAT3 in Lymphoma Relaxes NK Cell-Mediated Tumor Surveillance

The transcription factors and proto-oncogenes STAT3 and STAT5 are highly activated in hematological malignancies and represent promising therapeutic targets. Whereas the importance of STAT5 as tumor promoter is beyond doubt, the role of STAT3 in hematological cancers is less well understood. Both, enforced as well as attenuated expression of STAT3 were reported in hematopoietic malignancies. Recent evidence implicates STAT3 as key player for tumor immune surveillance as it both mediates the production of and response to inflammatory cytokines. Here we investigated the effects of STAT3 deletion in a BCR/ABL-induced lymphoma model, which is tightly controlled by natural killer (NK) cells in vivo. Upon STAT3 deletion tumor growth is significantly enhanced when compared to STAT3-expressing controls. The increased tumor size upon loss of STAT3 was accompanied by reduced NK cell infiltration and decreased levels of the cytokine IFN-γ and the chemokine RANTES. Upon transplantation into NK cell-deficient mice differences in lymphoma size were abolished indicating that STAT3 expression in the tumor cells controls NK cell-dependent tumor surveillance. Our findings indicate that STAT3 inhibition in lymphoma patients will impair NK cell-mediated tumor surveillance, which needs to be taken into account when testing STAT3 inhibitors in preclinical or clinical trials.

CDK8-Mediated STAT1-S727 Phosphorylation Restrains NK Cell Cytotoxicity and Tumor Surveillance

SummaryThe transcription factor STAT1 is important in natural killer (NK) cells, which provide immediate defense against tumor and virally infected cells. We show that mutation of a single phosphorylation site (Stat1-S727A) enhances NK cell cytotoxicity against a range of tumor cells, accompanied by increased expression of perforin and granzyme B. Stat1-S727A mice display significantly delayed disease onset in NK cell-surveilled tumor models including melanoma, leukemia, and metastasizing breast cancer. Constitutive phosphorylation of S727 depends on cyclin-dependent kinase 8 (CDK8). Inhibition of CDK8-mediated STAT1-S727 phosphorylation may thus represent a therapeutic strategy for stimulating NK cell-mediated tumor surveillance.

Conditional IFNAR1 ablation reveals distinct requirements of Type I IFN signaling for NK cell maturation and tumor surveillance

Mice with an impaired Type I interferon (IFN) signaling (IFNAR1- and IFNβ-deficient mice) display an increased susceptibility toward v-ABL-induced B-cell leukemia/lymphoma. The enhanced leukemogenesis in the absence of an intact Type I IFN signaling is caused by alterations within the tumor environment. Deletion of Ifnar1 in tumor cells (as obtained in Ifnar1f/f CD19-Cre mice) failed to impact on disease latency or type. In line with this observation, the initial transformation and proliferative capacity of tumor cells were unaltered irrespective of whether the cells expressed IFNAR1 or not. v-ABL-induced leukemogenesis is mainly subjected to natural killer (NK) cell-mediated tumor surveillance. Thus, we concentrated on NK cell functions in IFNAR1 deficient animals. Ifnar1-/- NK cells displayed maturation defects as well as an impaired cytolytic activity. When we deleted Ifnar1 selectively in mature NK cells (by crossing Ncr1-iCre mice to Ifnar1f/f animals), maturation was not altered. However, NK cells derived from Ifnar1f/f Ncr1-iCre mice showed a significant cytolytic defect in vitro against the hematopoietic cell lines YAC-1 and RMA-S, but not against the melanoma cell line B16F10. Interestingly, this defect was not related to an in vivo phenotype as v-ABL-induced leukemogenesis was unaltered in Ifnar1f/f Ncr1-iCre compared with Ifnar1f/f control mice. Moreover, the ability of Ifnar1f/f Ncr1-iCre NK cells to kill B16F10 melanoma cells was unaltered, both in vitro and in vivo. Our data reveal that despite the necessity for Type I IFN in NK cell maturation the expression of IFNAR1 on mature murine NK cells is not required for efficient tumor surveillance.

Abstract 3661: The impact of tumor-infiltrating natural killer cells on ovarian cancer progression

Abstract Cancers adopt diverse strategies to safeguard their survival by evading tumor surveillance. Natural killer (NK) cells and CD8 T-lymphocytes are capable of destroying tumor cells thus playing a critical role in tumor immunity. In previous studies, we showed that NK cell derived TRAIL is essential for the cytotoxic activity of the DR5 agonistic antibody AD5-10, since depletion of NK cells abolished the antitumor activity of AD5-10 in a xenograft ovarian cancer (OC) mouse model. In the present study, we investigated whether NK cells are associated with clinical outcome as well as with the immune infiltrate showing anti-tumor immunity in OC. We analyzed NK cell infiltration in human primary ovarian tumor tissues using immunohistochemical analysis of a representative population of OC patients on a tissue microarray. NK tumor-infiltrating cells were detected within tumor tissues, whereas CD3 tumor-infiltrating T-lymphocytes were almost undetectable. NK cells in addition inversely correlated with FIGO stage (r=−0.51, p<0.001) and tumor grade (r=−0.3, p=0.03). These data indicate that the presence of intratumoral NK cells correlates with improved clinical outcome in OC. When we analyzed the cytotoxic capacity of human NK cells against OC cells in vitro, we found that human NK cells were capable to induce apoptosis in a concentration-and time-dependent manner in several OC cell lines. Interestingly, the addition of the DR5 agonistic antibody AD5-10 sensitized TRAIL resistant OC cell lines to NK cells mediated cytolysis. To study tumor surveillance of OC in vivo, we are currently setting up mouse models. Transformed murine ovarian surface epithelial (MOSE) cell lines derived from C57BL/6 mice have been implanted intraperitoneally into syngenic wild type, RAG2 -/-, RAG2 -/- γ -/-, NK depleted, CD8 depleted C57BL/6 recipient mice. The outcome of these studies will be presented. In summary, our findings point at a critical role for NK cell mediated tumor surveillance for OC development. Importantly, NK cell infiltration correlates with prognosis in human ovarian carcinoma. Thus, our study may open novel therapeutic opportunities by interfering with host immunity in the future. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 3661. doi:10.1158/1538-7445.AM2011-3661

A novel Ncr1-Cre mouse reveals the essential role of STAT5 for NK-cell survival and development

AbstractWe generated a transgenic mouse line that expresses the Cre recombinase under the control of the Ncr1 (p46) promoter. Cre-mediated recombination was tightly restricted to natural killer (NK) cells, as revealed by crossing Ncr1-iCreTg mice to the eGFP-LSLTg reporter strain. Ncr1-iCreTg mice were further used to study NK cell–specific functions of Stat5 (signal transducers and activators of transcription 5) by generating Stat5f/fNcr1-iCreTg animals. Stat5f/fNcr1-iCreTg mice were largely devoid of NK cells in peripheral lymphoid organs. In the bone marrow, NK-cell maturation was abrogated at the NK cell–precursor stage. Moreover, we found that in vitro deletion of Stat5 in interleukin 2–expanded NK cells was incompatible with NK-cell viability. In vivo assays confirmed the complete abrogation of NK cell–mediated tumor control against B16F10-melanoma cells. In contrast, T cell–mediated tumor surveillance against MC38-adenocarcinoma cells was undisturbed. In summary, the results of our study show that STAT5 has a cell-intrinsic role in NK-cell development and that Ncr1-iCreTg mice are a powerful novel tool with which to study NK-cell development, biology, and function.

Requirements for control of B‐cell lymphoma by NK cells

The role of NK cells in the control of endogenously arising tumors is still unclear. We monitored activation and effector functions of NK cells in a c-myc-transgenic mouse model of spontaneously arising lymphoma. At early stages, tumors demonstrated reduced MHC class I expression and increased expression of natural killer group 2D ligands (NKG2D-L). NK cells in these tumors showed an activated phenotype that correlated with the loss of tumor MHC class I. With increasing tumor load however, NK-cell effector functions became progressively paralyzed or exhausted. In later stages of disease, tumors re-expressed MHC class I and lost NKG2D-L, suggesting a role of these two signals for NK cell-mediated tumor control. Testing a panel of lymphoma cell lines expressing various MHC class I and NKG2D-L levels suggested that NK cell-dependent tumor control required a priming and a triggering signal that were provided by MHC class I down-regulation and by NKG2D-L, respectively. Deleting either of the "two signals" resulted in tumor escape. At early disease stages, immune stimulation through TLR-ligands in vivo efficiently delayed lymphoma growth in a strictly NK cell-dependent manner. Thus, NK-receptor coengagement is crucial for NK-cell functions in vivo and especially for NK cell-mediated tumor surveillance.

Unexpected role of STAT1 serine727 for NK cell function

Background Natural killer (NK) cells are important key players of the innate immune system and provide immediate defense against viral infection and tumor transformation. Therefore, their potential in cancer immunotherapy has grown prominently in the last years [1]. As is known from the literature, the Signal Transducer and Activator of Transcription 1 (STAT1) plays an important role for NK cell function, since STAT1-deficient mice display impaired basal NK cytolytic activity in vitro and are unable to reject transplanted tumors in vivo [2]. STAT1 mediates signals downstream of interferons and gets activated by phosphorylation of several tyrosine and serine residues. In particular phosphorylation of S727 is considered a prerequisite for the full-fledged activation of STAT1 [3]. The aim of this project is to investigate the role of STAT1-S727 in NK cell-mediated cytotoxicity and tumor surveillance. Methods The analysis of STAT1 −/− , STAT1-S727A and wild-type mice includes the preparation of primary splenic NK cells and their investigation regarding proliferation ([ 3 H]thymidineincorporation), cytotoxicity (standard [ 51 Cr]-release) and cytokine production (ELISA, multi-plex bead arrays). In vivo tumor models are employed using NK-sensitive tumor cell lines (v-abl + leukemia, B16 melanoma, 4T1 breast cancer). Results

Deficiency of GMDS Leads to Escape from NK Cell-Mediated Tumor Surveillance Through Modulation of TRAIL Signaling

Tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) promotes apoptosis in cancer cells, but not normal cells, and is critically involved in tumor rejection through natural killer (NK) cell-mediated immune surveillance. Oligosaccharides are involved in various aspects in carcinogenesis, and fucosylation is one of the most important oligosaccharide modifications in cancer. Here, we report for the first time mutations of the GDP-mannose-4,6-dehydratase (GMDS) gene, which plays a pivotal role in fucosylation, in human colon cancer. The mutations resulted in resistance to TRAIL-induced apoptosis followed by escape from immune surveillance. The mock and GMDS-rescued HCT116 cells were investigated in terms of NK cell-mediated tumor surveillance by TRAIL signaling both in vitro and in vivo. The mutational analysis for GMDS was performed with kinds of cancer cell lines and tissues. The mutation found here led to a virtually complete deficiency of cellular fucosylation, and transfection of the wild-type GMDS into HCT116 cells restored the cellular fucosylation. When mock and GMDS-rescued cells were transplanted into athymic mice, tumor growth and metastasis of the GMDS-rescued cells were dramatically suppressed through NK cell-mediated tumor surveillance. Furthermore, the GMDS-rescued cells showed high susceptibility to TRAIL-induced apoptosis, and anti-TRAIL blocking antibody suppressed the accelerated direct cell lysis of the GMDS-rescued cells by splenocytes. Similar mutations of the GMDS were found in certain human cancer tissues and other cell lines. This pathway by GMDS mutation could be a novel type of cancer progression through cellular fucosylation and NK cell-mediated tumor surveillance.

STAT1 Ser727 – key regulator for NK cell-mediated cytotoxicity and tumor surveillance

The Janus kinase/signal transducer and activator of transcription (JAK/STAT) signaling cascade plays an important role in hematopoiesis. A constitutive activation of this pathway is found in a broad variety of diverse human and murine leukemias and lymphomas. Whereas STAT3 and STAT5 accelerate and initiate tumor formation, STAT1 is generally considered a tumor suppressor. As shown by Kovacic et al. [1], STAT1 accelerates leukemia formation by up-regulation of MHC class I on leukemic cells allowing them to escape natural killer (NK) cell-mediated lysis. In the present study we investigate the role of the STAT1 serine727 phosphorylation site for leukemia initiation and progression. After retroviral leukemia induction STAT1S727A knock-in mice show enhanced disease latency compared to wild type (WT) mice. Upon injection of B16 melanoma cells, numbers of lung metastases were increased in STAT1-/- recipients, but significantly reduced in STAT1S727A mice when compared to WT mice. This indicates that the effect of STAT1S727A may not be cell-intrinsic but rather results from altered interactions with the host immune system. Clearance of leukemic and B16 cells is mainly mediated by NK cells. Therefore, differences in NK cells might explain our in vivo data. As determined in a [3H]thymidine incorporation assay, STAT1S727A NK cells showed enhanced proliferation rates compared to WT cells. Moreover, in a classical [51Cr]-release assay STAT1S727A NK cells were able to lyse leukemic cells more efficiently than WT NK cells. NK cells can be divided into different functional subsets according to cell surface expression of DX5, Mac-1 and CD27. Ex vivo fluorescence-activated cell sorting (FACS)-based analysis revealed a distinct expression pattern in STAT1S727A NK cells (Mac-1+, DX5+, CD27+), that is characteristic for a pre-activated NK cell phenotype [2] and is found in STAT1S727A mice in spite of the absence of any activating stimulus. These experiments indicate that phosphorylation of STAT1 serine727 in NK cells is relevant for activation, cytolytic function and as a consequence for their ability to eradicate tumor cells in vivo.

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