Natural Killer Cell-mediated Tumor Surveillance Research Articles

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.

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.

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.

Loss of STAT3 in murine NK cells enhances NK cell–dependent tumor surveillance

AbstractThe members of the signal transducer and activator of transcription (STAT) family of transcription factors modulate the development and function of natural killer (NK) cells. NK cell–mediated tumor surveillance is particularly important in the body’s defense against hematological malignancies such as leukemia. STAT3 inhibitors are currently being developed, although their potential effects on NK cells are not clear. We have investigated the function of STAT3 in NK cells with Stat3Δ/ΔNcr1-iCreTg mice, whose NK cells lack STAT3. In the absence of STAT3, NK cells develop normally and in normal numbers, but display alterations in the kinetics of interferon-γ (IFN-γ) production. We report that STAT3 directly binds the IFN-γ promoter. In various in vivo models of hematological diseases, loss of STAT3 in NK cells enhances tumor surveillance. The reduced tumor burden is paralleled by increased expression of the activating receptor DNAM-1 and the lytic enzymes perforin and granzyme B. Our findings imply that STAT3 inhibitors will stimulate the cytolytic activity of NK cells against leukemia, thereby providing an additional therapeutic benefit.

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.

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

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.

TRAIL and apoptosis induction by TNF-family death receptors.

Tumor necrosis factor-related apoptosis-inducing ligand or Apo 2 ligand (TRAIL/Apo2L) is a member of the tumor necrosis factor (TNF) family of ligands capable of initiating apoptosis through engagement of its death receptors. TRAIL selectively induces apoptosis of a variety of tumor cells and transformed cells, but not most normal cells, and therefore has garnered intense interest as a promising agent for cancer therapy. TRAIL is expressed on different cells of the immune system and plays a role in both T-cell- and natural killer cell-mediated tumor surveillance and suppression of suppressing tumor metastasis. Some mismatch-repair-deficient tumors evade TRAIL-induced apoptosis and acquire TRAIL resistance through different mechanisms. Death receptors, members of the TNF receptor family, signal apoptosis independently of the p53 tumor-suppressor gene. TRAIL treatment in combination with chemo- or radiotherapy enhances TRAIL sensitivity or reverses TRAIL resistance by regulating the downstream effectors. Efforts to identify agents that activate death receptors or block specific effectors may improve therapeutic design. In this review, we summarize recent insights into the apoptosis-signaling pathways stimulated by TRAIL, present our current understanding of the physiological role of this ligand and the potential of its application for cancer therapy and prevention.

T cells require TRAIL for optimal graft-versus-tumor activity.

Tumor necrosis factor (TNF)-related apoptosis-inducing ligand (TRAIL) is a member of the TNF superfamily that exhibits specific tumoricidal activity against a variety of tumors. It is expressed on different cells of the immune system and plays a role in natural killer cell-mediated tumor surveillance. In allogeneic hematopoietic-cell transplantation, the reactivity of the donor T cell against malignant cells is essential for the graft-versus-tumor (GVT) effect. Cytolytic activity of T cells is primarily mediated through the Fas-Fas ligand and perforin-granzyme pathways. However, T cells deficient for both Fas ligand and perforin can still exert GVT activity in vivo in mouse models. To uncover a potential role for TRAIL in donor T cell-mediated GVT activity, we compared donor T cells from TRAIL-deficient and wild-type mice in clinically relevant mouse bone-marrow transplantation models. We found that alloreactive T cells can express TRAIL, but the absence of TRAIL had no effect on their proliferative and cytokine response to alloantigens. TRAIL-deficient T cells showed significantly lower GVT activity than did TRAIL-expressing T cells, but no important differences in graft-versus-host disease, a major complication of allogeneic hematopoietic cell transplantation, were observed. These data suggest that strategies to enhance TRAIL-mediated GVT activity could decrease relapse rates of malignancies after hematopoietic cell transplantation without exacerbation of graft-versus-host disease.