NK Cell Attack Research Articles

Understanding glioblastoma stromal barriers against NK cell attack using tri-culture 3D spheroid model

Glioblastoma multiforme (GBM), a highly aggressive tumor type with a dismal survival rate, has a poor outcome which is at least partly attributed to the crosstalk between cancer cells and cells from the tumor microenvironment such as astrocytes and microglia. We aimed to decipher the effect of these cells on GBM progression and on cell-based therapies using 3D co-cultures. Co-culturing of glioblastoma cells with patient-derived astrocytes or microglia or both formed dense and heterogeneous spheroids. Both, astrocytes and microglia, enhanced the spheroid growth rate and formed a physical barrier for macromolecules penetration, while only astrocytes enhanced the migration. Interestingly bi-/tri-cultured spheroids showed significant resistance against NK-92 cells, likely attributed to dense stroma and induced expression of immunosuppressive genes such as IDO1 or PTGES2. Altogether, our novel 3D GBM spheroid model recapitulates the cell-to-cell interactions of human glioblastoma and can serve as a suitable platform for evaluating cancer therapeutics.

Extra centrosomes induce PIDD1-mediated inflammation and immunosurveillance.

Unscheduled increases in ploidy underlie defects in tissue function, premature aging, and malignancy. A concomitant event to polyploidization is the amplification of centrosomes, the main microtubule organization centers in animal cells. Supernumerary centrosomes are frequent in tumors, correlating with higher aggressiveness and poor prognosis. However, extra centrosomes initially also exert an onco-protective effect by activating p53-induced cell cycle arrest. If additional signaling events initiated by centrosomes help prevent pathology is unknown. Here, we report that extra centrosomes, arising during unscheduled polyploidization or aberrant centriole biogenesis, induce activation of NF-κB signaling and sterile inflammation. This signaling requires the NEMO-PIDDosome, a multi-protein complex composed of PIDD1, RIPK1, and NEMO/IKKγ. Remarkably, the presence of supernumerary centrosomes suffices to induce a paracrine chemokine and cytokine profile, able to polarize macrophages into a pro-inflammatory phenotype. Furthermore, extra centrosomes increase the immunogenicity of cancer cells and render them more susceptible to NK-cell attack. Hence, the PIDDosome acts as a dual effector, able to engage not only the p53 network for cell cycle control but also NF-κB signaling to instruct innate immunity.

The Function of NK Cells in Tumor Metastasis and NK Cell-Based Immunotherapy

Metastatic tumors cause the most deaths in cancer patients. Treating metastasis remains the primary goal of current cancer research. Although the immune system prevents and kills the tumor cells, the function of the immune system in metastatic cancer has been unappreciated for decades because tumors are able to develop complex signaling pathways to suppress immune responses, leading them to escape detection and elimination. Studies showed NK cell-based therapies have many advantages and promise for fighting metastatic cancers. We here review the function of the immune system in tumor progression, specifically focusing on the ability of NK cells in antimetastasis, how metastatic tumors escape the NK cell attack, as well as the recent development of effective antimetastatic immunotherapies.

Altered-Self MHC Class I Sensing via Functionally Disparate Paired NK Cell Receptors Counters Murine Cytomegalovirus gp34-Mediated Immune Evasion.

The murine CMV (MCMV) immunoevasin m04/gp34 escorts MHC class I (MHC I) molecules to the surface of infected cells where these complexes bind Ly49 inhibitory receptors (IRs) and prevent NK cell attack. Nonetheless, certain self-MHC I-binding Ly49 activating and inhibitory receptors are able to promote robust NK cell expansion and antiviral immunity during MCMV infection. A basis for MHC I-dependent NK cell sensing of MCMV-infected targets and control of MCMV infection however remains unclear. In this study, we discovered that the Ly49R activation receptor is selectively triggered during MCMV infection on antiviral NK cells licensed by the Ly49G2 IR. Ly49R activating receptor recognition of MCMV-infected targets is dependent on MHC I Dk and MCMV gp34 expression. Remarkably, although Ly49R is critical for Ly49G2-dependent antiviral immunity, blockade of the activation receptor in Ly49G2-deficient mice has no impact on virus control, suggesting that paired Ly49G2 MCMV sensing might enable Ly49R+ NK cells to better engage viral targets. Indeed, MCMV gp34 facilitates Ly49G2 binding to infected cells, and the IR is required to counter gp34-mediated immune evasion. A specific requirement for Ly49G2 in antiviral immunity is further explained by its capacity to license cytokine receptor signaling pathways and enhance Ly49R+ NK cell proliferation during infection. These findings advance our understanding of the molecular basis for functionally disparate self-receptor enhancement of antiviral NK cell immunity.

Promoting T and NK cell attack: preserving tumor MICA/B by vaccines.

Promoting T and NK cell attack: preserving tumor MICA/B by vaccines.

Circulating tumor cell clusters exhibit enhanced immune evasion from natural killer cells

Abstract During cancer metastasis, the ability to evade immunosurveillance is key to the survival of circulating tumor cells (CTCs). Recent studies have found that in addition to single CTCs, multicellular clusters of CTCs can be detected in patient blood. Strikingly, CTC clusters show higher metastatic potential than single CTCs, but the molecular mechanism is unclear. We hypothesize that CTC clusters adopt immune evasive strategies, which enhance their metastatic ability. In mouse models of breast cancer, CTC clusters show enhanced metastatic growth over single cells in immunocompetent mice, but this difference is abrogated in immunodeficient mice lacking NK cells or mice treated with NK cell-depleting antibodies. Adoptive transfer of NK cells into NK cell-deficient hosts selectively suppresses metastatic growth by single CTCs, suggesting that single CTCs are more sensitive to NK cells than clusters. Analysis of cell line and patient RNA-seq data reveal that CTC clusters have elevated expression of cell-cell adhesion and epithelial genes as compared to single cells, which is in turn associated with decreased expression of NK cell-activating NKG2D ligands. Furthermore, modulation of tumor cell epithelial status alters NK ligand expression and sensitivity to NK cell killing, but this effect is attenuated by the addition of an NKG2D-blocking antibody. Taken together, we propose a model in which the epithelial characteristics of CTC clusters promotes their resistance to NK cell attack and thus their overall metastatic success. These findings reveal that NK cells play an important role in determining the fate of CTCs of different epithelial/mesenchymal states, and illuminate our understanding of immune evasion mechanisms by CTCs.

90P - High MICB expression confers prognostic benefit in colorectal cancer

BackgroundImmune surveillance is closely related to MHC and its associated molecules. The MHC class I chain related B molecule (MICB) is one of the ligands of NKG2D receptor. NKG2D receptor exists in NK cells and CD8+ T cells, which mediate anti-tumor response and immune surveillance. MICB is expressed by intestinal epithelium and epithelial tumors as well. Cancer cells express MICB as the consequence of cellular stress. But tumor cells might develop evasive pathways to avoid NK cell attack. Shedding is a way for cancer cells to remove or avoid the surface expression of MICB. Previous studies haven’t clearly figured out the prognostic value of MICB in colorectal cancer (CRC). Here, we figured out the relationship between MICB and prognosis in a CRC cohort of Zhongshan Hospital. The prognostic benefit was also validated in GSE39582 from Gene Expression Omnibus repository. Methods863 consecutive CRC patients from 2008 to 2012 without prior treatment were enrolled. 556 CRC patients between 1987 to 2007 were collected from GSE39582. MICB was detected by immunochemistry. MICB score equaled MICB intensity multiplied by the percentage of positive cells among all tumor cells. The cut-off value of MICB score was calculated by X-tile. The association between clinicopathological features and MICB were accessed by chi-square test. Kaplan-Meier analysis and log-rank test were performed to evaluate the relationship between MICB and overall survival. Univariate and multivariate cox regression analyses were performed to identify the independent prognostic factors. ResultsHigh MICB was significantly associated with non-mucinous histological type (p < 0.001) and ≤4.0cm tumor size (p = 0.001). Kaplan-Meier analyses and log-rank test showed high MICB group had a better overall survival (p = 0.002). In cox regression analyses of Zhongshan cohort, MICB was confirmed as an independent prognostic factor of OS (p = 0.008, HR = 0.741, 95% CI = 0.594-0.924). ConclusionsMICB was identified as a new independent prognostic factor in stage one to stage four CRC patients. CRC with high MICB expression conferred survival benefit. Legal entity responsible for the studyZhongshan Hospital, Fudan University, Shanghai, China. FundingHas not received any funding. DisclosureThe author has declared no conflicts of interest.

NANOG helps cancer cells escape NK cell attack by downregulating ICAM1 during tumorigenesis

BackgroundAt the beginning of tumorigenesis, newly born cancer cells must successfully avoid attack by the immune system. Although most abnormal cells are efficiently identified and destroyed by the immune system, particularly by NK cells, the molecular mechanisms by which newly born cancer cells evade NK cell surveillance are not fully understood.MethodsNK cell resistance of highly tumorigenic population of human prostate cancer (PCa) cells were confirmed by xenograft in SCID mice with or without NK cell neutralization. The mechanisms by which the tumorigenic PCa cells evaded NK cell attack were investigated by RNAseq, ChIPseq, generation of several transformants and xenograft in SCID mice.ResultsHere, we show that PCa cells have a strengthened ability to escape NK cell attack due to NANOG, a pluripotent-related transcription factor, mediating the repression of ICAM1, a cell adhesion molecule, during tumorigenesis. Mechanistically, NANOG directly binds to the region upstream of ICAM1. As the binding between NANOG and the upstream ICAM1 region increases, p300 binding to this region is diminished, resulting in decreased ICAM1 expression. High NANOG expression confers PCa cells the ability to resist NK cell attack via the repression of ICAM1. Consistent with these results, low ICAM1 expression is significantly correlated with a high recurrence rate in patients with PCa.ConclusionsOur findings indicate that repression of ICAM1 is a critical mechanism by which cancer cells evade attack from NK cells during tumorigenesis. These results suggest a pivotal role of NANOG in establishing a gene expression profile for escaping the immune system.

Medulloblastoma rendered susceptible to NK-cell attack by TGF\u03b2 neutralization

BackgroundMedulloblastoma (MB), the most common pediatric brain cancer, presents with a poor prognosis in a subset of patients with high risk disease, or at recurrence, where current therapies are ineffective. Cord blood (CB) natural killer (NK) cells may be promising off-the-shelf effector cells for immunotherapy due to their recognition of malignant cells without the need for a known target, ready availability from multiple banks, and their potential to expand exponentially. However, they are currently limited by immune suppressive cytokines secreted in the MB tumor microenvironment including Transforming Growth Factor β (TGF-β). Here, we address this challenge in in vitro models of MB.MethodsCB-derived NK cells were modified to express a dominant negative TGF-β receptor II (DNRII) using retroviral transduction. The ability of transduced CB cells to maintain function in the presence of medulloblastoma-conditioned media was then assessed.ResultsWe observed that the cytotoxic ability of nontransduced CB-NK cells was reduced in the presence of TGF-β-rich, medulloblastoma-conditioned media (21.21 ± 1.19% killing at E:T 5:1 in the absence vs. 14.98 ± 2.11% in the presence of medulloblastoma-conditioned media, n = 8, p = 0.02), but was unaffected in CB-derived DNRII-transduced NK cells (21.11 ± 1.84% killing at E:T 5:1 in the absence vs. 21.81 ± 3.37 in the presence of medulloblastoma-conditioned media, n = 8, p = 0.85. We also observed decreased expression of CCR2 in untransduced NK cells (mean CCR2 MFI 826 ± 117 in untransduced NK + MB supernatant from mean CCR2 MFI 1639.29 ± 215 in no MB supernatant, n = 7, p = 0.0156), but not in the transduced cells. Finally, we observed that CB-derived DNRII-transduced NK cells may protect surrounding immune cells by providing a cytokine sink for TGF-β (decreased TGF-β levels of 610 ± 265 pg/mL in CB-derived DNRII-transduced NK cells vs. 1817 ± 342 pg/mL in untransduced cells; p = 0.008).ConclusionsCB NK cells expressing a TGF-β DNRII may have a functional advantage over unmodified NK cells in the presence of TGF-β-rich MB, warranting further investigation on its potential applications for patients with medulloblastoma.

Two morphological changes of cancer cells under natural killer cell killing

Abstract Natural killer (NK) cells use granule exocytosis to kill cancer cells, which involves perforin-mediated delivery of granzymes from NK cells to cancer cells. Once inside the cancer cells, granzyme B, a member of serine protease family, activates caspase-3, which activates the serine/threonine kinase Rho-associated coiled coil–containing protein kinase (ROCK) I, an effector of the small GTPase Rho. Activated ROCK I increases the phosphorylation of myosin regulatory light chain and thus stimulates actomyosin contraction, required for apoptotic membrane blebbing. Ultimately, cancer cells under NK cell attack show rounding, shrinkage, and membrane rupture, which are classical morphological changes observed at the onset of apoptosis. Although much has been learned about these morphological changes, a fundamental question of how melanoma cell death is induced by NK cells remains unanswered. Do all melanoma cell lines undergo the classical dying process? If not, is there another dying process? To address this simple issue, we examined the dying of B16 melanoma cell lines under NK cell attack by using time-lapse imaging. Upon contact with NK cells, B16-F10 cells rounded and most of them showed membrane rupture (98 min); however, B16 parent cells showed writhing and delayed membrane rupture (235 min). This morphological difference depended on the expression levels of myosin regulatory light chain 9 (MYL9) but not activating ligands (CD112, CD155, Rae-1, and MULT-1), SPI, FasL, or PD-L1. Taken together, our data show that melanoma cells show two distinct types of morphological changes upon contact with NK cells and suggest that a strategy to decrease MYL9 expression by melanoma cells may improve the efficacy of NK cell–based immunotherapy.

Medulloblastoma rendered susceptible to NK-cell attack by TGFß neutralization

Background & Aim Medulloblastoma (MB), the most common pediatric brain cancer, presents with a poor prognosis in patients with high-risk disease, and traditional therapies often cause significant permanent morbidity. Cord blood (CB) natural killer (NK) cells may be promising off-the-shelf effector cells for immunotherapy because they recognize malignant cells without the need for a known target, they are readily available from multiple banks, and they expand to significant numbers. However, they are currently limited by immune suppressive cytokines secreted in the MB tumor microenvironment, such as Transforming Growth Factor β (TGF-β). Methods, Results & Conclusion To overcome the detrimental effects of TGF-β, we modified CB-derived NK cells to express a dominant negative TGF-β receptor II (DNRII) by retroviral transduction and evaluated their ability to kill a TGF-β-secreting MB cell line (Daoy). We observed that the cytotoxic ability of nontransduced CB-NK cells was reduced in the presence ofmedulloblastoma-conditioned, TGF-β-richmedia (decreasing to 14.9±2.1% killing at an E:T ratio of 5:1 from 25.1±2.9%, n=10, p Hence, CB NK cells expressing a TGF-β DNRII may have a functional advantage over unmodified NK cells in the presence of TGF-β-rich MB, warranting further investigation as a novel therapeutic for the treatment of patients with high-risk medulloblastoma.

Genomic loss of HLA alleles may affect the clinical outcome in low-risk myelodysplastic syndrome patients

The Revised International Prognostic Score and some somatic mutations in myelodysplastic syndrome (MDS) are independently associated with transformation to acute myeloid leukemia (AML). Immunity has also been implicated in the pathogenesis of MDS, although the underlying mechanism remains unclear. We performed a SNP array on chromosome 6 in CD34+ purified blasts from 19 patients diagnosed with advanced MDS and 8 patients with other myeloid malignancies to evaluate the presence of loss of heterozygosity (LOH) in HLA and its impact on disease progression. Three patients had acquired copy-neutral LOH (CN-LOH) on 6p arms, which may disrupt antigen presentation and act as a mechanism for immune system evasion. Interestingly, these patients had previously been classified at low risk of AML progression, and the poor outcome cannot be explained by the acquisition of adverse mutations. LOH HLA was not detected in the remaining 24 patients, who all had adverse risk factors. In summary, the clinical outcome of patients with advanced MDS might be influenced by HLA allelic loss, wich allows subclonal expansions to evade cytotoxic-T and NK cell attack. CN-LOH HLA may therefore be a factor favoring MDS progression to AML independently of the somatic tumor mutation load.

Actin Cytoskeleton Remodeling Drives Breast Cancer Cell Escape from Natural Killer-Mediated Cytotoxicity.

Elucidation of the underlying molecular mechanisms of immune evasion in cancer is critical for the development of immunotherapies aimed to restore and stimulate effective antitumor immunity. Here, we evaluate the role of the actin cytoskeleton in breast cancer cell resistance to cytotoxic natural killer (NK) cells. A significant fraction of breast cancer cells responded to NK-cell attack via a surprisingly rapid and massive accumulation of F-actin near the immunologic synapse, a process we termed "actin response." Live-cell imaging provided direct evidence that the actin response is associated with tumor cell resistance to NK-cell-mediated cell death. High-throughput imaging flow cytometry analyses showed that breast cancer cell lines highly resistant to NK cells were significantly enriched in actin response-competent cells as compared with susceptible cell lines. The actin response was not associated with a defect in NK-cell activation but correlated with reduced intracellular levels of the cytotoxic protease granzyme B and a lower rate of apoptosis in target cells. Inhibition of the actin response by knocking down CDC42 or N-WASP led to a significant increase in granzyme B levels in target cells and was sufficient to convert resistant breast cancer cell lines into a highly susceptible phenotype. The actin response and its protective effects were fully recapitulated using donor-derived primary NK cells as effector cells. Together, these findings establish the pivotal role of actin remodeling in breast cancer cell resistance to NK-cell-mediated killing.Significance: These findings establish the pivotal role of the actin cytoskeleton in driving breast cancer cell resistance to natural killer cells, a subset of cytotoxic lymphocytes with important roles in innate antitumor immunity. Cancer Res; 78(19); 5631-43. ©2018 AACR.

NK-cell Editing Mediates Epithelial-to-Mesenchymal Transition via Phenotypic and Proteomic Changes in Melanoma Cell Lines.

Tumor cell plasticity is a major obstacle for the cure of malignancies as it makes tumor cells highly adaptable to microenvironmental changes, enables their phenotype switching among different forms, and favors the generation of prometastatic tumor cell subsets. Phenotype switching toward more aggressive forms involves different functional, phenotypic, and morphologic changes, which are often related to the process known as epithelial-mesenchymal transition (EMT). In this study, we report natural killer (NK) cells may increase the malignancy of melanoma cells by inducing changes relevant to EMT and, more broadly, to phenotype switching from proliferative to invasive forms. In coculture, NK cells induced effects on tumor cells similar to those induced by EMT-promoting cytokines, including upregulation of stemness and EMT markers, morphologic transition, inhibition of proliferation, and increased capacity for Matrigel invasion. Most changes were dependent on the engagement of NKp30 or NKG2D and the release of cytokines including IFNγ and TNFα. Moreover, EMT induction also favored escape from NK-cell attack. Melanoma cells undergoing EMT either increased NK-protective HLA-I expression on their surface or downregulated several tumor-recognizing activating receptors on NK cells. Mass spectrometry-based proteomic analysis revealed in two different melanoma cell lines a partial overlap between proteomic profiles induced by NK cells or by EMT cytokines, indicating that various processes or pathways related to tumor progression are induced by exposure to NK cells.Significance: NK cells can induce prometastatic properties on melanoma cells that escape from killing, providing important clues to improve the efficacy of NK cells in innovative antitumor therapies. Cancer Res; 78(14); 3913-25. ©2018 AACR.

Impaired NK cell recognition of vemurafenib-treated melanoma cells is overcome by simultaneous application of histone deacetylase inhibitors

ABSTRACTTherapy of metastatic melanoma advanced recently with the clinical implementation of signalling pathway inhibitors, such as vemurafenib, specifically targeting mutant BRAFV600E. In general, patients experience remarkable clinical responses under BRAF inhibitor (BRAFi) treatment but eventually progress within 6–8 months due to resistance development. Responding metastases show an increased immune cell infiltrate, including also NK cells, that, however, is no longer detectable in BRAFi-resistant lesions, suggesting NK cell activity should be exploited to prevent disease progression. Here, we examined the effects of BRAFi on the expression of ligands targeting activating NK cells receptors immediately after treatment onset, prior to resistance development. We demonstrate that BRAFV600E mutant melanoma cells cultured in the presence of vemurafenib, strongly decreased surface expression of ligands for NK activating receptors including the NKG2D-ligand, MICA, and the DNAM-1 ligand, CD155, and became significantly less susceptible to NK cell attack. NKG2D-ligand protein downregulation was due to a significant decrease in mRNA levels, already detectable 24 h after drug treatment. Interestingly, vemurafenib-induced MICA downregulation could be counteracted by treatment of melanoma cells with the histone deacetylase (HDAC) inhibitor (HDACi) sodium butyrate, that also upregulated the DNAM1-ligand, Nectin-2. HDACi treatment enhanced surface expression of NKG2D-ligands in the presence of BRAFi, accompanied by recovery of NK cell recognition, but only upon simultaneous drug application. These results suggest that co-administration of BRAFi and HDAC inhibitors as well as having direct effects on melanoma cell survival, could also synergise to improve NK cell recognition and avoid tumour immune evasion.

Abstract 4639: HLA and NKG2D ligand abnormalities and IFN-γ unnresponsiveness in human colorectal carcinoma cell lines

Abstract Background: Cetuximab, an anti-epidermal growth factor receptor (EGFR) monoclonal antibody, has shown promising efficacy on wild-type RAS metastatic colorectal cancer (CRC) patients. Cetuximab demonstrates anti-cancer effect via NK cells and subsequent immunogenic cell death. Chemotherapy or targeted therapy may change immune surface markers. Methods: We characterized a panel of 6 CRC cell lines with different genetic features. The impacts of interferon-γ (IFN-γ) on cell surface expressions of major histocompatibility complex (MHC) class I (including subtypes), MHC class II (including subtypes), MHC class 1 related molecule A (MICA, the NK cell ligand), Intercellular Adhesion Molecule 1 (ICAM-1, the immunoglobulin superfamily), EGFR, and Chondroitin Sulfate Proteoglycan 4 (CSPG-4, pericyte attaching marker) before and after treatment with IFN-γ (100 U/ml, 48 h) were explored in selected cell lines Results: Among six human colon cancer cell lines analyzed, DLD-1, HCT15, and LoVo exhibited no expression of HLA-A and HLA-B,C. Colo-320 demonstrated both low HLA-A and HLA-B,C expression and irresponsive to IFN-γ stimulation. In contrast, both HT-29 and SW-480 showed low HLA-A and HLA-B,C expression, but the expression of both HLA-A and HLA-B,C was corrected after IFN-γ stimulation. All six cell lines possessed low MHC class II expression and irresponsive to IFN-γ stimulation. All six cell lines possessed low MIC expression and irresponsive to IFN-γ stimulation. All six cell lines showed low ICAM-1 expression, but only HT-29 and SW-480 were responsive to IFN-γ stimulation. LOVO and SW-480 demonstrated high EGFR expression and irresponsive to IFN-γ stimulation. Only HT-29 possessed high CSPG-4 expression. Conclusion: These findings reveal that regardless of their genetic features, all six CRC cell lines possess a phenotype that may allow them to escape cytotoxic T and NK cell attack. Table Cell LineMSICIMPKRASBRAFPI3KCATP53DLD-1MSI+G13DWTE545KS241FHCT-15MSI+G13DWTE545KS241FLOVOMSI-G13DWTWTWTCOLO-320MSS-WTWTWTR248WHT-29MSS+WTV600EP449TR273HSW-480MSS-G12VWTWTR273H Citation Format: Yi-Hsin Liang, Yen-Cheng Lin, Kuo-Hsin Chen, Chiu-Hwa Kao, Ann-Lii Cheng, Kun-Huei Yeh, Chien-Chung Chang. HLA and NKG2D ligand abnormalities and IFN-γ unnresponsiveness in human colorectal carcinoma cell lines [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 4639. doi:10.1158/1538-7445.AM2017-4639

RIG-I Resists Hypoxia-Induced Immunosuppression and Dedifferentiation.

A hypoxic tumor microenvironment is linked to poor prognosis. It promotes tumor cell dedifferentiation and metastasis and desensitizes tumor cells to type-I IFN, chemotherapy, and irradiation. The cytoplasmic immunoreceptor retinoic acid-inducible gene-I (RIG-I) is ubiquitously expressed in tumor cells and upon activation by 5'-triphosphate RNA (3pRNA) drives the induction of type I IFN and immunogenic cell death. Here, we analyzed the impact of hypoxia on the expression of RIG-I in various human and murine tumor and nonmalignant cell types and further investigated its function in hypoxic murine melanoma. 3pRNA-inducible RIG-I-expression was reduced in hypoxic melanoma cells compared with normoxic controls, a phenomenon that depended on the hypoxia-associated transcription factor HIF1α. Still, RIG-I functionality was conserved in hypoxic melanoma cells, whereas responsiveness to recombinant type-I IFN was abolished, due to hypoxia-induced loss of type I IFN receptor expression. Likewise, RIG-I activation in hypoxic melanoma cells, but not exposure to recombinant IFNα, provoked melanocyte antigen-specific CD8+ T-cell and NK-cell attack. Scavenging of hypoxia-induced reactive oxygen species by vitamin C restored the inducible expression of RIG-I under hypoxia in vitro, boosted in vitro anti-melanoma NK- and CD8+ T-cell attack, and augmented 3pRNA antitumor efficacy in vivo These results demonstrate that RIG-I remains operational under hypoxia and that RIG-I function is largely insensitive to lower cell surface expression of the IFNα receptor. RIG-I function could be fortified under hypoxia by the combined use of 3pRNA with antioxidants. Cancer Immunol Res; 5(6); 455-67. ©2017 AACR.

MHC Class I Expression by Donor Hematopoietic Stem Cells Is Required to Prevent NK Cell Attack in Allogeneic, but Not Syngeneic Recipient Mice

NK cells resist engraftment of syngeneic and allogeneic bone marrow (BM) cells lacking major histocompatibility (MHC) class I molecules, suggesting a critical role for donor MHC class I molecules in preventing NK cell attack against donor hematopoietic stem and progenitor cells (HSPCs), and their derivatives. However, using high-resolution in vivo imaging, we demonstrated here that syngeneic MHC class I knockout (KO) donor HSPCs persist with the same survival frequencies as wild-type donor HSPCs. In contrast, syngeneic MHC class I KO differentiated hematopoietic cells and allogeneic MHC class I KO HSPCs were rejected in a manner that was significantly inhibited by NK cell depletion. In vivo time-lapse imaging demonstrated that mice receiving allogeneic MHC class I KO HSPCs showed a significant increase in NK cell motility and proliferation as well as frequencies of NK cell contact with and killing of HSPCs as compared to mice receiving wild-type HSPCs. The data indicate that donor MHC class I molecules are required to prevent NK cell-mediated rejection of syngeneic differentiated cells and allogeneic HSPCs, but not of syngeneic HSPCs.

Resistance of Hematopoietic Stem Cells Lacking the KIR Ligand to Autologous NK Cell Attacks in Patients with Acquired Aplastic Anemia

Normal blood cells, including hematopoietic stem cells (HSCs), express KIR ligands (KIR-Ls) to protect themselves from an autologous NK cell attack, and malignant cells lacking KIR-Ls elicit NK cell-mediated killing of themselves. This missing-self mechanism is believed to play an important role in the elimination of malignant cells. However, the mechanisms underlying the killing of KIR-L-lacking malignant cells by NK cells remain unclear due to the heterogeneity of tumor cells in terms of their proliferative capacity, and also because other accessory molecules may be involved in the NK cell attacks, in addition to KIR-Ls. This makes it difficult to clarify the interaction between NK cells and KIR-L-lacking target cells. The lack of class I HLA occurs not only in malignant blood cells, but also in the normal leukocytes of patients with acquired aplastic anemia (AA). These HLA-lacking leukocytes, detectable in 13% of patients with AA, are derived from HSCs that undergo copy number neutral loss of heterozygosity of the short arm of chromosome 6 (6pLOH), and thereby escape the cytotoxic T-cell (CTL) attack against HSCs. The 6pLOH may involve KIR-L loss in some patients, leading to a change in the susceptibility of the affected HSCs to NK cell-mediated killing. Unlike malignant cells, HLA-lacking leukocytes are essentially the same as the wild-type leukocytes, except for the HLA expression. Studying 6pLOH (+) AA patients with leukocytes lacking KIR-Ls should therefore be useful for clarifying the roles of KIR-Ls and other accessory molecules in the target cell killing by NK cells. Screening of 389 patients with AA using flow cytometry and a SNP array analysis revealed that there were HLA-A allele-lacking leukocytes in 60 (15.4%) patients, which included 36 C1/C2 and 24 Bw4/Bw6 heterozygotes. Unexpectedly, a lack of KIR-Ls as a result of 6pUPD was found in five patients (13.9%, C1 missing in two and C2 missing in three) of the 36 C1/C2 heterozygotes and in five (20.8%) of the 24 Bw4/Bw6 heterozygotes, although the proportion of patients lacking a KIR-L-containing haplotype (20.8%) was significantly lower than that of patients lacking a haplotype that did not contain KIR-Ls (79.2%). Moreover, the median percentage of HLA-A-lacking granulocytes in the 10 patients who lacked a KIR-L-containing haplotype (12.4%, 0.44%-50.3%) was significantly lower than that (55.3%, 1.4%-99.4%) in the 26 patients who lacked a haplotype that did not contain KIR-Ls, suggesting that the HSCs lacking KIR-Ls or their progenies are susceptible to autologous NK cells to some extent, but are not eliminated completely. To clarify the mechanisms underlying the HSC resistance to NK cells, we determined the KIR gene repertoire and the haplotype of seven patients whose 6pLOH(+) leukocytes were lacking a KIR-L-containing haplotype. All patients possessed inhibitory KIR genes responsive to corresponding KIR-Ls, a finding that negates the possibility that NK cells failed to undergo licensing in these patients. Although the frequency of the KIR-B haplotype, a haplotype associated with a higher cytotoxic function of NK cells, in the seven patients was lower (14%) than that in Japanese healthy individuals (40.1%), two patients possessed the KIR-B haplotype. Phenotypic analyses of the NK cell subsets defined by anti-2DL1, anti-2DL2/2DL3 and anti-3DL1 antibodies showed that all seven patients had a similar percentage of the eight different NK cell subsets, which included 0.5 to 8% of effector NK cells capable of killing leukocytes lacking corresponding KIR-Ls. The expression level of HLA-E was comparable between HLA-A-lacking and HLA-A-retaining monocytes. The expression of NKG2A on the effector NK cells was also comparable to that of the other NK cell subsets in the 6pLOH(+) patients. Our study demonstrated, for the first time, that HSCs lacking KIR-Ls can evade autologous NK cell attack through an as yet unknown mechanism(s) and can continue to generate blood cells in patients with AA. DisclosuresNo relevant conflicts of interest to declare.

NK receptors: tools for a polyvalent cell family.

NK receptors: tools for a polyvalent cell family.