Immune Modifications in Fetal Membranes Overlying the Cervix Precede Parturition in Humans.

In humans, parturition is currently viewed as an intrauterine outbreak of inflammation, accompanied by a massive release of proinflammatory cytokines at the maternal-fetal interface that comprises the maternal decidua, placenta, and fetal membranes. At term, fetal membranes overlying the cervix, the future site of rupture, show altered morphology and are termed the zone of altered morphology (ZAM). These alterations occur in normal fetal membranes during late pregnancy, in preparation for labor. In this study, transcriptome, flow cytometry, electron microscopy, and immunohistochemistry analyses collectively highlight a local shift in gene expression and lymphocyte activation in the ZAM. Just before labor, we show that highly polymorphic HLA-A, -B, and -C determinants of fetal origin are selectively exposed in the ZAM to the maternal immune system. A graft rejection-like program occurs in the ZAM, which involves 1) the activation of cytotoxic decidual NK cells, and 2) the decline of decidual immunotolerant M2-like macrophages. Comparison with a prior cohort of fetal membranes shows that acute inflammation only takes place after these first steps of immune modifications. Our results therefore strongly argue in favor of local immune remodeling at the onset of parturition.

High number of CD56(bright) NK-cells and persistently low CD4+ T-cells in a hemophiliac HIV/HCV co-infected patient without opportunistic infections.

BACKGROUND: Both the human immunodeficiency virus (HIV) and hepatitis C virus (HCV), either alone or as coinfections, persist in their hosts by destroying and/or escaping immune defenses, with high morbidity as consequence. In some cases, however, a balance between infection and immunity is reached, leading to prolonged asymptomatic periods. We report a case of such an indolent co-infection, which could be explained by the development of a peculiar subset of Natural Killer (NK) cells. RESULTS: Persistently high peripheral levels of CD56+ NK cells were observed in a peculiar hemophiliac HIV/HCV co-infected patient with low CD4 counts, almost undetectable HIV viral load and no opportunistic infections. Thorough analysis of NK-subsets allowed to identify a marked increase in the CD56bright/dim cell ratio and low numbers of CD16+/CD56- cells. These cells have high levels of natural cytotoxicity receptors but low NCR2 and CD69, and lack both CD57 and CD25 expression. The degranulation potential of NK-cells which correlates with target cytolysis was atypically mainly performed by CD56bright NK-cells, whereas no production of interferon γ (IFN-γ) was observed following NK activation by K562 cells. CONCLUSIONS: These data suggest that the expansion and lytic capacity of the CD56bright NK subset may be involved in the protection of this « rare ¼ HIV/HCV co-infected hemophiliac A patient from opportunistic infections and virus-related cancers despite very low CD4+ cell counts.

Myelodysplastic Syndrome associated TET2 mutations affect NK cell function and genome methylation.

Myelodysplastic syndromes (MDS) are clonal hematopoietic disorders, representing high risk of progression to acute myeloid leukaemia, and frequently associated to somatic mutations, notably in the epigenetic regulator TET2. Natural Killer (NK) cells play a role in the anti-leukemic immune response via their cytolytic activity. Here we show that patients with MDS clones harbouring mutations in the TET2 gene are characterised by phenotypic defects in their circulating NK cells. Remarkably, NK cells and MDS clones from the same patient share the TET2 genotype, and the NK cells are characterised by increased methylation of genomic DNA and reduced expression of Killer Immunoglobulin-like receptors (KIR), perforin, and TNF-α. In vitro inhibition of TET2 in NK cells of healthy donors reduces their cytotoxicity, supporting its critical role in NK cell function. Conversely, NK cells from patients treated with azacytidine (#NCT02985190; https://clinicaltrials.gov/ ) show increased KIR and cytolytic protein expression, and IFN-γ production. Altogether, our findings show that, in addition to their oncogenic consequences in the myeloid cell subsets, TET2 mutations contribute to repressing NK-cell function in MDS patients.

Innate lymphoid cells: NK and cytotoxic ILC3 subsets infiltrate metastatic breast cancer lymph nodes.

Innate lymphoid cells (ILCs) - which include cytotoxic Natural Killer (NK) cells and helper-type ILC - are important regulators of tissue immune homeostasis, with possible roles in tumor surveillance. We analyzed ILC and their functionality in human lymph nodes (LN). In LN, NK cells and ILC3 were the prominent subpopulations. Among the ILC3s, we identified a CD56+/ILC3 subset with a phenotype close to ILC3 but also expressing cytotoxicity genes shared with NK. In tumor-draining LNs (TD-LNs) and tumor samples from breast cancer (BC) patients, NK cells were prominent, and proportions of ILC3 subsets were low. In tumors and TD-LN, NK cells display reduced levels of NCR (Natural cytotoxicity receptors), despite high transcript levels and included a small subset CD127- CD56- NK cells with reduced function. Activated by cytokines CD56+/ILC3 cells from donor and patients LN acquired cytotoxic capacity and produced IFNg. In TD-LN, all cytokine activated ILC populations produced TNFα in response to BC cell line. Analyses of cytotoxic and helper ILC indicate a switch toward NK cells in TD-LN. The local tumor microenvironment inhibited NK cell functions through downregulation of NCR, but cytokine stimulation restored their functionality.

Specific Patterns of Blood ILCs in Metastatic Melanoma Patients and Their Modulations in Response to Immunotherapy.

Immunotherapy targeting immune checkpoint receptors brought a breakthrough in the treatment of metastatic melanoma patients. However, a number of patients still resist these immunotherapies. Present on CD8+T cells, immune checkpoint receptors are expressed by innate lymphoid cells (ILCs), which may contribute to the clinical response. ILCs are composed of natural killer (NK) cells, which are cytotoxic effectors involved in tumor immunosurveillance. NK cell activation is regulated by a balance between activating receptors that detect stress molecules on tumor cells and HLA-I-specific inhibitory receptors. Helper ILCs (h-ILCs) are newly characterized ILCs that secrete cytokines and regulate the immune homeostasis of tissue. We investigated the modulation of blood ILCs in melanoma patients treated with ipilimumab. Circulating ILCs from metastatic stage IV melanoma patients and healthy donors were studied for their complete phenotypic status. Patients were studied before and at 3, 6, and 12 weeks of ipilimumab treatment. A comparison of blood ILC populations from donors and melanoma patients before treatment showed changes in proportions of ILC subsets, and a significant inverse correlation of CD56dim NK cells and h-ILC subsets was identified in patients. During treatment with ipilimumab, percentages of all ILC subsets were reduced. Ipilimumab also impacted the expression of the CD96/TIGIT/DNAM-1 pathway in all ILCs and increased CD161 and CTLA-4 expression by h-ILCs. When considering the response to the treatment, patients without disease control were characterized by higher percentages of CD56bright NK cells and ILC1. Patients with disease control displayed larger populations of activated CD56dimCD16+ DNAM-1+ NK cells, while anergic CD56dimCD16-DNAM-1- NK cells were prominent in patients without disease control. These results provide original findings on the distribution of ILC subsets in advanced melanoma patients and their modulation through immunotherapy. The effects of ipilimumab on these ILC subsets may critically influence therapeutic outcomes. These data indicate the importance of considering these innate cell subsets in immunotherapeutic strategies for melanoma patients.

Two opposite signaling outputs are driven by the KIR2DL1 receptor in human CD4+ T cells.

Inhibitory killer Ig-like receptors (KIR), expressed by human natural killer cells and effector memory CD8(+) T-cell subsets, bind HLA-C molecules and suppress cell activation through recruitment of the Src homology 2 domain-containing protein tyrosine phosphatase 1 (SHP-1). To further analyze the still largely unclear role of inhibitory KIR receptors on CD4(+) T cells, KIR2DL1 transfectants were obtained from a CD4(+) T-cell line and primary cells. Transfection of CD4(+) T cells with KIR2DL1 dramatically increased the T-cell receptor (TCR)-induced production of interleukin-2 independently of ligand binding but inhibited TCR-induced activation after ligation. KIR-mediated costimulation of TCR activation involves intact KIR2DL1-ITIM phosphorylation, SHP-2 recruitment, and PKC- phosphorylation. Synapses leading to activation were characterized by an increase in the recruitment of p-Tyr, SHP-2, and p-PKC-, but not of SHP-1. Interaction of KIR2DL1 with its ligand led to a strong synaptic accumulation of KIR2DL1 and the recruitment of SHP-1/2, inhibiting TCR-induced interleukin-2 production. KIR2DL1 may induce 2 opposite signaling outputs in CD4(+) T cells, depending on whether the KIR receptor is bound to its ligand. These data highlight unexpected aspects of the regulation of T cells by KIR2DL1 receptors, the therapeutic manipulation of which is currently being evaluated.

Dendritic cell and natural killer cell cross-talk: a pivotal role of CX3CL1 in NK cytoskeleton organization and activation.

Initial molecular events leading to natural killer lymphocyte (NK) and dendritic cell (DC) interactions are largely unknown. Here, the role of CX3CL1 (fractalkine), a chemokine expressed on mature dendritic cells (mDCs) has been investigated. We show that CX3CL1 promotes NK activation by mDCs. After blocking of CX3CL1 by antibody, no activation occurred but major histocompatibility complex (MHC) class I neutralization restored DC-mediated NK activation, suggesting an interaction between CX3CL1 signaling and the functioning of inhibitory KIR. Then the YTS NK cell line, in which the inhibitory receptor KIR2DL1 had been introduced, was used. The presence of KIR2DL1 did not decrease YTS activation by HLA-Cw4 DC when CX3CL1 was functional. In contrast, CX3CL1 neutralization led to killer cell immunoglobulin-like receptor (KIR) phosphorylation and SHP-1 recruitment in YTS(KIR2DL1) cultured with HLA-Cw4 mDCs. Moreover, CX3CL1 neutralization promoted dispersion of lipid rafts and the formation of a multiprotein complex required for cytoskeletal rearrangements in YTS NK cells. These findings point to a pivotal role of CX3CL1 in the activation of resting NK cells by mature DCs.

Two-dimensional dynamic evaluation of natural killer cell-mediated lysis of adherent target cells.

Cell-mediated cytotoxicity is a major function of cytotoxic lymphocytes. The cytotoxic function of immune effectors requires accurate and sensitive quantification as tumor immunotherapies are actively developed to treat growing types of tumors. Various methods have been developed to quantify this function. A first approach consists in measuring the externalization of LAMP-1 (lysosomal associated membrane 1), CD107a molecules transitory expressed at the cell surface by degranulating cytotoxic cells and is determined by flow cytometry. The focus of the chapter concerns the second approach that quantifies target cell lysis resulting from the close contact interaction with cytotoxic Natural Killer (NK) lymphocytes. For long time, target cell lysis was evaluated by chromium release assay, requiring use of radioactive labeled salt (51Cr) and specific devices not compatible with repeated tests performed for immunomonitoring of patients. Other methods include fluorimetric and bioluminescence assays. Monitoring immune cell-mediated lysis of adherent targets by the dynamic measure of cell proliferation using the Real time cell analyzer (RTCA) is a good alternative. The test relies on sensitive dynamic measure of cell index values during their interactions with cytotoxic immune effectors. The cell index increasing with cell proliferation rapidly drops in presence of immune cells. The lysis is quantified in reference with targets alone and expressed as percentages of lysis curves. Moreover, the dynamic monitoring of target cell index allows the evaluation of drugs, cytokines, mAbs on target cell lysis. Here we describe a robust and sensitive method for quantification of immune cell-mediated lysis of adherent targets.

BRAF inhibitor resistance of melanoma cells triggers increased susceptibility to natural killer cell-mediated lysis.

BACKGROUND: Targeted therapies and immunotherapies are first-line treatments for patients with advanced melanoma. Serine-threonine protein kinase B-RAF (BRAF) and mitogen-activated protein kinase (MEK) inhibition leads to a 70% response rate in patients with advanced melanoma with a BRAFV600E/K mutation. However, acquired resistance occurs in the majority of patients, leading to relapse. Immunotherapies that activate immune cytotoxic effectors induce long-lasting responses in 30% of patients. In that context, combination of targeted therapies with immunotherapy (IT) is a promising approach. We considered boosting natural killer (NK) cell tumor immunosurveillance, as melanoma cells express stress-induced molecules and activate NK cell lysis. METHODS: Here we have generated vemurafenib (a BRAF inihibitor)-resistant (R) cells from BRAFV600E SK28 and M14-sensitive (S) melanoma cell lines and investigated how resistance interferes with immunogenicity to NK cells. We determined the levels of several soluble molecules including NK ligands in 61 melanoma patients at baseline and 6 months M post-treatment with targeted therapies or immunotherapies. RESULTS: Vemurafenib resistance involved activation of p-AKT in SK28R and of p-MEK/p-ERK in M14R cells and was accompanied by modulation of NK ligands. Compared with S cells, SK28R displayed an increased expression of natural killer group 2 D (NKG2D) receptor ligands (major histocompatibility complex class (MHC) I chain-related protein A (MICA) and UL16-binding protein 2 (ULBP2)) whereas M14R exhibited decreased ULBP2 . SK28R and M14R cells induced higher NK degranulation and interferon gamma secretion and were more efficiently lysed by donor and patient NK cells. SK28R showed increased tumor necrosis factor-related apoptosis-inducing ligand receptor II (TRAIL-RII) expression and TRAIL-induced apoptosis, and TRAIL-induced apoptosis of M14R was decreased. Combined BRAF/MEK inhibitors abrogated the growth of SK28S, M14S, and M14R cells, while growth of SK28R was maintained. BRAF/MEK inhibition attenuated NK activity but R cell lines activated polyfunctional NK cells and were lysed with high efficiency. We investigated the relationship of soluble NK ligands and response to treatment in a series of melanoma patients. Soluble NKG2D ligands known to regulate the receptor function have been associated to cancer progression. Serum analysis of patients treated with target therapies or IT indicates that soluble forms of NK ligands (MICA, B7H6, programmed cell death ligand 1, and carcinoembryonic antigen cell adhesion molecule 1) may correlate with clinical response. CONCLUSION: These results support strategies combining targeted therapies and NK-based immunotherapies.

Membrane-bound interleukin (IL)-15 on renal tumor cells rescues natural killer cells from IL-2 starvation-induced apoptosis.

Renal cell carcinoma primary tumors and lung metastases are infiltrated by activated natural killer (NK) cells. Interleukin (IL)-15, a major cytokine involved in cross-talk between accessory cells (dendritic cells and macrophages) and NK cells, is produced by epithelial renal cells. We show that renal cell carcinoma cells and normal renal cells express IL-15 mRNA and membrane-bound IL-15 (MbIL-15). These cells also express IL-15 receptor alpha (IL-15Ralpha). Silencing of IL-15Ralpha by specific small interfering RNA in renal cell carcinoma had no effect on MbIL-15 production, indicating that the cytokine is not cross-presented by IL-15Ralpha in renal cell carcinoma cells but anchored to the membrane. Furthermore, we show that MbIL-15 from renal cell carcinoma cells is functional and involved in rapid nuclear translocation of phosphorylated signal transducers and activators of transcription 3 in IL-2-starved NK cells. MbIL-15 on the target did not interfere with resting NK cell activation and target cell cytolysis but rescued NK cells from IL-2 starvation-induced apoptosis through contact-dependent interaction. Masking of MbIL-15 with soluble IL-15Ralpha molecules restored NK cell apoptosis. These findings suggest that IL-15 produced by renal tumor cells is involved in the maintenance of active NK cells at the tumor site.

NKG2D/NKG2-Ligand Pathway Offers New Opportunities in Cancer Treatment.

The antitumor functions of NK cells are regulated by the integration of positive and negative signals triggered by numerous membrane receptors present on the NK cells themselves. Among the main activating receptors, NKG2D binds several stress-induced molecules on tumor targets. Engagement of NKG2D by its ligands (NKG2D-Ls) induces NK cell activation leading to production of cytokines and target cell lysis. These effects have therapeutic potential as NKG2D-Ls are widely expressed by solid tumors, whereas their expression in healthy cells is limited. Here, we describe the genetic and environmental factors regulating the NKG2D/NKG2D-L pathway in tumors. NKG2D-L expression is linked to cellular stress and cell proliferation, and has been associated with oncogenic mutations. Tumors have been found to alter their to NKG2D-L expression as they progress, which interferes with the antitumor function of the pathway. Nevertheless, this pathway could be advantageously exploited for cancer therapy. Various cancer treatments, including chemotherapy and targeted therapies, indirectly interfere with the cellular and soluble forms of NKG2D-Ls. In addition, NKG2D introduced into chimeric antigen receptors in T- and NK cells is a promising tumor immunotherapy approach.

CD16+NKG2Ahigh Natural Killer Cells Infiltrate Breast Cancer-Draining Lymph Nodes.

Tumor-draining lymph nodes (TD-LNs) are the first site of metastasis of breast cancer. Natural killer (NK) cells that infiltrate TD-LNs [including noninvaded (NI) or metastatic (M)-LNs from breast cancer patients] and NK cells from healthy donor (HD)-LNs were characterized, and their phenotype analyzed by flow cytometry. Low percentages of tumor cells invaded M-LNs, and these cells expressed ULBP2 and HLA class I molecules. Although NK cells from paired NI and M-LNs were similar, they expressed different markers compared with HD-LN NK cells. Compared with HD-LNs, TD-LN NK cells expressed activating DNAM-1, NKG2C and inhibitory NKG2A receptors, and exhibited elevated CXCR3 expression. CD16, NKG2A, and NKp46 expression were shown to be increased in stage IIIA breast cancer patients. TD-LNs contained a large proportion of activated CD56brightCD16+ NK cells with high expression of NKG2A. We also showed that a subset of LN NK cells expressed PD-1, expression of which was correlated with NKp30 and NKG2C expression. LN NK cell activation status was evaluated by degranulation potential and lytic capacity toward breast cancer cells. NK cells from TD-LNs degranulated after coculture with breast cancer cell lines. Cytokine-activated TD-LN NK cells exerted greater lysis of breast cancer cell lines than HD-LN NK cells and preferentially lysed the HLA class Ilow MCF-7 breast cancer cell line. TD-LNs from breast cancer patients, thus, contained activated lytic NK cells. The expression of inhibitory receptor NKG2A and checkpoint PD-1 by NK cells infiltrating breast cancer-draining LNs supports their potential as targets for immunotherapies using anti-NKG2A and/or anti-PD-1.

Circulating NKp46+ Natural Killer cells have a potential regulatory property and predict distinct survival in Non-Small Cell Lung Cancer.

Natural killer (NK) cells are innate effector lymphocytes widely involved in cancer immunosurveillance. In this study, we described three circulating NK cell subsets in patients with non-small cell lung cancer (NSCLC). Compared to healthy donors (HD), lower rate of the cytotoxic CD56dim CD16+ NK cells was found in NSCLC patients (76.1% vs 82.4%, P = 0.0041). In contrast, the rate of CD56bright NK cells was similar between patients and HD. We showed in NSCLC patients a higher rate of a NK cell subset with CD56dim CD16- phenotype (16.7% vs 9.9% P = 0.0001). The degranulation property and cytokines production were mainly drive by CD56dim CD16- NK cell subset in patients. Analysis of natural cytotoxicity receptors (NCRs) expression identified four distinct clusters of patients with distinct NK cell subset profiles as compared to one major cluster in HD. Notably the cluster characterized by a low circulating level of NKp46+ NK cell subsets was absent in HD. We showed that the rate of circulating NKp46+ CD56dim CD16+ NK cells influenced the patients' survival. Indeed, the median overall survival in patients exhibiting high versus low level of this NK cell subset was 16 and 27 months respectively (P = 0.02). Finally, we demonstrated that blocking NKp46 receptor in vitro was able to restore spontaneous tumor specific T cell responses in NSCLC patients. In conclusion, this study showed a distinct distribution and phenotype of circulating NK cell subsets in NSCLC. It also supports the regulatory role of NKp46+ NK cell subset in NSCLC patients.

Activation of cytotoxic T-cell receptor gammadelta T lymphocytes in response to specific stimulation in myelodysplastic syndromes.

BACKGROUND: We previously reported that the function and proliferation of natural killer cells in myelodysplastic syndromes are defective. T-cell receptor gammadelta T cells are other important components of innate immunity that have been recently implicated in the immune response against hematologic malignancies. DESIGN AND METHODS: We evaluated the phenotype, function, and in vitro expansion of myelodysplastic syndrome patient-derived gammadelta T cells in response to interleukin-2 and bromohalohydrin pyrophosphate, a synthetic phosphoantigen with a potent T-cell receptor gammadelta agonist effect that specifically activates and amplifies this T-cell population. RESULTS: Vgamma9Vdelta2 T cells, the major circulating gammadelta T-cell subset, were reduced in myelodysplastic syndromes, but mainly in myelodysplastic syndromes' patients with associated autoimmune diseases, suggesting that this anomaly was largely due to the autoimmune component. On the other hand, bromohalohydrin pyrophosphate-induced expansion of the Vgamma9Vdelta2 T-cell population in all 15 control samples, but in only 26 of 43 (60%) myelodysplastic syndromes patients. The response to bromohalohydrin pyrophosphate was independent of World Health Organization subtype, cytogenetic findings and International Prognostic Scoring System score. In responding myelodysplastic syndromes patients, expanded Vgamma 9Vdelta2 T cells exhibited normal cytolytic and secretory activity against leukemic and myelodysplastic syndromes cell lines; fluorescence in situ hybridization analysis indicated that these Vgamma 9Vdelta2 T cells were not derived from the myelodysplastic syndromes clone. However, these Vgamma 9Vdelta2 T cells from the MDS patients had limited proliferative capacity in response to interleukin-2 despite having normal expression of interleukin-2 receptor chains (alpha beta gamma ). CONCLUSIONS: These results, combined with our previous findings concerning natural killer cells, suggest that there are immune surveillance defects in myelodysplastic syndromes, which may contribute to the pathogenesis of these syndromes.

TNFR2/BIRC3-TRAF1 signaling pathway as a novel NK cell immune checkpoint in cancer.

Natural Killer (NK) cells control metastatic dissemination of murine tumors and are an important prognostic factor in several human malignancies. However, tumor cells hijack many of the NK cell functional features compromising their tumoricidal activity. Here, we show a deleterious role of the TNFα/TNFR2/BIRC3/TRAF1 signaling cascade in NK cells from the tumor microenvironment (TME). TNFα induces BIRC3/cIAP2 transcripts and reduces NKp46/NCR1 transcription and surface expression on NK cells, promoting metastases dissemination in mice and poor prognosis in GIST patients. NKp30 engagement, by promoting the release of TNFα, also contributes to BIRC3 upregulation, and more so in patients expressing predominantly NKp30C isoforms. These findings reveal that in the absence of IL-12 or a Th1-geared TME, TNFα can be considered as a negative regulatory cytokine for innate effectors.

Altered IFNgamma signaling and preserved susceptibility to activated natural killer cell-mediated lysis of BCR/ABL targets.

Previous studies have shown that BCR/ABL oncogene, the molecular counterpart of the Ph1 chromosome, could represent a privileged target to natural killer (NK) cells. In the present study, we showed that activated peripheral NK cells killed high-level BCR/ABL transfectant UT-7/9 derived from the pluripotent hematopoietic cell line UT-7 with a high efficiency. To further define the mechanisms controlling BCR/ABL target susceptibility to NK-mediated lysis, we studied the effect of IFNgamma, a key cytokine secreted by activated NK cells, on the lysis of these targets. Treatment of UT-7, UT-7/neo, and low BCR/ABL transfectant UT-7/E8 cells with IFNgamma resulted in a dramatic induction of human leukocyte antigen class I (HLA-I) molecules and subsequently in their reduced susceptibility to NK-mediated cytolysis likely as a consequence of inhibitory NK receptors engagement. In contrast, such treatment neither affected HLA-I expression on transfectants expressing high level of BCR/ABL (UT-7/9) nor modulated their lysis by NK cells. Our data further show that the high-level BCR/ABL in UT-7/9 cells display an altered IFNgamma signaling, as evidenced by a decrease in IFN regulatory factor-1 (IRF-1) and signal transducers and activators of transcription (STAT) 1 induction and activation in response to IFNgamma, whereas this pathway is normal in UT-7 and UT-7/E8 cells. A decreased HLA-I induction and nuclear phospho-STAT1 nuclear translocation were also observed in blasts from most chronic myelogenous leukemia patients in response to IFNgamma. These results outline the crucial role of IFNgamma in the control of target cell susceptibility to lysis by activated NK cells and indicate that the altered response to IFNgamma in BCR/ABL targets may preserve these cells from the cytokine-induced negative regulatory effect on their susceptibility to NK-mediated lysis.

BCR/ABL promotes dendritic cell-mediated natural killer cell activation.

BCR/ABL fusion gene, encoding a paradigmatic tyrosine kinase involved in chronic myelogenous leukemia (CML), can modulate the expression of genes involved in natural killer (NK) cell target recognition. Recent reports outline the role of allogeneic antileukemic NK effectors in the graft-versus-leukemia effect but the regulation of NK cell activation in the setting of graft-versus-leukemia effect remains unknown. Here we show that dendritic cells derived from monocytes of CML patients are selectively endowed with NK cell stimulatory capacity in vitro. We further show, using a gene transfer approach in mouse bone marrow progenitors, that ABL/ABL is necessary to promote dendritic cell-mediated NK cell activation. The dendritic cell/NK cell cross-talk in ABL/ABL-induced CML seems unique because JunB or IFN consensus sequence binding protein loss of functions, associated with other myeloproliferative disorders, do not promote dendritic cell-mediated NK cell activation. NK cell activation by leukemic dendritic cells involves NKG2D activating receptors and is blocked by imatinib mesylate. Indeed, ABL/ABL translocation enhances the expression levels of the NKG2D ligands on dendritic cells, which is counteracted by imatinib mesylate. Altogether, the clonal ABL/ABL dendritic cells display the unique and selective ability to activate NK cells and may participate in the NK cell control of CML. This study also highlights the deleterious role of imatinib mesylate at the dendritic cell level for NK cell activation.

Tumor-Derived Mesenchymal Stem Cells Use Distinct Mechanisms to Block the Activity of Natural Killer Cell Subsets.

Mesenchymal stem cells (MSCs) display pleiotropic functions, which include secretion of soluble factors with immunosuppressive activity implicated in cancer progression. We compared the immunomodulatory effects on natural killer (NK) cells of paired intratumor (T)- and adjacent non-tumor tissue (N)-derived MSCs from patients with squamous cell lung carcinoma (SCC). We observed that T-MSCs were more strongly immunosuppressive than N-MSCs and affected both NK function and phenotype, as defined by CD56 expression. T-MSCs shifted NK cells toward the CD56dim phenotype and differentially modulated CD56bright/dim subset functions. Whereas MSCs affected both degranulation and activating receptor expression in the CD56dim subset, they primarily inhibited interferon-γ production in the CD56bright subset. Pharmacological inhibition of prostaglandin E2 (PGE2) synthesis and, in some MSCs, interleukin-6 (IL-6) activity restored NK function, whereas NK cell stimulation by PGE2 alone mimicked T-MSC-mediated immunosuppression. Our observations provide insight into how stromal responses to cancer dampen NK cell activity in human lung SCC.

Patient's Natural Killer Cells in the Era of Targeted Therapies: Role for Tumor Killers.

Natural killer (NK) cells are potent antitumor effectors, involved in hematological malignancies and solid tumor immunosurveillance. They infiltrate various solid tumors, and their numbers are correlated with good outcome. The function of NK cells extends their lytic capacities toward tumor cells expressing stress-induced ligands, through secretion of immunoregulatory cytokines, and interactions with other immune cells. Altered NK cell function due to tumor immune escape is frequent in advanced tumors; however, strategies to release the function of NK infiltrating tumors are emerging. Recent therapies targeting specific oncogenic mutations improved the treatment of cancer patients, but patients often relapse. The actual development consists in combined therapeutic strategies including agents targeting the proliferation of tumor cells and others restorating functional antitumor immune effectors for efficient and durable efficacy of anticancer treatment. In that context, we discuss the recent results of the literature to propose hypotheses concerning the potential use of NK cells, potent antitumor cytotoxic effectors, to design novel antitumor strategies.