Jacqueline Marvel

The XC chemokine receptor 1 is a conserved selective marker of mammalian cells homologous to mouse CD8α+ dendritic cells

Human BDCA3+ dendritic cells (DCs) were suggested to be homologous to mouse CD8α+ DCs. We demonstrate that human BDCA3+ DCs are more efficient than their BDCA1+ counterparts or plasmacytoid DCs (pDCs) in cross-presenting antigen and activating CD8+ T cells, which is similar to mouse CD8α+ DCs as compared with CD11b+ DCs or pDCs, although with more moderate differences between human DC subsets. Yet, no specific marker was known to be shared between homologous DC subsets across species. We found that XC chemokine receptor 1 (XCR1) is specifically expressed and active in mouse CD8α+, human BDCA3+, and sheep CD26+ DCs and is conserved across species. The mRNA encoding the XCR1 ligand chemokine (C motif) ligand 1 (XCL1) is selectively expressed in natural killer (NK) and CD8+ T lymphocytes at steady-state and is enhanced upon activation. Moreover, the Xcl1 mRNA is selectively expressed at high levels in central memory compared with naive CD8+ T lymphocytes. Finally, XCR1−/− mice have decreased early CD8+ T cell responses to Listeria monocytogenes infection, which is associated with higher bacterial loads early in infection. Therefore, XCR1 constitutes the first conserved specific marker for cell subsets homologous to mouse CD8α+ DCs in higher vertebrates and promotes their ability to activate early CD8+ T cell defenses against an intracellular pathogenic bacteria.

T-bet and Eomes instruct the development of two distinct natural killer cell lineages in the liver and in the bone marrow

Mutually exclusive expression of T-bet and Eomes drives the development of distinct NK cell lineages with complementary functions.

Involvement of inhibitory NKRs in the survival of a subset of memory-phenotype CD8+ T cells

Inhibitory natural killer receptors (NKRs) such as killer cell immunoglobulin-like receptors (KIRs) in humans and Ly49 molecules in mice are expressed on NK cells and recognize multiple major histocompatibility (MHC) class I proteins. In humans and mice, a subset of CD8+ T cells also expresses NKRs and harbors a memory phenotype. Using mice that are transgenic for KIR2DL3 and its cognate HLA-Cw3 ligand, we show that engagement of inhibitory NKRs selectively drives the in vivo accumulation of a subset of memory-phenotype CD8+ T cells that express the β chain of the interleukin 2 receptor. In vitro, recognition of MHC class I molecules by inhibitory NKRs on T cells down-regulated activation-induced cell death. These results unveil an MHC class I–dependent pathway that promotes the survival of a subset of memory-phenotype CD8+ T cells and also reveal an unexpected biological function for inhibitory NKRs on T cells.NOTE: Incorrect reference numbering appeared in both the original print and web versions of this article. The instances of these errors are marked by asterisks (*) in the online version. The errors are: (i) Ref. 28 was printed incorrectly and should be Ref. 31; (ii) Ref. 29 was printed incorrectly and should be Ref. 32; (iii) References 28–32 should read as follows: 28. Zajac, A. J. et al. Impaired Anti-viral T cell responses due to expression of the LY49A inhibitory receptor. J. Immunol. 163, 5526-5534 (1999). 29. Pauza, M. et al. Transgenic expression of Ly-49A in thymocytes alters repertoire selection. J. Immunol. 164, 884-892 (2000). 30. Fahlen, L. et al. Ly49A expression on T cells alters T cell selection. Int. Immunol. 12, 215-222 (2000). 31. Marti, F. et al. LCK-phosphorylated human killer cell-inhibitory receptors recruit and activate phosphatidylinositol 3-kinase. Proc. Natl Acad. Sci. USA. 95, 11810-11815 (1998). 32. Bieganowska, K. et al. Direct analysis of viral-specific CD8+ T cells with soluble HLA-A2/Tax11-19 tetramer complexes in patients with human T cell lymphotropic virus-associated myelopathy. J. Immunol. 162, 1765-1771 (1999). We apologize for any confusion this may have caused. The most updated version of the article is available in PDF format.

Role of PI3-kinase in Bcl-X induction and apoptosis inhibition mediated by IL-3 or IGF-1 in Baf-3 cells.

In Baf-3 cells, IL-3 and IGF-1 both inhibit cell death. These growth factors act at least on two different pathways involved in the inhibition of apoptosis. They both upregulate Bcl-X at the mRNA and protein levels and also activate a pathway which inhibits apoptosis in the absence of protein synthesis. Recently, these two growth factors have been shown to activate the PI3-kinase-AKT pathway which leads to the phosphorylation of the pro-apoptotic Bcl-XL regulator Bad. In this study, we have investigated the role of PI3-kinase in the regulation of Bcl-X expression and in the survival of Baf-3 cells. We show that PI3-kinase activation is involved in the upregulation of Bcl-X mRNA induced by both IL-3 and IGF-1. Moreover, PI3-kinase activity is also necessary for inhibition of apoptosis and caspase regulation by IGF-1 but not IL-3.

TGF-β inhibits the activation and functions of NK cells by repressing the mTOR pathway

Blocking TGF-β signaling in natural killer cells enhances their metabolism and ability to kill tumor cells. Relieving NK cell suppression The immunosuppressive cytokine transforming growth factor–β (TGF-β) has beneficial effects when it resolves inflammation and prevents autoimmunity, but not when it inhibits antitumor immune responses. Viel et al. found that TGF-β signaling in mouse and human natural killer (NK) cells, cytotoxic cells that target tumor cells, inhibited the activation of the kinase mTOR, a central regulator of cellular metabolism and cytotoxic function. NK cells deficient in a TGF-β receptor subunit showed enhanced antitumor activity in mouse models of metastasis, suggesting that enhancing metabolism in NK cells may provide a therapeutic strategy to kill cancer cells. Transforming growth factor–β (TGF-β) is a major immunosuppressive cytokine that maintains immune homeostasis and prevents autoimmunity through its antiproliferative and anti-inflammatory properties in various immune cell types. We provide genetic, pharmacologic, and biochemical evidence that a critical target of TGF-β signaling in mouse and human natural killer (NK) cells is the serine and threonine kinase mTOR (mammalian target of rapamycin). Treatment of mouse or human NK cells with TGF-β in vitro blocked interleukin-15 (IL-15)–induced activation of mTOR. TGF-β and the mTOR inhibitor rapamycin both reduced the metabolic activity and proliferation of NK cells and reduced the abundances of various NK cell receptors and the cytotoxic activity of NK cells. In vivo, constitutive TGF-β signaling or depletion of mTOR arrested NK cell development, whereas deletion of the TGF-β receptor subunit TGF-βRII enhanced mTOR activity and the cytotoxic activity of the NK cells in response to IL-15. Suppression of TGF-β signaling in NK cells did not affect either NK cell development or homeostasis; however, it enhanced the ability of NK cells to limit metastases in two different tumor models in mice. Together, these results suggest that the kinase mTOR is a crucial signaling integrator of pro- and anti-inflammatory cytokines in NK cells. Moreover, we propose that boosting the metabolic activity of antitumor lymphocytes could be an effective strategy to promote immune-mediated tumor suppression.

Regulation of mouse NK cell development and function by cytokines

Natural Killer (NK) cells are innate lymphocytes with an important role in the early defense against intracellular pathogens and against tumors. Like other immune cells, almost every aspects of their biology are regulated by cytokines. Interleukin (IL)-15 is pivotal for their development, homeostasis, and activation. Moreover, numerous other activating or inhibitory cytokines such as IL-2, IL-4, IL-7, IL-10, IL-12, IL-18, IL-21, Transforming growth factor-β (TGFβ) and type I interferons regulate their activation and their effector functions at different stages of the immune response. In this review we summarize the current understanding on the effect of these different cytokines on NK cell development, homeostasis, and functions during steady-state or upon infection by different pathogens. We try to delineate the cellular sources of these cytokines, the intracellular pathways they trigger and the transcription factors they regulate. We describe the known synergies or antagonisms between different cytokines and highlight outstanding questions in this field of investigation. Finally, we discuss how a better knowledge of cytokine action on NK cells could help improve strategies to manipulate NK cells in different clinical situations.

Sequential desensitization of CXCR4 and S1P5 controls natural killer cell trafficking

During development, natural killer (NK) cells exit the BM to reach the blood. CXCR4 retains NK cells in the BM, whereas the sphingosine-1 phosphate receptor 5 (S1P5) promotes their exit from this organ. However, how the action of these receptors is coordinated to preserve NK-cell development in the BM parenchyma while providing mature NK cells at the periphery is unclear. The role of CXCR4 and S1P5 in NK-cell recirculation at the periphery is also unknown. In the present study, we show that, during NK-cell differentiation, CXCR4 expression decreases whereas S1P5 expression increases, thus favoring the exit of mature NK cells via BM sinusoids. Using S1P5(-/-) mice and a new knockin mouse model in which CXCR4 cannot be desensitized (a mouse model of warts, hypogammaglobulinemia, infections, and myelokathexis [WHIM] syndrome), we demonstrate that NK-cell exit from the BM requires both CXCR4 desensitization and S1P5 engagement. These 2 signals occur independently of each other: CXCR4 desensitization is not induced by S1P5 engagement and vice versa. Once in the blood, the S1P concentration increases and S1P5 responsiveness decreases. This responsiveness is recovered in the lymph nodes to allow NK-cell exit via lymphatics in a CXCR4-independent manner. Therefore, coordinated changes in CXCR4 and S1P5 responsiveness govern NK-cell trafficking.

TLR2 Engagement on CD8 T Cells Enables Generation of Functional Memory Cells in Response to a Suboptimal TCR Signal

TLR are involved in the detection of microbial infection as well as endogenous ligands that signal tissue and cell damage in mammals. This recognition plays an essential role in innate immune response and the initiation of adaptive immune response. We have previously shown that murine CD8 T cells express TLR2, and that costimulation of Ag-activated CD8 T cells with TLR2 ligands enhances their proliferation, survival, and effector functions. We also demonstrated that TLR2 engagement on CD8 T cells significantly reduces their need for costimulatory signals delivered by APC. We show in this study that TLR2 engagement on CD8 T cells lowers the Ag concentration required for optimal activation, and converts a partial activation into a productive process leading to a significant expansion of cells. Using altered peptide ligands, we demonstrate that TLR2 engagement increases CD8 T cell activation and enables the generation of functional memory cells in response to a low TCR signal. This increased activation is associated with an augmented activation of the PI3K. Taken together, our results demonstrate that TLR2 engagement on CD8 T cells lowers their activation threshold for TCR signal strength and enables efficient memory cell generation in response to a weak TCR signal.

Overexpression of Sp1 transcription factor induces apoptosis.

Transcription factor Sp1 has recently been shown to be overexpressed in a number of human cancers and its overexpression contributes to malignant transformation. Sp1 regulates the expression of a number of genes participating in multiple aspects of tumorigenesis such as angiogenesis, cell growth and apoptosis resistance. To better understand the role of increased Sp1 levels on apoptosis regulation we have used retroviruses to overexpress this protein in haematopoietic Baf-3 cells and in 3T3 fibroblasts. We have also used inducible expression systems to control ectopic Sp1 levels in different cell types. Surprisingly, Sp1 overexpression on its own induces apoptosis in all the cellular models tested. The apoptotic pathways induced by Sp1 overexpression are cell type specific. Finally, using a truncated form of Sp1, we show that Sp1-induced apoptosis requires its DNA-binding domain. Our results highlight that Sp1 levels in untransformed cells must be tightly regulated as Sp1 overexpression leads to the induction of apoptosis. Our results also suggest that cancer cells overexpressing Sp1 can avoid Sp1-induced apoptosis.

Tumor Promotion by Intratumoral Plasmacytoid Dendritic Cells Is Reversed by TLR7 Ligand Treatment

Plasmacytoid dendritic cells (pDC) are key regulators of antiviral immunity. In previous studies, we reported that pDC-infiltrating human primary breast tumors represent an independent prognostic factor associated with poor outcome. To understand this negative impact of tumor-associated pDC (TApDC), we developed an orthotopic murine mammary tumor model that closely mimics the human pathology, including pDC and regulatory T cell (Treg) infiltration. We showed that TApDC are mostly immature and maintain their ability to internalize antigens in vivo and to activate CD4(+) T cells. Most importantly, TApDC were specifically altered for cytokine production in response to Toll-like receptor (TLR)-9 ligands in vitro while preserving unaltered response to TLR7 ligands (TLR7L). In vivo pDC depletion delayed tumor growth, showing that TApDC provide an immune-subversive environment, most likely through Treg activation, thus favoring tumor progression. However, in vivo intratumoral administration of TLR7L led to TApDC activation and displayed a potent curative effect. Depletion of pDC and type I IFN neutralization prevented TLR7L antitumoral effect. Our results establish a direct contribution of TApDC to primary breast tumor progression and rationalize the application of TLR7 ligands to restore TApDC activation in breast cancer. Cancer Res; 73(15); 4629-40. ©2013 AACR.