Chrystelle Lamagna

Dual role of macrophages in tumor growth and angiogenesis

During the neoplastic progression, macrophages as well as dendritic and NK cells are attracted into the tumor site and initiate the immune response against transformed cells. They activate and present tumor antigens to T cells, which are then activated to kill tumor cells. However, tumor cells are often capable of escaping the immune machinery. As the immune surveillance is not sufficient anymore, tumor‐associated macrophages contribute to tumor progression. It is notable that tumor‐associated macrophages promote the proliferation of tumor cells directly by secreting growth factors. They also participate in tumor progression by acting on endothelial cells and thus promoting the neovascularization of the tumor. Tumor‐associated macrophages are indeed key protagonists during angiogenesis and promote each step of the angiogenesis cascade.

The bone marrow constitutes a reservoir of pericyte progenitors

Adult bone marrow is a rich reservoir of hematopoietic and mesenchymal stem and progenitor cells. Mobilization and recruitment of bone marrow‐derived cells to injured or ischemic tissue or tumors endorse the initiation and maintenance of angiogenic processes in the adult by incorporating endothelial progenitor cells (EPC) into the developing vasculature and by recruiting accessory hematopoietic cells. Recent data have now revealed that the origin of bone marrow‐derived vascular cells is not restricted to endothelial cells but also includes pericytes—the perivascular support cells. Several laboratories have now reported the existence of pericyte progenitor cells, and these cells, like EPC, can be mobilized and recruited to the remodeling vasculature under ischemic conditions and in tumors. This review focuses on pericytes in vessel formation and on recent discoveries about their bone marrow origin in the adult.

Junctional Adhesion Molecule-C Regulates the Early Influx of Leukocytes into Tissues during Inflammation

Leukocyte recruitment from blood to inflammatory sites occurs in a multistep process that involves discrete molecular interactions between circulating and endothelial cells. Junctional adhesion molecule (JAM)-C is expressed at different levels on endothelial cells of lymphoid organs and peripheral tissues and has been proposed to regulate neutrophil migration by its interaction with the leukocyte integrin Mac-1. In the present study, we show that the accumulation of leukocytes in alveoli during acute pulmonary inflammation in mice is partially blocked using neutralizing Abs against JAM-C. To confirm the function of JAM-C in regulating leukocyte migration in vivo, we then generated a strain of transgenic mice overexpressing JAM-C under the control of the endothelial specific promotor Tie2. The transgenic animals accumulate more leukocytes to inflammatory sites compared with littermate control mice. Intravital microscopy shows that this is the result of increased leukocyte adhesion and transmigration, whereas rolling of leukocytes is not significantly affected in transgenic mice compared with littermates. Thus, JAM-C participates in the later steps of the leukoendothelial adhesion cascade.

Antibody against Junctional Adhesion Molecule-C Inhibits Angiogenesis and Tumor Growth

The junctional adhesion molecule-C (JAM-C) was recently described as an adhesion molecule localized at interendothelial contacts and involved in leukocyte transendothelial migration. The protein JAM-C interacts with polarity complex molecules and regulates the activity of the small GTPase Cdc42. The angiogenesis process involves rearrangement of endothelial junctions and implicates modulation of cell polarity. We tested whether JAM-C plays a role in angiogenesis using tumor grafts and hypoxia-induced retinal neovascularization. Treatment with a monoclonal antibody directed against JAM-C reduces tumor growth and infiltration of macrophages into tumors. The antibody decreases angiogenesis in the model of hypoxia-induced retinal neovascularization in vivo and vessel outgrowth from aortic rings in vitro. Importantly, the antibody does not induce pathologic side effects in vivo. These findings show for the first time a role for JAM-C in angiogenesis and define JAM-C as a valuable target for antitumor therapies.

B Cell–Specific Loss of Lyn Kinase Leads to Autoimmunity

The Lyn tyrosine kinase regulates inhibitory signaling in B and myeloid cells: loss of Lyn results in a lupus-like autoimmune disease with hyperactive B cells and myeloproliferation. We have characterized the relative contribution of Lyn-regulated signaling pathways in B cells specifically to the development of autoimmunity by crossing the novel lynflox/flox animals with mice carrying the Cre recombinase under the control of the Cd79a promoter, resulting in deletion of Lyn in B cells. The specific deletion of Lyn in B cells is sufficient for the development of immune complex–mediated glomerulonephritis. The B cell–specific Lyn-deficient mice have no defects in early bone marrow B cell development but have reduced numbers of mature B cells with poor germinal centers, as well as increased numbers of plasma and B1a cells, similar to the lyn−/− animals. Within 8 mo of life, B cell–specific Lyn mutant mice develop high titers of IgG anti–Smith Ag ribonucleoprotein and anti-dsDNA autoantibodies, which deposit in their kidneys, resulting in glomerulonephritis. B cell–specific Lyn mutant mice also develop myeloproliferation, similar to the lyn−/− animals. The additional deletion of MyD88 in B cells, achieved by crossing lynflox/floxCd79a-cre mice with myd88flox/flox animals, reversed the autoimmune phenotype observed in B cell–specific Lyn-deficient mice by blocking production of class-switched pathogenic IgG autoantibodies. Our results demonstrate that B cell–intrinsic Lyn-dependent signaling pathways regulate B cell homeostasis and activation, which in concert with B cell–specific MyD88 signaling pathways can drive the development of autoimmune disease.

Requirement for MyD88 Signaling in B Cells and Dendritic Cells for Germinal Center Anti-Nuclear Antibody Production in Lyn-Deficient Mice

The intracellular tyrosine kinase Lyn mediates inhibitory receptor function in B cells and myeloid cells, and Lyn−/− mice spontaneously develop an autoimmune and inflammatory disease that closely resembles human systemic lupus erythematosus. TLR-signaling pathways have been implicated in the production of anti-nuclear Abs in systemic lupus erythematosus and mouse models of it. We used a conditional allele of Myd88 to determine whether the autoimmunity of Lyn−/− mice is dependent on TLR/MyD88 signaling in B cells and/or in dendritic cells (DCs). The production of IgG anti-nuclear Abs, as well as the deposition of these Abs in the glomeruli of the kidneys, leading to glomerulonephritis in Lyn−/− mice, were completely abolished by selective deletion of Myd88 in B cells, and autoantibody production and glomerulonephritis were delayed or decreased by deletion of Myd88 in DCs. The reduced autoantibody production in mice lacking MyD88 in B cells or DCs was accompanied by a dramatic decrease in the spontaneous germinal center (GC) response, suggesting that autoantibodies in Lyn−/− mice may depend on GC responses. Consistent with this view, IgG anti-nuclear Abs were absent if T cells were deleted (TCRβ−/− TCRδ−/− mice) or if T cells were unable to contribute to GC responses as the result of mutation of the adaptor molecule SAP. Thus, the autoimmunity of Lyn−/− mice was dependent on T cells and on TLR/MyD88 signaling in B cells and in DCs, supporting a model in which DC hyperactivity combines with defects in tolerance in B cells to lead to a T cell–dependent systemic autoimmunity in Lyn−/− mice.

Hyperactivated MyD88 signaling in dendritic cells, through specific deletion of Lyn kinase, causes severe autoimmunity and inflammation

Significance The pathogenesis of systemic lupus erythematosus, a complex autoimmune inflammatory disease triggered by genetic and environmental factors, is generally attributed to defects in lymphocyte function. We show that dendritic cells (DCs) also drive autoimmune disease in mice. Our observations that dysregulation of Toll-like receptor signaling (a key pathway that alerts the immune system of encounter with infectious agents) in DCs alone is sufficient to induce autoimmunity sheds new light on the pathogenesis of this disease. This work implies that DC-specific reduction of Toll-like receptor signaling may prove to be a highly specific approach to reduce the symptoms of autoimmune diseases. Deletion of lyn, a Src-family tyrosine kinase expressed by B, myeloid, and dendritic cells (DCs), triggers lupus-like disease in mice, characterized by autoantibody production and renal immune complex deposition leading to chronic glomerulonephritis. B cells from these mice are hyperactive to antigen-receptor stimulation owing to a loss of inhibitory signaling mediated by Lyn kinase. The hyperactive B-cell responses are thought to underlie the development of autoimmunity in this model. Lyn-deficient mice also manifest significant myeloexpansion. To test the contribution of different immune cell types to the lupus-like disease in this model, we generated a lynflox/flox transgenic mouse strain. To our surprise, when we crossed these mice to Cd11c-cre animals, generating DC-specific deletion of Lyn, the animals developed spontaneous B- and T-cell activation and subsequent production of autoantibodies and severe nephritis. Remarkably, the DC-specific Lyn-deficient mice also developed severe tissue inflammatory disease, which was not present in the global lyn−/− strain. Lyn-deficient DCs were hyperactivated and hyperresponsive to Toll-like receptor agonists and IL-1β. To test whether dysregulation of these signaling pathways in DCs contributed to the inflammatory/autoimmune phenotype, we crossed the lynf/f Cd11c-cre+ mice to myd88f/f animals, generating double-mutant mice lacking both Lyn and the adaptor protein myeloid differentiation factor 88 (MyD88) in DCs, specifically. Deletion of MyD88 in DCs alone completely reversed the inflammatory autoimmunity in the DC-specific Lyn-mutant mice. Thus, we demonstrate that hyperactivation of MyD88-dependent signaling in DCs is sufficient to drive pathogenesis of lupus-like disease, illuminating the fact that dysregulation in innate immune cells alone can lead to autoimmunity.

B cell-derived IL-10 suppresses inflammatory disease in Lyn-deficient mice

Lyn kinase deficient mice represent a well established genetic model of autoimmune/autoinflammatory disease that resembles systemic lupus erythematosus. We report that IL-10 plays a crucial immunosuppressive role in this model, modulating the inflammatory component of the disease caused by myeloid and T-cell activation. Double-mutant lyn−/−IL-10−/− mice manifested severe splenomegaly and lymphadenopathy, dramatically increased proinflammatory cytokine production, and severe tissue inflammation. Single-mutant lyn−/−mice showed expansion of IL-10–producing B cells. Interestingly, WT B cells adoptively transferred into lyn−/− mice showed increased differentiation into IL-10–producing B cells that assumed a similar phenotype to endogenous lyn−/− IL-10–producing B cells, suggesting that the inflammatory environment present in lyn−/− mice induces IL-10–producing B-cell differentiation. B cells, but not T or myeloid cells, were the critical source of IL-10 able to reduce inflammation and autoimmunity in double mutant lyn−/−IL-10−/− mice. IL-10 secretion by B cells was also crucial to sustain transcription factor Forkhead Box P3 (Foxp3) expression in regulatory T cells during disease development. These data reveal a dominant immunosuppressive function of B-cell–derived IL-10 in the Lyn-deficient model of autoimmunity, extending our current understanding of the role of IL-10 and IL-10–producing B cells in systemic lupus erythematosus.

Junctional Adhesion Molecules and Interendothelial Junctions

Similar to epithelia, endothelial cells are linked to each other via intercellular junctional complexes including gap junctions, adherens junctions and tight junctions. While polarized epithelial cells show a high degree of spatial sorting of junctional complexes, endothelia organize their junctions randomly. For this reason the nature of endothelial contacts may be highly adaptable to the need of permeability and leukocyte transmigration. For instance, high endothelial venules (HEVs) in lymphoid organs, where lymphocytes continuously exit the bloodstream, generally show more leaky contacts than brain with its impermeable blood-brain barrier. We recently identified an Ig superfamily molecule named JAM-2 which is specifically expressed in junctions of lymphatic endothelial cells and HEVs. We showed that JAM-2 belongs to the novel CTX molecular family and we now cloned the human equivalent of JAM-2. The presence of JAM-2 at sites of constitutive lymphocyte circulation argues for a role of this molecule in facilitating transmigration. This is supported by the increased transmigration in vitro across endothelial cells overexpressing JAM-2 at intercellular contacts.

Chapter 3. Bone marrow-derived vascular progenitors and proangiogenic monocytes in tumors.

In tumors, new blood vessels develop not only from pre-existing vessels (angiogenesis), but can also be comprised of circulating vascular progenitor cells originating from the bone marrow (vasculogenesis). Besides endothelial progenitor cells (EPC) and pericyte progenitor cells (PPCs) that are incorporated into the growing vasculature, other subpopulations of bone marrow-derived cells (BMDC) contribute indirectly to tumor neovascularization by providing growth factors, cytokines, and other key proangiogenic molecules. Here, we describe specific methods that allow for the identification and functional characterization of these distinct BMDC populations in tumors as exemplified in mouse models of pancreatic neuroendocrine tumors and glioblastomas.