Lucie Peduto

In vivo equilibrium of proinflammatory IL-17+ and regulatory IL-10+ Foxp3+ RORγt+ T cells

The nuclear hormone receptor retinoic acid receptor–related orphan receptor γt (RORγt) is required for the generation of T helper 17 cells expressing the proinflammatory cytokine interleukin (IL)-17. In vivo, however, less than half of RORγt+ T cells express IL-17. We report here that RORγt+ Tαβ cells include Foxp3+ cells that coexist with IL-17–producing RORγt+ Tαβ cells in all tissues examined. The Foxp3+ RORγt+ Tαβ express IL-10 and CCL20, and function as regulatory T cells. Furthermore, the ratio of Foxp3+ to IL-17–producing RORγt+ Tαβ cells remains remarkably constant in mice enduring infection and inflammation. This equilibrium is tuned in favor of IL-10 production by Foxp3 and CCL20, and in favor of IL-17 production by IL-6 and IL-23. In the lung and skin, the largest population of RORγt+ T cells express the γδ T cell receptor and produce the highest levels of IL-17 independently of IL-6. Thus, potentially antagonistic proinflammatory IL-17–producing and regulatory Foxp3+ RORγt+ T cells coexist and are tightly controlled, suggesting that a perturbed equilibrium in RORγt+ T cells might lead to decreased immunoreactivity or, in contrast, to pathological inflammation.

Lineage tracing and genetic ablation of ADAM12+ perivascular cells identify a major source of profibrotic cells during acute tissue injury

Profibrotic cells that develop upon injury generate permanent scar tissue and impair organ recovery, though their origin and fate are unclear. Here we show that transient expression of ADAM12 (a disintegrin and metalloprotease 12) identifies a distinct proinflammatory subset of platelet-derived growth factor receptor-α–positive stromal cells that are activated upon acute injury in the muscle and dermis. By inducible genetic fate mapping, we demonstrate in vivo that injury-induced ADAM12+ cells are specific progenitors of a major fraction of collagen-overproducing cells generated during scarring, which are progressively eliminated during healing. Genetic ablation of ADAM12+ cells, or knockdown of ADAM12, is sufficient to limit generation of profibrotic cells and interstitial collagen accumulation. ADAM12+ cells induced upon injury are developmentally distinct from muscle and skin lineage cells and are derived from fetal ADAM12+ cells programmed during vascular wall development. Thus, our data identify injury-activated profibrotic progenitors residing in the perivascular space that can be targeted through ADAM12 to limit tissue scarring.

Type I IFN controls chikungunya virus via its action on nonhematopoietic cells.

Chikungunya virus (CHIKV) is the causative agent of an outbreak that began in La Réunion in 2005 and remains a major public health concern in India, Southeast Asia, and southern Europe. CHIKV is transmitted to humans by mosquitoes and the associated disease is characterized by fever, myalgia, arthralgia, and rash. As viral load in infected patients declines before the appearance of neutralizing antibodies, we studied the role of type I interferon (IFN) in CHIKV pathogenesis. Based on human studies and mouse experimentation, we show that CHIKV does not directly stimulate type I IFN production in immune cells. Instead, infected nonhematopoietic cells sense viral RNA in a Cardif-dependent manner and participate in the control of infection through their production of type I IFNs. Although the Cardif signaling pathway contributes to the immune response, we also find evidence for a MyD88-dependent sensor that is critical for preventing viral dissemination. Moreover, we demonstrate that IFN-α/β receptor (IFNAR) expression is required in the periphery but not on immune cells, as IFNAR−/−→WT bone marrow chimeras are capable of clearing the infection, whereas WT→IFNAR−/− chimeras succumb. This study defines an essential role for type I IFN, produced via cooperation between multiple host sensors and acting directly on nonhematopoietic cells, in the control of CHIKV.

Chikungunya virus–induced autophagy delays caspase-dependent cell death

Chikungunya virus induces autophagy by triggering ER and oxidative stress, and this autophagy restricts apoptosis and viral propagation.

Characterization of the thymic IL-7 niche in vivo

The thymus represents the “cradle” for T cell development, with thymic stroma providing multiple soluble and membrane cues to developing thymocytes. Although IL-7 is recognized as an essential factor for thymopoiesis, the “environmental niche” of thymic IL-7 activity remains poorly characterized in vivo. Using bacterial artificial chromosome transgenic mice in which YFP is under control of IL-7 promoter, we identify a subset of thymic epithelial cells (TECs) that co-express YFP and high levels of Il7 transcripts (IL-7hi cells). IL-7hi TECs arise during early fetal development, persist throughout life, and co-express homeostatic chemokines (Ccl19, Ccl25, Cxcl12) and cytokines (Il15) that are critical for normal thymopoiesis. In the adult thymus, IL-7hi cells localize to the cortico-medullary junction and display traits of both cortical and medullary TECs. Interestingly, the frequency of IL-7hi cells decreases with age, suggesting a mechanism for the age-related thymic involution that is associated with declining IL-7 levels. Our temporal-spatial analysis of IL-7-producing cells in the thymus in vivo suggests that thymic IL-7 levels are dynamically regulated under distinct physiological conditions. This IL-7 reporter mouse provides a valuable tool to further dissect the mechanisms that govern thymic IL-7 expression in vivo.

Preexisting BCG-Specific T Cells Improve Intravesical Immunotherapy for Bladder Cancer

Preexisting immunity to BCG improves treatment response to intravesical BCG therapy for bladder cancer in mouse models and humans. Bugs as Drugs Although still in its infancy for the treatment of many tumor types, immunotherapy has been and remains the standard of care for patients with bladder cancer. The concept behind this success is repeated instillations of bacillus Calmette-Guérin (BCG; the same bacteria used as a vaccine for Mycobacterium tuberculosis) in the bladder, inducing an immune response that fights the cancer. The clinical response rate in bladder cancer patients is 50 to 70%, higher than any other immunotherapy but still leaving room for improvement. Biot et al. provide new insight into the mechanisms behind BCG’s success in the bladder and suggest that parenteral BCG exposure may boost the success rate for bladder cancer treatment. Using a mouse model of bladder cancer, the authors show that a single instillation of BCG induced an immune response, but repetitive instillations were required for robust T cell trafficking to the bladder. Previous parenteral exposure to BCG overcame this requirement in the mice, inducing an enhanced innate immune response, accelerating T cell trafficking to the bladder, and improving the immune response to the tumor. Furthermore, bladder cancer patients who had preexisting immunity to BCG (secondary to their childhood M. tuberculosis vaccination) showed improved recurrence-free survival after standard BCG therapy relative to those patients without preexisting immunity. Thus, immunizing BCG-naïve cancer patients before therapy may provide a simple strategy that could improve therapeutic response. Therapeutic intravesical instillation of bacillus Calmette-Guérin (BCG) is effective at triggering inflammation and eliciting successful tumor immunity in patients with non–muscle invasive bladder cancer, with 50 to 70% clinical response. Therapeutic success relies on repeated instillations of live BCG administered as adjuvant therapy shortly after tumor resection; however, the precise mechanisms remain unclear. Using an experimental model, we demonstrate that after a single instillation, BCG could disseminate to bladder draining lymph nodes and prime interferon-γ–producing T cells. Nonetheless, repeated instillations with live BCG were necessary for a robust T cell infiltration into the bladder. Parenteral exposure to BCG before instillation overcame this requirement; after the first intravesical instillation, BCG triggered a more robust acute inflammatory process and accelerated T cell entry into the bladder, as compared to the standard protocol. Moreover, parenteral exposure to BCG before intravesical treatment of an orthotopic tumor markedly improved response to therapy. Indeed, patients with sustained preexisting immunity to BCG showed a significant improvement in recurrence-free survival. Together, these data suggest that monitoring patients’ response to purified protein derivative, and, in their absence, boosting BCG responses by parenteral exposure before intravesical treatment initiation, may be a safe and effective means of improving intravesical BCG-induced clinical responses.

Inflammation Recapitulates the Ontogeny of Lymphoid Stromal Cells

Stromal cells in lymphoid tissues regulate lymphocyte recruitment and survival through the expression of specific chemokines and cytokines. During inflammation, the same signals recruit lymphocytes to the site of injury; however, the “lymphoid” stromal (LS) cells producing these signals remain poorly characterized. We find that mouse inflammatory lesions and tumors develop gp38+ LS cells, in recapitulation of the development of LS cells early during the ontogeny of lymphoid organs and the intestine, and express a set of genes that promotes the development of lymphocyte-permissive tissues. These gp38+ LS cells are induced by a robust pathway that requires myeloid cells but not known Toll- or NOD-like receptors, the inflammasome, or adaptive immunity. Parabiosis and inducible genetic cell fate mapping experiments indicate that local precursors, presumably resident fibroblasts rather that circulating precursors, massively proliferate and give rise to LS cells during inflammation. Our results show that LS cells are both programmed during ontogeny and reinduced during inflammation.

CD34+ mesenchymal cells are a major component of the intestinal stem cells niche at homeostasis and after injury

Significance Maintenance of stem cells in adult organs requires a specialized microenvironment called the niche, which provides structural cues and paracrine signals to ensure stemness. In the intestine, increasing evidence points toward a major role for the mesenchyme close to crypts to perform this function; however, such putative mesenchymal niche remains poorly characterized. Here, we identify nonmyofibroblastic CD34+ Gp38+ mesenchymal cells as a major component of the intestinal epithelial stem cells (IESCs) niche. We show that CD34+ Gp38+ mesenchymal cells develop after birth and contribute to the maintenance of IESCs at homeostasis and organization of intestinal inflammation after injury. The intestinal epithelium is continuously renewed by intestinal epithelial stem cells (IESCs) positioned at the base of each crypt. Mesenchymal-derived factors are essential to maintain IESCs; however, the cellular composition and development of such mesenchymal niche remains unclear. Here, we identify pericryptal CD34+ Gp38+ αSMA– mesenchymal cells closely associated with Lgr5+ IESCs. We demonstrate that CD34+ Gp38+ cells are the major intestinal producers of the niche factors Wnt2b, Gremlin1, and R-spondin1, and are sufficient to promote maintenance of Lgr5+ IESCs in intestinal organoids, an effect mainly mediated by Gremlin1. CD34+ Gp38+ cells develop after birth in the intestinal submucosa and expand around the crypts during the third week of life in mice, independently of the microbiota. We further show that pericryptal CD34+gp38+ cells are rapidly activated by intestinal injury, up-regulating niche factors Gremlin1 and R-spondin1 as well as chemokines, proinflammatory cytokines, and growth factors with key roles in gut immunity and tissue repair, including IL-7, Ccl2, Ptgs2, and Amphiregulin. Our results indicate that CD34+ Gp38+ mesenchymal cells are programmed to develop in the intestine after birth to constitute a specialized microenvironment that maintains IESCs at homeostasis and contribute to intestinal inflammation and repair after injury.

Chikungunya-induced cell death is limited by ER and oxidative stress-induced autophagy

It has been recognized that macroautophagy constitutes an important survival mechanism that allows both the maintenance of cellular homeostasis and the regulation of programmed cell death pathways (e.g., apoptosis). Although several pathogens have been described to induce autophagy, the prosurvival function of this process in infectious models remains poorly characterized. Our recent studies on chikungunya virus (CHIKV), the causative agent of major epidemics in India, Southeast Asia and southern Europe, reveal a novel mechanism by which autophagy limits the cytopathic effects of CHIKV by impinging upon virus-induced cell death pathways.

Oxysterol Sensing through the Receptor GPR183 Promotes the Lymphoid-Tissue-Inducing Function of Innate Lymphoid Cells and Colonic Inflammation

Summary Group 3 innate lymphoid cells (ILC3s) sense environmental signals and are critical for tissue integrity in the intestine. Yet, which signals are sensed and what receptors control ILC3 function remain poorly understood. Here, we show that ILC3s with a lymphoid‐tissue‐inducer (LTi) phenotype expressed G‐protein‐coupled receptor 183 (GPR183) and migrated to its oxysterol ligand 7&agr;,25‐hydroxycholesterol (7&agr;,25‐OHC). In mice lacking Gpr183 or 7&agr;,25‐OHC, ILC3s failed to localize to cryptopatches (CPs) and isolated lymphoid follicles (ILFs). Gpr183 deficiency in ILC3s caused a defect in CP and ILF formation in the colon, but not in the small intestine. Localized oxysterol production by fibroblastic stromal cells provided an essential signal for colonic lymphoid tissue development, and inflammation‐induced increased oxysterol production caused colitis through GPR183‐mediated cell recruitment. Our findings show that GPR183 promotes lymphoid organ development and indicate that oxysterol‐GPR183‐dependent positioning within tissues controls ILC3 activity and intestinal homeostasis. Graphical Abstract Figure. No Caption available. HighlightsILC3s sense cholesterol metabolites (oxysterols) through the receptor GPR183GPR183 and its ligand 7&agr;,25‐OHC promote ILC3 migration to CPs and ILFsGPR183 and 7&agr;,25‐OHC are critical for CP and ILF formation in the colonGPR183 controls inflammatory tissue remodeling during immune‐mediated colitis &NA; ILC3s maintain healthy organ function in the intestine, but how ILC3s directly detect environmental cues is poorly understood. Emgård et al. find that GPR183 and oxysterols control the localization and LTi function of ILC3s and thereby promote the formation of colonic lymphoid tissues in the steady state and inflammation.