Inflammatory Bowel Disease Susceptibility Gene C1ORF106 Regulates Intestinal Epithelial Permeability.

Intestinal epithelial cells form a physical barrier that is tightly regulated to control intestinal permeability. Proinflammatory cytokines, such as TNF-α, increase epithelial permeability through disruption of epithelial junctions. The regulation of the epithelial barrier in inflammatory gastrointestinal disease remains to be fully characterized. In this article, we show that the human inflammatory bowel disease genetic susceptibility gene C1ORF106 plays a key role in regulating gut epithelial permeability. C1ORF106 directly interacts with cytohesins to maintain functional epithelial cell junctions. C1orf106-deficient mice are hypersensitive to TNF-α-induced increase in epithelial permeability, and this is associated with increased diarrhea. This study identifies C1ORF106 as an epithelial cell junction protein, and the loss of C1ORF106 augments TNF-α-induced intestinal epithelial leakage and diarrhea that may play a critical role in the development of inflammatory bowel disease.

Combination central tolerance and peripheral checkpoint blockade unleashes antimelanoma immunity.

Blockade of immune checkpoint proteins (e.g., CTLA-4, PD-1) improves overall survival in advanced melanoma; however, therapeutic benefit is limited to only a subset of patients. Because checkpoint blockade acts by "removing the brakes" on effector T cells, the efficacy of checkpoint blockade may be constrained by the limited pool of melanoma-reactive T cells in the periphery. In the thymus, autoimmune regulator (Aire) promotes deletion of T cells reactive against self-antigens that are also expressed by tumors. Thus, while protecting against autoimmunity, Aire also limits the generation of melanoma-reactive T cells. Here, we show that Aire deficiency in mice expands the pool of CD4+ T cells capable of melanoma cell eradication and has additive effects with anti-CTLA-4 antibody in slowing melanoma tumor growth and increasing survival. Moreover, pharmacologic blockade of central T cell tolerance and peripheral checkpoint blockade in combination enhanced antimelanoma immunity in a synergistic manner. In melanoma patients treated with anti-CTLA-4 antibody, clinical response to therapy was associated with a human Aire polymorphism. Together, these findings suggest that Aire-mediated central tolerance constrains the efficacy of peripheral checkpoint inhibition and point to simultaneous blockade of Aire and checkpoint inhibitors as a novel strategy to enhance antimelanoma immunity.

Enhancement of an anti-tumor immune response by transient blockade of central T cell tolerance.

Thymic central tolerance is a critical process that prevents autoimmunity but also presents a challenge to the generation of anti-tumor immune responses. Medullary thymic epithelial cells (mTECs) eliminate self-reactive T cells by displaying a diverse repertoire of tissue-specific antigens (TSAs) that are also shared by tumors. Therefore, while protecting against autoimmunity, mTECs simultaneously limit the generation of tumor-specific effector T cells by expressing tumor self-antigens. This ectopic expression of TSAs largely depends on autoimmune regulator (Aire), which is expressed in mature mTECs. Thus, therapies to deplete Aire-expressing mTECs represent an attractive strategy to increase the pool of tumor-specific effector T cells. Recent work has implicated the TNF family members RANK and RANK-Ligand (RANKL) in the development of Aire-expressing mTECs. We show that in vivo RANKL blockade selectively and transiently depletes Aire and TSA expression in the thymus to create a window of defective negative selection. Furthermore, we demonstrate that RANKL blockade can rescue melanoma-specific T cells from thymic deletion and that persistence of these tumor-specific effector T cells promoted increased host survival in response to tumor challenge. These results indicate that modulating central tolerance through RANKL can alter thymic output and potentially provide therapeutic benefit by enhancing anti-tumor immunity.

Central tolerance induction.

A critical function of the thymus is to help enforce tolerance to self. The importance of central tolerance in preventing autoimmunity has been enlightened by a deeper understanding of the interactions of developing T cells with a diverse population of thymic antigen presenting cell populations. Furthermore, there has been rapid progress in our understanding of how autoreactive T cell specificities are diverted into the T regulatory lineage. Here we review and highlight the recent progress in how tolerance is imposed on the developing thymocyte repertoire.

Lineage tracing and cell ablation identify a post-Aire-expressing thymic epithelial cell population.

Thymic epithelial cells in the medulla (mTECs) play a critical role in enforcing central tolerance through expression and presentation of tissue-specific antigens (TSAs) and deletion of autoreactive thymocytes. TSA expression requires autoimmune regulator (Aire), a transcriptional activator present in a subset of mTECs characterized by high CD80 and major histocompatibility complex II expression and a lack of potential for differentiation or proliferation. Here, using an Aire-DTR transgenic line, we show that short-term ablation specifically targets Aire(+) mTECs, which quickly undergo RANK-dependent recovery. Repeated ablation also affects Aire(-) mTECs, and using an inducible Aire-Cre fate-mapping system, we find that this results from the loss of a subset of mTECs that showed prior expression of Aire, maintains intermediate TSA expression, and preferentially migrates toward the center of the medulla. These results clearly identify a distinct stage of mTEC development and underscore the diversity of mTECs that play a key role in maintaining tolerance.

Transmembrane mutations in Toll-like receptor 9 bypass the requirement for ectodomain proteolysis and induce fatal inflammation.

Recognition of nucleic acids as a signature of infection by Toll-like receptors (TLRs) 7 and 9 exposes the host to potential self-recognition and autoimmunity. It has been proposed that intracellular compartmentalization is largely responsible for reliable self versus nonself discrimination by these receptors. We have previously shown that TLR9 and TLR7 require processing prior to activation, which may further reinforce receptor compartmentalization and tolerance to self, yet this possibility remains untested. Here we report that residues within the TLR9 transmembrane (TM) region conferred the requirement for ectodomain proteolysis. TLR9 TM mutants responded to extracellular DNA, and mice expressing such receptors died from systemic inflammation and anemia. This inflammatory disease did not require lymphocytes and appeared to require recognition of self-DNA by dendritic cells. To our knowledge, these results provide the first demonstration that TLR-intrinsic mutations can lead to a break in tolerance.

Nucleic acid recognition by the innate immune system.

Receptors of the innate immune system recognize conserved microbial features and provide key signals that initiate immune responses. Multiple transmembrane and cytosolic receptors have evolved to recognize RNA and DNA, including members of the Toll-like receptor and RIG-I-like receptor families and several DNA sensors. This strategy enables recognition of a broad range of pathogens; however, in some cases, this benefit is weighed against the cost of potential self recognition. Recognition of self nucleic acids by the innate immune system contributes to the pathology associated with several autoimmune or autoinflammatory diseases. In this review, we highlight our current understanding of nucleic acid sensing by innate immune receptors and discuss the regulatory mechanisms that normally prevent inappropriate responses to self.

Multimodal imaging analysis of tumor progression and bone resorption in a murine cancer model.

OBJECTIVE: This study evaluates the use of multimodal imaging to qualitatively and quantitatively measure tumor progression and bone resorption in a xenotransplanted tumor model of human neuroblastoma. METHODS: Human neuroblastoma cells expressing a luciferase reporter gene were injected into the femur of nu/nu mice. Tumor progression with and without zoledronic acid treatment was monitored using radiographs, D-luciferin-induced luminescence, micro-computer tomography (CT) and micro-magnetic resonance imaging (MRI). RESULTS: We observed a gradual increase in D-luciferin-based bioluminescence concomitant with detectable osteolytic lesions. Tumor growth was inhibited (P=0.003-0.07) with zoledronic acid treatment. Micro-CT analysis in vivo provided a method to quantify bone loss, and its prevention by zoledronic acid. High-resolution MRI images allowed the observation of tumor cells within the bone marrow cavity, as well as distant metastasis. CONCLUSION: Multimodal imaging allows to measure tumor growth and bone resorption simultaneously in vivo and also proved useful in the detection distant metastasis.