Neonatally imprinted stromal cell subsets induce tolerogenic dendritic cells in mesenteric lymph nodes.

Gut-draining mesenteric lymph nodes (mLNs) are important for inducing peripheral tolerance towards food and commensal antigens by providing an optimal microenvironment for de novo generation of Foxp3+ regulatory T cells (Tregs). We previously identified microbiota-imprinted mLN stromal cells as a critical component in tolerance induction. Here we show that this imprinting process already takes place in the neonatal phase, and renders the mLN stromal cell compartment resistant to inflammatory perturbations later in life. LN transplantation and single-cell RNA-seq uncover stably imprinted expression signatures in mLN fibroblastic stromal cells. Subsetting common stromal cells across gut-draining mLNs and skin-draining LNs further refine their location-specific immunomodulatory functions, such as subset-specific expression of Aldh1a2/3. Finally, we demonstrate that mLN stromal cells shape resident dendritic cells to attain high Treg-inducing capacity in a Bmp2-dependent manner. Thus, crosstalk between mLN stromal and resident dendritic cells provides a robust regulatory mechanism for the maintenance of intestinal tolerance.

Transient ablation of regulatory T cells improves antitumor immunity in colitis-associated colon cancer.

Regulatory T cells (Treg) are supportive to cancer development in most tissues, but their role in colitis-associated colon cancer (CAC) remains unclear. In this study, we investigated the role of CD4(+)Foxp3(+) Treg in a mouse model of CAC and in patients with colon cancer. These Treg were increased strongly in number in a mouse model of CAC and in the peripheral blood of patients with colon cancer, exhibiting an activated phenotype as defined by elevated expression of GARP, CD103, CTLA-4, and IL10, along with an increased suppressive effect on the proliferation and Th1 cytokine expression of CD4(+)CD25(-) responder T cells ex vivo. Transient ablation of CD4(+)Foxp3(+) Treg during tumor development in the CAC model suppressed tumor outgrowth and distribution, accompanied by an increased number of CD8(+)IFNγ/granzyme B-producing effector T cells. Conversely, inactivation of IL10 in Treg did not elevate the antitumor response but instead further boosted tumor development. Our results establish a tumor-promoting function for Treg during CAC formation, but they also suggest that a selective, transient ablation of Treg can evoke antitumor responses, with implications for immunotherapeutic interventions in patients with CAC.

Commensal microbiota drive proliferation of conventional and Foxp3(+) regulatory CD4(+) T cells in mesenteric lymph nodes and Peyer's patches.

Compelling evidence demonstrates that intestinal commensal microbiota modulate conventional and regulatory T cell (Treg) responses that are required for effective host defence against pathogens and avoidance of autoimmunity and other immunopathologic conditions. Here, we investigated the contribution of the commensal microbiota and Toll-like receptor (TLR) signaling to homeostasis of Foxp3(-) conventional CD4(+) T cells and Foxp3(+) Tregs. Upon long-term antibiotics treatment, we observed a significant reduction of conventional CD4(+) T cell proliferation in a systemic manner, whereas Foxp3(+) Treg proliferation was locally impaired in gut-draining mesenteric lymph nodes and Peyer's patches. The proliferative response to microbial components was not mediated by TLRs as MyD88- and various TLR-deficient mice displayed normal or even increased conventional T cell and Foxp3(+) Treg proliferation. Thus, commensal microbiota-derived stimuli support cycling of both conventional CD4(+) T cells and Foxp3(+) Tregs with TLR-mediated recognition of bacterial components not being the major mechanism controlling microbiota-driven T cell homeostasis.

Generation and function of immunosuppressive human and murine CD8+ T cells by transforming growth factor-ß and retinoic acid.

The intestinal immune system is constantly challenged by foreign antigens and commensal bacteria. Therefore, proper control of the intestinal microenvironment is required. One important arm of this regulatory network consists of regulatory T cells. In contrast to CD4(+) Foxp3(+) regulatory T cells, which have been well characterized, immunomodulatory CD8(+) T cells that express Foxp3 are less well defined in terms of their generation and function. Failures of these regulatory mechanisms contribute to the development of inflammatory bowel disease. In this study we demonstrate that the frequency of CD8(+) Foxp3(+) T cells is reduced in the peripheral blood of patients with ulcerative colitis. As these cells might play a currently underestimated role in the maintenance of intestinal homeostasis, we have investigated human and murine CD8(+) Foxp3(+) T cells generated by stimulating naive CD8(+) T cells in the presence of transforming growth factor-ß and retinoic acid, mediators that are abundantly produced in the intestinal mucosa. These CD8(+) Foxp3(+) fully competent regulatory T cells show strong expression of regulatory molecules CD25, Gpr83 and CTLA-4 and exhibit cell-cell contact-dependent immunosuppressive activity in vitro. Our study illustrates a previously unappreciated critical role of CD8(+) Foxp3(+) T cells in controlling potentially dangerous T cells and in the maintenance of intestinal homeostasis.

Local induction of immunosuppressive CD8+ T cells in the gut-associated lymphoid tissues.

BACKGROUND: In contrast to intestinal CD4(+) regulatory T cells (T(regs)), the generation and function of immunomodulatory intestinal CD8(+) T cells is less well defined. To dissect the immunologic mechanisms of CD8(+) T cell function in the mucosa, reactivity against hemagglutinin (HA) expressed in intestinal epithelial cells of mice bearing a MHC class-I-restricted T-cell-receptor specific for HA was studied. METHODOLOGY AND PRINCIPAL FINDINGS: HA-specific CD8(+) T cells were isolated from gut-associated tissues and phenotypically and functionally characterized for the expression of Foxp3(+) and their suppressive capacity. We demonstrate that intestinal HA expression led to peripheral induction of HA-specific CD8(+)Foxp3(+) T cells. Antigen-experienced CD8(+) T cells in this transgenic mouse model suppressed the proliferation of CD8(+) and CD4(+) T cells in vitro. Gene expression analysis of suppressive HA-specific CD8(+) T cells revealed a specific up-regulation of CD103, Nrp1, Tnfrsf9 and Pdcd1, molecules also expressed on CD4(+) T(reg) subsets. Finally, gut-associated dendritic cells were able to induce HA-specific CD8(+)Foxp3(+) T cells. CONCLUSION AND SIGNIFICANCE: We demonstrate that gut specific antigen presentation is sufficient to induce CD8(+) T(regs)in vivo which may maintain intestinal homeostasis by down-modulating effector functions of T cells.

T cells, dendritic cells and epithelial cells in intestinal homeostasis.

The mucosal immune system of the intestinal tract is continuously exposed to both potential pathogens and beneficial commensal microorganism. A variety of mechanisms contribute to the ability of the gut to either react or remain tolerant to antigen present in the intestinal lumen. Antigens of the gut commensals are not simply ignored, but rather trigger an active immunosuppressive process, which prevents the outcome of immunopathology. The aim of this review is to provide an update on the mechanism of intestinal homeostasis, with particular focus on the complex crosstalk between T cells, dendritic cells and intestinal epithelial cells.

Autoimmune-mediated intestinal inflammation-impact and regulation of antigen-specific CD8+ T cells.

BACKGROUND & AIMS: Few data exist regarding mechanisms of mucosal CD8+ T-cell reactivity to epithelial-specific antigen. To dissect the immunologic mechanisms underlying CD8+ T-cell dysregulation, reactivity to a self-antigen expressed in intestinal epithelium of mice bearing a major histocompatibility complex class I-restricted T-cell receptor specific for this antigen was studied. In addition, antigen-specific regulatory CD4+ T cells induced in vivo were tested to control these autoreactive CD8+ T cells. METHODS: Transgenic VILLIN-HA mice were mated with CL4-TCR transgenic mice. Alternatively, adoptive transfer of CL4-TCR transgenic CD8+ T cells into VILLIN-HA transgenic mice was performed to mimic spontaneous encounter of neoantigen. Mucosal CD8+ T cells were characterized under different conditions of tolerance, immunopathology, and active immunosuppression. RESULTS: Transgenic CD8+ T cells from VILLIN-HA x CL4-TCR transgenic mice preferentially migrated and expanded in mucosal lymphoid tissues. Although transgenic CD8+ T cells showed signs of T-cell activation, they failed to cause tissue damage. This was accompanied by the induction/expansion of CD4+ and CD8+, Foxp3-expressing T cells. In contrast, adoptive transfer of naive transgenic CD8+ T cells from CL4-TCR transgenic mice into VILLIN-HA transgenic mice induced severe intestinal inflammation with poor clinical course of disease. Transgenic CD8+ T cells secreted vigorous amounts of proinflammatory cytokines like interferon gamma/tumor necrosis factor alpha. Strikingly, this acute wasting disease was significantly ameliorated by cotransfer of antigen-specific regulatory CD4+ T cells. CONCLUSIONS: Epithelial-specific antigen expression is sufficient to trigger severe antigen-specific CD8+ T-cell-mediated intestinal inflammation; this might be controlled by antigen-specific regulatory T cells under physiological conditions.