ICOS ligand and IL-10 synergize to promote host-microbiota mutualism.

Genome-wide association studies have identified ICOSLG, which encodes the inducible costimulator ligand (ICOSLG or ICOSL) as a susceptibility locus for inflammatory bowel disease. ICOSL has been implicated in the enhancement of pattern recognition receptor signaling in dendritic cells, induction of IL-10 production by CD4 T cells, and the generation of high-affinity antibodies to specific antigens-all of which can potentially explain its involvement in gastrointestinal inflammation. Here, we show that murine ICOSL deficiency results in significant enrichment of IL-10-producing CD4 T cells particularly in the proximal large intestine. Transient depletion of IL-10-producing cells from adult ICOSL-deficient mice induced severe colonic inflammation that was prevented when mice were first treated with metronidazole. ICOSL-deficient mice displayed reduced IgA and IgG antibodies in the colon mucus and impaired serum antibody recognition of microbial antigens, including flagellins derived from mucus-associated bacteria of the Lachnospiraceae family. Confirming the synergy between ICOSL and IL-10, ICOSL deficiency coupled with CD4-specific deletion of the Il10 gene resulted in juvenile onset colitis that was impeded when pups were fostered by ICOSL-sufficient dams. In this setting, we found that both maternally acquired and host-derived antibodies contribute to the life anti-commensal antibody repertoire that mediates this protection in early life. Collectively, our findings reveal a partnership between ICOSL-dependent anti-commensal antibodies and IL-10 in adaptive immune regulation of the microbiota in the large intestine. Furthermore, we identify ICOSL deficiency as an effective platform for exploring the functions of anti-commensal antibodies in host-microbiota mutualism.

Cutting Edge: ICOS-Deficient Regulatory T Cells Display Normal Induction of Il10 but Readily Downregulate Expression of Foxp3.

The ICOS pathway has been implicated in the development and functions of regulatory T (Treg) cells, including those producing IL-10. Treg cell-derived IL-10 is indispensable for the establishment and maintenance of intestinal immune homeostasis. We examined the possible involvement of the ICOS pathway in the accumulation of murine colonic Foxp3- and/or IL-10-expressing cells. We show that ICOS deficiency does not impair induction of IL-10 by intestinal CD4 T cells but, instead, triggers substantial reductions in gut-resident and peripherally derived Foxp3+ Treg cells. ICOS deficiency is associated with reduced demethylation of Foxp3 CNS2 and enhanced loss of Foxp3. This instability significantly limits the ability of ICOS-deficient Treg cells to reverse ongoing inflammation. Collectively, our results identify a novel role for ICOS costimulation in imprinting the functional stability of Foxp3 that is required for the retention of full Treg cell function in the periphery.

GNTI-122: an autologous antigen-specific engineered Treg cell therapy for type 1 diabetes.

Tregs have the potential to establish long-term immune tolerance in patients recently diagnosed with type 1 diabetes (T1D) by preserving ß cell function. Adoptive transfer of autologous thymic Tregs, although safe, exhibited limited efficacy in previous T1D clinical trials, likely reflecting a lack of tissue specificity, limited IL-2 signaling support, and in vivo plasticity of Tregs. Here, we report a cell engineering strategy using bulk CD4+ T cells to generate a Treg cell therapy (GNTI-122) that stably expresses FOXP3, targets the pancreas and draining lymph nodes, and incorporates a chemically inducible signaling complex (CISC). GNTI-122 cells maintained an expression profile consistent with Treg phenotype and function. Activation of CISC using rapamycin mediated concentration-dependent STAT5 phosphorylation and, in concert with T cell receptor engagement, promoted cell proliferation. In response to the cognate antigen, GNTI-122 exhibited direct and bystander suppression of polyclonal, islet-specific effector T cells from patients with T1D. In an adoptive transfer mouse model of T1D, a mouse engineered-Treg analog of GNTI-122 trafficked to the pancreas, decreased the severity of insulitis, and prevented progression to diabetes. Taken together, these findings demonstrate in vitro and in vivo activity and support further development of GNTI-122 as a potential treatment for T1D.

Bone marrow Tregs mediate stromal cell function and support hematopoiesis via IL-10.

The nonimmune roles of Tregs have been described in various tissues, including the BM. In this study, we comprehensively phenotyped marrow Tregs, elucidating their key features and tissue-specific functions. We show that marrow Tregs are migratory and home back to the marrow. For trafficking, marrow Tregs use S1P gradients, and disruption of this axis allows for specific targeting of the marrow Treg pool. Following Treg depletion, the function and phenotype of both mesenchymal stromal cells (MSCs) and hematopoietic stem cells (HSCs) was impaired. Transplantation also revealed that a Treg-depleted niche has a reduced capacity to support hematopoiesis. Finally, we found that marrow Tregs are high producers of IL-10 and that Treg-secreted IL-10 has direct effects on MSC function. This is the first report to our knowledge revealing that Treg-secreted IL-10 is necessary for stromal cell maintenance, and our work outlines an alternative mechanism by which this cytokine regulates hematopoiesis.

Development of endocytosis, degradative activity, and antigen processing capacity during GM-CSF driven differentiation of murine bone marrow.

Dendritic cells (DC) are sentinels of the immune system, alerting and enlisting T cells to clear pathogenic threats. As such, numerous studies have demonstrated their effective uptake and proteolytic activities coupled with antigen processing and presentation functions. Yet, less is known about how these cellular mechanisms change and develop as myeloid cells progress from progenitor cells to more differentiated cell types such as DC. Thus, our study comparatively examined these functions at different stages of myeloid cell development driven by the GM-CSF. To measure these activities at different stages of development, GM-CSF driven bone marrow cells were sorted based on expression of Ly6C, CD115, and CD11c. This strategy enables isolation of cells representing five distinct myeloid cell types: Common Myeloid Progenitor (CMP), Granulocyte/Macrophage Progenitor (GMP), monocytes, monocyte-derived Macrophage/monocyte-derived Dendritic cell Precursors (moMac/moDP), and monocyte-derived DC (moDC). We observed significant differences in the uptake capacity, proteolysis, and antigen processing and presentation functions between these myeloid cell populations. CMP showed minimal uptake capacity with no detectable antigen processing and presenting function. The GMP population showed higher uptake capacity, modest proteolytic activity, and little T cell stimulatory function. In the monocyte population, the uptake capacity reached its peak, yet this cell type had minimal antigen processing and presentation function. Finally, moMac/moDP and moDC had a modestly decreased uptake capacity, high degradative capacity and strong antigen processing and presentation functions. These insights into when antigen processing and presentation function develop in myeloid cells during GM-CSF driven differentiation are crucial to the development of vaccines, allowing targeting of the most qualified cells as an ideal vaccine vehicles.

TCR-independent functions of Th17 cells mediated by the synergistic actions of cytokines of the IL-12 and IL-1 families.

The development of Th17 cells is accompanied by the acquisition of responsiveness to both IL-12 and IL-23, cytokines with established roles in the development and/or function of Th1 and Th17 cells, respectively. IL-12 signaling promotes antigen-dependent Th1 differentiation but, in combination with IL-18, allows the antigen-independent perpetuation of Th1 responses. On the other hand, while IL-23 is dispensable for initial commitment to the Th17 lineage, it promotes the pathogenic function of the Th17 cells. In this study, we have examined the overlap between Th1 and Th17 cells in their responsiveness to common pro-inflammatory cytokines and how this affects the antigen-independent cytokine responses of Th17 cells. We found that in addition to the IL-1 receptor, developing Th17 cells also up-regulate the IL-18 receptor. Consequently, in the presence of IL-1ß or IL-18, and in the absence of TCR activation, Th17 cells produce Th17 lineage cytokines in a STAT3-dependent manner when stimulated with IL-23, and IFN© via a STAT4-dependent mechanism when stimulated with IL-12. Thus, building on previous findings of antigen-induced plasticity of Th17 cells, our results indicate that this potential of Th17 cells extends to their cytokine-dependent antigen-independent responses. Collectively, our data suggest a model whereby signaling via either IL-1ß or IL-18 allows for bystander responses of Th17 cells to pathogens or pathogen products that differentially activate innate cell production of IL-12 or IL-23.