IL-22BP is produced by eosinophils in human gut and blocks IL-22 protective actions during colitis.

Crohn's disease and ulcerative colitis, the two major forms of inflammatory bowel diseases (IBDs), are characterized by high levels of IL-22 production. Rodent studies revealed that this cytokine is protective during colitis but whether this is true in IBDs is unclear. We show here that levels of the soluble inhibitor of IL-22, interleukin 22-binding protein (IL-22BP), are significantly enhanced during IBDs owing to increased numbers of IL-22BP-producing eosinophils, that we unexpectedly identify as the most abundant source of IL-22BP protein in human gut. In addition, using IL-22BP-deficient rats, we confirm that endogenous IL-22BP is effective at blocking protective actions of IL-22 during acute colitis. In conclusion, our study provides new important insights regarding the biology of IL-22 and IL-22BP in the gut and indicates that protective actions of IL-22 are likely to be suboptimal in IBDs thus making IL-22BP a new relevant therapeutic target.

Autologous dendritic cells prolong allograft survival through Tmem176b-dependent antigen cross-presentation.

The administration of autologous (recipient-derived) tolerogenic dendritic cells (ATDCs) is under clinical evaluation. However, the molecular mechanisms by which these cells prolong graft survival in a donor-specific manner is unknown. Here, we tested mouse ATDCs for their therapeutic potential in a skin transplantation model. ATDC injection in combination with anti-CD3 treatment induced the accumulation of CD8(+) CD11c(+) T cells and significantly prolonged allograft survival. TMEM176B is an intracellular protein expressed in ATDCs and initially identified in allograft tolerance. We show that Tmem176b(-/-) ATDCs completely failed to trigger both phenomena but recovered their effect when loaded with donor peptides before injection. These results strongly suggested that ATDCs require TMEM176B to cross-present antigens in a tolerogenic fashion. In agreement with this, Tmem176b(-/-) ATDCs specifically failed to cross-present male antigens or ovalbumin to CD8(+) T cells. Finally, we observed that a Tmem176b-dependent cation current controls phagosomal pH, a critical parameter in cross-presentation. Thus, ATDCs require TMEM176B to cross-present donor antigens to induce donor-specific CD8(+) CD11c(+) T cells with regulatory properties and prolong graft survival.

Interleukin-22 binding protein (IL-22BP) is constitutively expressed by a subset of conventional dendritic cells and is strongly induced by retinoic acid.

Interleukin-22 (IL-22) is mainly produced at barrier surfaces by T cells and innate lymphoid cells and is crucial to maintain epithelial integrity. However, dysregulated IL-22 action leads to deleterious inflammation and is involved in diseases such as psoriasis, intestinal inflammation, and cancer. IL-22 binding protein (IL-22BP) is a soluble inhibitory IL-22 receptor and may represent a crucial regulator of IL-22. We show both in rats and mice that, in the steady state, the main source of IL-22BP is constituted by a subset of conventional dendritic cells (DCs) in lymphoid and non-lymphoid tissues. In mouse intestine, IL-22BP was specifically expressed in lamina propria CD103(+)CD11b(+) DC. In humans, IL-22BP was expressed in immature monocyte-derived DC and strongly induced by retinoic acid but dramatically reduced upon maturation. Our data suggest that a subset of immature DCs may actively participate in the regulation of IL-22 activity in the gut by producing high levels of IL-22BP.

Cell therapy with autologous tolerogenic dendritic cells induces allograft tolerance through interferon-gamma and epstein-barr virus-induced gene 3.

Innovative therapeutic strategies are needed to diminish the impact of harmful immunosuppression in transplantation. Dendritic cell (DC)-based therapy is a promising approach for induction of antigen-specific tolerance. Using a heart allograft model in rats, we analyzed the immunoregulatory mechanisms by which injection of autologous tolerogenic DCs (ATDCs) plus suboptimal immunosuppression promotes indefinite graft survival. Surprisingly, we determined that Interferon-gamma (IFNG), a cytokine expected to be propathogenic, was threefold increased in the spleen of tolerant rats. Importantly, its blockade led to allograft rejection [Mean Survival Time (MST) = 25.6 ± 4 days], showing that IFNG plays a critical role in immunoregulatory mechanisms triggered by ATDCs. IFNG was expressed by TCRαß(+) CD3(+) CD4(-) CD8(-) NKRP1(-) cells (double negative T cells, DNT), which accumulated in the spleen of tolerant rats. Interestingly, ATDCs specifically induced IFNG production by DNT cells. ATDCs expressed the cytokinic chain Epstein-Barr virus-induced gene 3 (EBI3), an IL-12 family member. EBI3 blockade or knock-down through siRNA completely abolished IFNG expression in DNT cells. Finally, EBI3 blockade in vivo led to allograft rejection (MST = 36.8 ± 19.7 days), demonstrating for the first time a role for EBI3 in transplantation tolerance. Taken together our results have important implications in the rationalization of DC-based therapy in transplantation as well as in the patient immunomonitoring follow-up.

Induction of tolerance by exosomes and short-term immunosuppression in a fully MHC-mismatched rat cardiac allograft model.

Exosomes are MHC-bearing vesicles secreted by a wide array of cells. We have previously shown that donor-haplotype exosomes from bone marrow dendritic cells (DCs) injected before transplantation significantly prolong heart allograft survival in congenic and fully MHC-mismatched Lewis rats. Here we show that donor exosomes administered after transplantation are similarly able to prolong allograft survival, however, without inducing tolerance. We therefore tested the effect of exosomes combined with short-term LF 15-0195 (LF) treatment, which blocks the maturation of DCs, so that donor-MHC antigens from exosomes could be presented in a more tolerogenic environment. LF treatment does not preclude the development of a strong antidonor cellular response, and while LF, but not exosome, treatment inhibits the antidonor humoral response and decreases leukocyte graft infiltration, allografts from LF-treated recipients were either acutely or strongly chronically rejected. Interestingly, when combined with LF treatment, exosomes induced a donor-specific allograft tolerance characterized by a strong inhibition of the antidonor proliferative response. This donor-specific tolerance was transferable to naïve allograft recipients. Moreover, exosomes/LF treatment prevented or considerably delayed the appearance of chronic rejection. These results suggest that under LF treatment, presentation of donor-MHC antigens (from exosomes) can induce regulatory responses that are able to modulate allograft rejection and to induce donor-specific allograft tolerance.