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Dendritic cells (DCs) are APCs essential in regulating the immune response. PGE 2 , produced during inflammation, has a pivotal role in the maturation of DCs and, therefore, is vital for the immune response. The large variety of biologic functions governed by PGE 2 is mediated by its signaling through 4 distinct E-type prostanoid (EP) receptors. Immunogenic DCs express EP 2 and EP 4 , which mediate the PGE 2 signaling. However, the expression and function of EP receptors in human tolerogenic DCs (tol-DCs), which present an inhibitory phenotype, have not yet, to our knowledge, been assessed. To clarify the role of EP receptors in tol-DCs, we examined the expression of different EP receptors and their effect using selective agonists in human cells. We find that EP 2 and EP 3 expression are up-regulated in in vitro-generated tol-DCs compared with mature DCs (mDCs). Activation of EP 2 -EP 4 has a direct effect on the surface expression of costimulatory molecules and maturation receptors, such as CD80, CD83, and CD86 or MHCII and CCR7 in tol-DCs, the latter being exclusively modulated by PGE 2 -EP 4 signaling. Importantly, we find that EP 2 and EP 3 receptors are involved in tolerance induction through IL-10 production by tol-DCs. These results are in sharp contrast with the inflammatory role of EP 4 Moreover, we show that DCs generated in the presence of agonists for EP receptors, induce naive T cell differentiation toward polarized Th1/Th17 cells. Given the differential effects of EP receptors, our results suggest that EP receptor agonist/antagonists might become relevant novel drug templates to modulate immune response., (© Society for Leukocyte Biology.)

The design of innovative strategies to selectively target cells, such antigen-presenting cells and dendritic cells, in vivo to induce immune tolerance is gaining interest and relevance for the treatment of immune-mediated diseases. A novel loaded-nanosystem strategy to generate tolerogenic dendritic cells (tol-DCs) was evaluated. Hence budesonide (BDS) was encapsulated in multiwalled polyurethane-polyurea nanoparticles (PUUa NPs-BDS) based on self-stratified polymers by hydrophobic interactions at the oil-water interface. DCs treated with encapsulated BDS presented a prominent downregulation of costimulatory molecules (CD80, CD83 and MHCII) and upregulation of inhibitory receptors. Moreover, DCs treated with these PUUa NPs-BDS also secreted large amounts of IL-10, a crucial anti-inflammatory cytokine to induce tolerance, and inhibited T lymphocyte activation in a specific manner compared to those cells generated with free BDS. These results demonstrate that PUUa NPs-BDS are a highly specific and efficient system through which to induce DCs with a tolerogenic profile. Given the capacity of PUUa NPs-BDS, this delivery system has a clear advantage for translation to in vivo studies., (Copyright © 2016 Elsevier B.V. All rights reserved.)

Background and Aims: Ex vivo-generated autologous tolerogenic dendritic cells [tolDCs] can restore immune tolerance in experimental colitis. The aim of this study was to determine the safety and tolerability of administration of autologous tolDCs in refractory Crohn's disease [CD] patients., Methods: A phase-I, single-centre, sequential-cohorts, dose-range study was designed. Stable tolDCs were generated ex vivo from monocytes following a previously developed protocol, and administered by sonography-guided intraperitoneal injection. Six sequential refractory-CD cohorts were established: the first three cohorts received a single intraperitoneal injection of tolDCs at escalating doses [2 x 10(6)/5 x 10(6)/10 x 10(6)]; and the last three cohorts received three biweekly intraperitoneal injections at same escalating doses. Safety was sequentially evaluated. Patients were assessed from week 0 to 12 and followed up for 1-year period for safety., Results: Nine patients were included. No adverse effects were detected during tolDC injection or follow-up. Three patients withdrew from the study due to CD worsening. Crohn's Disease Activity Index [CDAI] decreased from 274 [60] {mean (standard deviation [SD])} to 222 [113] [p = 0.3]; one [11%] patient reached clinical remission [CDAI < 150] and two [22%] clinical response [CDAI decrease ≥ 100]. Crohn's Disease Endoscopic Index of Severity [CDEIS] decreased from 18 [5] to 13 [8] [p = 0.4]; lesions improved markedly in three patients [33%]. Quality of life (inflammatory bowel disease questionnaire [IBDQ]) changed from 125 [27] to 131 [38] [p = 0.7]; remission [IBDQ at Week 12 ≥ 170] was reached in one [11%] case and response [IBDQ score increase ≥ 16] in two [22%]., Conclusions: Intraperitoneal administration of autologous tolDCs appears safe and feasible in refractory CD patients. Further studies should be developed to test clinical benefit, determine the optimal administration route and dose, and monitor the immune responses; See [www.eudract.ema.europa.eu, EudraCT number 2007-003469-42; www.aemps.gob.es number PEI 08-049]., (Copyright © 2015 European Crohn’s and Colitis Organisation (ECCO). Published by Oxford University Press. All rights reserved. For permissions, please email: journals.permissions@oup.com.)

The aim of this study was to test the hypothesis whether MERTK, which is up-regulated in human DCs treated with immunosuppressive agents, is directly involved in modulating T cell activation. MERTK is a member of the TAM family and contributes to regulating innate immune response to ACs by inhibiting DC activation in animal models. However, whether MERTK interacts directly with T cells has not been addressed. Here, we show that MERTK is highly expressed on dex-induced human tol-DCs and participates in their tolerogenic effect. Neutralization of MERTK in allogenic MLR, as well as autologous DC-T cell cultures, leads to increased T cell proliferation and IFN-γ production. Additionally, we identify a previously unrecognized noncell-autonomous regulatory function of MERTK expressed on DCs. Mer-Fc protein, used to mimic MERTK on DCs, suppresses naïve and antigen-specific memory T cell activation. This mechanism is mediated by the neutralization of the MERTK ligand PROS1. We find that MERTK and PROS1 are expressed in human T cells upon TCR activation and drive an autocrine proproliferative mechanism. Collectively, these results suggest that MERTK on DCs controls T cell activation and expansion through the competition for PROS1 interaction with MERTK in the T cells. In conclusion, this report identified MERTK as a potent suppressor of T cell response., (© Society for Leukocyte Biology.)

LFA-1 is a leukocyte specific β2 integrin that plays a major role in regulating adhesion and migration of different immune cells. Recent data suggest that LFA-1 on mature dendritic cells (mDCs) may function as a chemokine-inducible anchor during homing of DCs through the afferent lymphatics into the lymph nodes, by transiently switching its molecular conformational state. However, the role of LFA-1 mobility in this process is not yet known, despite that the importance of lateral organization and dynamics for LFA-1-mediated adhesion regulation is broadly recognized. Using single particle tracking approaches we here show that LFA-1 exhibits higher mobility on resting mDCs compared to monocytes. Lymphoid chemokine CCL21 stimulation of the LFA-1 high affinity state on mDCs, led to a significant reduction of mobility and an increase on the fraction of stationary receptors, consistent with re-activation of the receptor. Addition of soluble monomeric ICAM-1 in the presence of CCL21 did not alter the diffusion profile of LFA-1 while soluble ICAM-1 nano-aggregates in the presence of CCL21 further reduced LFA-1 mobility and readily bound to the receptor. Overall, our results emphasize the importance of LFA-1 lateral mobility across the membrane on the regulation of integrin activation and its function as adhesion receptor. Importantly, our data show that chemokines alone are not sufficient to trigger the high affinity state of the integrin based on the strict definition that affinity refers to the adhesion capacity of a single receptor to its ligand in solution. Instead our data indicate that nanoclustering of the receptor, induced by multi-ligand binding, is required to maintain stable cell adhesion once LFA-1 high affinity state is transiently triggered by inside-out signals.

The gut mucosa undergoes continuous antigenic exposure from food antigens, commensal flora derived ligands, and pathogens. This constant stimulation results in controlled inflammatory responses that are effectively suppressed by multiple factors. This tight regulation, necessary to maintain intestinal homeostasis, is affected during inflammatory bowel diseases (IBD) resulting in altered immune responses to harmless microorganisms. Dendritic cells (DCs) are sentinels of immunity, located in peripheral and lymphoid tissues, which are essential for homeostasis of T cell-dependent immune responses. The expression of a particular set of pathogen recognition receptors allows DCs to initiate immune responses. However, in the absence of danger signals, different DC subsets can induce active tolerance by inducing regulatory T cells (Treg), inhibiting inflammatory T helper cell responses, or both. Interestingly, several protocols to generate clinical grade tolerogenic DC (tol-DCs) in vitro have been described, opening the possibility to restore the intestinal homeostasis to bacterial flora by cellular therapy. In this review, we discuss different DC subsets and their role in IBD. Additionally, we will review preclinical studies performed in animal models while describing recent characterization of tol-DCs from Crohn's disease patients for clinical application.

Autoimmune diseases, or immune-mediated diseases, are characterized by loss of tolerance to autoantigens and immune system activation causing damage to one or multiple organs. The mechanisms through which this abnormal immune response is started and maintained are not fully established. The therapeutic approach to these diseases is generally based on corticosteroids, immunomodulators, and monoclonal antibodies. Given the exceptional capacity of dendritic cells to induce immunogenicity, early results in humans for the treatment of tumors (melanoma) or infections (HIV) with immunogenic dendritic cells have recently been obtained. Identification of dendritic cells with tolerogenic capacity and the results in experimental models of autoimmune diseases (autoimmune encephalomyelitis, diabetes mellitus, colitis) suggests that treatment with tolerogenic dendritic cells could be a beneficial therapeutic alternative in the treatment of autoimmune diseases or immune-mediated diseases such as Crohn's disease., (Copyright © 2010 Elsevier España, S.L. All rights reserved.)