Peripheral Tolerance Induction Using Ethylenecarbodiimide-Fixed APCs Uses both Direct and Indirect Mechanisms of Antigen Presentation for Prevention of Experimental Autoimmune Encephalomyelitis

Abstract

MHC class II (MHC II)-restricted T cell responses are a common driving force of autoimmune disease. Accordingly, numerous therapeutic strategies target CD4+ T cells with the hope of attenuating autoimmune responses and restoring self-tolerance. We have previously reported that i.v. treatment with Ag-pulsed, ethylenecarbodiimide (ECDI)-fixed splenocytes (Ag-SPs) is an efficient protocol to induce Ag-specific tolerance for prevention and treatment of experimental autoimmune encephalomyelitis (EAE). Ag-SPs coupled with peptide can directly present peptide:MHC II complexes to target CD4+ T cells in the absence of costimulation to induce anergy. However, Ag-SPs coupled with whole protein also efficiently attenuates Ag-specific T cell responses suggesting the potential contribution of alternative indirect mechanisms/interactions between the Ag-SPs and target CD4+ T cells. Thus, we investigated whether MHC II compatibility was essential to the underlying mechanisms by which Ag-SP induces tolerance during autoimmune disease. Using MHC-deficient, allogeneic, and/or syngeneic donor Ag-SPs, we show that MHC compatibility between the Ag-SP donor and the host is not required for tolerance induction. Interestingly, we found that ECDI treatment induces apoptosis of the donor cell population which promotes uptake and reprocessing of donor cell peptides by host APCs resulting in the apparent MHC II-independent induction of tolerance. However, syngeneic donor cells are more efficient at inducing tolerance, suggesting that Ag-SPs induce functional Ag-SP tolerance via both direct and indirect (cross-tolerance) mechanisms leading to prevention and effective treatment of autoimmune disease.

ECDI-fixed allogeneic splenocytes induce donor-specific tolerance for long-term survival of islet transplants via two distinct mechanisms

“…Recent studies indicate that ECDI treatment induces the cells to undergo rapid apoptosis and that tolerance is induced by both direct and indirect antigen presentation (18). Cell tracking indicates that ECDI-treated cells distribute widely, but intact cells disappear within 48 hours (S.D.M., unpublished observations).…”

“…infusion of ECDI-treated donor splenocytes induced indefinite donor-specific tolerance in allogeneic islet cell transplantation. Here, the antigens of interest are mainly donor MHC class I and II molecules that are an integral surface component of donor lymphocytes, and ECDI treatment presumably interferes with costimulatory signals leading to tolerance induction to the membrane-bound allogeneic MHC antigens (18,19). Two previous studies examined the efficacy of ECDI-treated donor dendritic cells or whole splenocytes in full MHC-mismatched heart and skin transplant models (20,21).…”

Current Theories for Multiple Sclerosis Pathogenesis and Treatment

“…Manipulation of T cell activation and differentiation pathways has been at the center of current tolerance induction theory, and the basis of tolerance induction utilizing current immunosuppressive agents. Over recent years, experimental models have shown that it is possible to exploit the mechanisms that normally maintain immune homeostasis and tolerance to self-antigens, as well as to reintroduce tolerance to self-antigen in an autoimmune setting (Getts et al, 2011;Kohm et al, 2005;Podojil et al, 2008;Turley and Miller, 2007). However, in the clinical setting the utilization of co-stimulatory blockade, soluble peptide, altered peptide ligands among others have yielded disappointing results.…”

Tolerance Strategies Employing Antigen-Coupled Apoptotic Cells and Carboxylated PLG Nanoparticles for the Treatment of Type 1 Diabetes

“…While there is clear evidence for the role of T cell anergy in Ag-ECDI-SP tolerance, subsequent studies have shown that splenocytes treated with antigen-processing inhibitors, MHC knock-out splenocytes, or donor red blood cells (RBCs) lacking MHC class II expression can still induce tolerance [16,23,24]. This suggests that T cell anergy through direct TCR engagement of the Ag-ECDI-SP is not required, rather tolerance induction is primarily achieved through indirect mechanisms involving host antigen-presenting cells (APCs)…”