In our earlier work, we had shown that GM-CSF treatment of CBA/J mice can suppress ongoing thyroiditis by inducing tolerogenic CD8α(-) DCs, which helped expand and/or induce CD4(+)Foxp3(+) Tregs. To identify the primary cell type that was affected by the GM-CSF treatment and understand the mechanism by which Tregs were induced, we compared the effect of GM-CSF on matured spDCs and BMDC precursors in vitro. Matured spDCs exposed to GM-CSF ex vivo induced only a modest increase in the percentage of Foxp3-expressing T cells in cocultures. In contrast, BM cells, when cultured in the presence of GM-CSF, gave rise to a population of CD11c(+)CD11b(Hi)CD8α(-) DCs (BMDCs), which were able to expand Foxp3(+) Tregs upon coculture with CD4(+) T cells. This contact-dependent expansion occurred in the absence of TCR stimulation and was abrogated by OX40L blockage. Additionally, the BMDCs secreted high levels of TGF-β, which was required and sufficient for adaptive differentiation of T cells to Foxp3(+) Tregs, only upon TCR stimulation. These results strongly suggest that the BMDCs differentiated by GM-CSF can expand nTregs and induce adaptive Tregs through different mechanisms.

Autoimmune thyroid diseases (AITD) are one of the most common organ-specific autoimmune disorders, of which Hashimoto's thyroiditis (HT) and Graves' disease (GD) are 2 of the most common clinical expressions. HT is characterized by hypothyroidism that results from the destruction of the thyroid by thyroglobulin-specific T cell-mediated autoimmune response. In contrast, GD is characterized by hyperthyroidism due to excessive production of thyroid hormone induced by thyrotropin receptor-specific stimulatory autoantibodies. Cytokines play a crucial role in modulating immune responses that affect the balance between maintenance of selftolerance and initiation of autoimmunity. However, the role of cytokines is often confusing and is neither independent nor exclusive of other immune mediators. A regulatory cytokine may either favor induction of tolerance against thyroid autoimmune disease or favor activation and/or exacerbation of autoimmune responses. These apparently contradictory functions of a given cytokine are primarily influenced by the nature of co-signaling delivered by other cytokines. Consequently, a thorough understanding of the role of a particular cytokine in the context of a specific immune response is essential for the development of appropriate strategies to modulate cytokine responses to maintain or restore health. This review provides a summary of recent research pertaining to the role of cytokines in the pathogenesis of AITD with a particular emphasis on the therapeutic applications of cytokine modulation.

Earlier, we had demonstrated that treatment with low dose of GM-CSF can prevent the development of experimental autoimmune thyroiditis (EAT), myasthenia gravis (EAMG) and type-1 diabetes; and could also reverse ongoing EAT and EAMG. The protective effect was mediated through the induction of tolerogenic CD11C+CD8α− DCs and consequent expansion of Foxp3+ T-regulatory cells (Tregs). Subsequently, we showed that GM-CSF acted specifically on bone marrow precursors and facilitated their differentiation into tolerogenic DCs (GM-BMDCs), which directed Treg expansion in a contact dependent manner. This novel mechanism of Treg expansion was independent of TCR mediated signalling but required exogenous IL-2 and co-signalling from DC bound OX40L. In the present study, we observed that OX40L mediated signalling by GM-BMDCs although necessary was not sufficient for Treg expansion and required signalling by Jagged1. Concurrent signalling induced by OX40L and Jagged1 via OX40 and Notch3 receptors expressed on Tregs was essential for the Treg expansion with sustained FoxP3 expression. Adoptive transfer of only OX40L+Jagged1+ BMDCs led to Treg expansion, increased production of IL-4 and IL-10, and suppression of EAT in the recipient mice. These results showed a critical role for OX40L and Jagged1 induced co-signalling in GM-BMDC-induced Treg expansion.

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To prepare a novel Bispecific Antibody (BsAb) as a potential targeted therapy for T1D, we produced a “functionally inert” monoclonal antibody (mAb) against Glucose transporter-2 (GLUT-2) expressed on β-cells to serve as an anchoring antibody. The therapeutic arm is an agonistic mAb against Cytotoxic T-Lymphocyte Antigen 4 (CTLA-4), a negative regulator of T-cell activation expressed on activated CD4+ T-cells. A BsAb was prepared by chemically coupling an anti-GLUT2 mAb to an agonistic anti-CTLA-4 mAb. This BsAb was able to bind to GLUT2 and CTLA-4 in vitro, and to pancreatic islets, both in vitro and in vivo. We tested the safety and efficacy of this BsAb by treating Non-Obese Diabetes (NOD) mice and found that it could delay the onset of diabetes with no apparent undesirable side effects. Thus, engagement of CTLA-4 on activated T cells from target tissue can be an effective way to treat type-1 diabetes.