Background/Purpose:  Tolerogenic dendritic cells (tDCs) play a critical role in immune tolerance and are involved in the pathogenesis of autoimmune diseases such as rheumatoid arthritis. Suppression by tDCs is primarily mediated via the induction of regulatory T cells (Treg). tDCs are induced in the presence of specific biological agents. Therefore, we screened the molecules that enhanced induction of tDCs from the libraries of lipids, nuclear receptor ligands, and kinase inhibitors. Of these, protein kinase C inhibitors (PKCIs) such as bisindolylmaleimide I, Go6983, and Ro32-0243, suppressed the expression of CD80, CD83, and CD86 on DCs and suppressed allogenic T cell responses. In this study, we showed the characterization of PKCI-treated human tDCs and application to the therapy for autoimmune diseases.

Methods: Mature DCs (mDCs) were prepared from human monocytes by treating with  GM-CSF and IL-4 for 5 days, and then induced maturation wtih TNF-alpha for 48h. PKCI-treated tDCs were generated by adding bisindolylmaleimide I, Go6983, or Ro32-0243 during this process. We analyzed the cell surface expression on DCs, cytokine production, and phagocytic ability. Furthermore, we examined the effects of these molecules on stability and plasticity of DCs, antigen presenting, allogenic T cell responses, and induction of Tr1 and Treg cells.

Results: DCs treated with PKC inhibitors such as bisindolylmaleimide I, Go6983, and Ro32-0243 decreased the expression levels of CD40, CD80, CD83, CD86, and HLA class I significantly but not those of CD1a, CD11c, and HLA classII compared with mDCs. Moreover, PKCI-treated tDCs produced 15-20-fold and 2-4-fold higher concentration of IL-10 and TGF-beta than mDCs, respectively, resulting in a strong reduction of allogenic T cell responses. From the co-culture of DCs and naïve T cells, PKCI-treated tDCs induced IL-10-producing Tr1 cells and Foxp3⁺ regulatory T cells. PKCI-treated tDCs retained phagocytic ability as well as immature DCs (iDCs). PKC I-treated tDCs kept the low expression levels of CD80, CD83, and CD86 and  suppressive properties at least one week after stimulated with a cocktail of proinflammatory cytokines or LPS, whereas iDCs recovered the similar expression levels to mDCs and did not have suppressive properties.

Conclusion: We showed that PKCI-treated human DCs acted as a strong and stable tDCs. PKCI-treated tDCs may be useful method to the therapy for autoimmune diseases.

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/protein-kinase-c-inhibitor-generates-human-tolerogenic-dendritic-cells-that-induce-tr1-and-foxp3-regulatory-t-cells/