Tolerogenic dendritic cells generated with dexamethasone and vitamin D3 regulate rheumatoid arthritis CD4+ T cells partly via transforming growth factor-β1

Tolerogenic dendritic cells (tolDC) are a new immunotherapeutic tool for the treatment of rheumatoid arthritis (RA) and other autoimmune disorders. We have established a method to generate stable tolDC by pharmacological modulation of human monocyte-derived DC. These tolDC exert potent pro-tolerogenic actions on CD4(+) T cells. Lack of interleukin (IL)-212p70 production is a key immunoregulatory attribute of tolDC but does not explain their action fully. Here we show that tolDC express transforming growth factor (TGF)-beta 1 at both mRNA and protein levels, and that expression of this immunoregulatory cytokine is significantly higher in tolDC than in mature monocyte-derived DC. By inhibiting TGF-beta 1 signalling we demonstrate that tolDC regulate CD4(+) T cell responses in a manner that is at least partly dependent upon this cytokine. Crucially, we also show that while there is no significant difference in expression of TGFbRII on CD4(+) T cells from RA patients and healthy controls, RA patient CD4(+) T cells are measurably less responsive to TGF-beta 1 than healthy control CD4(+) T cells [reduced TGF-beta-induced mothers against decapentaplegic homologue (Smad) 2/3 phosphorylation, forkhead box protein 3 (FoxP3) expression and suppression of (IFN)-gamma secretion]. However, CD4(+) T cells from RA patients can, nonetheless, be regulated efficiently by tolDC in a TGF-beta 1-dependent manner. This work is important for the design and development of future studies investigating the potential use of tolDC as a novel immunotherapy for the treatment of RA.