Limiting the severity of inflammation and promoting its eventual resolution are vital for protecting host tissues both in autoimmunity and chronic infection. The aim of this study was to determine the suitability of repurposing anti-CD3 monoclonal antibody (mAb) therapy for rheumatoid arthritis (RA) by analyzing its ability to induce CD8+FoxP3+ Treg cells from peripheral blood mononuclear cells (PBMCs).
Anti-CD3 mAb was cultured with RA PBMCs to induce CD8+FoxP3+ Treg cells, which were analyzed by flow cytometry to determine their phenotype. Treg cell induction was investigated via neutralization or blocking antibodies, cellular depletion, or ImageStream technology. Blotting was used to determine the signaling pathways involved in CD8+FoxP3+ Treg cell induction. Suppression of CD4+ T cell effector responses was assessed by Treg cell suppression assays and Mosaic enzyme-linked immunosorbent assay.
Potent CD8+FoxP3+ Treg cells were induced from RA PBMCs by anti-CD3 mAb. Unlike their CD4+ counterparts, CD8+FoxP3+ Treg cells inhibited Th17 responses in a contact-dependent manner, thereby functioning to limit a wider range of inflammatory pathways. CD8+FoxP3+ Treg cell induction was supported both by p38 phosphorylation intrinsic to naive CD8+ T cells and by monocytes via CD86 and membrane tumor necrosis factor α (TNFα). Artificially increasing monocyte membrane TNFα or inhibiting CD8+ T cell p38 phosphorylation drove FoxP3 expression in a subset of initially unresponsive CD8+ T cells.
These data define an unknown mechanism of CD8+FoxP3+ Treg cell induction by anti-CD3 mAb, which could be combined with a p38 inhibitor to improve therapeutic efficacy in RA patients and resolve chronic inflammation via the restoration of tolerance.