Effectiveness of Soluble CTLA-4-Fc in the Inhibition of Bone Marrow T-Cell Activation in Context of Indoleamine 2.3-Dioxygenase (IDO) and CD4(+)Foxp3(+) Treg Induction

BACKGROUND: Rheumatoid arthritis (RA) is a chronic autoimmune disease with systemic inflammation finally resulting in damaged joints. One of the RA development models suggests bone marrow (BM) as a place of inflammation development further leading to disease progression. We aimed to investigate the potential of CTLA-4-Fc molecule in inducing tolerogenic milieu in BM measured as indoleamine 2,3-dioxygenase (IDO) expression, CD4(+)Foxp3(+) Treg induction, and T cell activation control. The expression of IDO-pathway genes was also examined in monocytes to estimate the tolerogenic potential in the periphery. METHODS: Bone marrow mononuclear cells (BMMC) were stimulated by pro-inflammatory cytokines and CTLA-4-Fc. Next IDO expression, CD4(+)CD69(+) and CD4(+)Foxp3(+) percentage were estimated by PCR and FACS staining, respectively. Enzymatic activity of IDO was confirmed by HPLC in BM plasma and blood plasma. Genes expressed in IDO-pathway were analyzed by NGS in peripheral monocytes isolated from RA patients and healthy controls. RESULTS: We found that CTLA-4-Fc and IFN-γ stimulation results in IDO production by BMMC. CTLA-4-Fc induced tryptophan catabolism can inhibit mitogen-induced CD4(+) T cells activation without influencing CD8(+) cells, but did not control CD25 nor Foxp3 expression in BM cells. Significantly higher expression of selected IDO-pathway genes was detected on peripheral monocytes isolated from RA as compared to healthy controls. CONCLUSION: This study sheds light on some immunosuppression aspects present or induced in BM. The potential of IDO-mediated pathways were confirmed in the periphery, what may represent the promising candidates for therapeutic strategies in RA.