An IL-2 mutein promotes Foxp3+ Treg-mediated suppression of dendritic cell activation in response to inflammatory stimuli

Abstract Foxp3+ regulatory T (Treg) cells are essential for maintaining immune tolerance and the development of strategies that boost Tregs is a promising approach for the treatment of autoimmune disorders. We previously developed a murine Fc-fused IL-2 mutein (Fc.Mut24) with decreased affinity for IL-2Rβ resulting in increased CD25 dependency and potent Treg selectivity. High-dose Fc.Mut24 administration prevents autoimmunity in the non-obese diabetic (NOD) mouse; however, the mechanisms by which Fc.Mut24 affects Treg suppressive function remain unclear. In this study, we have performed a phenotypic analysis of Treg and classical dendritic cells (DC) from IL-2 mutein-treated mice. We have found that Fc.Mut24 treatment increases CTLA-4 recycling/expression on Treg with a concurrent decrease in PD-1 expression specifically on effector regulatory T (eTreg) cells. Both CD8+ cDC1 and DCIR2+ cDC2 subsets from Fc.Mut24-treated mice have reduced expression of the co-stimulatory molecules CD80/CD86 following lipopolysaccharide (LPS) injection. Furthermore, RNA-sequencing reveals that Tregs regulate the transcriptional response of DCs to LPS and may preferentially suppress cDC1 activation in vivo. These results suggest that a major mechanism of action by IL-2 mutein may be promoting CTLA-4-mediated transendocytosis of CD80/CD86 while simultaneously reducing PD-1: PD-L1 co-inhibitory signaling between eTreg and DCs. Our findings address unanswered questions about the role of IL-2 in modulating Treg suppressive function and have important implications for the use of Treg-selective IL-2 therapeutics in the clinic. B.L.J. is supported by a postdoctoral fellowship from the Washington Research Foundation.