Induction of Treg by monocyte‐derived DC modulated by vitamin D₃ or dexamethasone: Differential role for PD‐L1

Abstract

Specific therapy with modulated DC may restore immunological tolerance, thereby obviating the need for chronic immunosuppression in transplantation or autoimmunity. In this study we compared the tolerizing capacity of dexamethasone (Dex)-and 1a,25-dihydroxyvitamin D3 (VD3)-modulated DC. Treatment of monocytes with either VD3 or Dex resulted in DC with stable, semi-mature phenotypes compared with standard DC, with intermediate levels of co-stimulatory and MHC class II molecules, which remained unaltered after subsequent pro-inflammatory stimulation. IL-12p70 secretion was lost by VD3-and Dex-DC, whereas IL-10 secretion was unaffected. VD3-DC distinctly produced large amounts of TNF-a. Both VD3-and Dex-DC possessed the capacity to convert CD4 T cells into IL-10-secreting Treg potently suppressing the proliferation of responder T cells. However, only Treg induced by VD3-DC exhibited antigen specificity. VD3-, but not Dex-, DC expressed significant high levels of PD-L1 (programmed death-1 ligand), upon activation. Blockade of PD-L1 during priming redirected T cells to produce IFN-c instead of IL-10 and abolished acquisition of regulatory capacity. Our findings demonstrate that both VD3-and Dex-DC possess durable but differential tolerogenic features, acting via different mechanisms. Both are potentially useful to specifically down-regulate unwanted immune responses and induce immune tolerance. These modulated DC appear suitable as adjuvant in antigen-specific clinical vaccination intervention strategies.Key words: Antigen specificity . Autoimmunity . Modulated DC . PD-L1 . Treg IntroductionRestoring immunological tolerance is the ''holy grail'' in the fields of autoimmunity and transplantation. Current applied therapies, which include immunosuppressive drugs, do not target the cause of the disease and, in addition, are associated with considerable non-specific side effects. Therefore, it is desirable to design therapies that specifically target the immunopathogenesis.DC are important modulators of T-cell activity [1]. Depending on the type of pathogen encountered and the profile of co-stimulatory and T-cell polarizing molecules, DC drive the development of either pro-inflammatory Th type 1 (Th1), type 2 (Th2) and type 17 (Th17) cells or protective Treg [2][3][4]. In conjunction with this, human monocyte-derived DC (moDC) can be differentiated into Th1-, Th2-, Th17-or Treg-promoting DC in vitro. Priming of moDC with microbial compounds or tissue-derived factors such as IFN-g, prostaglandin E2 (PGE2) or IL-23 and IL-1 results in enhanced expression of MHC class II and co-stimulatory molecules and drives the development of effector Th1, Th2 and Th17 cells [5][6][7]. It is now clear that certain immunosuppressive drugs and anti-inflammatory agents induce DC with tolerogenic properties [8][9][10][11][12][13][14][15]. For example, DC treated with either dexamethasone (Dex) or the active form of vitamin D, 1a,25-dihydroxyvitamin D 3 (VD3), arrest DC in a semimature state and prevent the up-regulation of co-stimulatory Trea...

1,25-Dihydroxyvitamin D3 Promotes Tolerogenic Dendritic Cells with Functional Migratory Properties in NOD Mice

“…Our data point to the expansion of preexisting Tregs, rather than the conversion from naive CD4 + T cells, because 1,25D 3 -mDCs failed to reproduce the characteristic increase in Treg frequency in vitro following coculture with CD25-depleted CD4 + T cells. In contrast, different groups (11,12,53) (54). In addition to pointing to the expansion of Tregs, our data show that CD4 + CD25 + Tregs expanded in the presence of 1,25D 3 -mDCs featured elevated levels of regulatory mediators, such as IL-10, which might be relevant for their increased suppressive function in vivo.…”

“…However, clinical applications of DC-based therapies in autoimmune disease intervention are hampered by the concern that iDCs will develop into immunostimulatory cells upon encountering inflammatory stimuli in vivo. In this sense, we (9,14,18) and other investigators (6,7,12) showed that mDCs differentiated and matured in vitro in the presence of the biologically active form of vitamin D, 1,25(OH) 2 D 3 , produced a stable phenotype, typically characterized by low levels of Ag-presenting and costimulatory molecules (MHCII, CD80, CD86), as well as a high ratio of PD-L1/CD86 and anti-inflammatory cytokines (IL-10, TGF-b). In this study, we further demonstrated the capacity of 1,25(OH) 2 D 3 to imprint a similar tolerogenic profile in mDCs derived from diabetes-prone mice and diabetes-resistant animals.…”

“…First, we evaluated different features of NOD-derived 1,25D 3 -mDCs that would point to an increased Treg-promoting capacity, such as an increased surface expression of the PD-L1/CD86 ratio, an important parameter for the induction of Tregs by 1,25D 3 -mDCs (12), and the production of immunoregulatory molecules, such as IL-10, TGF-b, and IDO. As depicted in Fig.…”

“…Exposure of differentiating DCs in vitro to 1,25(OH) 2 D 3 initiates a complex and autonomous molecular process (4,5) that ultimately interferes with their differentiation and maturation (6)(7)(8)(9), locking the cells in a semimature state (10). Tolerogenic 1,25(OH) 2 D 3 -treated mature DCs (1,25D 3 -mDCs) lose their ability to activate autoreactive T cells and stimulate the generation of regulatory T cells (Tregs) (9,(11)(12)(13)(14). Importantly, the induction of a tolerogenic DC phenotype by 1,25(OH) 2 D 3 is stable after removal of the compound (14).…”

Is autoimmunity the Achilles' heel of cancer immunotherapy?

“…Both macrophages and T reg cells are implicated in the above studies. PD-L1 expression on dendritic cells (DCs) is required for the induction of T reg cells by vitamin D3, perhaps through reverse signaling by PD-L1 to DCs 80 . It is possible that the regulation of PD-1-PD-L1 signaling at discrete stages during the immune response could diminish immunotoxicity in individuals with cancer.…”