Increase of Intermediate Monocytes in Graft-versus-Host Disease: Correlation with MDR1+Th17.1 Levels and the Effect of Prednisolone and 1α,25-Dihydroxyvitamin D3.

Graft-versus-host disease (GVHD) remains one of the major complications after allogeneic hematopoietic stem cell transplantation that is mainly treated with glucocorticoids such as prednisolone. In this study the influence of monocyte subpopulations, prednisolone, and 1α,25-dihydroxyvitamin D3 (1α,25-(OH)2D3) on the induction of a proinflammatory subset of Th17 cells (MDR+Th17.1) characterized by CCR6+CXCR3hiCCR4loCCR10-CD161+ and stable expression of the multidrug resistance protein type 1 (MDR1) was investigated. Our results demonstrate that intermediate monocytes are increased in patients with acute GVHD, promoting the induction of proinflammatory MDR1+Th17.1 cells. Furthermore, prednisolone induces the development of MDR1+Th17.1 cells, whereas 1α,25-(OH)2D3 acts as an anti-inflammatory, leading to diminished percentages of proinflammatory MDR1+Th17.1 cells in the presence of prednisolone after stimulation with the TLR4-ligand S100A8/S100A9. Moreover, 1α,25-(OH)2D3 decreased the expression level of the targets JAK2 and CD74, both associated with T cell activation, in monocytes. Thus, in steroid-resistant GVHD, 1α,25-(OH)2D3 could be an important regulator in monocyte-induced development of proinflammatory MDR1+Th17.1 cells and might therefore be a potential therapeutic agent in combination with glucocorticoids for GVHD treatment.

Characterization of monocyte subtypes regarding their phenotype and development in the context of graft-versus-host disease.

Graft-versus-host disease (GvHD) is a major cause of morbidity and mortality after allogeneic hematopoietic cell transplantation (HCT). In this study, monocyte subtypes were characterized regarding cytokine expression pattern and development in the context of GvHD. Using inflammatory S100 proteins for monocyte stimulation, it could be demonstrated that intermediate monocytes are the main producers of inflammatory cytokines such as IL-6 and TNFα known to be involved in the development of Th17 cells pointing towards an inflammatory phenotype of this monocyte subtype. Furthermore, novel aspects regarding monocyte subtype development were found. Our data reveal that prednisolone promotes the induction of intermediate monocytes from classical monocytes which correlates with HSP70 expression levels. However, 1α,25-Dihydroxyvitamin D3 treatment results in the abrogation of the prednisolone-mediated induction of this inflammatory monocyte subset and low HSP70 expression levels. Treatment of classical monocytes with pifithrin-µ, a specific HSP70 inhibitor, also leads to an inhibited induction of intermediate monocytes in the presence of prednisolone. These data point towards a predominant role of HSP70 in the development of intermediate monocytes. Thus, HSP70 might be a promising target for GvHD therapy, especially in combination with glucocorticoids, in order to decrease intermediate monocyte subset levels.