Involvement Of S100 Proteins and Hsp90 In The Pathogenesis Of Graft-Versus-Host Disease After Allogeneic Hematopoetic Cell Transplantation

Graft-versus-host disease (GvHD) is one of the major live threatening complications of allogeneic hematopoietic cell transplantation (HCT). The pathophysiology of GvHD is complex and not fully understood yet. However, it has been shown that Th17 cells play an important role in the pathogenesis of acute and chronic GvHD. Therefore, the development of Th17 cells in patients with GvHD was further investigated in the present study. The influence of monocytes and their activation with proinflammatory S100 proteins and 90 kDa heat shock protein (Hsp90) on the induction of Th17 cells was examined. Furthermore, the suitability of S100 proteins as diagnostic markers for intestinal GvHD was analyzed.

In the present study, it could be demonstrated that monocytes from patients with acute and chronic skin or intestinal GvHD grade I-IV (n=13) induced significant higher percentages of Th17 cells compared to monocytes from healthy donors (n=32) or patients without GvHD at several timepoints after HCT (n=21) (p<0.001). It is known that faecal S100A12 is a potential non-invasive marker for inflammatory bowel disease. Therefore, the concentration of S100A12 in the stool of patients with and without intestinal GvHD was determined. The obtained results showed that the concentration of S100A12 was significantly increased in the stool of patients with intestinal GvHD (n=7) compared to patients without GvHD (n=16) (p<0.05). Furthermore, S100A9 and S100A12 could be detected immunohistochemically in intestinal tissue from patients with intestinal GvHD indicating that S100 proteins of the calgranulin subfamily could be potential diagnostic markers for intestinal GvHD. Additionally, the effect of S100A8, S100A9 and the heterodimer S100A8/9 on the induction of Th17 cells was investigated. Monocytes from healthy donors stimulated with these S100 proteins induced significant higher percentages of Th17 cells compared to unstimulated monocytes (n=7) (p<0.05). Furthermore, the influence of the 90 kDa heat shock protein (Hsp90) in monocytes on the induction of Th17 cells was examined. Therefore, Hsp90 was inhibited by the geldanamycin analog 17-(dimethylaminoethylamino)-17-demethoxygeldanamycin (17-DMAG) in monocytes from patients with GvHD and the effect on the induction of Th17 cells was analyzed. It could be shown that inhibition of Hsp90 resulted in a significant decrease in the percentage of induced Th17 cells (n=3) (p<0.001). Further results indicated that stimulation of monocytes with S100A8, S100A9 and S100A8/9 induces an elevation in Hsp90 expression levels.

In conclusion, our findings suggest that monocytes may play a major role in the pathogenesis of GvHD by triggering the induction of Th17 cells. Monocyte-induced Th17 cell development could further be enhanced by stimulation of monocytes with purified S100 proteins. The chaperone Hsp90 could be an important regulator in monocyte-induced development of Th17 cells and therefore be a therapeutic target for GvHD. Furthermore, S100 proteins might be novel diagnostic markers in intestinal tissue and potential non-invasive markers in the stool for intestinal GvHD.