The CCR4/CCL17 axis drives intestinal acute Graft versus Host disease after allogeneic bone marrow transplantation

Acute-Graft-versus-Host disease (aGvHD) is a life-threatening complication after allogeneic stem-cell-transplantation. It is mediated by alloreactive T cells whose trafficking to aGvHD target organs is orchestrated by chemokines. We here asked whether CCL17 and its corresponding receptor CCR4 are involved in aGvHD development and severity. We applied an experimental mouse model of aGvHD in CCR4/CCL17 knockout mice and analyzed gut biopsies of GvHD patients. We show that the absence of CCR4 in transplanted T cells induced significantly less severe aGvHD. This was accompanied by reduced expression of Gata3. Mechanistically, only CD4+, but not CD8+CCR4-/- T cells protected from aGvHD. We next identified dendritic cells in the small intestine to produce CCL17, which selectively recruited CD4+ T cells. IL-4 production by intestinal CD4+ T cells promoted proliferation of CD8+ T cells. In line, we detected an upregulation of CCL17 and Gata3 in human aGvHD samples. Our results indicate that local CCL17 production in aGvHD target organs recruits T cells, reinforcing local tissue damage and immune cell recruitment. We identified the JAK1/2-inhibitor ruxolitinib to dampen CCL17-expression, thereby reducing GvHD severity. We here dissect a to date unknown role of the CCL17-CCR4 axis in aGvHD, which might help to develop novel therapeutic strategies.