of an opportunistic infection following treatment of high dose steroids. Patient 4 had multi-organ failure prior to start of treatment with vedolizumab and died. Patients 5 and 6 have no symptoms of serious GvHD after 2 and 3 doses of vedolizumab. Four out of 6 patients could be discharged from hospital. Immunophenotyping of peripheral blood revealed initial high levels of CD25 + Treg cells in 4 out of 6 evaluable patients and the values showed a decline into normal range after start of therapy and with signs of clinical effect. Conclusions: This case series suggests that targeting integrin a4b7 is feasible, safe and gives clinical responses in steroid refractory intestinal GvHD. The mechanism of action is not known, but may be due to the inhibition of alloreactive T-cells homing to the intestinal mucosa. The mechanism behind the Treg patterns is unclear. One might speculate that the initially high levels of Tregs are part of the physiologic reaction to the alloreactive inflammation in the intestinal mucosa.
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