RSPO1 and graft versus host disease: While most studies report therapy-response of aGVHD including a cumulative grade of skin, liver and intestinal tract manifestations, there is a lack of information specifically on lower gastrointestinal tract aGVHD (GI-GVHD) therapy-response, which is highly relevant in light of novel therapies that target intestinal regeneration such as IL-22, R-spondin or GLP-2.