Small and large bowel, liver, and skin were assessed by experts in a blinded fashion. Organs were preserved in formalin, transferred to 70% ethanol, and then embedded in paraffin, sectioned, stained with hematoxylin and eosin, and scored with a semi-quantitative scoring system. Bowel and liver were scored for 19 to 22 different parameters associated with GVHD (detailed in Table S1 ); skin was evaluated for number of apoptotic cells/mm 2 of epidermis via terminal deoxynucleotide transferase dUTP nick end labeling (TUNEL).