Histopathologic evidence of acute GVHD after donor T_BM, but not FC, transplantation. Small intestines were harvested from HSC+T_BM and HSC+FC recipients on day 28. Paraffin-embedded sections were stained with H&E and were histologically analyzed for evidence of GVHD. (A) Small intestine of a representative HSC+T_BM recipient (n = 7) exhibits villous shortening, crypt dropout, and extensive lymphocytic infiltration of the lamina propria (original magnification, × 200). (B) In these same mice, lymphocytic infiltration of crypts with apoptosis (open arrow) and the formation of a crypt abscess (closed arrow) is observed at higher magnification (original magnification, × 400). These findings are indicative of moderate to severe GVHD. (C) Small intestine of a representative HSC+FC recipient (n = 7). There is no evidence of GVHD (original magnification, × 200).