An ADCC-defective variant of the anti-Fn14 monoclonal antibody (mAb) 18D reduces acute GVHD and prolongs survival after allo-HCT. (A) Increased expression of Fn14 in intestinal epithelial cells of GVHD patients. Sections of normal mucosa (left) and mucosa with GVHD associated changes (middle and right) were stained with an anti-Fn14 antibody (ITEM-4) (shown in brown). Representative results are shown. Original magnification ×200. Fn14-positive immune cells are present in the lamina propria of both sample types, whereas Fn14-positive epithelial cells are only observed in GVHD samples. (B-D) Balb/c (H-2^d) mice were myeloablatively irradiated and transplanted with 5 × 10⁶ B6 (H-2^b) BM cells and 1 × 10⁶ enriched B6.L2G85.CD90.1 (H-2^b) T cells. Starting on day 1 posttransplantation, mice were treated daily with 100 µg of 18D1-dead, 18D1-enhanced, or an irrelevant hIgG1 control antibody. Shown are combined data from 3 independent experiments (18D1-dead: n = 20; 18D1-enhanced: n = 10; and hIgG1: n = 20). To control the efficacy of the myeloablative conditioning (irradiation only) and BM engraftment (BM control), mice were irradiated without transplantation or were irradiated and only transplanted with B6 (H-2^b) BM cells. (B) Survival of allo-HCT recipients. (C) Mice were weighed at the indicated times after allo-HCT. Weight measurements are shown in percent of initial weight. (D) Mice were assessed for clinical signs of GVHD at the indicated time points. Mean ± SEM. *P ≤ .05; **P ≤ .01 (hIgG1 vs 18D1-dead).