Treatment of allo-HCT recipients with the ADCC-defective anti-Fn14 mAb variant 18D1-dead does not affect donor T-cell target organ infiltration and cytokine production. Lethally irradiated Balb/c (H-2^d) mice were transplanted with 5 × 10⁶ B6 (H-2^b) BM cells alone or together with 1 × 10⁶ enriched B6.L2G85.CD90.1 (H-2^b) T cells. Mice of the latter group were treated daily with 100 µg of 18D1-dead or an irrelevant hIgG1 control antibody for 6 days. All mice (n = 5 per group) were then euthanized for ex vivo assessment of T-cell expansion, cytokine production, and cell death induction in the GI tract. (A) In vivo bioluminescence imaging of B6.L2G85.CD90.1 (H-2^b) cells in transplanted antibody-treated mice. Bioluminescence was imaged at indicated time points and light emission of donor T cells quantified. The upper panel shows the average light emission from ventral view and the lower panels show images from 1 representative mouse of each group. (B) Internal organs were analyzed ex vivo for donor T-cell–derived bioluminescence activity. Bioluminescence images of the organs of 1 representative mouse of each group are shown in the upper panel. The organ-derived averaged emissions are shown in the lower panel. (C) Large bowel biopsies of 18D1-dead and control hIgG1-treated GVHD mice and of untreated control mice were analyzed by qPCR for TNF expression. (D) Concentrations of various cytokines in serum were determined with the help of a cytometric bead array. Mean ± SEM. **P ≤ .01. cae, cecum; cLN, cervical lymph nodes; hea, heart; iLN, inguinal lymph nodes; ki, kidney; lb, large bowel; li, liver; lu, lung; mLN, mesenteric lymph nodes; sb, small bowel; sp, spleen; st, stomach; thy, thymus.