Administration of ICOS mAb at tracer doses does not impact murine acute GvHD or the GvT effect. GvHD score (A) and animal survival (B) after allogeneic HCT. Two-way analysis of variance was used to compare GvHD score and log-rank test to compare survival curve between GvHD mice receiving 10 μg of cold anti-ICOS mAb (continuous red line) and isotype mAb (dashed red line) IV at day 4 post–allogenic transplantation. (C) Representative in vivo BLI images of A20^luc+ cell burden 7 days post-HCT in GvHD mice and BM controls having received cold anti-ICOS mAb or isotope control at day 4 post-HCT. Results are pooled from 2 independent experiments (n = 10 mice/group) and compared using a nonparametric Mann-Whitney U test.