⁸⁹Zr-DFO-ICOS mAb immunoPET imaging of acute GvHD. (A) Representative BLI of a mouse with acute GvHD at day 4 post-HCT. (B) Reference atlas indicating the location of key clearance and lymphoid organs as well as GvHD target tissues. (C) Representative ⁸⁹Zr-DFO-ICOS mAb PET/CT images acquired 48 hours after tracer administration at day 4 after HCT in TBI control (n = 5), bone marrow control (n = 7), or GvHD (n = 11) mice. Key organs, namely spleen (red arrow), cervical lymph node (cLN) (black arrow), mLN (green arrow), and intestine (yellow arrow), are highlighted. Images are representative of 2 independent experiments. %ID/g, percent injected dose per gram.