In this study, we radiolabeled anti-mouse and anti-human CD4-targeting Mbs with 89Zr using the chelator desferrioxamine (dfo) and extensively validated both immunotracers in xenograft, syngeneic, and hCD4 knock-in (KI) tumor mouse models to assess their specificity and cross-species comparability. The gene discussed is CD4; the disease is neoplasm.