Proteolytically activated, but not inactive, EGFR-CD3 T cell-engaging antibody showed specific EGFR-dependent tumor cell killing in vitro and caused tumor regression in preclinical tumor models, while a nonhuman primate study established that the maximum tolerated dose increased by 60-fold when the EGFR-CD3 antibody was administered in the masked form. Here, EGFR is linked to neoplasm.