Dosing optimization of CCR4 immunotoxin for improved depletion of CCR4(+) Treg in nonhuman primates

Recently, we have developed a diphtheria toxin‐based recombinant anti‐human CCR4 immunotoxin for targeting CCR4(+) tumors and Tregs. In this study, we further optimized the dosing schedule for improved CCR4(+) Treg depletion. We have demonstrated that up to a 90% depletion was achieved and the depletion extended to approximately 2 weeks in the peripheral blood and more than 48 days in the lymph node at 25 μg·kg(−1), BID for 8 consecutive days in cynomolgus monkeys. Expansion was observed including monocytes and NK cells. Antibody against the CCR4 immunotoxin was detected after approximately 2 weeks, affecting further depletion efficacy for multiple course treatment.