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.

Treg depletion in non-human primates using a novel diphtheria toxin-based anti-human CCR4 immunotoxin.

Regulatory T cells (Treg) play an important role in modulating the immune response and has attracted increasing attention in diverse fields such as cancer treatment, transplantation and autoimmune diseases. CC chemokine receptor 4 (CCR4) is expressed on the majority of Tregs, especially on effector Tregs. Recently we have developed a diphtheria-toxin based anti-human CCR4 immunotoxin for depleting CCR4(+) cells in vivo. In this study, we demonstrated that the anti-human CCR4 immunotoxin bound and depleted monkey CCR4(+) cells in vitro. We also demonstrated that the immunotoxin bound to the CCR4(+)Foxp3(+) monkey Tregs in vitro. In vivo studies performed in two naive cynomolgus monkeys revealed 78-89% CCR4(+)Foxp3(+) Treg depletion in peripheral blood lasting approximately 10 days. In lymph nodes, 89-96% CCR4(+)Foxp3(+) Tregs were depleted. No effect was observed in other cell populations including CD8(+) T cells, other CD4(+) T cells, B cells and NK cells. To our knowledge, this is the first agent that effectively depleted non-human primate (NHP) Tregs. This immunotoxin has potential to deplete effector Tregs for combined cancer treatment.