Porcine Treg depletion with a novel diphtheria toxin-based anti-human CCR4 immunotoxin

Regulatory T cells (Tregs) are known to play an important role in immunoregulation and have been shown to facilitate induction of transplantation tolerance. Chemokine (C-C motif) receptor 4 (CCR4) is expressed on the surface of effector Tregs involved in controlling alloimmune and autoimmune responses. Recently we have developed a novel diphtheria-toxin based anti-human CCR4 immunotoxin for depleting CCR4⁺ cells in vivo. In this study, we have demonstrated that the anti-human CCR4 immunotoxin bound to porcine lymphocytes including CD4⁺FoxP3⁺ Tregs. Anti-human CCR4 immunotoxin effectively depleted CCR4⁺ Foxp3⁺ porcine Tregs in vivo. We observed depletion of up to 70-85% of the CCR4⁺Foxp3⁺ porcine Tregs in the peripheral blood and 85-91% in the lymph nodes following the anti-human CCR4 immunotoxin treatment in Massachusetts General Hospital (MGH) miniature swine. The depletion lasted for about one week with no significant reduction observed within CCR4^- cell populations including CD8α⁺ T cells, CCR4^-CD4⁺ T cells and B cells. In summary, anti-human CCR4 immunotoxin effectively depleted CCR4⁺Foxp3⁺ porcine Tregs in both peripheral blood and lymph nodes.