CD25 Appears Non Essential for Human Peripheral T(reg) Maintenance In Vivo

BACKGROUND: IL-2 has been reported to be critical for peripheral T(reg) survival in mouse models. Here, we examined T(reg) maintenance in a series of paediatric liver transplant recipients who received basiliximab, a therapeutic anti-CD25 monoclonal antibody. METHODOLOGY/PRINCIPAL FINDINGS: FoxP3(+) CD4 T cells were analyzed by flow cytometry before liver grafting and more than 9 months later. We found that in vivo CD25 blockade did not lead to T(reg) depletion: the proportion of FoxP3(+) cells among CD4 T cells and the level of FoxP3 expression were both unchanged. IL-2Rβ expression was enhanced in FoxP3(+) cells both before and after basiliximab treatment, while the level of IL-2Rγ expression was similar in T(regs) and non-T(regs). No significant change in the weak or absent expression of IL-7Rα and IL-15Rα expression on FoxP3(+) cells was observed. Although the proportion of FoxP3(+) cells among CD4 T cells did not vary, food allergies occurred more rapidly after liver grafting in patients who received basiliximab, raising questions as to T(reg) functionality in vivo in the absence of functional CD25. CONCLUSIONS: CD25 appears non essential for human T(reg) peripheral maintenance in vivo. However, our results raise questions as to T(reg) functionality after therapeutic CD25 targeting.