CD25 Appears Non Essential for Human Peripheral Treg 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 Treg depletion: the proportion of FoxP3(+) cells among CD4 T cells and the level of FoxP3 expression were both unchanged. IL-2R beta expression was enhanced in FoxP3(+) cells both before and after basiliximab treatment, while the level of IL-2R gamma expression was similar in T-regs and non-T-regs. No significant change in the weak or absent expression of IL-7R alpha and IL-15R alpha 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.