CD25 appears non essential for human peripheral T(reg) maintenance in vivo

Abstract

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-2Rbeta expression was enhanced in FoxP3+ cells both before and after basiliximab treatment, while the level of IL-2Rgamma expression was similar in T(regs) and non-T(regs). No significant change in the weak or absent expression of IL-7Ralpha and IL-15Ralpha 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.

Figure 1. No significant effect of a blocking anti-CD25 antibody on the proportion of human FoxP3⁺ CD4 T cells in vivo.

The proportion of CD25⁺FoxP3⁺ (1A), CD25⁻FoxP3⁺ (1B) and total FoxP3⁺ cells (1C) among CD4 T lymphocytes was determined before liver grafting and basiliximab injection, and for more than 9 months thereafter; data are means (curves) and SEM at the different time points. In 1D, the FoxP3⁺/FoxP3⁻ and FoxP3^hi/FoxP3⁻ MFI ratios were used to compare the level of intracellular FoxP3 expression (see Methods). Means and SEM are shown. The Mann Whitney test was used for statistical analysis. The number of patients tested at each time point is indicated. Only statistically significant differences are indicated.

Figure 2. Human FoxP3⁺ CD4 T cells express high levels of IL-2 Rβ.

IL-2Rβ (Fig. 2A, 2B), IL-2Rγ (Fig. 2A, 2C), IL-15Rα (Fig. 2A, 2D) and IL-7Rα (Fig. 2A, 2E) expression was analyzed by flow cytometry in FoxP3⁺ and FoxP3⁻ CD4 T cells before liver grafting and basiliximab injection (Figs. 2B to 2E), and at various times thereafter (2B to 2E). Fig. A shows a representative pre-graft staining profile. Figs. 2B to 2E represent the mean (SEM) MFI ratios (see Methods). The Wilcoxon test was used to compare FoxP3⁺ and FoxP3⁻ CD4 T cells. The Mann Whitney test was used to analyze the time course of expression in a given cell subset. Only significant differences are indicated.