Impact of Basiliximab on regulatory T‐cells early after kidney transplantation: down‐regulation of CD25 by receptor modulation

Monoclonal anti‐CD25‐antibodies are successfully applied in organ transplantation to reduce the incidence of acute graft rejection. However, targeting the CD25 molecule might not only affect activated T‐cells but also regulatory T‐cells (T_regs) constitutively expressing the CD4⁺CD25⁺CD127^lowFoxP3⁺ phenotype. In this study, we investigated the influence of the anti‐CD25‐antibody Basiliximab on the frequency of T_regs early after kidney transplantation comparing individuals receiving/not receiving induction therapy (n = 14 and n = 7). Following Basiliximab administration, a distinct loss of CD4⁺CD25^high T‐cells was observed lasting for at least 6 weeks. This was not accompanied by a disappearance of the entire CD4⁺CD25⁺FoxP3⁺ T_regs but rather a decreased expression density of CD25 on the latter. In addition, a transient rise in CD4⁺CD25^?FoxP3⁺ T‐cells was found which expressed the CD127^low phenotype. Thus, a phenotypic shift of T_regs from the CD25⁺ to the CD25^? compartment was suggested. This was supported by in vitro findings showing that the disappearance of CD4⁺CD25^high cells in the presence of Basiliximab was due to down‐regulation of CD25 expression meanwhile the suppressive function of these cells was maintained. In conclusion, Basiliximab therapy directly affects CD4⁺CD25⁺CD127^lowFoxP3⁺ T_regs but does not seem to be associated with functional consequences. Thus, it is unlikely that Basiliximab treatment negatively influences strategies involving T_regs to promote tolerance after organ transplantation.