Introduction: T regulatory lymphocytes (Tregs) are considered pivotal in immune response homeostasis and the induction of graft tolerance. They are CD4+CD25+ T cells expressing the transcriptional factor FoxP3. Moreover, CD25 is the therapeutic target of the chimeric monoclonal antibody basiliximab which is extensively used as part of the induction immunosuppression therapy. As immunosuppressive protocols might affect Tregs as well, we studied FoxP3 expression before and after renal transplantation.
Materials and Methods: Subpopulations of CD4+CD25+ και CD4+CD25+FoxP3+ Τ lymphocytes were measured, by flow cytometry, in 34 end stage renal disease patients before renal transplantation (26 from cadaveric donors). All patients received basiliximab and triple immunosuppressive regimen as a standard therapeutic protocol. In 25 of those patients, the same measurements were repeated 3 months after the transplantation.  
Results and Discussion: Before transplantation the proportion of CD4+CD25+FoxP3+ Τ lymphocytes was 2.9 ± 1.3% of the CD4+ lymphocytes. Absolute numbers of CD4+CD25+FoxP3+ were inversely related to patient age (r=-0.44, p=0.008) and dialysis vintage (r=-0.39, p=0.023). In the measurement 3 months after the transplantation, the proportion of Tregs remained stable at 2.8 ± 1.2% respectively, while their absolute number increased significantly from 18±12 to 26±17 μ/L (p=0.042). The proportion of CD25+ reduced from 6±2.5% of the CD4+ lymphocytes before transplantation to 4.9±2%, 3 months later.
Conclusion: Despite immunosuppression therapy targeting CD25+ helper T cells early at renal transplantation, the absolute number of Tregs is increased 3 months after transplantation.