Calcitriol started in the donor, expands the population of CD4+CD25+ T cells in renal transplant recipients

Objectives. Alloreactive T cells recognize antigens via direct and indirect pathways. The competency of costimulatory molecules on antigen-presenting cells (APC) is important. An active form of vitamin D (1,25(OH)(2)D-3, calcitriol) inhibits APC cell maturation and expression of costimulatory molecules. Herein we studied the immunosuppressive effects of calcitriol, which was started in the donors and continued in the kidney recipients. Methods. In this prospective study, candidates for living donor renal transplantation were randomly assigned into two groups: the treatment group were prescribed calcitriol (0.5 mu g/day) started in the donor 6 days before donation and continued in recipient side for 6 months after transplantation. The control group received the conventional immunosuppressive regimen, namely, cyclosporine/mycophenolate mofetil and prednisolone. In each group, a recipient blood sample was obtained before and 6 months after transplantation. Diagnostic study of the T-cell markers-CD3, CD4, and CD25-were performed with a flow cytometery technique. Results. The mean values of CD3CD4CD25 T cells in the treatment group (four women and five men; 40.8 +/- 8.5 years) and the control group (four women and six men; 37.2 +/- 10 years) were at 14.2 +/- 4.2% and 15.4 +/- 4.5% of total peripheral lymphocytes. Six months after transplantation, these percentages increased to 29 +/- 6.3% in the treatment group and decreased to 12.1 +/- 4.5% in the controls (P <.0001). No clinical rejection was detected in either group during the study period. Conclusion. Calcitriol started in the donors and continued in the kidney allograft recipients lead to expansion of CD4(+)CD25(+) regulatory T cells in recipients. We speculated that costimulatory deficient APC for both direct and in-direct pathways may play a role.