No difference in degree of interstitial Sirius red-stained area in serial biopsies from area under concentration-over-time curves-guided cyclosporine versus tacrolimus-treated renal transplant recipients at one year.

Interstitial fibrosis is the main characteristic of chronic allograft nephropathy and long-term graft failure. Cyclosporin (CsA) is thought to be more fibrogenic than tacrolimus. In a prospective, randomized, multicenter trial using a calcineurin-sparing regimen, renal interstitial volume was compared in CsA- and tacrolimus-treated renal transplant recipients by image analysis of Sirius red (SR)-stained cortical areas in protocol biopsies obtained at 6 mo (n = 94) and 12 mo (n = 97) after transplantation. Immunosuppression consisted of CsA or tacrolimus, CD25 mAb, mycophenolate mofetil, and prednisolone. CsA therapy increased the 6-mo risk for subclinical rejection. The prevalence of subclinical rejection was 38.8% in the CsA-treated and 15.2% in the tacrolimus-treated patient group (P = 0.012). Strikingly, no difference in the degree of interstitial SR-stained area was detectable between the two treatment groups. In particular, previous subclinical rejection episodes did not influence the degree of interstitial volume. Also, no difference in GFR occurred at 1 yr, when the mean GFR mounted 63 ml/min. No significant differences in the degree of interstitial SR-stained area could be observed at 6 and 12 mo between CsA- and tacrolimus-treated renal transplant recipients. Although CsA-treated patients developed significantly more subclinical rejections at 6 mo, this did not influence the degree of SR staining or the change in renal function at 1 yr.