In the Spare-the-Nephron (STN) study (Weir MR et al. Kidney Int 2011;79:897-907) kidney transplant recipients randomized about 115 days post-transplant to convert from CNI (calcineurin inhibitor)/MMF to sirolimus (SRL) /MMF had a significantly greater improvement in measured GFR (mGFR) at 12 months compared to those kept on CNI/MMF. The difference at 24 months was not statistically significant.

From 13 top enrolling centers, 126 of 162 patients identified with a functioning graft at 2 years consented to enroll in an observational, non-interventional extension study to collect retrospectively and prospectively annual follow-up data for the interval since baseline (completion of the parent STN study at 24 months post-transplant). Immunosuppression at and follow-up since baseline of the extension study are summarized in the table.

Overall 9 patients have died, including 4 (6.1%) in the SRL/MMF group and 5 (8.3%) in the CNI/MMF group. 18 grafts have been lost including 8 (12.1%) in the SRL/MMF arm and 10 (16.7%) in the CNI/MMF arm. Death and chronic rejection were the most common causes of graft loss in both arms.

Estimated creatinine clearance (Cockcroft-Gault) from baseline out to 4 additional years (6 years post-transplant, ITT analysis, SRL/MMF, n = 49; CNI/MMF, n = 40) is shown in the figure. The differences between the groups (ITT analysis) are not statistically significant, but there is a clinically meaningful trend for improved long-term renal function in the SRL/MMF group compared to the CNI/MMF group.

Conclusion: Sample size limits the statistical power of the analysis, but patients converted to SRL/MMF within 3 – 4 months of transplantation show a progressive long-term trend to improved renal function without significant differences in graft or patient loss out to 6 years post-transplant. Follow-up is ongoing.

Weir, M.: Grant/Research Support, Pfizer.

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