Randomized Conversion of Calcineurin-Inhibitors in Renal Allograft Recipients

For this research study, between 6 and 24 Months post-transplant, we plan to prospectively randomize 2:1 renal transplant patients to either: * Substitute tacrolimus (TAC) with sirolimus and continue mycophenolate mofetil (MMF) or * Continue with tacrolimus (TAC) and mycophenolate mofetil (MMF) A total of 400 patients are expected to be screened for the randomization. We expect to randomize 275 renal transplant patients into this protocol (275 donors to be recruited). The following data will be collected at the time of randomization: Recipient demographics: (i) age at transplantation, (ii) sex, and (iii) race. Clinical history: (i) causes of end-stage renal disease, and (ii) past medical history. Transplant related information: (i) donor age, (ii) cadaveric versus living kidney transplant, (iii) histocompatibility and cross match data, (iv) viral serology, (v) history of acute rejection and delayed graft function, (vi) use of induction therapy and immunosuppressants, (vii) use of ACEI and/or ARB, and (viii) level of renal allograft function-estimated GFR (e-GFR(12) using MDRD formula, proteinuria. Peripheral blood leukocytes will be obtained from renal transplant recipients for baseline (prior to randomization) lymphocytes functional activity and characterization of lymphocytes subpopulations by flow cytometry analysis. Peripheral donor leukocytes (from living donor patients) will also be obtained at the time of randomization. These donor leukocytes will be used as stimulator cells to study the functional activity of the recipient's lymphocytes function. The recipients assigned to continue with tacrolimus and MMF will be routinely followed at the outpatient Comprehensive Transplant Center (CTC) with monthly labs. In addition to labs at baseline pre-randomization, 6, 12 and 24 Months post-randomization, peripheral blood leukocytes will be obtained to study lymphocytes functional activity and to characterize lymphocytes subpopulations by flow cytometry analysis. Post randomization: The recipients assigned to switch from tacrolimus to sirolimus and continue with MMF will be routinely followed at the CTC with monthly labs. During the period of conversion from tacrolimus to sirolimus, weekly labs will be obtained to monitor renal function and bone marrow function. In addition to labs at baseline pre-randomization, 6, 12 and 24 Months post-randomization, peripheral blood leukocytes will be obtained to study lymphocytes functional activity to characterize lymphocytes subpopulations by flow cytometry analysis. Urine will be collected to assess tubular toxicity by evaluating urinary biomarkers. Both groups of patients will be followed for 2 years post-randomization. In addition to monitoring renal allograft function, we will evaluate the incidence of acute rejection, patient and graft survival, impact of CI conversion on the lipid profile, incidence of hypertension, malignancies, opportunistic infections, and post-transplant diabetes mellitus (DM). For those willing to undergo an optional kidney biopsy, one will be performed at the end of the second year in order to evaluate renal allograft pathology and renal allograft tissue gene expression profiles of the two groups. With the peripheral leukocytes obtained at baseline prior to randomization and at 6, 12 and 24 Months post-randomization, we will investigate possible modifications of lymphocytes function and the lymphocytes subpopulations that might have occurred as a consequence of the switch from tacrolimus to sirolimus. Obtaining renal allograft tissue samples at 24 months post randomization can have potential important ramifications to help explain the mechanisms of fibrosis and tubular atrophy typically associated with CI and the role of CI elimination with the substitution of sirolimus (SRL). All data will then be analyzed comparing gene expression profiles of peripheral blood (Pax gene tubes are routinely collected at the different time points as part of the original study). Based on power analysis, we will perform 24 months post randomization biopsies in 70% of the total subjects enrolled in the study (approximately 46 subjects from the tacrolimus/MMF group and approximately 93 subjects from the sirolimus/MMF group). We plan to obtain renal allograft biopsies at 24 Months for those that consent for this additional biopsy. This will be compared to the standard of care 12 months post-transplant biopsy to allow us to address the effect of immunosuppressive modifications on renal allograft pathology at 24 months post randomization. Renal allograft biopsies will also be stored in RNA later to further extend our knowledge on the effect of CI free immunosuppression on gene expression profiles.