Although the triple immunosuppressive regimen based on calcineurin inhibitors (CNIs) has greatly improved the short-term prognosis of renal transplantation, the long-term prognosis of renal transplantation has not significantly improved. CNIs associated nephrotoxicity is a major risk factor affecting the graft survival.
It is feasible to improve the long-term prognosis by reducing the dose of CNIs or removing the CNIs. Studies have demonstrated that the combination of sirolimus (SRL) with low-dose CNIs can both reduce CNI-related nephrotoxicity and improve graft function without increasing the risk of acute rejection (AR), which helps to improve long-term graft survival.  However, the validation of mammalian target of rapamycin inhibitor as an immunosuppression regimen and the timing of its application in renal transplantation is still needed. The aim of this study was to investigate the effects of early conversion to low-dose CNIs and SRL on the long-term prognosis of renal transplantation. 
The study design has been described previously in detail.
The study protocol was approved by the Ethics Committee of the Research Institute Beijing Chao-yang Hospital, Capital Medical University (No. 2018-Ke-188), and regular meetings were held to monitor the progress of the study. Informed consent was obtained from all participants. This study was carried out in 15 renal transplantation centers in China. Patients who received the standard immunosuppressive regimen of CNIs + mycophenolic acid (MPA) + glucocorticoid for 4 weeks after renal transplantation were enrolled and randomized. The immunosuppressive regimen of patients in the experimental group was changed as follows: SRL + low-dose CNIs + withdrawal of MPA + glucocorticoid; the control group was maintained standard calcineurin inhibitors (sCNIs) + MPA + glucocorticoid. The estimated glomerular filtration rate (eGFR), adverse events, and graft survival were recorded at baseline and follow-up at weeks 12, 24, 36, 48, 72, and 104 after conversion. Further details of the experimental procedure are shown in Supplementary Figure 1,  . The study was registered at Chinese Clinical Trial Registry, ChiCTR1800017277 ( https://links.lww.com/CM9/B436 ). www.chictr.org.cn/
From August 2018 to November 2022, a total of 254 patients gave consent and were randomized at 15 renal transplantation centers in China, including 155 participants to the reduced calcineurin inhibitor (rCNI) + SRL treatment group and 99 participants to the sCNI + MPA treatment group [Supplementary Figure 2,
]. All patients were treated with induction therapy of basiliximab or rabbit anti-human thymocyte immunoglobulin before surgery. https://links.lww.com/CM9/B436
Participants were followed up for a mean of 51.6 weeks and a median of 48 weeks. The percentages of participants who completed clinical follow-up were 79.5%, 65.7%, 57.1%, 53.9%, 42.9%, and 24.0% at 12, 24, 36, 48, and 72 weeks after renal transplantation, respectively. As shown in Supplementary Table 1,
, there were no significant differences between the two groups in the baseline demographics. https://links.lww.com/CM9/B436
Changes in eGFR, blood urea nitrogen (BUN), and serum creatinine (sCr) by treatment regimens are shown in
Figure 1. The eGFR of the rCNI + SRL treatment group was higher than that of the sCNI + MPA treatment group at all follow-up time points. However, there was no statistical difference between the effect of rCNI + SRL and sCNI + MPA on eGFR over the study. The BUN and sCr of the rCNI + SRL treatment group were lower than that of the sCNI + MPA treatment group, and the differences were not significant. As shown in Supplementary Figure 3, , the levels of leukocyte, platelet, and hemoglobin in the two groups were largely maintained in the normal range from baseline. https://links.lww.com/CM9/B436 Figure 1:
Comparison of renal function between rCNI + SRL treatment group and sCNI + MPA treatment group: (A) treatment regimens, (B) treatment regimens, and (C) treatment regimens.
∗ P < 0.05. BUN: Blood urea nitrogen; rCNI + SRL: Reduced calcineurin inhibitor + sirolimus; sCNI + MPA: Standard calcineurin inhibitor + mycophenolic acid; sCr: Serum creatinine; eGFR: Estimated glomerular filtration rate.
Adverse events were reported in 26 participants (16.8%) in rCNI + SRL treatment group compared with 12 (12.1%) in the sCNI + MPA treatment group (
P > 0.05). Notably, although not statistically significant, the urinary infection rate and the incidence of thrombocytopenia (0 vs. 1.0%) and hyperglycemia (0.6% vs. 1.0%) were lower in the rCNI + SRL treatment group than in the sCNI + MPA treatment group. The incidence of adverse events in the rCNI + SRL treatment group was higher than in the sCNI + MPA treatment, including creatinine elevation (1.3% [2/155] vs. 1.0% [1/99]), proteinuria (3.9% [6/155] vs. 0 [0/99]), leukopenia (0.6% [1/155] vs. 0 [0/99]), hyperlipidemia (2.6% [4/155] vs. 1.0% [1/99]), abnormal liver function (1.9% [3/155] vs. 1.0% [1/99]), respiratory infection (2.6% [4/155] vs. 1.0% [1/99]), microvirus infection (2.6% [4/155] vs. 2.0% [2/99]), and BK polyomavirus (BK virus) infection (2.6% [4/155] vs. 1.0% [1/99]); however, there was also no significant difference between the two groups [Supplementary Table 2, ]. The mean concentration levels of the tacrolimus and sirolimus involved in the study are shown in Supplementary Figure 4, https://links.lww.com/CM9/B436 . https://links.lww.com/CM9/B436
The nephrotoxicity of CNIs is a risk factor for graft loss. Therefore, the application of immunosuppressive regimens with CNIs replacement or CNIs dose reduction may be able to improve the long-term prognosis of renal transplantation.
Rapamycin is now widely used as an alternative to CNIs in immunosuppressive regimens associated with combined CNIs reduction or withdrawal after renal transplantation. However, SRL conversion therapy is directly associated with an increased risk of AR; furthermore, SRL is closely associated with delayed wound healing, hyperlipidemia, and urinary protein exacerbation.
The key is to find a balance between AR, chronic graft nephropathy associated with CNIs nephrotoxicity, SRL-related adverse events, and long-term prognosis of renal transplantation to achieve an optimal immunosuppressive regimen with SRL after renal transplantation and improve the graft function and the long-term prognosis. 
The data from our follow-up showed that the eGFR was higher in the rCNI + SRL treatment group than in the sCNI + MPA at baseline and during the follow-up period, but not statistically significant, suggesting that both immunosuppressive regimens could improve graft function after renal transplantation.
This study was a randomized controlled clinical study conducted in 15 transplantation centers in China, and many difficulties and limitations were inevitably encountered in the conduct of the trial. First of all, affected by the epidemic of Coronavirus Disease 2019 (COVID-19), the implementation of organ transplantation surgery has been reduced. Among the patients who were followed up after surgery, due to the prevalence of COVID-19, some patients turned to follow-up online not face-to-face, and relevant data were temporarily unavailable to us, moreover, for various reasons, the proportion of patients who were lost to follow-up increased. Secondly, transplant doctors were more aggressive in the management of complications induced by SRL in the rCNI + SRL treatment group, preferring to discontinue sirolimus, while being relatively conservative in the management of complications in the sCNI + MPA treatment group. This may lead to no statistically significant differences between the two groups. Thirdly, this study was conducted in multiple centers across the country and lasted for a long time. So, there were differences in the implementation of the experimental protocol among the centers, which was directly related to the uneven follow-up data. Besides, the follow-up period of patients from the beginning of the study to the present is too short, and to some extent, it is still a comparison of the short-term prognosis of renal transplantation. The records of adverse events related to SRL were not comprehensive enough, for example, the data on virus infection and urine protein were missing. For the diagnosis of AR, no procedural biopsy was performed to confirm the diagnosis, and the events were all clinically suspicious. It should be emphasized that SRL conversion therapy is more suitable for patients with low immune risk and normal urine protein and that the ability of SRL conversion therapy early after renal transplantation to prolong long-term survival of the graft and recipient remains to be confirmed in a further expanded sample. At present, this study is still in progress. In the future, we will try to expand the sample size, reduce the variation in patient follow-up data from various centers, minimize the limitations of the experiment, and overcome the difficulties to obtain more meaningful results to benefit more renal transplant patients.
Early conversion to a low-dose CNI combined with sirolimus improved graft function after renal transplantation without significant adverse events, and early active conversion to low-dose CNI combined with sirolimus had a safety and efficacy and was well tolerated by patients.
The study was supported by a grant from the China International Medical Foundation (No. RUPUS-ISRT-20180114).
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