Is there Enough Evidence to Support Calcineurin Inhibitor Minimization or Avoidance in Renal Transplantation?

For patients with end stage renal disease (ESRD) renal transplantation offers the best survival advantage compared to other modalities of renal replacement therapy [1]. After pairing of the donor and recipient and immunological risk is ascertained the next step in renal transplantation is immunosuppression. Immunosuppression is done in two stages; induction followed by maintenance immunosuppression. The induction phase is where intense immunosuppressive agents are administered at the very onset of transplantation to minimize the burden of acute allograft rejection. Protocols are not standard across all transplant units as optimal induction immunosuppression therapy remains controversial [2,3]. However, it can broadly be classified into two strategies. The first one is based on the use of significant doses of standard immunosuppressive therapy (a calcineurin inhibitor, an antimetabolite and glucocorticoids). The other strategy employs antibodies targeted at T-cells in addition to standard immunosuppressive therapy. The choice of agent is based on the recipient’s risk of developing acute rejection. Gebel et al. [4] stratified the prospective renal transplant patients into various categories according to immunological risk in renal transplantations. Based on this with further additions the principles of risk assessment are as follows:

a. High Immunological risk: During transplant high titers of circulating antibodies targeting mismatched donor HLA also known as donor-specific antibodies are present. This can lead to hyperacute rejection. The presence of DSA precludes transplantation. However, there are reports of innovative pre-transplant desensitisation regimens to reduce this risk.

b. Intermediate immunological risk: The low titer of DSA at the time of transplantation and historic DSA is not detectable. It may be acceptable to consider intensified immunosuppression as well as immunological monitoring in the post-transplant period

c. Standard immunological risk: Where there is no evidence of donor-directed sensitization to HLA.

It is worth noting that recipients of a renal allograft who currently have a functioning solid-organ transplant (such as heart, lung or liver) and are on maintenance immunosuppression are often spared from induction immunosuppression. However, this is not the standard in all centers, and some still prefer some form of induction agent [5]. Recipients of two haplotype identical living related kidneys who are Caucasian have a significantly low risk of acute rejection and do not require induction therapy [6].

Maintenance immunosuppression

Standard immunosuppressive therapy for maintenance immunosuppression entails a calcineurin inhibitor, an antimetabolite and a glucocorticoid. Since the advent of calcineurin inhibitors (CNIs) in the 1980s; short and intermediate-term allograft survival had improved. However, post-transplant graft failure rate beyond ten years has remained unaffected [7]. The two leading causes of late renal allograft loss are chronic allograft nephropathy (CAN) and death with a functioning graft (DFG). Cardiovascular disease and malignancy are attributed as the primary causes of DFG. The underlying pathogenesis of CAN is not entirely understood. It which manifests histologically as interstitial fibrosis and tubular atrophy. Both immunological and non-immunological elements have been identified as causes of CAN [8,9]. Chronic CNI exposure has been recognized as a risk factor for CAN [10]. Treatment regimens have therefore focused to either minimize their use or to avoid them completely, however, this strategy has proven to be quite disappointing due to the resultant increase in rates of acute rejection [11-14]. Apart from the resultant allograft associated complications, CNI use has been associated with the development of new-onset diabetes after transplantation (NODAT), hyperlipidemia and hypertension [15,16]. In an attempt to move away from CNIs there has been significant focus on the employment of mammalian target of rapamycin inhibitors (mTORi) like everolimus and sirolimus in renal transplantation [17,18].

CNI minimization

Given the potential harm to both recipient and allograft from long term CNI exposure, several RCTs were conducted to test strategies to minimize exposure. Minimization is carried out by lowering the target blood levels which are routinely done to titrate dosing. Minimization of CNI target blood levels has been tested for both (Ciclosporin) CsA and (Tacrolimus) TAC. Minimization has also been tried with several combinations of induction agents and other immunosuppressive drugs. A total of 36 RCTs (Table 1) were conducted so far evaluating CNI minimization [19]. CsA minimization alone was studied in 22 RCTs and TAC alone in seven studies. Seven other studies pooled groups that received TAC or CsA. Mycophenolate is both its formulations were used as the main combination immunosuppressive agent in 19 studies. mTORi in combination with CNI were evaluated in 14 studies. Two studies had multiple therapies including CNI, mTORi, MMF and AZA. Vathsala et al. [20] evaluated a single agent CsA without an antimetabolite. Nearly all studies used a steroid (prednisone) in both intervention and control arm. Induction therapy was used in most of these trials except two of them, and eleven other studies did not report on induction. Basiliximab was the most employed induction agent used most of them. Three of them used daclizumab, two used rATG and one used alemtuzumab. In one study, the induction therapy was not uniform and followed local protocol. 29 studies had begun CNI minimization within the first six months post-transplantation, three of them delayed the process till six months had elapsed and four postponed until one year.

Table 1: CNI minimization studies.

Three measures of outcome were renal allograft function, the risk of BPAR and graft loss. Combinations with MMF and lowdose CsA have better results for all three measures as mentioned above compared with standard-dose CsA. With MMF and TAC, there is a sizeable benefit for renal function, but current evidence fails to make conclusions for the other outcomes. Combinations with mTORi and low-dose CsA revealed better renal function but no difference in BPAR compared to standard-dose regimens. Data for mTORi with TAC are scarce. Basiliximab induction with mTORi and low dose CNIs is associated with better renal allograft function but no difference in the risk of BPAR and graft loss. The evidence is too little to conclude the combination of basiliximab induction with MMF. CNI minimization started within the first six months post-transplantation in MMF combination is linked to improved allograft function, lowered BPAR, infection and graft loss compared to standard-dose combinations. However, minimization postponed to after six months or later of transplantation has been linked with greater rates of acute rejection. The Symphony trial compared four treatment protocols [16,21].

a) No induction followed by standard-dose CsA, MMF and corticosteroids. b) Daclizumab induction followed by low-dose CsA, MMF and corticosteroids. c) Daclizumab induction followed by low-dose TAC, MMF and corticosteroids. d) Daclizumab induction followed by low dose sirolimus, MMF and corticosteroids.

Daclizumab induction followed by low-dose tacrolimus, 2g of MMF and corticosteroids had the most favorable results with better renal allograft function, lower incidence of BPAR and rate of graft loss. The Campath (alemtuzumab), CNI reduction and CAN (3C) study is an open label, multicenter randomized controlled trial that aimed to answer two key questions. First to evaluate outcomes between campath (alemtuzumab) versus basiliximab induction for renal transplant recipients. Those receiving alemtuzumab will have low-dose TAC, MMF and no steroids, while those receiving basiliximab will have standard dose TAC, MMF and steroids. It includes most categories of patients eligible for renal transplantation. These include previously transplanted patients, those receiving a deceased or living donor kidney as well as those who are highly sensitized. Secondly, after six months of maintenance with immunosuppression with TAC based immunosuppression, they will be re-randomized to either stay on TAC for long term or switched to SRL based maintenance immunosuppression as a CNI minimization strategy [22]. 7% of 426 renal transplant recipients who received alemtuzumab had one occurrence of biopsy-proven acute rejection (BPAR) in the first six months post-transplantation. At the same time, 16% of those who received basiliximab had an episode of BPAR. This corresponds to a 58% reduction with alemtuzumab induction. The study is an ongoing and long-term follow-up with determining if these initial findings would translate to better transplant outcomes [23].

CNI withdrawal

As discussed previously CNI minimization has proven to be of benefit. Studies have been conducted to evaluate if recipients with a CNI based regimen could benefit by having the CNI withdrawn while continuing on alternative immunosuppressive drugs. To date, 15 randomised control trials (Table 2) have evaluated CNI withdrawal. MMF was included as a primary alternative to CNI in nine of them and mTORi in six of them. In ten studies CsA was withdrawn, four with EVR or SRL and six with MMF. In two studies TAC was withdrawn with SRL used. In three of the studies, MMF was used with combined data for those on CsA or TAC. Nine of them initiated CNI withdrawal within six months’ post-transplant while five studies withdrew CNI after six months or longer after transplantation [67-72]. In conclusion, these studies revealed that CNI withdrawal is linked with a greater risk of BPAR for patients on mycophenolate acid formulations or mTORi compared to those on combination therapy with a CNI plus adjunctive therapy. Where CNI was withdrawn from patients continuing on MMF the risk of graft loss was higher as compared to those on combination CNI and MMF. Continuing on MMF after CNI withdrawal, however, was linked to improved renal function compared to combination therapy with a CNI.

Table 2: CNI withdrawal studies.

Early vs. late CNI withdrawal

When assessing the timing of CNI withdrawal, three studies began CNI withdrawal within the first six months after transplantation, and this is termed ‘early withdrawal’, and five studies began CNI withdrawal six months or later post-transplantation termed ‘late withdrawal’. Early withdrawal revealed an increased risk of graft loss and death and the evidence was inconclusive for BPAR and allograft function. The ZEUS trial [73] investigated 300 de novo renal transplant recipients randomized to remain on CsA or switch to everolimus at four and a half months into the post-transplant period. This early withdrawal of CNI was associated with improved renal function with follow-up up to 5 years, and the resultant increase in mild BPAR did not impact long term allograft function. Similar results have been reported in the HERAKLES study [74]. The CONCEPT study [75] evaluated the conversion from CsA to SRL 3 months post-transplant. All patients also received MMF and oral steroids which were to discontinue at eight months. The conversion of CsA to SRL 90 days’ post-transplant combined with MMF was associated with improved renal allograft function. In the CONVERT trial [76] renal transplant recipient on CsA or TAC were randomly assigned to either continue on the CNI or convert to SRL from CNI. This showed that at two years in patients who were converted to SRL had promising graft and patient survival with no significant difference in BPAR. Importantly it revealed a lower incidence of malignancy as compared to continuation of CNI therapy. In other studies, with late withdrawal, there was a greater risk of BPAR on maintenance MMF post-CNI withdrawal; there wasn’t enough evidence to support any conclusion on infection outcomes in these subgroups. As with strategies employing conversion, induction therapy was not expected to have any clinically significant impact during the later period when most studies initiated CNI withdrawal [19].

CNI avoidance

Given the degree of CNI-associated toxicity, studies were also done to assess if they could be completely avoided. To date nine RCT’s have looked at immunosuppressive protocols which are CNI free and were based on SRL or belatacept (table 3). SRL was alone in one study, in combination with AZA in another and finally with MMF in 5 of them. BENEFIT [77] and BENEFIT-EXT study [78] were two large scale multinational trials that compared belatacept and MMF to CsA and MMF after BAS induction for both groups. Only expanded criteria donors were enrolled in the BENEFIT-EXT study as these were associated with suboptimal clinical outcomes. Strong and less intensive treatment regimens for belatacept was compared in both BENEFIT studies. The ORION trial [71] looked at the safety and efficacy of SRL. Recipients of renal transplantation were randomised to three groups:

A. Group 1 - SRL and TAC with the elimination of TAC at week 13

B. Group 2 - SRL and MMF

C. Group 3 - TAC and MMF

Group 2 resulted in greater than expected BPAR and so was terminated early on. The study concluded that SRL based failed to show improved outcomes for renal transplant recipients. Given the available data, it is difficult to conclude if CNI avoidance regimes are successful as these studies resulted in inconclusive results and included small patient numbers (Table 3). Furthermore, a uniform recommendation could not be drawn as the immunosuppressive therapeutic regimes, and induction agents in individual studies were heterogeneous. There was no difference in death or graft loss when belatacept was compared to CsA however belatacept was associated with better renal parameters [79-83]. CNI-free studies where mTORi and MMF were used revealed improved renal function, but the risk of graft loss was greater when compared to tacrolimus-based regimens. When compared to CsA regimens there was no difference in the risk of graft loss [19].

Table 3: CNI avoidance studies.

With a lot of conflicting study results, the optimal immunosuppressive regimen remains controversial. Recipients of a renal allograft should have induction immunosuppressive therapy that consists of an antibody (rATG, basiliximab or alemtuzumab) plus maintenance immunosuppressive therapy (tacrolimus, mycophenolate mofetil or azathioprine and glucocorticoids) rather than maintenance immunosuppressive therapy alone [6]. Considering all the published data in the 36 trials focusing on CNI minimisation, it revealed that compared to standard dose immunosuppression, early minimization of CNI was clearly associated with positive outcomes - better renal function, lowered risk of BPAR and graft loss.

There was also a lower incidence of opportunistic infections in the immunocompromised host including a lower CMV incidence. BK virus infection was an exception as the evidence proved to be inconclusive. There was no difference observed amongst the different regimens for patient death [19]. CNI withdrawal was associated with a greater risk of BPAR for patients on mycophenolate acid formulations or mTORi compared to those on combination therapy with a CNI plus adjunctive therapy. Where CNI was replaced with mTORi studies have revealed that at two years in patients who were converted to SRL, there was promising graft and patient survival with no significant difference in BPAR. Importantly it revealed a lower incidence of malignancy as compared to continuation of CNI therapy. Given the literature, it is challenging to conclude if CNI avoidance regimes are successful as current studies had small patient numbers and moreover revealed inconclusive results, however, CNI minimization has a positive effect and should joudioulsy be reduced over time.

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