Author Affiliations: Department of Hepatobiliary Pancreatic Surgery, First Affiliated Hospital, Zhejiang University School of Medicine, Hangzhou 310003, China (Zhang W); Division of Transplant Surgery, University of Chicago, Chicago 60637, USA (Fung J)

Corresponding Author: John Fung, MD, PhD, Professor of Surgery and Chief, Division of Transplant Surgery, University of Chicago, Chicago 60637, USA (Tel: +773-702-9682; Fax: +773-702-2126; Email: jfung@surgery.bsd.uchicago.edu)

 

© 2017, Hepatobiliary Pancreat Dis Int. All rights reserved.

doi: 10.1016/S1499-3872(16)60167-4

Published online December 28, 2016.

 

 

Contributors: FJ proposed the study, ZW and FJ wrote the draft. Both authors contributed to the design and interpretation of the study and to further drafts. FJ is the guarantor.

Funding: None.

Ethical approval: Not needed.

Competing interest: No benefits in any form have been received or will be received from a commercial party related directly or indirectly to the subject of this article.

 

 

BACKGROUND: The use of calcineurin inhibitor (CNI)-based immunosuppressive regimens following liver transplantation (LTx) has improved the outcomes of the recipients. However, CNI has nephrotoxicity and causes short- and long-term renal complications. The progressive structural changes can be irreversible in the long-term, leading to chronic kidney dysfunction. The present review was to evaluate the different strategies of CNI application to renal function in liver recipients.

 

DATA SOURCES: PubMed database was searched for relevant articles in English on the issue of immunosuppressive regimen and kidney injury that related to early minimization of CNI after LTx.

 

RESULTS: Total avoidance of CNI from post-LTx immunosuppressive regimens has been associated with unacceptable high rates of acute, steroid resistant rejections; late conversion from CNI to non-nephrotoxic immunosuppressant failed to recover renal function. Early CNI minimization and conversion to non-nephrotoxic immunosuppressant, although had no effect on patient survival rates, improved glomerular filtration rate. The combination of everolimus (a mammalian target of rapamycin inhibitor) and tacrolimus not only maintains immunosuppressive efficacy but also minimizes kidney injury.

 

CONCLUSIONS: Up to now, protocols entirely avoiding CNI have not passed the primary safety endpoint of patient and graft survival, as well as the FDA mandated endpoint of biopsy proven acute rejection. Thus, early CNI minimization after LTx is the most rational approach preserving post-transplant renal function.

 

(Hepatobiliary Pancreat Dis Int 2017;16:27-32)

 

KEY WORDS: liver transplantation; immunosuppression; chronic kidney disease

 

The immunosuppressive regimens initially used in liver transplantation (LTx) included anti-metabolite purine analog, azathioprine and steroids, with or without anti-lymphocyte globulin preparations. However, the 1-year patient survival rate was only 33%.^[1] The introduction of the calcineurin inhibitors (CNIs), first exemplified by cyclosporine (CSA) in the early 1980s, significantly improved LTx patient survival, with 1-year survival rate of 70% under CSA and corticosteroids (CS).^[2] Later improvements were associated with the introduction of another CNI, tacrolimus (TAC), with improved 1-year patient survival rate approaching 90%.^[3]

 

Despite the improvement in short-term patient and graft survival through reduction of acute rejection (AR) rates, the association of these agents with complications, such as metabolic disturbances, increased rates of de novo malignancies, recurrent disease, cardiovascular complications and worsened renal function, compromises long-term LTx recipient survival. The significance of advanced chronic kidney disease (CKD) [defined as glomerular filtration rate (GFR) <30 mL/min/1.73 m²] in LTx recipients was illustrated by an analysis of UNOS data.^[4] In this registry analysis, the cumulative incidence of CKD Stages 4 and 5 approached 20% by 3 years post-LTx and was associated with more than a four-fold increased risk of recipient death. The rate of nephrotoxicity is particularly concerning in pediatric recipients, who have a longer lifetime exposure to immunosuppressive therapy. Indeed, renal dysfunction has been reported in as many as 32% of pediatric liver recipients at an average follow-up of 7.6 years after LTx.^[5] In addition, the emphasis of prioritizing LTx candidates with pre-existing renal dysfunction in the MELD era has increased the incidence of renal dysfunction following LTx.^[6]

 

Although deterioration in renal function following LTx is clearly multifactorial,^[7] CNI-induced nephrotoxicity plays a major role in short- and long-term deterioration, presumably mediated by afferent arteriolar vasoconstriction.^[8] In addition, CNI-induced renal dysfunction initially is reversible. However, the progressive structural damage such as glomerular sclerosis, tubular atrophy and interstitial fibrosis may be irreversible and lead to chronic kidney dysfunction.^[9] Thus successful efforts to improve renal function following LTx will depend heavily on the degree of structural changes associated with CNI.^[10] Therefore, clinicians attempted to minimize or withdraw CNI to improve renal function after LTx. A large prospective, open-label, randomized trial evaluated conversion from CNI to the non-nephrotoxic immunosuppressive agent, sirolimus (SRL, rapamycin) for preservation of renal function in LTx patients. Eligible LTx patients had been maintained on CNI immunosuppression for 6-144 months prior to SRL conversion. A total of 607 patients were randomized (2:1) to abrupt conversion (<24 hours) from CNI to SRL (n=393) or CNI continuation (n=214) for up to 6 years of follow-up. This approach resulted in a higher rate of biopsy-confirmed AR (P=0.02) and discontinuations (P<0.001) in the SRL conversion group without any significant changes in baseline-adjusted mean Cockcroft-Gault (CG) creatinine clearance (CrCl) at month 12 (primary efficacy endpoint). While the authors stated that LTx patients showed no demonstrable benefit one year after conversion from CNI to SRL based immunosuppression, they cautioned that a substantial proportion of patients had extended CNI exposure (>85% for one year or more) and may have incurred irreversible renal damage prior to SRL conversion.^[11]

 

Delaying the introduction of CNIs, reducing CNI exposure or avoiding CNI exposure entirely, have been strategies explored to lower the adverse events associated with CNIs. One approach in recipients has been to administer short-term induction therapy (polyclonal or monoclonal antibodies) with delayed introduction of CNIs. Other approaches have focused on reducing or eliminating CNIs within the first several months post-LTx. Lastly, avoidance of CNIs altogether with other immunosuppressive agents has also been examined. This review compared the patient outcomes of CNI avoidance, CNI delayed exposure, CNI early minimization or withdrawal after LTx (less than one year after LTx) and the associated impact on renal function.

 

 

Studies that have aimed at CNI avoidance or CNI delay have utilized antibody induction along with a non-nephrotoxic immunosuppressant. This approach avoids the synergistic vasoconstrictive effects of CNI with known early peri-operative risk factors associated with post-surgical acute kidney injury (AKI), such as volume depletion/shifts, hemodynamic instability and use of vasopressors, increased intra-abdominal pressures, poor liver allograft function and excessive blood transfusions.^[12] Given the limitations of depending solely on the current armamentarium of non-nephrotoxic baseline immunosuppressive agents, this approach relies heavily on the use of induction antibody preparations and length of time that CNI introduction is delayed. Although mycophenolate mofetil (MMF) was evaluated as a strategy to avoid CNIs in a pilot study, the incidence of AR with the use of daclizumab (DAC) and MMF alone was 100% and all were steroid resistant rejections.^[13] It has been concluded that MMF alone as a baseline immunosuppressant is insufficient.

 

An open, randomized, multicenter^[14] trial evaluated the benefit of DAC induction with delayed but standard dose TAC on renal function post-LTx, and assessed the impact of simply delaying CNI under the cover of antibody induction. LTx patients with intact renal function received either delayed TAC with DAC induction (n=98) or standard TAC (n=101), both combined with MMF+CS. The primary endpoint was the incidence of serum creatinine >1.43 mg/dL at 6 months. The incidence of renal dysfunction using this arbitrary threshold was 22.4% with delayed TAC+DAC and 29.7% with standard TAC (not significant), which remained unchanged at 12 months (21.6% and 23.9%). This suggests that any benefit of delaying TAC was abrogated by chronic exposure to standard TAC levels.

 

Two studies also examined the effect of not only delaying introduction of TAC but also aiming for lower maintenance TAC levels on renal function with the premise that antibody induction with delayed low dose TAC would lead to improvement of renal function after LTx. Yoshida and other Canadian collaborators^[15] conducted a multicenter, randomized trial in de novo LTx recipients where TAC was not only delayed, but was maintained at lower levels immediately following LTx, specifically DAC+MMF+CS+delayed low-dose TAC (target trough level 4-8 ng/mL, starting day 4-6) (n=72) compared to MMF+CS+standard TAC maintenance dosage (target trough level 10-15 ng/mL for first month, then reducing to 4-8 ng/mL) (n=76). The endpoints assessed Modification of Diet in Renal Disease (MDRD) and estimated glomerular filtration rate (eGFR) as a measure of renal function. There were no significant differences in either patient survival or AR. However, statistically significant differences in median eGFR were found in favor of the DAC+delayed low-dose TAC at the first post-transplant month (86.8 vs 70.1 mL/min/1.73 m²; P<0.001) and at month 6 (75.4 vs 69.5 mL/min/1.73 m²; P=0.038). This was validated in a European multicenter, prospective, randomized, open-label trial, which enrolled 525 adult LTx patients and then were randomized to receive standard dose TAC (target trough levels >10 ng/mL)+CS (n=183); MMF 2 g/day, reduced-dose TAC (target trough levels ≤8 ng/mL)+CS (n=170); or DAC induction+MMF+reduced-dose TAC (delayed until the fifth day post-transplant)+CS (n=172). The primary endpoint was the comparison of eGFR from baseline to 1-year post-LTx. The authors reported that the eGFR decreased by 23.61, 21.22 and 13.63 mL/min in standard TAC+CS, reduced TAC+MMF+CS and DAC+ reduced-dose and delayed TAC+MMF+CS, respectively (statistical significance was only noted between standard TAC+CS vs DAC+reduced-dose and delayed TAC+MMF+CS, P=0.012). As with the Canadian study, there were no significant differences in either patient or graft survival or AR rates.^[16]

 

The strategy of utilizing MMF to minimize CNI was employed in multicenter French prospective study that randomized 195 de novo LTx patients to standard TAC (n=100) or reduced TAC+MMF (n=95).^[17] AR occurred in 46 (46%) and 28 (30%) patients in the standard TAC and reduced TAC+MMF groups, respectively (HR=0.59; P=0.024). Renal dysfunction (defined as plasma creatinine increase greater than 30% of baseline) occurred in 42 (42%) and 23 (24%) patients in the standard TAC and reduced TAC+MMF groups, respectively (HR=0.49; P=0.004). At the end of one year, the eGFR was higher (90±30 vs 78±26 mL/min/1.73 m²; P=0.018) in the reduced TAC+MMF group than that in the standard TAC group. While this can be attributed in part to reduced TAC exposure, some have also suggested that MMF may provide some protection from intrinsic fibrosis associated with CNI.^[18]

 

Development of the mammalian target of rapamycin (mTOR) inhibitors has generated considerable interest, especially in view of their potential to reduce or eliminate CNIs. SRL was introduced first in the late 1990s for prophylaxis of rejection in organ transplantation. Everolimus (EVR) is a 40-O-(2-hydroxyethyl) derivative of SRL, which significantly alters its pharmacokinetic properties. The hydroxyethyl group confers faster absorption and a shorter half-life than SRL. Unlike SRL, no loading dose is required for EVR, and the twice-daily dosing schedule allows more tailored and incremental dose adjustments.^[19] The use of SRL in de novo LTx was assessed in a phase II prospective, randomized, open-label, active-controlled trial in which 222 primary LTx recipients were assigned immediately after transplantation to conventional-dose TAC (trough: 7-15 ng/mL) or SRL (loading dose: 15 mg; initial dose: 5 mg titrated to a trough of 4-11 ng/mL) and reduced-dose TAC (trough: 3-7 ng/mL).^[20] The 24-month cumulative incidence of graft loss (26.4% vs 12.5%, P=0.009) and patient death (20% vs 8%, P=0.010) was higher in subjects receiving SRL and the trial was terminated. A numerically higher rate of hepatic artery thrombosis (HAT)/portal vein thrombosis was observed in the SRL arm (8% vs 3%, P=0.065). Incidentally, no significant benefit was noted in this study regarding preservation of renal function. As a result, SRL carries a black box warning from the US FDA for use in de novo LTx recipients because of a high incidence of HAT, graft loss and death.

 

In spite of the concerns of use of SRL in de novo LTx and knowing the limitations of late term conversions to SRL (reviewed earlier), several studies converting patients from CNI to SRL in the shorter term after LTx have been conducted.^[21] The Concept study was a prospective, open-label, multicenter randomized study to evaluate conversion from a CSA-based regimen to a SRL-based regimen 3 months after LTx.^[22] One hundred ninety-two of 237 patients were eligible at 3 months to be converted to SRL+MMF+CS (n=95) or to remain on CSA+MMF+CS (n=97). The primary endpoint was renal function 1 year after conversion. The results demonstrated significantly improvement of kidney function in the SRL group (MDRD-eGFR: 61.2 vs 53.9 mL/min/1.73 m², P=0.002), but the degree of chronic injury is reflected by the significant lack of recovery of renal function on average. There was no difference in either patient and graft survival or the incidence of AR episodes. The follow-up of Concept study was the Postconcept trial, in which 77 patients in the SRL group and 85 in the CSA group were followed for 4 years after conversion. Renal function (MDRD-eGFR) was significantly better in the SRL group (58.7 vs 51.4 mL/min/1.73 m², P=0.002), but the same caveat on the overall degree of renal dysfunction as CKD Class III.^[23]

 

In the multicenter Spare-the-Nephron Liver trial, 293 subjects maintained on MMF and CNI were prospectively randomized 4-12 weeks after LTx to receive open-label MMF and SRL (n=148) or maintained on MMF and CNI (n=145).^[24] The primary efficacy endpoints were the mean percentage change in the eGFR and a composite of biopsy-proven AR, graft loss, death, and lost to follow-up 12 months after LTx. Patients were randomized an average of 52.5 days following LTx and then followed for a median of 519 days after randomization. The MMF+SRL group demonstrated a significantly greater renal function improvement from baseline with a mean percentage increase in eGFR of 19.7% compared with 1.2% for the MMF+CNI group (P=0.0012). However, the proportion of patients with biopsy proven AR was significantly greater in the MMF+SRL group (18/148 or 12.2%) vs the MMF+CNI group (6/145 or 4.1%, P=0.02) without differences in patient or graft survival.

 

Another non-nephrotoxic immunosuppressive regimen was trialed using Belatacept (BELA). BELA is a chimeric fusion protein that consists of the extracellular domain of CTLA-4 and the Fc domain of IgG blocks the B7 (CD80, CD86)/CD28 pathway, which results in inhibition of T-cell activation. This agent has been approved in kidney transplantation and demonstrated preservation of renal function in long-term follow-up.^[25] BELA was investigated in a phase II multicenter prospective partially-blind clinical trial in LTx which enrolled a total of 260 LTx patients and randomized into 5 treatment groups (3 BELA-containing groups: induction basiliximab+BELA more intensive [MI]+MMF; BELA MI+MMF; BELA less intensive [LI]+MMF and 2 TAC-containing groups: TAC+MMF; and TAC).^[26] A total of 147 LTx were randomized to receive BELA. Over the first 12 months of the study, there were 2 deaths in the BELA cohorts related to opportunistic infections, 1 from post-transplant lymphoproliferative disorder and the other from progressive multifocal leukoencephalopathy. During the follow-up period to 12 months post-transplant, a higher number of deaths were observed in BELA groups when compared to the TAC+MMF group. The frequencies of death were 12%, 21% and 22% in the basiliximab+BELA MI+MMF, BELA MI+MMF, and BELA LI+MMF groups, respectively, in comparison to 6% in the TAC+MMF group and 14% in the TAC group. In this trial, calculation of GFR by MDRD revealed that by month 12 in the intent-to-treat (ITT) analysis, the mean eGFR was 89-93 mL/min in the BELA groups and 71-75 mL/minin the TAC groups, validating the benefit of a CNI-free regimen in preserving post-LTx renal function. Nevertheless, the study was halted due to the imbalance in deaths in the BELA treated patients.

 

The pivotal phase III trial in de novo LTx evaluated early introduction of EVR one month after LTx, in combination with reduced TAC, compared to standard-exposure TAC. The trial was designed to delay conversion to mTOR for a period of one month after LTx to avoid the concerns of de novo use of an mTOR inhibitor, while avoiding irreversible structural changes that would minimize recovery of renal function. The primary endpoint of the study was a composite efficacy failure (defined as graft loss, death, treated biopsy proven AR or lost-to-follow-up) and the secondary endpoint was renal function measured by eGFR based on the four-variable MDRD equation (MDRD4) with results reported at month 12,^[27] 24,^[28] and 36 after LTx.^[29] The composite efficacy failure rate in the EVR plus reduced-exposure TAC group was lower compared to that in the TAC control group at month 12 (6.7% vs 9.7%), 24 (10.3% vs 12.5%) and 36 (11.5% vs 14.6%), respectively. EVR plus reduced-exposure TAC also demonstrated significantly fewer episodes and less severe grades of AR between day 30 and month 36 (excluding events that occurred prior to randomization). The key secondary endpoint, assessment of renal function, from one month after starting EVR plus reduced TAC, compared to standard-exposure TAC, the adjusted mean difference in MDRD4 eGFR change for EVR plus reduced TAC vs TAC control was +8.5 mL/min/1.73 m² at month 12 (P<0.001) and this difference in eGFR was maintained to month 36 (P=0.005).

 

The utility of EVR conversion to preserve renal function has been validated in the other studies. The PROTECT study was a multicenter, prospective, open-label trial, where 203 LTx patients were randomized at week 4 to start EVR and discontinue CNI (n=101), or continue their current CNI-based regimen (n=102).^[30] The primary endpoint was adjusted eGFR at 1-year post-LTx (ITT population). Although the CG-CrCl formula revealed no significant difference between treatments (+2.9 mL/min in favor of EVR; P=0.46), using the MDRD formula for eGFR showed superiority for EVR (+7.8 mL/min; P=0.021). Rates of mortality (EVR: 4.2% vs CNI: 4.1%), biopsy-proven AR (17.7% vs 15.3%), and efficacy failure (20.8% vs 20.4%) were similar. A 24-month extension phase followed 81/114 (71.1%) of eligible patients to 3 years post-LTx.^[31] The adjusted mean eGFR benefit from randomization to year 3 post-LTx was +10.1 mL/min (P=0.082) in favor of CNI-free vs CNI using the CG-CrCl formula, +9.4 mL/min/1.73 m² (P=0.053) by MDRD4 determination, highlighting the inexorable decline in renal function in the CNI group.

 

Given the apparent utility of initiating early CNI minimization along with low dose EVR at 1-month post-LTx, the concept of earlier implementation to facilitate the logistics (inpatient vs outpatient conversion) is attractive. One study will randomize patients to receive EVR (trough levels 3-8 ng/mL) with reduced TAC (trough levels <5 ng/mL), or standard TAC (trough levels 6-10 ng/mL) after entering a run-in period (3-5 days post-transplantation). In the run-in period, patients are treated with induction therapy, MMF, TAC, and CS.^[32]

 

 

In conclusion, to-date, protocols avoiding CNI entirely have not passed the primary safety check of assuring current expectations for patient and graft survival. Therefore, CNI minimization after LTx is a rational approach preserving post-transplant renal function. Delay of CNI exposure avoids exacerbating peri-operative risk factors associated with AKI and requires antibody induction with MMF and CS. Successful early control of AR without concomitantly increasing post-transplant complications such as infection, wound complications and vascular thrombosis requires CNI, preferably low dose TAC. Long-term success at maintaining renal function requires early introduction of an adjunctive agent with concomitant reduction in CNI dosing (before 6 months and preferably within 1-3 months post-LTx, using a non-nephrotoxic immunosuppressive agent).

 

 

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