EXPERIMENTAL AND CLINICAL TRANSPLANTATION

Objectives: There is no consensus on the best immuno-suppressive regimen for elderly renal transplant recipients. The objective of this study was to assess cytomegalovirus infection incidence and kidney transplant outcomes in elderly recipients treated with mammalian target of rapamycin inhibitors sirolimus/ tacrolimus at low doses compared with those receiving tacrolimus/mycophenolate sodium.

Materials and Methods: In this single-center prospec-tive randomized study (Trial Registration No. NCT02683291), kidney transplant recipients over 60 years of age were randomly allocated into 2 groups: tacrolimus-sirolimus (21 patients) and tacrolimus-mycophenolate (23 patients). Cytomegalovirus infec-tion rate and patient survival, biopsy-proven acute rejection, and renal function at 12 months were assessed.

Results: Cytomegalovirus infection rate was higher in the mycophenolate group (60.9%) than in the sirolimus group (16.7%; P = .004). The rates of biopsy-proven acute rejection, patient survival, graft survival, and estimated glomerular filtration rate over 12 months did not significantly differ between groups.

Conclusions: The incidence of cytomegalovirus infection was significantly lower in the sirolimus group. The use of tacrolimus combined with sirolimus in elderly kidney transplant recipients is safe.

Key words : Aged, Cytomegalovirus, Frail elderly, Renal transplantation, Target of rapamycin serine-threonine kinases

Kidney transplant is the best treatment for end-stage renal disease, as it is associated with lower rates of mortality and cardiovascular events compared with dialysis.¹ These benefits have also been observed in high cardiovascular risk populations such as the elderly.^2-6 Compared with their younger counter-parts, older individuals have a significantly lower risk for acute rejection, but show a greater risk of infection and malignancy, as well as a particular vulnerability to the immunosuppressive medications used in renal transplant.

The aging process results in physiologic changes that can impact drug metabolism and pharmacoki-netics.^5,7 However, most kidney transplant trials do not focus on the elderly, and no immunosuppressive regimen specific for this age group has been established.^5,7-9 Suggested modifications for older recipients include the reduction of the total immuno-suppressive load to avoid the serious adverse effects related to immunosuppressive treatment that elderly recipients are more prone to develop, while still preventing rejection.

After kidney transplant, older recipients are more likely to have cytomegalovirus (CMV) infection, which is associated with adverse outcomes that include increases in acute rejections, decreases in graft and patient survival, and predisposition to infections and malignancy.^4-9

Several studies have shown that mammalian target of rapamycin (mTOR) inhibitors can lower the risk of cardiovascular disease,^10,11 malignancy,¹² and CMV infection¹³ and therefore represent an attractive option for the elderly. Thus, the aim of this study was to assess CMV infection incidence and kidney transplant outcomes in elderly recipients treated with mTOR inhibitor sirolimus-tacrolimus at low doses compared with those receiving tacrolimus-mycophenolate sodium.

Materials and Methods

Design and population
This prospective, 12-month randomized controlled trial included patients aged > 60 years who under-went ABO-compatible kidney transplant from deceased donors between January 2014 and January 2015 and were followed-up until January 2016 at our center. Multiple-organ recipients, recipients with body mass index > 35 kg/m2, donors after cardiac death, and donors aged < 5 or > 65 years were excluded.

Written informed consent was obtained from all participants. The study was approved by the insti-tutional review board (No. 16966913.6.0000.5411) and conducted according to good clinical practices and the Declaration of Helsinki.

Randomization
Before surgery, study participants were randomized (1:1) by a transplant physician to one of the treatments under study. A computer-generated randomization sequence was obtained at www.randomization.com by an individual outside of the study, and the sequence was placed in sequentially numbered opaque envelopes. The study was blinded to those assessing the outcomes.

Study groups
Patients in the sirolimus group received tacrolimus (starting with 0.1 mg/kg twice daily adjusted to target serum levels by 4-8 ng/mL at the 3rd month and then 3-7 ng/mL from the 3rd month to the 12th month) and sirolimus at 2 mg/day (adjusted serum levels at 4-8 ng/mL throughout the study period).

Patients in the mycophenolate (control) group were given tacrolimus (starting with 0.1 mg/kg twice daily adjusted to target serum levels by 4-8 ng/mL at the 3rd month and then 3-7 ng/mL from the 3rd month to the 12th month) and mycophenolate sodium 720 mg twice daily. A dose reduction of mycophenolate sodium to 720 mg/day was accepted due to adverse effects of the drug.

In both groups, all patients received prednisone 30 mg/day (in the first month with weekly reductions up to 5 mg/day at the end of the 2nd month). Induction therapy consisted of basiliximab or antithymocyte globulin (thymoglobulin, Sanofi Aventis Canada Inc, Quebec, Canada). Thymoglobulin was used in patients with panel reactivity class I > 50% (at 1 mg/kg for 5 days).

Prophylaxis against infections
All patients received oral trimethoprim-sulfameth-oxazole for 6 months after transplant. A preemptive strategy was used for CMV control based on weekly monitoring viral replication by pp65 immuno-fluorescence antigenemia testing (weekly until the 4th month and monthly thereafter, until the end of the study).

Variables and measures
Data collected included recipient age, sex, race, body mass index (BMI), underlying disease, time on dialysis before transplant, length of hospital stay, panel reactivity class I, number of HLA mismatches, type of induction therapy (basiliximab or thymog-lobulin), and donor characteristics.

The incidence of CMV infection was determined based on the presence of CMV infection diagnosed by a pp65 antigenemia > 0 in asymptomatic patients. Cytomegalovirus disease was defined based on the evidence of CMV infection with related symptoms. Positive cases were treated with ganciclovir 5 mg/kg/day twice daily adjusted for renal function for at least 14 days. Treatment was prolonged for 1 week after the first negative CMV pp65 antigenemia test.

Transplant outcome measures included patient survival, biopsy-proven acute rejection, graft loss, death-censored graft survival, serum creatinine, 12-month estimated glomerular filtration rate (eGFR), delayed graft function, spot urine protein-to-creatinine ratio, new-onset diabetes after transplant, and lipid profile (total cholesterol and fractions). Glomerular filtration rate was estimated by the Modification of Diet in Renal Disease equation at 1, 3, 6, and 12 months after transplant.

Statistical analyses
Statistical analyses were performed using SPSS software (SPSS: An IBM Company, version 20, IBM Corporation, Armonk, NY, USA). Sample size was estimated as 40 patients (20 participants per group) to detect a 25% reduction in CMV infection (50% in the sirolimus group and 25% in the mycophenolate group) at α = 0.05 and β = 0.10, assuming an attrition rate of 20%.14 A t test or the Mann-Whitney test was used for the analysis of continuous variables where appropriate. For categorical variables, the chi-square test or Fisher exact test was used where appropriate. Survival analysis was performed by Kaplan-Meier curve and log-rank tests. Linear mixed models were used to analyze creatinine, eGFR, urine protein/creatinine ratio, and lipid profile over time (1, 3, 6, and 12 months), with group as a fixed factor. Multivariate binary logistic regression was carried out for risk factors associated with infection by CMV. Cytomegalovirus infection was considered as a dependent variable, whereas recipient age, group (sirolimus and mycophenolate), presence of delayed graft function, and type of induction therapy were considered as covariates. Significance level was set at P < .05.

Study population
Of 50 patients screened, 6 were considered ineligible. Thus, 44 patients were randomized and included in the final analysis (Figure 1). Patient baseline charac-teristics did not differ between groups (Table 1).

The incidence of CMV infection was higher in the mycophenolate group (60.9 %) than in the sirolimus group (16.7%; P = .004) (Table 2). The relative risk of developing CMV disease was 3.54 (1.2-10.3) in the mycophenolate group. Multivariate analysis showed that for every 1-year increment in recipient age, there was a 1.5 increase in the risk of developing CMV and an 81.7 increase in the risk of CMV infection in the mycophenolate group (Table 3).

Throughout the study period, mean tacrolimus concentration was 6.8 ± 0.3 ng/mL with a range of 4 to 8 ng/mL in the mycophenolate group (Figure 2A) and 6.1 ± 3.2 ng/mL with a range of 4 to 8 ng/mL in the sirolimus group (Figure 2B). Mean sirolimus concentration was 6.2 ± 0.24 ng/mL with a range of 3 to 7.5 ng/mL (Figure 2C). No differences in glomerular filtration rate and mean creatinine level were observed over time or between groups (Figure 3B). Patient survival at 12 months did not differ between groups (97.6% in the mycophenolate group and 87.3% in the sirolimus group). Overall, there were 3 deaths and 2 graft losses. In the myco-phenolate group, 1 patient died with a functioning graft 2 months after transplant; in the sirolimus group, 1 patient died due to septic shock after an incarcerated hernia at 6 months and the other died of undetermined cause (possibly cardiovascular).

The rate of biopsy-proven acute rejection did not differ between groups (Table 2). Death-censored graft survival at 12 months was 100% in the myco-phenolate group and 90.5% in the sirolimus group.

No differences in delayed graft function, length of stay, wound infection, and new-onset diabetes after transplant were observed between groups (Table 2).

The average proteinuria 12 months after trans-plant was 0.22 ± 0.7 mg/mg in the mycop-henolate group and 0.20 ± 0.37 mg/mg in the sirolimus group. The protein-to-creatinine ratio was similarly reduced in both groups at 1 month compared with the remaining months (P = .04) (Figure 3C).

The average total cholesterol after 12 months was higher in the sirolimus group (175.18 ± 31.2 mg/dL) than in the mycophenolate group (149 ± 36 mg/dL; P = .002) (Figure 4A). The average high-density lipoprotein (HDL) cholesterol at 12 months was higher in the sirolimus group (58.5 ± 27.3 mg/dL) than in the mycophenolate group (45 ± 10.6 mg/dL; P < .0001). There was a reduction in HDL over time in both groups (P = .048) (Figure 4B). The average triglycerides after 12 months was 167.2 ± 40.9 mg/dL in the mycophenolate group and 173.2 ± 78.2 in the sirolimus group, with no differences over time and between groups (Figure 4C).

In this study, the incidence of CMV infection was remarkably reduced (40%) in the sirolimus group, with recipient age and treatment with mycophe-nolate being independently associated with higher rates of CMV infection. Several studies indicate that mTOR inhibitors have an anti-CMV effect.^13,15,16 In a recent meta-analysis, it is suggested that CMV prophylaxis may be dispensable with the use of mTOR inhibitors with or without calcineurin inhibitors.¹⁷ Another meta-analysis of mTOR inhibitors or mycophenolic acid with a calcineurin inhibitor as the primary immunosuppression regimen showed that mTOR reduced the risk of CMV infection by 57%.¹⁸ One possible explanation for these findings is the association of mTOR inhibitors with increased CMV-specific CD4+ and CD8+ T-cell counts, which may be a possible mechanism of action of mTOR inhibitors in preventing CMV infections.¹⁹

In this study, the rates of biopsy-proven acute rejection, patient survival, graft survival, and eGFR over 12 months did not significantly differ between elderly kidney transplant recipients taking tacrolimus-sirolimus at low doses and those taking tacrolimus-mycophenolate. Some previous studies comparing tacrolimus with everolimus have shown similar results,^20,21 whereas others have reported lower renal function and higher rates of rejection and adverse events in patients given tacrolimus-sirolimus.^22-24 Still, in another study comparing tacrolimus-sirolimus with tacrolimus-mycophenolate mofetil over 8.5 years (tacrolimus concentrations were 8-10 ng/mL during the first 3 months), long-term renal graft survival and function were significantly worse in the tacrolimus-sirolimus group than in the tacrolimus-mycophenolate mofetil group.²⁵ A recent meta-analysis of calcineurin inhibitors combined with mTOR versus mycophenolic acid showed increased graft loss, lower renal function, and higher incidence of adverse effects in the sirolimus group.¹⁸ In all the studies reviewed, tacrolimus trough level was high (about 6-10 ng/mL), suggesting that the tacrolimus plus sirolimus combination has different safety profiles that might be related to the trough levels of both drugs, as well as with the immunologic risk of individual kidney recipients. Although in patients at high immunologic risk the tacrolimus-sirolimus combination has an inferior safety profile, it is likely to be safe in low to moderate risk recipients.²⁶ The use of reduced tacrolimus (3-7 ng/mL) combined with low doses of sirolimus has been associated with better outcomes with similar rates of renal function and survival.^27,28 In agreement with these findings, similar eGFR and graft survival results at 12 months were observed in the present study with the use of reduced tacrolimus combined with reduced sirolimus (trough levels of 4-8 ng/mL), which has been suggested to be the ideal combination to avoid rejection and prevent nephrotoxicity.²⁹

Our results regarding major adverse events related to mTOR inhibitors³⁰ show that there were no differences in the rates of wound infection, delayed graft function, new-onset diabetes after transplant, and protein-to-creatinine ratio over 12 months between groups.

Total and HDL cholesterol levels were higher in the sirolimus group. This finding suggests that sirolimus might have had a protective effect against atherosclerosis in this group, as the administration of mTOR inhibitors in atherosclerotic animal models has been associated with reduced atherosclerosis despite hypercholesterolemia.^31,32 Several mechanisms may be responsible for this protective effect that regulates both cholesterol homeostasis and inflammatory responses. Reduced cholesterol accumulation in the artery wall due to decreased expression of lipoprotein receptors (low-density lipoprotein receptors, very low-density lipoprotein receptors, and CD36) and increased expression of genes involved in cholesterol efflux, attenuation of monocyte chemotaxis, and reduced neointimal macrophage counts have all been suggested to delay the formation of atherosclerotic plaques.³³

The major limitation of this study is its single-center nature. Nonetheless, our data are consistent with the reported findings and indicate that further studies with long-term follow-up are necessary to assess the use of mTOR inhibitors as the primary immunosuppression regimen in elderly patients.

In brief, CMV infection was significantly lower with the use of tacrolimus-sirolimus at low doses com-pared with tacrolimus-mycophenolate in elderly transplant recipients. Glomerular filtration rate after 12 months and the rates of adverse events associated with mTOR inhibitors were similar between groups.

Volume: 16 Issue: 3 June 2018

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