A randomized 2×2 factorial trial, part 1: single-dose rabbit antithymocyte globulin induction may improve renal transplantation outcomes

Abstract

Background: We conducted a randomized and unblinded 2 × 2 sequential-factorial trial, composed of an induction arm (part 1) comparing single-dose (SD) versus divided-dose rabbit antithymocyte globulin (rATG), and a maintenance arm (part 2) comparing tacrolimus minimization versus withdrawal. We report the long-term safety and efficacy of SD-rATG induction in the context of early steroid withdrawal and tacrolimus minimization or withdrawal.

Methods: Patients (n=180) received 6 mg/kg rATG, SD or four alternate-day doses (1.5 mg/kg/dose), with early steroid withdrawal and tacrolimus or sirolimus maintenance. After 6 months targeted maintenance levels were tacrolimus, 2 to 4 ng/mL and sirolimus, 4 to 6 ng/mL or, if calcineurin inhibitor-withdrawn, sirolimus 8 to 12 ng/mL with mycophenolate mofetil 2 g two times per day. Primary endpoints were renal function (abbreviated modification of diet in renal disease) and chronic graft histopathology (Banff). Secondary endpoints included patient survival, graft survival, biopsy-proven rejection, and infectious or noninfectious complications.

Results: Follow-up averaged longer than 4 years. Tacrolimus or sirolimus and mycophenolate mofetil exposure was identical between groups. The SD-rATG associated with improved renal function (2-36 months; P<0.001) in deceased donor recipients. The SD-rATG associated with quicker lymphocyte, CD4 T cell, and CD4-CD8 recovery and fewer infections. Cox multivariate hazard modeling showed divided-dose-rATG (P=0.019), deceased donor (P=0.003), serious infection (P=0.0.018), and lower lymphocyte count (P=0.001) associated with increased mortality. Patients with all four covariates showed a 27-fold increased likelihood of death (P=0.00002). Chronic graft histopathology, rejection rates, and death-censored graft survival were not significantly different between groups.

Conclusion: The SD-rATG induction improves the 3-year renal function in recipients of deceased donor kidneys. This benefit, along with possibly improved patient survival and fewer infections suggest that how rATG is administered may impact its efficacy and safety.

Trial registration: ClinicalTrials.gov NCT00556933.

Conflict of interest statement

The authors declare no conflicts of interest.

Figures

FIGURE 1

2×2 factorial trial of rATG induction dosing and CNI withdrawal. Between April 20, 2004, and April 14, 2009, at the University of Nebraska Medical Center, 180 recipients of renal transplants were enrolled in a single center, prospective, randomized, unblinded 2×2 factorial trial of single-dose versus divided-dose rATG induction (6 mg/kg over 24 hr vs. 1.5 mg/kg × 4 alternate-day doses) followed after 6 months by CNI minimization or CNI withdrawal and replacement with MMF (IRB # 286–03; ClinicalTrials.gov #NCT00556933). Two patients not meeting enrollment criteria were consented and randomized in error, but were identified before transplantation and removed from participation in the trial. Sirolimus introduction was delayed in favor of MMF use until weeks 3 to 6 in patients with ATN-DGF or who were at high risk for wound complications (e.g., truncal obesity). We determined that 160 patients would provide 80% power with a two-sided 0.05 α level to detect a 10% difference in calculated GFR during the first year. (Enrollment was raised to 180 during the trial to guarantee sufficient patients to undergo eventual CNI withdrawal.) Randomization included stratification by race (white/Asian vs. non-white/Asian), donor type (living vs. deceased), and whether listed for eventual pancreas transplantation. Randomized assignments for both part 1 and part 2 treatment were contained in sequentially numbered, sealed envelopes opened after obtaining consent for trial participation to maintain allocation concealment. All analyses are intent-to-treat. MMF, mycophenolate mofetil; GFR, glomerular filtration rate; ATN, acute tubular necrosis; DGF, delayed graft function; rATG, rabbit antithymocyte globulin; CNI, calcineurin inhibitor.

FIGURE 2

A, Graft function was assessed by using the aMDRD equation to estimate GFR,, using all blood draws that provided serum creatinine measurements. Greater blood draw frequency during the first 6 months allowed weekly averages for each group to be compared, followed by monthly averages after 6 months. The GFR between treatment groups was compared and analyzed using a general linear model for repeated measures with maximum likelihood estimation, an approach sensitive to differences between small groups despite large intrapatient variance over time. Ordinary least-squares regression was not used because in the context of repeated measures, it can fail to recognize significant effects in the model because of faulty estimation of the covariance structure of the data. Although more patients in the single-dose group developed ATN-DGF, this trend did not reach statistical significance (P=0.11). This likely reflects our failure early in the trial to administer sufficient steroids to single-dose recipients; total steroid exposure, after our initial 20 patients, was increased from 6 mg/kg to 12 mg/kg. B, Frequencies for each induction group’s individual Banff categories were compared by Kruskal-Wallis rank testing. At 12 months, among single-dose recipients, there were five instances of suspicious or borderline rejection and nine among single-dose recipients. Among 24-month protocol biopsies, there were five instances of suspicious or borderline rejection in single-dose recipients and eight in the divided-dose group. There were no observations of recurrent disease among the protocol biopsies. aMDRD, abbreviated modification of diet in renal disease; GFR, glomerular filtration rate; ATN, acute tubular necrosis; DGF, delayed graft function.

FIGURE 2

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FIGURE 3

A, Rates of patient survival, graft survival, and rejection were compared with Kaplan-Meier analyses and log-rank tests. Patient deaths occurred at an average of 2.3±1.4 years after transplantation, of causes that included myocardial infarction, cancer, sepsis, drug overdose, and pulmonary embolus (Table S2, SDC,http://links.lww.com/TP/B12). Rejection was confirmed by ultrasound-guided biopsies (biopsy-proven acute rejection) graded according to Banff 1997 or 2005 criteria.. There were eight acute cellular rejection episodes in the single-dose group; five Banff grade IA, three grade IB. There were five cellular rejections in the divided-dose group; 1 grade IA, 3 grade IB, 1 grade IIA. B, There were eight episodes of suspicious or borderline rejection in each group not included. There were three instances of DSA+ AMR observed among our study patients, all in the divided-dose rATGgroup, at 9 days, 9months, and 14 months after transplantation. Only one of these grafts has been lost, at 2 years in the patient who experienced AMR at 14 months. The treatment of acute cellular rejection was guided by specific Banff classification (Table S4, SDC,http://links.lww.com/TP/B12). (B) Kaplan-Meier estimates of likelihood of infection after rATG induction and renal transplantation. The first of any infection after transplantation was scored, including pneumonia, abscess, UTI, bacteremia, “other” bacterial, BK (viruria or disease),CMV, Epstein-Barr virus, post-transplantation lymphoproliferative disorder, “other” viral, and fungal. C, In both rATG induction groups, lymphocyte counts immediately declined steeply after rATG infusion, but recovered significantly more rapidly in the single-dose group. D and E, T-cell subset data were obtained from only the first 80 patients because of the cost. Although CD8 numbers recovered rapidly and equally in both groups, CD4 counts and the CD4-to-CD8 ratio recovered significantly faster in the single-dose group. DSA+, donor-specific antibody positive; AMR, antibody-mediated rejection; rATG, rabbit antithymocyte globulin; CMV, cytomegalovirus; UTI, urinary tract infection.

FIGURE 3

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