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Reduced Dose Rabbit Anti-Thymocyte Globulin Induction for Prevention of Acute Rejection in High-Risk Kidney Transplant Recipients

Klem, Patrick1; Cooper, James E.2; Weiss, Andrew S.2; Gralla, Jane3; Owen, Phillip1; Chan, Laurence2; Wiseman, Alexander C.2,4

doi: 10.1097/TP.0b013e3181b6f38c
Clinical and Translational Research

Background. Despite the prevalent use of rabbit antithymocyte globulin (rATG) as an induction agent in kidney transplantation, the appropriate dose for preventing acute rejection in high-risk patients is not known. Few studies have examined total exposure of rATG less than 6 mg/kg, with fewer studies examining lower dose rATG in patients with increased risk factors for acute rejection.

Methods. We retrospectively analyzed outcomes of 83 kidney transplant recipients at increased risk for acute rejection (repeat transplant, African American race, and panel reactive antibody ≥20%) from July 2004 to July 2007 who were treated with rATG 1.5 mg/kg per day for 3 (n=39) or 4 (n=44) doses for induction to determine the impact of reduced-exposure rATG in the prevention of acute rejection. rATG was initiated intraoperatively and continued on consecutive days. All patients received triple maintenance immunosuppression including prednisone and calcineurin inhibitor. Patients requiring dialysis within 48 hr after transplant were excluded from analysis.

Results. One-year acute rejection rates were 10% and 11% in the 3- and 4-dose cohorts, respectively, with 100% patient and graft survival at 1 year in both groups. Patients in the 3-dose cohort were discharged from the hospital sooner than the 4-dose cohort (median length of hospital stay, 3 vs. 4 days; P=0.004).

Conclusions. Our results suggest that a 3- or 4-dose course of rATG (1.5 mg/kg/dose) provides excellent protection against acute rejection even in patients at increased risk, with the potential for cost savings from a reduction in hospital stay and medication administration.

1 Department of Pharmacy, University of Colorado Denver, CO.

2 Division of Renal Diseases and Hypertension, University of Colorado Denver, CO.

3 Department of Pediatrics, University of Colorado Denver, CO.

The authors declare no conflicts of interest.

Patrick Klem participated in research design, performance of the research, and writing; James E. Cooper participated in the performance of the research; Andrew S. Weiss participated in the performance of the research; Jane Gralla participated in the data analysis and writing of the manuscript; Phillip Owen participated in the performance of research; Laurence Chan participated in the research design and writing of the manuscript; and Alexander C. Wiseman participated in research design, performance of the research, data analysis and writing of the manuscript.

4 Address correspondence to: Alexander C. Wiseman, M.D., Transplant Center, University of Colorado Health Sciences Center, Mail Stop F749, AOP 7089, 1635 North Ursula Street, Aurora, CO 80045.


Received 23 March 2009. Revision requested 15 April 2009.

Accepted 16 June 2009.

The use of rabbit antithymocyte globulin (rATG, Thymoglobulin) as induction therapy for renal transplantation has increased during the past decade (1), primarily due to emerging data demonstrating its superiority over other induction agents in the prevention of acute rejection (2, 3). During this same period, acute rejection rates have significantly decreased (4), whereas concerns of infectious complications and malignancy have resurfaced (5, 6). These complications are occasionally correlated with previous depleting antibody therapy (7, 8).

Although rATG is indicated by the Food and Drug Administration in the United States for treatment of acute renal allograft rejection with recommended doses of 1.5 mg/kg per day for 7 to 14 days (9), the appropriate regimen for induction therapy has not been defined for low- or high-risk subgroups. A number of reports suggest that a total dose of 6.0 to 11.5 mg/kg is effective (10–14), with few studies attempting to study the efficacy of a total dose less than 6 mg/kg (15–17) or higher risk populations (17, 18). Specifically, no studies have reported outcomes of reduced dose (1.5 mg/kg/day for 3 days) rATG in a high immunologic risk patient population undergoing renal transplantation. Reduced dosing would decrease both medication cost and potentially minimize the risks associated with excessive immunosuppression.

A four-dose, 1.5 mg/kg per day induction regimen has been described in lower risk patients and in steroid withdrawal protocols (13, 19). Total rATG dosing of less than 6 mg/kg has also been described in patients with increased risk for delayed graft function (16, 17). However, neither of these doses has been fully described in patients with immunologic risk factors that specifically place them at increased risk for acute rejection. We report our experience with reduced induction dose rATG 1.5 mg/kg per day for 3 to 4 days given on consecutive days in the prevention of acute rejection in kidney transplant recipients with increased immunologic risk.

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We performed a retrospective analysis of patients at increased risk of rejection who received a kidney transplant and were given induction therapy with rATG 1.5 mg/kg per day for three or four doses from July 2004 to July 2007. Decisions regarding 3- vs. 4-dose administration were made when considering the recipient’s postoperative course and suitability for hospital discharge. Inclusion criteria for analysis were recipients of a single-organ kidney transplant who had one of the following characteristics: (a) repeat transplant, (b) African American race, or (c) panel reactive antibody (PRA) assessment more than or equal to 20%. PRA was measured by solid phase assays, including ELISA and Luminex phenotype beads with purified human leukocyte antigen class I and class II targets. The selection of more than or equal to 20% PRA as an inclusion criterion for the analysis was adopted based on a similar threshold used in a large multicenter study of induction therapy in patients at increased risk of rejection and delayed graft function (DGF) (2). Exclusion criteria were as follows: (a) patients with multiorgan transplants and (b) patients with DGF requiring dialysis within the first 48 hr of transplant. These patients with DGF defined early after transplant were excluded from the analysis because our center’s practice for early DGF requiring dialysis entails withholding calcineurin inhibitor (CNI) and continuing rATG for up to seven doses until recovery of renal function is evident. Because patients with early DGF typically received more than or equal to 6 mg/kg total dose of rATG, this would confound any comparisons of outcomes and duration of hospital stay between treatment groups, and they were therefore excluded. The first dose of rATG was administered at 1.5 mg/kg per day rounded to the nearest 25 mg intraoperatively and followed by subsequent daily dosing. All patients were placed on triple agent immunosuppression with prednisone, a CNI, and a mycophenolate agent (mycophenolate mofetil or enteric-coated mycophenolate sodium) or sirolimus. CNI administration was begun at low dose (1–2 mg of tacrolimus [TAC] orally or 100–150 mg of cyclosporine microemulsion orally twice daily) on evidence of graft function defined by a decrease in serum creatinine of more than 25%. Goal calcineurin inhibitor trough levels for TAC (months 0–3: 7–10 ng/dL; months 3–12: 5–8 ng/dL; after 1 year: 4–7 ng/dL) or cyclosporine (months 0–3: 200–300 ng/dL; months 3–12: 150–250 ng/dL; after 1 year: 100–150 ng/dL) were the same for each cohort. Intravenous methyprednisolone 500 mg was given intraoperatively, followed by 250 mg on day 2, with oral prednisone initiation on day 3 at 20 mg daily, tapered to 15 mg daily at 1 month, 10 mg daily at 2 to 3 months, and 5 mg daily at 6 to 12 months after transplant. Antiproliferative agent dosing was mycophenolate (mycophenolate mofetil 1000 mg twice a day or enteric-coated mycophenolic acid 720 mg twice a day) or sirolimus (SRL; 2 mg daily with trough level monitoring and adjustment to achieve trough levels more than 5 ng/dL). Selection of SRL or mycophenolic acid (MPA) was made at the surgeon’s discretion during a period in which our center was comparing the efficacy of these agents in unsenstizitized primary kidney transplant recipients (20). Selection was random without regard to donor or recipient characteristics. Prednisone and antiproliferative agent goals were the same between cohorts. Acute rejection episodes were treated with methylprednisolone 500 mg intravenously for 3 days. Depleting antibody therapy (Muromonab CD3 5 mg intravenously for 7–14 days or rATG 1.5 mg/kg intravenously for 7–14 days) was given if there was inadequate response to methylprednisolone therapy. Acute humoral rejection was treated with a combination of plasma exchange and intravenous immunoglobulin.

All patients received anti-infective prophylaxis with trimethoprim-sulfamethoxazole single-strength (SS) daily or inhaled pentamidine 300 mg monthly for 6 months in the setting of sulfa allergy. Patients received risk-stratified prophylaxis against cytomegalovirus (CMV) with valganciclovir (450 mg daily for 3 months in CMV IgG positive recipients or for 6 months if the recipient was CMV IgG negative and received a kidney from a CMV IgG positive donor). BK virus (BKV) surveillance was performed with urine and blood BKV PCR testing at 1, 6, and 12 months after transplant.

Outcome measurements were biopsy-proven or treated acute rejection rates, patient survival, graft survival, median hospitalization length of stay for transplantation surgery, estimated glomerular filtration rate (eGFR) based on abbreviated Modification of Diet in Renal Disease equation (21), and infectious complications. BKV viremia without renal dysfunction prompted dose reduction of immunosuppression, whereas BKV viremia associated with graft dysfunction prompted biopsy accompanied by dose reduction. Measurements were evaluated at months 6 and 12 after transplant.

Statistical analyses were performed using chi-square tests, Fisher’s exact tests, two-group t-tests, and Wilcoxon rank sum test (to compare length of hospital stay). This study was reviewed and approved by the Colorado Institutional Review Board.

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A total of 83 patients met inclusion criteria for analysis (Table 1). Thirty-nine patients received 3-dose rATG and 44 patients received 4-dose rATG. Patients were not prospectively randomized to receive 3- vs. 4-dose rATG, and those who received 3-dose rATG were found to have lower serum creatinine levels on day 2 (the third dosing day of rATG) than those receiving 4-dose rATG. Patients were predominately on a TAC-based regimen, white, and recipients of deceased donor kidneys. Overall, 76% of patients had elevated PRA level more than or equal to 20% (45% of the total population had PRA ≥80%), 54% of patients had received a prior transplant, and 18% were African American. When examining baseline characteristics of patients with PRA less than 80% who were recipients of primary kidney transplants, five patients in the 3-dose arm and eight patients in the 4-dose arm (16% of total) met inclusion criteria with PRA 20% to 79%. Of the African American cohort, five patients in the 3-dose arm and three patients in the 4-dose arm (10% of total) met criteria based solely on race (primary transplant recipients with PRA <20%). Although mean drug exposure was similar between arms for individual agents, maintenance immunosuppression regimens were different between the cohorts in that a greater percentage of patients in the 3-dose rATG group were placed on a TAC/MPA/Pred regimen and patients in the 4-dose rATG group were more frequently placed on a TAC/SRL/Pred regimen (Table 2).





Mean follow-up time was 37 months posttransplant. For the primary efficacy assessment of acute rejection, the acute rejection rate was 10% at 6 months and 11% at 12 months and was similar for both subgroups (3-dose arm: 10%, 10%; 4-dose arm: 9%, 11%; p=ns, Table 3). The majority of acute rejection episodes were steroid responsive. Of the patients who experienced acute rejection within the first year (n=9), two of 37 patients with PRA more than or equal to 80% experienced acute rejection, whereas two of 13 patients with a PRA 20% to 79% and one of eight African Americans with no other risk factors experienced acute rejection. Patient and graft survival at 1 year was 100% for each group. During the entire period of follow-up, graft survival was 92% and patient survival was 97%, with no differences between 3-dose or 4-dose cohorts. Additional analyses of the median length of hospital stay (LOS) and eGFR demonstrated that the LOS in the 3-dose group was shorter than the 4-dose group (LOS 3 days vs. 4 days, respectively, P=0.004) and the eGFR was significantly higher in the 3-dose rATG group at both 6 months and 1 year (at 6 months: 3-dose=64 mL/min vs. 4-dose=57 mL/min, P=0.03; at 1 year: 3-dose=63 mL/min vs. 4-dose=55 mL/min, P=0.03).



The rate of infectious complications was not statistically different between the subgroups (Table 3). At 1 year, the most common infections in the 3-dose group were bacterial infections (25.6%; upper respiratory/pneumonia n=3, urinary tract infection/pyelonephritis n=3, other=3), CMV disease (5.1%), and BKV viremia (5.1%). In the 4-dose group, the incidence of infection overall was similar and included bacterial infections (15.9%; upper respiratory/pneumonia n=1, urinary tract infection/pyelonephritis n=4, other=3), and BKV viremia (18.2%) with no patients experiencing CMV disease. The incidence of neutropenia within the first year was 7.2% overall and not significantly different between subgroups. Although there was a trend toward a lower frequency of BKV viremia in the 3-dose (4.5 mg/kg) group, this difference did not reach statistical significance (P=0.09). Of those patients with BK viremia, two patients in the 3-dose arm and one patient in the 4-dose arm developed biopsy-proven BKV nephropathy with graft dysfunction within the first year posttransplant; whereas two additional cases of BKV nephropathy occurred after the 12-month assessment in the 4-dose arm. When excluding patients with BK viremia from the analysis, eGFR differences persisted between the 3-dose and 4-dose arms (mean eGFR at 6 months: 3-dose=65 mL/min vs. 4-dose=58 mL/min, P=0.05; at 1 year: 3-dose=65 mL/min vs. 4-dose=55 mL/min, P=0.02).

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This study is the first to report the efficacy of two defined low-exposure dosing regimens (3 or 4 consecutive days, 1.5 mg/kg/day rounded to the nearest 25 mg) of rATG as an induction agent in patients at increased immunologic risk of acute rejection and is the largest report of “lower-dose” (4.5 mg/kg total) rATG use in a subset of our patient population. The findings of low acute rejection rates and excellent patient and graft survival at 1 year with either approach support either strategy in this “high risk” group and provide a rationale for further studies to optimize rATG use.

The optimal use of rATG as induction therapy in low- or high-immunologic risk patients has not been studied in a randomized prospective trial. Only one published study, a retrospective analysis by Gurk-Turner et al. (18), has compared the safety and efficacy of rATG at different dosing thresholds in high-risk kidney transplant recipients. In 96 patients, doses of less than or equal to 7.5 mg/kg in 33 patients resulted in an incidence of acute rejection at 12 months (9.5%) that was comparable with the rejection rate of 63 patients treated with more than 7.5 mg/kg (8.8%). Within this trial, the mean total rATG dose within each group was 5.7 vs. 10.3 mg/kg, respectively. When comparing these findings to our study, it is important to note that in the study by Gurk-Turner et al., patients with delayed graft function were not excluded, whereas patients with PRA more than 40% formed only 19% of their cohort and African Americans comprised 37%. Our exclusion of patients with early DGF may have contributed to the low acute rejection rates that we report, but our inclusion of a greater number of patients with higher immunological risk factors would be expected to predispose to a higher risk for acute rejection. Despite these important differences, our results extend observations made by Gurk-Turner et al., demonstrating excellent efficacy and safety with an even greater reduction in rATG dose in a high-risk patient population.

Others have reported the efficacy of rATG at lower doses in patients with different risk profiles. A single-center report of 16 patients, all of whom were primary transplants with low PRA, examined the efficacy of 3.0 vs. 4.5 mg/kg total dose rATG for 3 days (15). No acute rejection was reported; interestingly, an analysis of peripheral T cell depletion showed that 4.5 mg/kg rATG resulted in more prolonged depletion of T cells at 1 and 6 months vs. 3.0 mg/kg. These findings were similar to a previous study of 58 low-immunologic risk patients at risk for delayed graft function, which demonstrated improved protection from acute rejection with intraoperative dosing and a total exposure of 4.6 mg/kg rATG (16). Finally, a prospective trial of 41 patients with risk factors for delayed graft function and acute rejection evaluated an intermittent rATG dosing strategy based on CD3+ lymphocyte depletion (17). The inclusion criteria were more heterogeneous within this trial than ours and included patients with simultaneous kidney pancreas transplants and patients at risk for delayed graft function exclusive of immunological risk factors for acute rejection. Despite these differences, the low acute rejection rate (12.2% of patients) achieved in this trial with a mean total cumulative dose of rATG of 4.2 mg/kg is comparable with our results. Together with our study, these studies suggest that a lower dosing range for rATG exists depending on indication and patient characteristics, which may be evaluated at intervals both pre- and posttransplantation.

Additional findings when comparing the 3-dose to 4-dose rATG subgroups are worthy of comment. Of secondary interest is the difference in median length of hospital stay between the 3-dose and 4-dose cohorts. Since the time of infusion of rATG often requires 4 to 6 hr after the first dose to avoid infusion-related side effects, a reduction in rATG total dose may permit a more rapid transition to an outpatient setting. This would be expected to result in a cost-savings by reducing both medication and hospital charges. However, because many facilities are capable of transitioning patients to an outpatient infusion center routinely, a strong relationship between dose reduction of rATG and cost savings related to early hospital discharge cannot be firmly stated. Differences in eGFR were noted between the 3- and 4-dose groups at both 6 and 12 months after transplant. One potential explanation for these findings was that the more frequent use of TAC/SRL/Pred in the 4-dose cohort may have resulted in a reduced eGFR due to enhanced CNI nephrotoxicity with this regimen compared with a TAC/MPA/Pred regimen (22–24), despite equivalent acute rejection rates. Although the differences in maintenance immunosuppression may have influenced eGFR differences, it is unlikely that this influenced the primary endpoint (the incidence of acute rejection), because acute rejection was not more prevalent with one antiproliferative agent than another (four patients taking MPA and five patients taking SRL had rejection). A final observation from this study was the trend to greater BK viremia in the 4-dose cohort. Given the differences in maintenance immunosuppression regimens, it is difficult to ascribe increased risk of BK viremia simply due to an additional 1.5 mg/kg dose of rATG. When excluding patients with BKV viremia from the eGFR comparison, the eGFR differences persisted between subgroups. Therefore, the eGFR findings cannot be attributed to a higher rate of renal dysfunction from BKV.

A number of limitations of our study should be considered. Despite the important finding of low acute rejection rates in both arms, the retrospective nature of the study does not permit determination of other variables that may be contributory when selecting patients for 3- vs. 4-dose therapy, and thus patients with unaccounted-for factors (e.g., a more rapid change in creatinine by day 3 or an uneventful postoperative course) may have influenced 3- vs. 4-dose therapy. Our results are limited to patients who did not develop delayed graft function (dialysis within 48 hr after transplant) because these patients would commonly remain on rATG for longer periods while calcineurin inhibitors were held to avoid additional nephrotoxicity in the early posttransplant period and would typically remain hospitalized for more prolonged periods. Given the immediate graft function in both groups and the lower serum creatinine values on day 2 in the 3-dose cohort, it is likely that the degree of immediate graft function contributed to medical decision-making regarding 3- vs. 4-dose strategies. Additionally, expanded criteria donors comprised a small percentage of deceased donors within this study, which limits the interpretation of this study for this subgroup. Reduced-dose rATG may indeed be reasonable in patients with expanded criteria donor kidneys or DGF as well. Our clinical practice during this era did not permit this assessment, and the study must be viewed within the context of these donor and recipient risk factors. We included African American race within our definition of increased immunologic risk, despite ongoing debate regarding its inclusion in the definition of “high risk” (25, 26). However, only eight of the 83 patients would have been excluded if this cohort were not considered at increased risk for acute rejection. We used a PRA cutoff of more than or equal to 20% for inclusion, a value that is variably applied to high-risk cohorts (2, 27). Despite these inclusion criteria, most patients were classified as high risk due to a previous transplant and had an elevated PRA more than or equal to 80%, and only 13 of 83 subjects would have been excluded from this study if the PRA threshold for inclusion were limited to PRA more than or equal to 80%. Using the more stringent definition of “immunologic high risk,” of the 62 patients with PRA more than or equal to 80% or who were retransplant recipients, the acute rejection rate was 8% at 1 year.

Despite these limitations, this report provides promising safety and efficacy data for the use of reduced dose rATG in high-risk renal transplant recipients. An additional economic benefit may exist with reduced dose rATG not only from medication cost savings but also a potential decrease in overall hospital costs. These data support the use of tailored rATG induction therapy for patients with elevated immunologic risk and immediate graft function and warrant further study in novel immunosuppression regimens and patient populations.

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Kidney transplantation; Induction; Thymoglobulin; ATG; Acute rejection

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