RESULTS OF THE DOUBLE-BLIND, RANDOMIZED, MULTICENTER, PHASE III CLINICAL TRIAL OF THYMOGLOBULIN VERSUS ATGAM IN THE TREATMENT OF ACUTE GRAFT REJECTION EPISODES AFTER RENAL TRANSPLANTATION1,2 : Transplantation

Journal Logo

Clinical Transplantation

RESULTS OF THE DOUBLE-BLIND, RANDOMIZED, MULTICENTER, PHASE III CLINICAL TRIAL OF THYMOGLOBULIN VERSUS ATGAM IN THE TREATMENT OF ACUTE GRAFT REJECTION EPISODES AFTER RENAL TRANSPLANTATION1,2

Gaber, A. Osama3,4; First, M. Roy; Tesi, Raymond J.; Gaston, Robert S.; Mendez, Robert; Mulloy, Laura L.; Light, Jimmy A.; Gaber, Lillian W.; Squires, Elizabeth; Taylor, Rodney J.; Neylan, John F.; Steiner, Robert W.; Knechtle, Stuart; Norman, Douglas J.; Shihab, Fuad; Basadonna, Giacomo; Brennan, Daniel C.; Hodge, Ernest E.; Kahan, Barry D.; Kahana, Lawrence; Steinberg, Steven; Woodle, Steve E.; Chan, Laurence; Ham, John M.; Stratta, Robert J.; Wahlstrom, Erik; Lamborn, Kathleen R.; Horn, H. Rossiter; Moran, Hana Berger; Pouletty, Philippe; Schroeder, Timothy J.

Author Information
  • Free

Abstract

*Abbreviations: MALG, Minnesota antilymphoblast globulin; NATS, Nashville antithymocyte serum.

Despite advances in immunosuppressive agents, acute allograft rejection is a common occurrence after transplantation, with approximately 25-60% of all renal transplant recipients experiencing at least one episode of rejection in the first 6 months after transplant (1,2). The occurrence of acute rejection is associated with early graft loss and may be linked to subsequent chronic rejection and late graft loss (3,4). Several factors seem to affect the progression from acute to chronic rejection, including early acute rejection episodes and aggressive antirejection treatment with antilymphocyte agents as first line therapy(5).

The need for potent agents for rejection reversal has stimulated the widespread use of both monoclonal and polyclonal antilymphocyte preparations. In the United States, however, the availability of antilymphocyte therapies has been limited, due to restrictions on the use of unapproved agents. Atgam(Pharmacia-Upjohn, Kalamazoo, MI) is the only polyclonal antibody preparation approved by the Federal Drug Administration for use in transplant recipients. Polyclonal antibodies were first used for the treatment of rejection in the late 1960s by Starzl (6). Since then, several polyclonal products have been effective in rescuing patients with steroid-resistant rejection and are commonly used for induction therapy (7-9). The introduction of the monoclonal antibody OKT3(muromonab-CD3; Ortho Biotech, Raritan, NJ) eliminated some concerns related to the variability in response frequently seen with earlier polyclonal preparations (10). However, the often serious side effects associated with OKT3 and the concern regarding xenosensitization have resulted in the continued clinical utilization of polyclonal antibodies(11). Several randomized trials have demonstrated the clinical equivalence of polyclonal agents with OKT3 in reversing acute rejection (12-16). Sensitization and therapeutic failures have also been reported with polyclonal antibodies, further limiting the options of antirejection therapy in some recipients, and thus increasing the importance of making alternative biological agents available (17).

Thymoglobulin (SangStat Medical Corp., Menlo Park, CA) is a purified immunoglobulin solution produced by the immunization of rabbits with human thymocytes. The solution is pasteurized to increase viral safety, then concentrated to 5 mg/ml and provided in lyophilized form (25 mg/vial). Thymoglobulin is known to consist of antibodies specific for T-cell epitopes including CD2, CD3, CD4, CD8, CD11a, CD18, CD25, HLA-DR, and HLA class I(18). Clinical studies have demonstrated Thymoglobulin to be effective as a prophylactic immunosuppressive agent after renal, cardiac, liver, and kidney-pancreas transplantation (19-23). In addition, Thymoglobulin has been shown to be effective in reversing steroid-resistant rejection in approximately 80-90% of cases (24,25). Atgam is a nonpasteurized, purified gamma globulin solution obtained by the immunization of horses with human thymocytes and is utilized for the prevention and treatment of allograft rejection in renal transplant patients. Purification is enhanced with size exclusion chromatography and electrophoresis. Atgam reduces the number of circulating T lymphocytes measured by the E-rosette inhibition assay. It has been shown to be effective in the treatment of rejection after solid organ transplantation, as well as to delay the onset of allograft rejection (26-30). The purpose of this study was, therefore, to compare the safety and efficacy of Thymoglobulin to Atgam for the treatment of acute rejection after renal transplantation in a multicenter, phase III trial to support regulatory approval.

MATERIALS AND METHODS

General study design. In this randomized, double-blind, parallel-group, multicenter trial, the safety and efficacy of Thymoglobulin was compared with that of Atgam in adult renal transplant recipients undergoing biopsy-proven acute rejection of their first or second renal transplant. Randomization to treatment was stratified according to the Banff classification of kidney transplant rejection; episodes of rejection were categorized as grade I (mild), grade II (moderate), or grade III(severe) (31). In addition, grade I rejections were required to exhibit steroid resistance for entry into the study; steroid resistance was defined as a minimum of 3 consecutive days of ≥250 mg/day of intravenous methylprednisolone with a serum creatinine level that had increased by 10% or more from the initiation of steroid therapy. Treatment regimens were to be administered for 7 to 14 consecutive days with patients being followed for 3 months. Safety surveillance was continued until 6 and 12 months after therapy.

Patient eligibility. Inclusion criteria: Recipients of a first or second renal transplant who were 18 years of age or older and had biopsy-proven rejection as described above were included. Donor age was required to be ≥5 years, and all patients were required to sign an informed consent statement.

Exclusion criteria: Patients were excluded if they had any prior treatment or known allergy to horse or rabbit anti-T-cell polyclonal agents, evidence of underlying chronic rejection if the serum creatinine level before rejection was >3 mg/dl, or an OKT3-resistant current rejection episode. Any patient with a platelet count <100,000/mm3 on day 0 (day of inclusion biopsy) of the study was excluded from consideration, as well as those judged by the principal investigator to have a contraindication to intense immunosuppression. Malignancy within the previous 2 years (except skin malignancies) was also an exclusion criterion. Pregnancy, lactation, or lack of acceptable contraception were causes for exclusion. Current exposure to other investigational drugs was a contraindication to study participation, as was serological evidence of infection with human immunodeficiency virus-1, human T-lymphotropic virus type-1, or hepatitis B surface antigen. Finally, patients with multiple organ transplants (except combined kidney-pancreas transplants) were excluded from consideration.

Randomization and treatment administration. Patients were randomized using a centralized procedure with each center having a unique randomization code. Enrollment was stratified based on the severity of rejection according to the Banff classification of the day 0 biopsy specimen. Only the pharmacist at each investigative site was unblinded and responsible for maintaining that investigators, staff, laboratory, and pathologists remained veiled to patient study drug grouping for 1 year from enrollment.

Study drug was prepared for infusion by dissolving the correct number of Thymoglobulin or Atgam vials in 250 ml of isotonic saline. A 7- to 14-day course of either Thymoglobulin (1.5 mg/kg/day) or Atgam (15 mg/kg/day) was initiated within 24 hr of the day 0 biopsy. The study drug was infused through a central line over at least 6 hr for the first infusion and over at least 4 hr for subsequent infusions. Premedication with up to 500 mg of intravenous methylprednisolone, as well as acetaminophen and/or diphenhydramine, was allowed. Concurrent immunosuppressive agents (i.e., azathioprine, prednisone, and cyclosporine) were administered according to local standards and could be reduced during study drug administration but were required to be reinstated to prerejection doses at least 3 days before the end of study drug dosing. Outpatient administration was allowed after 3 days of inpatient therapy. The dose of study drug was allowed to be reduced by half if the platelet count fell to 50,000 to 75,000 cells/mm3 or if the white blood cell count fell to 2,000 to 3,000 cells/mm3 during the course of therapy. Likewise, treatment could be stopped if platelets were <50,000 or white blood cells were <2,000 cells/mm3.

Discontinuation of treatment. Patients could be withdrawn from the study for reasons such as adverse events, intercurrent illness, inappropriate enrollment, protocol noncompliance, request by patient, failure to respond to treatment, graft failure, or death. If, after 5 days of study drug therapy, there was an increase in the serum creatinine level, a repeat biopsy was performed to determine rejection status. If no improvement was noted on histology or if the rejection grade worsened, patients were allowed to be treated with alternative therapy.

Study protocol and visits. Vital signs and adverse events were assessed every 15 min for the first 2 hr of study drug infusion, every hour for the next 4 hr, and then every 4 hr until the next infusion of study drug. Similar procedures were repeated daily during study drug administration, and laboratory parameters were monitored at days 14, 21, 30, and 90.

Efficacy assessments and criteria. Treatment efficacy was evaluated by measuring the serum creatinine on day 0 though the end of therapy, and on days 14, 21, 30, and 90. A subset of centers also performed a follow-up biopsy within a week after the end of therapy for the evaluation of rejection resolution. The primary end point was a successful response, defined as a return of the serum creatinine level to or below baseline (day 0 value) on two consecutive measurements taken at least 2 days apart at the end of therapy or 14 days after the institution of therapy. Secondary end points included: (1) graft survival at day 30; (2) serum creatinine level at day 30 as a percent of baseline; and (3) improvement in posttreatment biopsy results relative to baseline biopsy results (defined as an improvement of at least one Banff grade). Supplemental efficacy parameters included rejection recurrence within 90 days after successful therapy. Rejection recurrence was defined three ways: (1) case report form definition, reflecting the individual investigator's assessment; (2) clinical definition, a ≥20% increase in serum creatinine level from the stable prerecurrent rejection value with institution of antirejection therapy; or (3) a ≥20% increase in serum creatinine level from the stable prerecurrent rejection creatinine level and a biopsy result confirming the diagnosis of recurrent rejection. One year after therapy, patient survival rate, graft survival rate, malignancy rate, and recurrent rejection incidence were also assessed.

Quality assurance of data. The sponsor and a contract research organization (The Hardardt Group, Parssipanny, NJ) made periodic visits to all study sites with audits performed before, during, and after the study. Verification of data against case report forms was conducted before unblinding the trial.

Statistical methods. The analysis of the study was based on pooled data from the individual study sites, generated using SAS Version 6.11(SAS Institute, Cary, NC), and compiled and reported by Statprobe (Ann Arbor, MI). Patient demographic information and baseline characteristics were summarized using descriptive statistics. For continuous variables, treatment groups were compared using the Wilcoxon rank-sum test. For categorical variables, treatment groups were compared using the Fisher's exact test. An intention-to-treat analysis was used for all patients entering the study who received treatment. The study was designed to demonstrate equivalence, therefore, the primary analysis method was based on one-sided confidence intervals for the key efficacy parameters. a lower bound for the one-sided 95% confidence interval of greater than -0.20 would demonstrate that Thymoglobulin was no more than 20 percentage points worse than Atgam and would be considered sufficient to demonstrate equivalence. However, if the lower bound for the confidence interval was greater than zero, Thymoglobulin would be assessed to have superior efficacy to Atgam.

For all end points calculated based on proportions (primary end point, grafts surviving 30 days, and improvement in biopsy result), for the purposes of display, simple proportions are presented. However, for the calculation of the confidence interval, proportions were calculated separately for each rejection severity Banff grade level, and an overall difference in response rate was calculated weighting the three differences based on the proportion of patients in each of the three grades. The usual methods for determining standard error for a combination of proportions were utilized in calculating the confidence interval.

For the secondary end point of serum creatinine level at day 30, the analysis was based on the log ratios, using an analysis of variance model with effect for center, treatment, and rejection severity. Confidence bounds were calculated on the log scale and displayed in the original scale by exponentiation of these bounds.

Time to event analyses (time to recurrent rejection, time to graft failure up to 1 year, and patient survival up to 1 year) were based on the log-rank test stratified for severity group. Because the time to event analyses were not originally planned as part of the demonstration of equivalence, these are reported as hypothesis tests using two-sided P values. For the purposes of analyzing time to recurrent rejection, only patients considered initially to be successes were included. For the purposes of evaluating graft survival, death with a functioning graft was considered an event, to estimate the percent surviving with a functioning graft, and included all cases in the intent-to-treat analysis. In all cases, time was calculated from date of study entry.

Adverse events were analyzed after mapping to preferred terms and body systems using a COSTART dictionary (32). Comparison of incidence was based on a two-tailed Fisher's exact test.

For the purpose of power calculations, the predicted overall success rate was unknown, and the study was planned to include 200 patients. This number of patients would be sufficient to provide good power even if the overall success rate was as low as 70% and would allow for patients lost to follow-up.

RESULTS

Patient disposition. The overall success rate of rejection reversal was higher than anticipated, and the rate of patient dropout was lower than expected. Therefore, with the Federal Drug Administration as an arbitrator, the study sponsor and investigators agreed to end the study early after enrolling 160 patients. Altogether, a total of 163 patients were randomized and enrolled in the study, 82 in the Thymoglobulin group and 81 in the Atgam group. One patient in the Atgam group was enrolled and treated in the study but was subsequently determined not to have biopsy-proven rejection and should not have been enrolled. This patient was, therefore, omitted from the intention-to-treat analysis for efficacy but was included in all analyses of safety, because study drug was received. Demographics and baseline characteristics for all patients are summarized by treatment group inTable 1. Patient and donor characteristics did not differ between treatment groups for age, gender, race, transplant donor type, transplant number, time to rejection, type of dialysis, pretransplant panel-reactive antibody, use of OKT3 induction therapy, pretransplant cytomegalovirus and Epstein Barr virus serology, or etiology of primary renal disease. Table 2 depicts the previous rejection history of patients in each study group. There were no differences between treatment groups with regard to previous acute rejection episodes, time since previous rejection occurrence, response to antirejection therapy, or concomitant immunosuppressive medications.

T1-5
Table 1:
Baseline demographics and patient characteristics for the use of Thymoglobulin compared with Atgam in the treatment of acute rejection
T2-5
Table 2:
Previous rejection history (before study enrollment) of all patients receiving Thymoglobulin versus Atgam

Treatment. The study entry rejection severity stratification was not different between the two groups. The majority of patients in both treatment groups had Banff grade II rejection (n=58, 71%, in the Thymoglobulin-treated patients; n=58, 73%, in the Atgam-treated patients) with grade I occurring in 10 (12%) and 8 (10%) patients, respectively, and grade III occurring in 17% in both treatment arms (n=14 Thymoglobulin patients and n=14 Atgam patients). No statistical difference was observed for severity across treatment groups. Study drug administration is summarized inTable 3. The average length of therapy was 10 days in both groups. Nine (11%) of the Thymoglobulin-treated patients received less than 7 days of therapy (two required rescue; two returned to dialysis; one was successful at day 5 but had an adverse reaction during study drug infusion and therapy was discontinued; four patients were considered early successes by the investigator and study drug was only infused for 6 days). Comparatively, 10(14%) of the Atgam-treated patients received fewer than 7 days of therapy (six required rescue therapy; three returned to dialysis; and one was considered successful by the investigator after 6 days of therapy and study drug was discontinued). During the 7- to 10-day study period, an additional two Thymoglobulin-treated patients required rescue therapy, whereas five Atgam-treated patients required rescue therapy and one returned to dialysis. However, Thymoglobulin-treated patients required more dose reductions (34% vs. 10%,P<0.001), which was most commonly related to leukopenia. The total steroid administration during the first 7 days of therapy was not different between the two study groups: 617±797 mg for Thymoglobulin-treated patients versus 772±812 mg for the Atgam-treated patients (P=0.21).

T3-5
Table 3:
Drug administration characteristics for patients receiving Thymoglobulin versus Atgam for treatment of acute rejection

Efficacy results. As stratified by rejection severity, Thymoglobulin was associated with a higher response rate than Atgam(Fig. 1). In each rejection severity category, there was a tendency toward improved response in the Thymoglobulin-treated group when compared with the Atgam-treated group. For grafts surviving at 30 days, 94% of the Thymoglobulin-treated group and 90% of the Atgam-treated group had functioning grafts to 30 days (Fig. 2). In each treatment group, allografts with biopsy specimens classified as grade I were more likely to function at day 30 than those with grade III rejections. Regardless of additional rescue therapy, graft survivors at day 30 exhibited similar serum creatinine levels. The median serum creatinine level at 30 days was 2.0 mg/dl in the Thymoglobulin-treated group and 1.9 mg/dl in the Atgam-treated group. A posttreatment biopsy specimen was evaluated in a subgroup of patients (n=38; 20 Thymoglobulin and 18 Atgam). Histological improvement in biopsy grade was not significantly different between the two groups (one Banff grade level improvement in posttreatment protocol biopsies, Thymoglobulin 65% versus Atgam 50%; P=0.15).

F1-5
Figure 1:
Successful response (percent of patients responding) to Thymoglobulin versus Atgam in the treatment of acute rejection shown as all successful cases and stratified by baseline biopsy specimen graded according to the Banff criteria. Difference is shown in proportions weighted by baseline rejection severity; the estimate of difference for Thymoglobulin-Atgam=11.4% and the lower one-sided 95% confidence bound of difference=1.6%.
F2-5
Figure 2:
Graft survival at day 30 (percent of grafts) for Thymoglobulin versus Atgam in the treatment of acute rejection shown collectively and stratified by baseline biopsy specimen graded according to the Banff criteria. Difference is shown in proportions weighted by baseline rejection severity; the estimate of difference for Thymoglobulin-Atgam=4.1% and the lower one-sided 95% confidence bound of difference=-2.9%.

T-cell subsets were performed by five study centers for CD2, CD3, CD4, and CD8 in 26 patients (n=12 Thymoglobulin, n=14 Atgam) during and after therapy. The use of Thymoglobulin was associated with a significantly greater degree of T-cell depletion as well as a more prolonged depletion of T cells than Atgam (Fig. 3). Furthermore, rebound to pretreatment levels occurred more rapidly in Atgam-treated patients. All T-cell subsets remained significantly lower at the end of therapy (median values for CD3 were: 5 cells/mm3 for Thymoglobulin and 147 cells/mm3 for Atgam, P=0.001) and at day 30 (CD3: 180 cells/mm3 for Thymoglobulin, 722 cells/mm3 for Atgam, P=0.016).

F3-5
Figure 3:
Comparison of T-cell response (CD2 and CD3) during therapy for acute rejection in patients receiving Thymoglobulin versus Atgam. Statistical test used was the Wilcoxon rank-sum test comparing Thymoglobulin to Atgam at the end of therapy. ▪, Thymoglobulin, CD2; ▴, Thymoglobulin, CD3; □, Atgam, CD2; ▵, Atgam, CD3.*P=1.000 for CD2, P=0.885 or CD3; **P=0.004 for CD2, P=0.001 for CD3.

In patients for whom therapeutic success was achieved, evaluation for subsequent rejection episodes revealed significantly fewer recurrent rejections for Thymoglobulin than Atgam. Recurrent rejection (whether defined by case report form, clinical criteria, or histological criteria) occurred less frequently in Thymoglobulin-treated patients compared with Atgam-treated patients throughout the 90-day period after therapy (Table 4).

T4-5
Table 4:
Recurrent rejection in patients receiving Thymoglobulin versus Atgam for treatment of acute rejection

At 1 year after study drug therapy, the overall graft survival rate was 79%. For Thymoglobulin, 83% of grafts survived to 1 year after rejection therapy; for Atgam, 75% of grafts survived to 1 year after rejection therapy (P=0.19). The log-rank test for significance between treatments, stratified by rejection severity with treatment as a covariate, was used (Fig. 4). When graft survival at 1 year is displayed by treatment group stratified by rejection severity, grade III rejection episodes are clearly delineated as having worse outcomes. In each rejection severity category, Thymoglobulin-treated grafts tended toward better outcomes (Fig. 5).

F4-5
Figure 4:
Overall 1-year postrejection therapy actuarial graft survival (Kaplan-Meier method), by acute rejection severity for renal transplant recipients treated with either Thymoglobulin or Atgam. Statistic used was the stratified log-rank test.
F5-5
Figure 5:
One-year postrejection therapy graft survival for renal transplant recipients with either Thymoglobulin or Atgam, grouped according to Banff grading for acute rejection.

Safety results. All patients in each group reported at least one treatment-emergent adverse event (defined as an adverse event beginning after the initiation of study drug or worsening after the initiation of study drug). Patients were evaluated for adverse events regardless of whether they continued with graft function or whether they completed the study. With the exception of serious adverse events, all reported adverse events occurred within 90 days after study initiation. For the 82 patients in the Thymoglobulin group, a total of 1203 treatment-emergent adverse events (or 14.6 events/patient) were reported, whereas 1160 treatment-emergent adverse events were reported by the 81 patients in the Atgam group (14.3 events/patient). When considering adverse events by body system, no significant difference was found between the two study groups(Table 5). During the 90-day follow-up period, the most frequently reported specific adverse events were fever, chills, and leukopenia. Leukopenia occurred more often in the Thymoglobulin group than in the Atgam group (57% versus 30%, P<0.001). Atgam was more likely associated with dizziness and dysuria (P=0.006 and 0.018, respectively). Adverse events reported for more than 25% but not more than 50% of patients in a treatment group were, by decreasing order of overall incidence: pain, thrombocytopenia, headache, diarrhea, peripheral edema, abdominal pain, hypertension, nausea, asthenia, tachycardia, hyperkalemia, and dyspnea. The incidence of infectious complications were not different between the two study groups (50% Thymoglobulin versus 51% Atgam). Bacterial infections occurred most frequently (29% Thymoglobulin versus 37% Atgam), with viral infections next in frequency (21% Thymoglobulin versus 11% Atgam); 9% of patients in both study groups experienced fungal infections.

T5-5
Table 5:
Treatment emergent adverse eventsa occurring in patients receiving Thymoglobulin or Atgam for treatment of acute rejection

There were six cases of malignancy reported during the 1-year follow-up period. Three patients in each treatment group developed malignancy. In the Thymoglobulin-treated group, two patients developed a lymphoma within the first year, and one patient was diagnosed with leukemia. Likewise, in the Atgam group, two patients developed lymphoma and one patient developed a skin malignancy. Two of the lymphomas reported during the study were detected by the blinded, central pathology retrospective reading of the inclusion biopsy specimen; this diagnosis was not made by the local pathologist. A total of nine patients died during the first year after treatment. The overall 1-year patient survival rate was 94%. Two patients died from malignancy (both were lymphomas: one Thymoglobulin-treated patient and one Atgam-treated patient). Five additional deaths occurred from the Thymoglobulin treatment group: two deaths were from myocardial infarction in patients with long-standing diabetes mellitus and three patients died from complications related to infections. In the Atgam-treated group, there were two additional deaths: one of which was from a myocardial infarction in a patient with diabetes mellitus and one patient who refused to return to dialysis after graft failure.

DISCUSSION

The objective of this phase III trial was to demonstrate the equivalence of Thymoglobulin and Atgam for treatment of acute rejection. Although powered to demonstrate equivalence, the study found Thymoglobulin to be significantly more effective than Atgam in reversing acute renal allograft rejections, particularly those of more severe histological grades (Banff grades II and III). In addition, Thymoglobulin significantly reduced the frequency of recurrent rejection. This enhanced immunosuppressive efficacy occurred without a corresponding increase in adverse events and indicates that Thymoglobulin is a significant addition to the therapeutic armamentarium available to transplant physicians in the United States.

Historically, the importance of anti-T-cell antibody therapy in clinical transplantation has been documented in multiple reports, which have been accompanied by three decades of clinical experience. Early studies of polyclonal preparations indicated efficacy in both treating and preventing acute rejection (8,25-28,33). In 1981, a prospective, randomized study compared Atgam to methylprednisolone for treatment of acute rejection and demonstrated significantly faster recovery with better graft and patient survival rates using Atgam (25). Other polyclonals, including Nashville antithymocyte serum (NATS*) and Minnesota antilymphoblast globulin (MALG), have also been used with substantial success. In a study of 128 kidney transplant recipients, NATS and Atgam were equally effective in reversing rejection, with significantly fewer side effects in the NATS-treated patients(34). More recently, a retrospective comparison of MALG and Atgam in 338 transplant recipients showed MALG to be superior induction therapy to Atgam, with no difference in side effects(35). Neither NATS or MALG is commercially available, however.

Introduction of the monoclonal antibody OKT3 in 1986 fueled speculation that polyclonal preparations had become antiquated and that transplantation was moving into a new, more specific era. OKT3 significantly improved rejection reversal rates when compared with conventional steroid therapy in 123 renal allograft recipients (36). However, the serious side effects associated with OKT3 use (including fever, chills, dyspnea, cardiopulmonary decompensation, nausea, diarrhea, headache, aseptic meningitis, and allograft thrombosis) have made clinicians reluctant to use the agent in many situations. Subsequent studies comparing the use of OKT3 to polyclonal agents, both for induction and treatment of acute rejection, have produced sometimes contradictory findings but overall indicate similar efficacy for both types of agents (14-16,37). Finally, although other monoclonal antibodies have been subject to clinical trials, OKT3 remains the only clinically available monoclonal agent for the treatment of acute rejection therapy. Although new humanized monoclonal antibody therapies are currently being evaluated, none have been shown to be effective in reversing established acute rejection.

The demonstrated clinical utility of polyclonal antibodies is supported by the recent recognition of the multiple diverse and redundant mechanisms by which lymphocytes can be activated. Because polyclonal preparations include antibodies with affinity for multiple T (and B) cell epitopes, the overall immunosuppression achieved may be enhanced. Thymoglobulin has been documented to contain antibodies recognizing CD2, CD3, CD4, CD8, CD11a, CD18, CD25, HLA DR, and HLA class I antigens. These data indicate that clinically effective immunosuppression may be more readily achieved with polyclonal agents.

Thymoglobulin is a rabbit antihuman polyclonal preparation, produced by immunizing rabbits with human thymocytes. The efficacy comparisons in this study clearly favored Thymoglobulin. However, the enhanced clinical efficacy may reflect the more effective lymphocyte depletion noted during and after Thymoglobulin administration. Several factors may have contributed to this effect. First, inclusion of sera from a large number of rabbits per batch enhances the homogeneity of the product and may diminish the batch-to-batch variability observed when fewer large animals (i.e., horses) are used. Second, rabbit immune globulin (with only one IgG subtype) seems to bind to human lymphocytes with higher affinity than equine antibodies, which demonstrate two subtypes of IgG with differing affinities. Finally, clinical investigations have demonstrated that, after multiple administrations, Thymoglobulin clearance decreases, resulting in an extended half-life(38). Rabbit immune globulin can be detected in the serum of recipients up to 40 or 50 days after the last dose, a finding that may have contributed to the reduced incidence of recurrent rejection noted in the Thymoglobulin-treated patients.

The downside of more effective immunosuppression is adverse events. The finding that Thymoglobulin was associated with significant and prolonged T-cell depletion has been previously noted in other studies (21,22,38). In the current trial, leukopenia occurred in 57% of Thymoglobulin-treated patients versus only 30% of those receiving Atgam. However, the overall incidence of infectious complications was similar in both groups, indicating the rather novel conclusion that for Thymoglobulin, leukopenia may be a marker of efficacy rather than overimmunosuppression(39). There was no difference between treatments in the incidence of posttransplant lymphoproliferative disorders or lymphomas arising during the follow-up period, again supporting the contention that the improved efficacy of Thymoglobulin was not accompanied by manifestations of excess immunosuppression. Clinically, Thymoglobulin and Atgam were equally well tolerated, with drug-related side effects, mainly fever and chills, occurring with similar frequency in both groups.

Apart from its prospective, double-blinded design, this study differed from previous studies of therapy of acute rejection in other ways as well. Its design demanded rapid pathologic confirmation of acute rejection, with the application of Banff criteria for interpretation. Groups were stratified by Banff classification, and treatment was instituted within 24 hr of biopsy. This emphasis on detailed definitions at entry and in interpretation of end points resulted in the rather novel, albeit intuitive, finding that the most severe histological rejections were less amenable to clinical intervention. Indeed, it was in patients with Banff grade II and III rejections that the greatest benefit of Thymoglobulin, with its pronounced lymphocyte depletion relative to Atgam, was evident. This was the first large-scale antirejection trial to attempt to adhere to such rigorous guidelines, and would appear, at least in part, to validate the Banff schema.

In summary, Thymoglobulin therapy (1.5 mg/kg/day for 7 to 14 days) resulted in a significantly higher success rate than Atgam (15 mg/kg/day for 7 to 14 days) in the treatment of acute graft rejection episodes after renal transplantation in adults, surpassing the intent of the study to demonstrate equivalence. Also, successfully treated Thymoglobulin patients had a significantly increased duration of subsequent rejection-free graft survival compared with Atgam-treated patients. Adverse events were observed equally for both treatment groups, but were generally not dose limiting and did not result in treatment withdrawal. Furthermore, the study design implemented in this trial was stringent and controlled for the severity of rejection and included objective measures of rejection response. Implementing similar protocols in clinical practice would enhance the reporting of rejection trials as well as reduce the variability in practice with regard to the diagnosis and evaluation of response, which makes comparisons across therapeutic regimens and between centers difficult.

Acknowledgments. The members of the Multicenter Thymoglobulin Study Group thank the following people for their contributions toward completing this project (listed by center in the following order [some individuals carried dual responsibilities and may appear twice in the list]: coinvestigators; coordinator; pathologist; pharmacist):

Bishop Clarkson Hospital: Thomas F. Knight, MD, Jerry L. Fischer, MD, Thomas V. Neumann, MD, Michael Hammeke, MD, Debra Sudan, MD, Gerald C. Groggle, MD, Inderbir S. Gill, MD; Kecia Frisbie, MSN, RN; Mary Fidler, MD; Scott McMullen, RPh.

Cleveland Clinic Foundation: David Goldfarb, MD, Stuart Flechner, MD, Vincent Dennis, MD, Joseph Nally, MD, Ben Brouhard, MD, William Braun, MD, Charles Modlin, MD, Raymond Tubbs, DO, Jonathan Myles, MD; Sonya Crook, RN, Sue Penko, RN; Raymond Tubbs, DO; Edward Jones, Pharm D.

Emory University Hospital: John D. Whelchel, MD, Thomas C. Pearson, MD, Christian P. Larson, MD, David P. O'Brien, MD, Ayten O.Someren, MD, Deepak Kikeri, MD, Fadi Lakkis, MD, Brian K. England, MD; Sallie White, RN; Ayten Someren, MD; Susan Rogers, RPh.

Loma Linda University: Siegmund Teichman, MD; Jill Freeman, Pharm D; Doug Weeks, MD; Jill Freeman, Pharm D.

Medical College of Georgia: James J. Wynn, MD, Arthur L. Humphries, MD; Martha Brown, RN, Michelle Christiano; Raghunhehah Rao, MD; Marjorie Phillips, MS, RPh.

Medical College of Virginia: Robert A. Fisher, MD, Pamela M. Kimball, MD, Marc P. Posner, MD, Anne L. King, MD, H. M. Lee, MD; Robin Godkin, PA-C; Paul Wakely, MD; Amy Philips, Pharm D.

National Institute of Transplantation: Rafael G. Mendez, MD, Paul Asai, MD, Umakant Khetan, MD, Eben Feinstein, MD, Robert Boken, MD, Hamid Shidban, MD, Moses Spira, MD, Thomas Bogaard, MD, Enrique Obispo, MD, Ramulfo Zapanta, MD, Marisa Magpayo, MD, Ronald Bangsil, MD, Saleh Aswad, MD; Ramulfo Zapanta, MD; Joseph Carberry, MD; Russell Leong, Pharm D.

Oregon Health Science University: William M. Bennett, MD, Mary M. Meyer, MD, Angelo M. DeMattos, MD; Cheryl Cannon, RN; Donald Houghton, MD; Karen Schoenbrun, RPh.

Sharp Memorial Hospital: Arturo Martinez, MD, Melody Briones, MD, Kathleen Moore, RN; Melody Briones, MD; Howard Robin, MD; Peter Lam, RPh.

SUNY Health Science Center-Syracuse: Frank Szmalc, MD; Suzanne Crowley, CNP; Paul Stanley, MD; Mariane McLaughlin, Pharm D.

Tampa General Hospital: Gary Chan, Pharm D, MS, Charles Wright, MD, Victor Bowers, MD, Denise Alveranga, MD, Samuel Weinstein, MD; Suzzie Glisson, ARNP; Sivaselvi Gunasekaran, MD; Linda Loetell, RPh.

Tulane University Medical Center: Suzanne Meleg-Smith, MD, Helen Calmes, MD; April Zarifan, RN; Suzanne Meleg-Smith, MD; Raymond Decuir, Jr., RPh.

University of Alabama at Birmingham School of Medicine: John J. Curtis, MD, Bruce A. Julian, MD, Charles E. Sanders, MD; Leigh Pollard, RN; Casey Weaver, MD; Steve Bernhard, RPh.

University of California-San Diego Medical Center: John Dunn, MD, Marquis Hart, MD, Shujun Li, MD; Julie Hatch, RN, FNP; Henry Krous, MD; Jim Gonzalez, Pharm D.

University of Chicago: M. Josephson, MD, J.R. Thistlethwaite, MD, J.B. Piper, MD, K.A. Newell, MD, J. Michael Millis, MD; Rita O'Laughlin, RN, Jane Charette, RN; Mark Haas, MD, PhD; Emmanual Semmes, RPh.

University of Cincinnati: J.W. Alexander, MD, R. Munda, MD, I. Penn, MD, S. Hariharan, MD, J. Munson, MD, P. Weiskittel, MSN; Pat Weiskittel, RN, MSN; Tito Cavallo, MD; Caron Sue, Pharm D.

University of Colorado Health Science Center: Igal Kam, MD, Penelope Baker, DO; Penelope Baker, DO; William Hammond, MD; Ken Easterday, RPh.

University of Nebraska Medical Center: Rodney J. Taylor, MD; Beverly Fleckten, Sharon Kochanowicz, RN; Mary Fidler, MD; Robert J. Rupprecht, RPh.

The University of Tennessee-Memphis: Rita R. Alloway, Pharm D, Santiago R. Vera, MD, Hosein Shoukou Amiri, MD, Lillian W. Gaber, MD; Rita R. Alloway, Pharm D; Lillian W. Gaber, MD; Sherry Davis, RPh.

University of Texas Health Science Center: Charles T. Van Buren, MD, Stephen Katz, MD; Jeannette Podbielski, RN; Regina Verani, MD; Brenda Mitchell, RPh.

University of Utah: Rajat Kaul, MD, John Holman, Jr., MD, Edward Nelson, MD, Pamela Thomas, RN; Pamela Thomas, RN; Michael Cohen, MD; Lisa Cox, Pharm D.

University of Wisconsin Hospital and Clinics: Anthony D'Alessandro, MD, John D. Pirsch, MD, Hans W. Sollinger, MD; Nancy Fass, MSN; Terry Oberley, MD; Rebecca Marnocha, Pharm D.

Washington Hospital Center: Truman M. Sasaki, MD, Alejandro Aquino, MD, Charles Currier, MD, Melissa Buick, MD, Anne Breakenridge, Pharm D; Michele Jordan, Deneen Fowlks; Melissa Buick, MD; Tayech Tesfaye, Pharm D.

Washington University School of Medicine: Gary G. Singer, MD, Todd K. Howard, MD, Jeffrey A. Lowell, MD, Surendra Shenoy, MD, Steven B. Miller, MD, David Hagerty, MD, Mitchell Mahon, RN; Mitchell Mahon, RN; John Ritter, MD; Kathryn Vehe, Pharm D.

Yale University School of Medicine: Marc I. Lorber, MD, Amy L. Friedman, MD; Kathy Lorber, MPH; Michael Kashgarian, MD; Valentine Pascale, RPh.

Safety-Steering Committee: Ronald D. Guttmann, MD, FRCP, McGill University Centre for Immunobiology and Transplantation; Daniel M. Canafax, Pharm D, University of Minnesota; Richard M. Lewis, MD, Loyola University Medical Center; Kathleen R. Lamborn, PhD, University of California at San Francisco.

Statprobe: Mark Becker, PhD, Lora Schwab, PhD.

SangStat Medical Corporation: David Winter, MD, Jennifer M. Kano, Jayne Meyer, Michelle Burton, Linda W. Moore.

REFERENCES

1. Cecka JM, Cho YW, Terasaki PI. Analyses of the UNOS scientific renal transplant registry at three years: early events affecting transplant success. Transplantation 1992; 53: 59.
2. Fisher RA, Tchervankov JI, Schroeder TJ, et al. Efficacy of induction therapy in cadaveric renal transplantation comparing rabbit antithymocyte serum and Minnesota antilymphoblast globulin. Transplant Proc 1991; 23: 1253.
3. Terasaki PI. Overview. In: Terasaki PI, Cecka JM, eds. Clinical transplants 1991. Los Angeles, CA: UCLA Tissue Typing Laboratory, 1992: 409.
4. Schweitzer EJ, Matas AS, Gillingham KJ, et al. Causes of renal allograft loss: progress in the 1980s, challenges for the 90s. Ann Surg 1991; 214: 679.
5. First MR, Schroeder TJ, Melvin DB, et al. OKT3 therapy in kidney, liver, heart, and pancreas transplantation. Clin Transplant 1988; 2: 185.
6. Starzl TE, Marchioro TL, Porter KA, et al. The use of heterologous antilymphoid agents in canine renal and liver homotransplantation and in human renal homotransplantation. Surg Gynecol Obstet 1967; 124: 301.
7. Light JA, Alijani MR, Biggers JA, et al. Antilymphocyte globulin reverses irreversible allograft rejection. Transplant Proc 1981; 13: 475.
8. Howard RJ, Condie CM, Sutherland DER, Simmons RL, Najarian JS. The use of antilymphoblast globulin in treatment of renal allograft rejection. Transplantation 1977; 24: 410.
9. Mannick JA, Davis RC, Cooperband SR, et al. Clinical use of rabbit antihuman lymphocyte globulin in cadaver-kidney transplantation. N Engl J Med 1971; 284: 1109.
10. Cosimi AB, Burton RC, Colvin RB, et al. Treatment of acute allograft rejection with OKT3 monoclonal antibody. Transplantation 1981; 32: 535.
11. Chatenoud L, Ferran C, Legendre C, et al. In vivo cell activation following OKT3 administration: systemic cytokine release and modulation by corticosteroids. Transplantation 1990; 49: 697.
12. Hanto DW, Jendrisak MD, So SKS, et al. Induction immunosuppression with antilymphocyte globulin or OKT3 in cadaver kidney transplantation. Transplantation 1994; 57: 377.
13. Ippoliti G, Negri M, Abelli P, et al. Preoperative prophylactic OKT3 vs. RATG, a randomized clinical study in heart transplant patients. Transplant Proc 1991; 23: 2272.
14. Grino JM, Castelao AM, Seron D, et al. Antilymphocyte globulin versus OKT3 induction therapy in cadaveric kidney transplantation: a prospective randomized study. Am J Kidney Dis 1992; 20: 603.
15. Cole EH, Cattran DC, Farewell VT, et al. A comparison of rabbit antithymocyte serum and OKT3 as prophylaxis against renal allograft rejection. Transplantation 1994; 57: 60.
16. Alamartine E, Bellakoul R, Berthoux F. Randomized prospective study comparing OKT3 and antithymocyte globulins for treatment of the first acute cellular rejection of kidney allografts. Transplant Proc 1994; 26: 273.
17. Filo RS, Book V, Pescovitz MD, et al. Association of sensitization to horse antilymphocyte/thymocyte globulin with recipient age and decreased renal allograft survival rates. Transplant Proc 1993; 25: 577.
18. Bonnefoy-Bernard N, Flacher M, Revillard JP. Anti-proliferative effect of antilymphocyte globulins on B-cells and B-cell lines. Blood 1992; 79: 2164.
19. Soulillou JP, Cantarovich D, Le Manff B, et al. Randomized controlled trial of a monoclonal antibody against the interleukin 2 receptor (33B3.1) as compared with rabbit antithymocyte globulin for the prophylaxis against rejection of renal allografts. N Engl J Med 1990; 322: 1175.
20. Steininger R, Muhlbacher F, Hamilton G, et al. Comparison of CYA, OKT3, and ATG immunoprophylaxis in human liver transplantation. Transplant Proc 1991; 23: 2269.
21. Ippoliti G, Rovati B, Graffigna A, et al. Prophylactic use of rabbit ATG versus horse ALG in heart transplanted patients under Sandimmune therapy: clinical and immunological effects. Clin Transplant 1989; 3: 1.
22. Clark KR, Forsythe JLR, Shenton BK, et al. Flow-cytometric monitoring of ATG therapy for steroid-resistant rejection. Transplant Proc 1992; 24: 315.
23. LeFrançois N, Raffaele P, Martinenghi S, et al. Prophylactic polyclonal versus monoclonal antibodies in kidney and pancreas transplantation. Transplant Proc 1990; 22: 632.
24. O'Donaghue DJ, Johnson RW, Mallick NP, et al. Rabbit antithymocyte globulin treatment of steroid resistant rejection in renal allograft recipients immunosuppressed with cyclosporine A. Transplant Proc 1989; 21: 1736.
25. Filo RS, Smith EJ, Leapman SB. Reversal of acute cadaveric renal allograft rejection with adjunctive ATG therapy. Transplant Proc 1981; 13: 482.
26. Nowygard R, Appel G, Hardy MA. Use of ATG for reversal of acute allograft rejection. Transplant Proc 1981; 13: 409.
27. Shield CF III, Cosimi AB, Tolkoff-Rubin N, et al. Use of antithymocyte globulin for reversal of acute allograft rejection. Transplantation 1979; 28: 461.
28. Hardy M, Nowygard R, Ellberg A, et al. Use of ATG in the treatment of steroid-resistant rejection. Transplantation 1980; 29: 162.
29. Benvenisty AI, Tannenbaum GA, Cohen DJ, et al. Use of anti-thymocyte globulin and cyclosporine to treat steroid-resistant rejection episodes in renal transplant recipients. Transplant Proc 1987; 19: 1889.
30. Bourdage JS, Hamlin DM. Comparative polyclonal anti-thymocyte globulin and antilymphocyte/antilymphoblast globulin anti-CD antigen analysis by flow cytometry. Transplantation 1995; 59: 1194.
31. Solez K, Axelsen RA, Benediktsson H, et al. International standardization of criteria for the histologic diagnosis of renal allograft rejection: the Banff working classification of kidney transplant pathology. Kidney Int 1993; 44: 411.
32. COSTART, Fourth Edition. Rockville, MD: FDA Department of Health and Human Services, Center for Drug Evaluation and Research, 1994.
33. Kountz SL, Butt KHM, Rao TKS, et al. Antithymocyte globulin dosage and graft survival in renal transplantation. Transplant Proc 1977; 9: 1023.
34. Johnson K, Niblack G, Richie R, et al. Multicenter comparison of rejection reversal: rabbit antihuman lymphocyte serum (ATS) versus horse anti-human lymphocyte globulin (ATGAM). Transplant Proc 1989; 21: 1734.
35. Lum CT, Umen AJ, Kasiske B, et al. Clinical impact of replacing Minnesota anti-lymphocyte globulin with ATGAM. Transplantation 1995; 59: 371.
36. Ortho Multicenter Transplant Study Group. A randomized clinical trial of OKT3 monoclonal antibody for acute rejection of cadaveric renal transplants. N Engl J Med 1985; 313: 337.
37. Frey DJ, Matas AJ, Gillingham KJ, et al. Sequential therapy: a prospective randomized trial of MALG versus OKT3 for prophylactic immunosuppression in cadaver renal allograft recipients. Transplantation 1992; 54: 50.
38. Guttmann RD, Fleming C. Sequential biologic immunosuppression: induction therapy with rabbit antithymocyte globulin. Clin Transplant 1997; 11: 185.
39. Bonnefoy-Berard N, Revillard JP. Mechanisms of immunosuppression induced by antithymocyte globulins and OKT3. J Heart Lung Transplant 1996; 15: 435.
© Williams & Wilkins 1998. All Rights Reserved.