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Clinical Transplantation

A BLINDED, RANDOMIZED CLINICAL TRIAL OF MYCOPHENOLATE MOFETIL FOR THE PREVENTION OF ACUTE REJECTION IN CADAVERIC RENAL TRANSPLANTATION1

 The Tricontinental Mycophenolate Mofetil Renal Transplantation Study Group2,3

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Abstract

Acute graft rejection remains perhaps the most important barrier to the success and safety of cadaveric renal transplantation. Rejection occurs predominantly within the first 6 months after transplantation, with a reported frequency ranging from 30% to 80%, depending upon the immunological status of the recipient, the degree of HLA match between donor and recipient, and the prophylactic immunosuppression used. Acute rejection is the principal cause of early graft loss and appears to increase the risk of late graft loss by predisposing to irreversible chronic rejection. Although rejection usually responds to treatment with high dose corticosteroids or antilymphocyte antibodies, this treatment also increases the risks, toxicity, and costs of renal transplantation (1-5).

Mycophenolate mofetil (MMF*) is a semisynthetic derivative of the antimetabolite mycophenolic acid, produced by the fungus Penicillium. MMF is a potent, noncompetitive, reversible inhibitor of the enzyme inosine monophosphate dehydrogenase. This enzyme catalyzes the conversion of inosine to guanine monophosphate, which is required for purine synthesis during cell division. T and B lymphocytes preferentially use the de novo pathway of purine synthesis and are therefore particularly sensitive to the inhibitory action of this drug. MMF inhibits the proliferation of T and B lymphocytes, the production of antibodies, and the generation of cytotoxic T cells in vitro following stimulation by mitogens or alloantigens (6-8). MMF has been shown to prevent acute graft rejection following renal transplantation in animal experiments and may have an important role in clinical transplantation (9, 10).

We report here the results of a multicenter, randomized, double-blind, controlled prospective trial designed to compare the efficacy and toxicity of MMF with azathioprine (AZA) in cadaveric renal transplantation. The study consisted of three arms, two of which received different doses of MMF while the third received AZA. The primary endpoint was treatment failure, defined as the occurrence of biopsyproven graft rejection, graft loss, patient death, or discontinuation of the study drug during the first 6 months after transplantation. Patients were followed for a period of 1 year to identify subsequent acute rejection, graft and patient survival, and adverse events.

MATERIALS AND METHODS

Organization and enrollment. Twenty-one transplant centers-4 in Australia, 11 in Europe, and 6 in Canada-participated in this double-blind study. Patient entry commenced in August 1992, and the study continued until September 7, 1994, by which point all patients had reached at least 1 year of follow-up. The protocol was approved by the ethics committee at each participating center and also conformed to the guidelines and standards set by the US Food and Drug Administration for investigational new drugs. Patients were informed of the study at the time of hospital admission for renal transplantation and were considered eligible for the study if they were receiving their first or second cadaveric renal transplant, were at least 18 years old, and were able to receive oral medication. Patients with a history of malignancy (except successfully treated nonmetastatic basal or squamous cell carcinoma of the skin), serologic evidence of human immunodeficiency virus or hepatitis B, systemic infections requiring continued antibiotic therapy at the time of entry, severe diarrhea, gastrointestinal disorders, or active peptic ulcer disease were excluded from entry, as were pregnant women, nursing mothers, and patients who did not agree to use adequate contraception.

Treatment plan. Patients who were willing to participate and who fulfilled the eligibility criteria were enrolled into the study pretransplant. A complete medical history and physical examination was performed for each patient at the time of transplantation. Baseline information included age, gender, etiology of renal disease, history of pretransplant blood transfusions, most recent and peak panel reactive antibody (PRA) levels, donor-recipient HLA and ABO match, donor age, cold ischemia time of the graft, and donor and recipient serologic status for cytomegalovirus (CMV), hepatitis B virus, and human immunodeficiency virus.

Patients were stratified according to first or second cadaveric renal transplant and were randomized equally within each center to receive treatment with MMF 1.5 g twice daily (MMF 3 g group), MMF 1.0 g twice daily (MMF 2 g group), or AZA once daily according to body weight (100 mg if body weight was less than 75 kg, 150 mg if 75 kg or more; AZA group). Cyclosporine and oral corticosteroids were administered concomitantly to all patients as maintenance immunosuppressive therapy. Treatment with the study drug was continued for 1 year, after which patients were given the option to continue in a 2-year extension of the trial.

The study drugs were administered using a blinded double-capsule format. Each patient received six capsules containing the appropriate dose of MMF or placebo twice daily and three capsules containing the appropriate dose of AZA or placebo once daily. The number of capsules remained constant throughout the study unless severe leukopenia or other important side effects occurred. In this event, both doses were simultaneously reduced by half, or eliminated completely, until the event resolved. Cyclosporine was administered according to the routine practice of each participating center. Treatment was generally started at the time of transplant or on the first postoperative day at a dose of 8-10 mg/kg/day orally or by continuous intravenous transfusion at 3 mg/kg/day. The dose was subsequently adjusted to maintain stable plasma or whole blood levels within the target range established at each center. Corticosteroids were administered according to the study protocol. A dose of up to 1 g of methylprednisolone was given intravenously before transplantation, followed by a second dose of up to 500 mg 12 hr later. Maintenance treatment with oral prednisone was then started at a dose of 30 mg/day, and tapered to 20 m/day at 2 weeks and 10 mg/day at day 84. Patients received prednisone at a dose of 10 mg/day until month 6, after which the gradual withdrawal of steroid therapy was permitted in stable patients.

Treatment of rejection episodes. Patients were monitored for evidence of graft rejection and for adverse events during the first year following transplantation. Study visits were scheduled for days 7, 14, 21, 28, and 42, weeks 8, 12, 16, and 20, and months 6, 9, and 12 after transplantation. Laboratory assessments performed at each of these time points included a complete blood count serum biochemistry, routine urinalysis, and a trough cyclosporine level. Rejection was suggested by standard clinical and laboratory parameters, including a rise in serum creatinine of more than 0.3 mg/dl (26 μmol/L), oliguria, an elevation in body temperature, swelling and tenderness of graft, reduced graft blood flow determined by Doppler ultrasonography, or evidence of diminished graft perfusion or excretion as shown by radionucleotide scan in the absence of other causes of graft dysfunction. Biopsy of the graft was required to confirm the diagnosis for the first episode of acute rejection in each patient. A biopsy was performed as soon as rejection was suspected and prior to the commencement of high dose intravenous methylprednisolone or antilymphocyte agents. Histologic reporting was standardized and interpreted using the Banff criteria (11). Acute rejection was treated with methylprednisolone 0.25-1 g daily for at least 3 days. Rejection episodes in which the serum creatinine did not fall after 3 days of therapy were defined as steroid resistant and treated with a course of antithymocyte globulin, antilymphocyte globulin, or muromonab-CD3 (OKT3). Use of antilymphocyte therapy before 3 days of methylprednisolone treatment had been completed was permitted only in patients who experienced rapidly deteriorating graft function with rejection confirmed by a graft biopsy showing a histologic score of grade III according to the Banff criteria.

Graft and patient survival. Patient death and graft loss were recorded for each treatment group. Graft loss was defined as graft nephrectomy, retransplantation, or a return to dialysis for at least 6 consecutive weeks.

Adverse events. Adverse events that occurred at or between study visits were documented according to the specific nature of the event, its severity, and its relationship to the study drug. The incidences of malignancy and infections were monitored similarly.

Statistical analysis. The primary endpoint for the study was treatment failure, defined by the occurrence of graft rejection confirmed histologically by core needle biopsy, graft loss, patient death, or discontinuation of the study drug during the first 6 months after transplantation. Episodes of acute rejection that could not be confirmed by histology were also analyzed, and were considered a subsidiary outcome. The sample size of 160 patients per treatment arm was chosen to detect a treatment failure rate of 30% or more for the AZA group versus 15% or less for MMF. Analysis of efficacy was by intention to treat and included all patients enrolled in the study. Secondary efficacy analyses and all safety analyses excluded six patients who were enrolled in the study but did not receive the study drug. All patients who withdrew from the trial were followed for graft loss, death, and the development of malignancy.

Statistical analysis was performed using the Cochran-Mantel-Haenszel (CMH) general association test, stratified by investigator (12). The Mantel-Haenszel estimates of relative risk and odds ratio were prepared along with the associated 97.5% confidence interval (CI). Statistical significance was assessed using a Bonferroni-adjusted alpha level of 0.025, reflecting comparison of each dose of MMF with AZA treatment (13). Comparability of the treatment groups was analyzed using a two-factor analysis of variance with a significance level of 0.10 for the continuous variables, and using the CMH general association test for categorical data. The comparability of PRA data was assessed with the CMH general association chi-square test. Continuous variables were analyzed using analysis of variance with factors for treatment center and treatment-by-center interaction. Treatment effects were assessed using type III sums of squares. To facilitate summarization of rejection treatment, a full course of antirejection therapy was defined as at least 3 days of corticosteroids with a cumulative dose of at least 600 mg or at least 1 day of antithymocyte globulin, antilymphocyte globulin, or OKT3 treatment. Adverse events were classified using a COSTART thesaurus of preferred terms (14). Summaries of cumulative incidence for adverse events and opportunistic infections were prepared using the Kaplan-Meier estimator. One-year graft and patient survival was analyzed using 97.5% CIs and a Mantel-Haenszel-type statistic adjusted by center and weighted proportional to sample size (15). All computations were prepared using SAS version 6.08 (16). Log-rank statistics were computed using BMDP 1990 Procedure 1L (17).

RESULTS

Patient entry and comparability. A total of 503 patients were entered into the trial; 443 were recipients of a first cadaveric renal graft and 60 were second graft recipients. One hundred sixty-four patients were randomized to MMF 3 g, 173 were randomized to MMF 2 g, and 166 were randomized to AZA. The three treatment groups were balanced for all principal prognostic variables except for the degree of PRA (P=0.038), with the greatest proportion of patients with PRA levels above 20% being in the MMF 2 g group (Table 1). Six patients who were enrolled in the study did not receive the study drug, in three cases because of acute tubular necrosis requiring antilymphocyte induction therapy, in two cases because of withdrawal of patient consent, and in one case because of inability to take oral medication during the 72 hr following transplantation. The graft functioned immediately in 133 patients in the MMF 3 g group, 133 patients in the MMF 2 g group, and 139 patients in the AZA group. Graft function was delayed in a further 30, 36, and 22 patients, respectively, while function was never achieved in 1 patient in the MMF 3 g group, 4 patients in the MMF 2 g group, and 7 patients in the AZA group.

Primary efficacy analysis. A total of 206 patients (40.9%) reached the primary endpoint of treatment failure within the first 6 months following transplantation. Fifty-seven (34.8%) of these were in the MMF 3 g group, 66 (38.2%) were in the MMF 2 g group, and 83 (50.0%) were in the AZA group (Fig. 1). Pairwise comparison showed no difference between the two groups receiving MMF, but did show an important difference between both of these groups and the AZA group (MMF 3 g vs. AZA: P=0.0045, 97.5% CI for relative risk = 0.50-0.92; MMF 2 g vs. AZA: P=0.0287, 97.5% CI for relative risk = 0.58-1.01). The incidence of treatment failure was consistently lower in patients receiving MMF than in those receiving AZA when analyzed by first or second transplant, age group, gender, PRA status, and treatment center. Reanalysis of the data by stratification for the PRA level for which the groups were statistically imbalanced showed the significance levels for MMF versus AZA to be identical to those stated above.

The causes of treatment failure are shown in Table 2. Biopsy-proven acute rejection occurred in 119 (23.6%) of the 503 patients in the study: 15.9% of patients on MMF 3 g, 19.7% on MMF 2 g, and 35.5% on AZA. Rejection episodes with a Banff score of grade II or higher were substantially less common in patients receiving MMF, occurring in 10 patients (6.1%) on MMF 3 g and 18 patients (10.4%) on MMF 2 g, compared with 33 patients (19.9%) on AZA. The study drug was withdrawn in a total of 66 (13.0%) of the 503 patients before the occurrence of acute rejection, graft loss, or death. Twenty-five of these patients (15.2%) were in the MMF 3 g group, 24 (13.9%) were in the MMF 2 g group, and 17 (10.2%) were in the AZA group. Graft loss and death without prior biopsy-proven rejection were infrequent, occurring in only 21 patients (4.2%). These outcomes were comparably distributed among the three treatment groups, with a combined incidence of 3.7% in the MMF 3 g group, 4.6% in the MMF 2 g group, and 4.2% in the AZA group.

A further 60 patients (11.9%) exhibited clinical or laboratory evidence of acute rejection that was not confirmed histologically during the first 6 months of the study. Of these, the biopsy was negative, equivocal, or showed other pathology in 36 patients (9 on MMF 3 g, 12 on MMF 2 g, and 15 on AZA), while biopsy was precluded by clinical or technical reasons in the remaining 24 patients (9 on MMF 3 g, 9 on MMF 2 g, and 6 on AZA). In total, therefore, 70 patients (42.7%) in the MMF 3 g group showed clinical or biopsy-proven rejection, lost their graft, died, or had the study drug withdrawn, compared with 83 patients (48.0%) in the MMF 2 g group and 98 patients (59.0%) in the AZA group. The incidence of these events was lower in the MMF groups than in the AZA group (MMF 3 g: P=0.0018, 97.5% CI for relative risk = 0.56 and 0.91; MMF 2 g: P=0.0372, 97.5% CI for relative risk is 0.63 and 1.02) (Fig. 2), but there was no difference between the groups receiving MMF.

One hundred seventy patients (33.6%) received a full course of treatment for acute rejection, which was defined as 3 or more consecutive days of high dose steroids or at least 1 day of antilymphocytes. These patients included 40 (24.4%) in the MMF 3 g group, 53 (31.0%) in the MMF 2 g group, and 77 (47.5%) in the AZA group (Fig. 3). Sixty-seven patients (13.3%), comprising 10 patients (6.1%) on MMF 3 g, 25 patients (14.6%) on MMF 2 g, and 32 patients (19.8%) on AZA, required two or more courses of treatment. The overall rate of treatment for rejection throughout the 6-month follow-up was 0.05 courses per patient per month in the MMF 3 g group, 0.08 courses per patient per month in the MMF 2 g group, and 0.13 courses per patient per month in the AZA group. Forty-eight patients (9.8%) required antilymphocyte agents for treatment of severe rejection. Thirty-four of these patients, 5 (3.0%) in the MMF 3 g group, 12 (6.9%) in the MMF 2 g group, and 17 (10.2%) in the AZA group, received antilymphocyte therapy for steroid-resistant rejection. An additional 14 patients, 3 (1.8%) on MMF 3 g, 3 (1.8%) on MMF 2 g, and 8 (4.9%) on AZA, were treated with lymphocyte antibodies without a full preceding course of steroids. The number of patients receiving antilymphocyte antibodies was therefore substantially lower in the MMF 3 g group (8 patients) and the MMF 2 g group (15 patients) than in the AZA group (25 patients). An additional 9 patients (4 on MMF 3 g, 3 on MMF 2 g, and 2 on AZA) with clinical or biopsy-proven rejection did not receive a complete course of therapy. Treatment was curtailed by nephrectomy in one patient receiving MMF 3 g, and was withheld on clinical grounds in the other eight patients.

There were no significant differences between the treatment groups with respect to the mean dose or trough level of cyclosporine at any point during the study. The mean (± SEM) dose at 1 week after transplantation was 8.1±0.2 mg/kg/day in the MMF 3 g group, 7.4±0.2 mg/kg/day in the MMF 2 g group, and 7.2±0.2 mg/kg/day in the AZA group. At month 1 after transplantation, the mean dose was 6.3±0.2 mg/kg/day in the MMF 3 g group, 5.8±0.2 mg/kg/day in the MMF 2 g group, and 6.1±0.2 mg/kg/day in the AZA group. The daily dose of cyclosporine was reduced throughout the study at a comparable rate in all three treatment groups. By 6 months after transplantation, the mean dose was 3.8±0.1 mg/kg/day in the MMF 3 g group, 3.9±0.1 mg/kg/day in the MMF 2 g group, and 3.8±0.1 mg/kg/day in the AZA group. The mean daily dose of prednisone also did not differ significantly among the three treatment groups at any point during the study. At 1 week after transplantation, the mean dose was 40.2±3.3 mg/day in the MMF 3 g group, 39.7±3.4 mg/day in the MMF 2 g group, and 37.3±3.6 mg/day in the AZA group. The dose of prednisone was reduced at a comparable rate in all three treatment groups throughout the study. At 6 months after transplantation, the mean dose was 10.1±0.2 mg/day, 10.1±0.2 mg/day, and 10.4±0.3 mg/day in the three treatment groups, respectively.

Compliance with treatment was comparable in the three study groups. The study drug was withheld for more than 20% of the study duration in only 3.0%, 1.2%, and 3.7% of the patients in the MMF 3 g, MMF 2 g, and AZA groups, respectively. A total of 26%, 27%, and 30% of the patients withdrew prematurely from the trial in each of these three treatment groups.

Evaluation at 1 year after transplantation. A further seven patients experienced biopsy-proven or clinical rejection between 6 and 12 months after transplantation. Three of these were in the MMF 3 g group, three were in the MMF 2 g, and one was in the AZA group. The difference between the three treatment groups remained unchanged from the primary efficacy analysis (Fig. 1). The cumulative incidence of graft failure and patient death at 12 months after transplantation was 11.0% in the MMF 3 g group, 11.7% in the MMF 2 g group, and 13.6% in the AZA group (Table 3). The weighted pairwise difference for MMF 3 g versus AZA indicated a 2.3% improvement in the MMF group (CI: -5.6% to 10.3%) and a 1.3% improvement for MMF 2 g versus AZA (CI: -6.5% to 9.1%). Graft failure occurred in 46 of the 503 patients in the study (9.1%). Thirteen of these losses (8.0%) were in the MMF 3 g group, 15 (8.8%) were in the MMF 2 g group, and 18 (11.2%) were in the AZA group. Rejection was the predominant reason for graft loss in all three treatment groups (MMF 3 g: n=4, MMF 2 g: n=4, and AZA: n=12). Thrombosis of the renal artery or vein was the next most common reason, followed by technical complications and sepsis. Other reasons for graft loss were: in the MMF 3 g group, unknown (n=2) and dialysis (n=1); in the MMF 2 g group, necrosis (n=2), dialysis (n=1), and kidney rupture (n=1); and in the AZA group, dialysis (n=1) and necrosis (n=1) (Table 3). Twenty of the 503 patients (4.0%) died during the 12 months of the study. Seven of these deaths occurred in the MMF 3 g group, 6 in the MMF 2 g group, and 7 in the AZA group. Patients in the MMF 3 g group died from sepsis (n=3), pulmonary embolism (n=1), stroke (n=1), acute asthma (n=1), and cancer (n=1). Patients in the MMF 2 g group died from cardiovascular disease (n=2), pulmonary embolism (n=2), sepsis (n=1), and cancer (n=1). Patients in the AZA group died from cardiovascular disease (n=2), sepsis (n=1), pulmonary embolism (n=1), acute pancreatitis (n=1), complications of diabetes (n=1), and biochemical abnormalities (n=1).

The function of surviving renal grafts was comparable in the three treatment groups. The mean serum creatinine values at month 1 after transplantation were 1.66±0.10 mg/dl in the MMF 3 g group, 2.00±0.10 mg/dl in the MMF 2 g group, and 1.99±0.10 mg/dl in the AZA group. At month 6, values were 1.44±0.08 mg/dl in the MMF 3 g group, 1.59±0.08 mg/dl in the MMF 2 g group, and 1.59±0.08 mg/dl in the AZA group. At month 12, values were 1.42±0.07 in the MMF 3 g group, 1.64±0.07 in the MMF 2 g group, and 1.60±0.07 in the AZA group. Serum creatinine levels above 2.5 mg/dl occurred in only 12% of the patients on MMF 3 g and 17.5% of the patients on MMF 2 g, compared with 25.2% of the patients on AZA between months 1 and 6 after transplant. Thirteen percent of patients in each MMF group had a serum creatinine level below 1.2 mg/dl during the same period, compared with only 4% in the AZA group. These differences in graft function diminished between months 6 and 12 after transplantation. Serum creatinine levels above 2.5 mg/dl occurred in 3.2% and 11.3% of patients on MMF 3 g and MMF 2 g, respectively, compared with 7.4% of the patients on AZA, while values below 1.2 mg/dl were observed in 22.4% and 18.8% of patients on MMF 3 g and MMF 2 g, respectively, compared with 11.6% of patients on AZA. Corresponding trends in calculated creatinine clearance were observed in all treatment groups.

Adverse events were analyzed for all 497 patients who received study drug (100% of randomized patients in the MMF 3 g group, 98.9% in the MMF 2 g group, and 97.6% in the AZA group) (Table 4). Leukopenia and gastrointestinal disorders were more frequent or severe in one or both MMF treatment groups, while thrombocytopenia, thrombophlebitis, and metabolic disorders were more frequent or severe in patients receiving AZA. Leukopenia was reported by the investigator in 35% of patients on MMF 3 g, 19% on MMF 2 g, and 30% on AZA. An absolute neutrophil count of less than 500 per microliter occurred in four patients receiving MMF 3 g. The dosage of study drug was reduced or administration was temporarily interrupted because of leukopenia in 29%, 15%, and 24% of the three groups, respectively. Treatment was discontinued because of this complication in 2-3% of patients in each group. Thrombocytopenia was observed in 5% of patients in the MMF 3 g group, 9% in the MMF 2 g group, and 12% in the AZA group and necessitated discontinuation of the study drug in no patients on MMF 3 g, 3 patients (1.8%) on MMF 2 g, and 4 patients (2.5%) on AZA. Gastrointestinal disorders were more common among patients receiving MMF than among those receiving AZA and occurred with highest frequency in those receiving the higher dose of MMF. The principal manifestations were diarrhea, abdominal pain, vomiting, and gastrointestinal infection. The more severe complications in patients receiving MMF 3 g included enteric infections (n=9), colitis (n=3), and hepatitis (n=5). Infection, colitis, diarrhea, and nausea were the predominant events leading to discontinuation or interruption of the study drug among patients receiving MMF 3 g. Most severe gastrointestinal adverse events occurred beyond 30 days after transplantation in both MMF groups, whereas the majority of complications among AZA-treated patients occurred within the first month. No other specific organ toxicity was observed in any of the three treatment groups.

Infectious complications and malignancies are shown in Table 5. Urinary tract infections were diagnosed in 42% of patients receiving MMF 3 g, compared with 41% receiving MMF 2 g and 35% receiving AZA. Bacteremia occurred in 1.8-2.3% of patients in all treatment groups, and unspecified systemic infections in 15-19% of patients in all treatment groups. CMV viremia or CMV syndrome was reported in 11-12% of patients in each of the three treatment groups. CMV disease with tissue invasion was more common in the MMF 3 g group (11%) than in the MMF 2 g group (7%) or the AZA group (6%) and predominantly reflected an increase in the frequency of CMV disease of the liver and gastrointestinal tract. The incidences of herpes simplex (21-25%) and herpes zoster (7-8%) were similar in all three groups. Infections due to Candida or Aspergillus also occurred with similar frequency in all three groups. Pneumocystis prophylaxis was balanced across the treatment groups, with 31-32% of patients receiving prophylaxis in each group. Pneumocystis carinii pneumonia occurred in three patients receiving AZA, none of whom had received prophylaxis.

Malignancies occurred during the study in 14 patients (9%) in the MMF 3 g group, 18 patients (11%) in the MMF 2 g group, and 12 patients (7%) in the AZA group. Basal or squamous cell carcinoma of the skin was the most common form of cancer, occurring in 8 patients (5%) on MMF 3 g, 15 patients (9%) on MMF 2 g, and 8 patients (5%) on AZA. Thirteen of the 14 squamous cell cancers developed in patients in Australian centers. In each case of skin cancer, the lesion was excised and the patient continued on study medication. Posttransplant lymphoproliferative disorders (PTLDs) were diagnosed in 5 patients: 2 patients (1%) receiving MMF 3 g, 2 patients (1%) receiving MMF 2 g, and 1 patients (<1%) receiving AZA. The PTLDs occurring in patients receiving MMF were confined to the brain. Of the 5 patients with PTLDs, 2 (1 receiving MMF 2 g and 1 receiving AZA) had received treatment with OKT3 prior to the development of the PTLD. Immunosuppressive treatment was reduced in all 5 patients, and MMF was discontinued in the 4 patients receiving MMF. One patient receiving MMF 2 g died from the complications of a cerebral lymphoma; all remaining patients were alive at 1 year after transplantation, with observation times of 280-409 days following diagnosis. Eight other solid-organ malignancies were diagnosed. Four occurred in the MMF 3 g group and included metastatic carcinoma of the liver, endometrial carcinoma, multiple myeloma, and cervical cancer. Squamous cell carcinoma of the epiglottis occurred in one patient in the MMF 2 g group, and a ductular carcinoma of the breast, a papillary carcinoma of the thyroid, and colon cancer were diagnosed in three patients in the AZA group. When combined with the lymphoproliferative disorders listed above, the overall incidence of noncutaneous malignancies was 3.7% (6/164) in the MMF 3 g group, 1.8% (3/171) in the MMF 2 g group, and 2.5% (4/162) in the AZA group.

Study withdrawals. One hundred thirty-eight of the 503 patients (27%) were withdrawn from the study during the first 6 months of follow-up. Forty-two of these patients (26%) were in the MMF 3 g group, 46 (27%) were in the MMF 2 g group, and 50 (30%) were in the AZA group. Among patients receiving MMF 3 g, withdrawal from the study occurred because of inappropriate enrollment (n=3), adverse events (n=25), unsatisfactory response to therapy (n=3), noncompliance with the treatment protocol (n=5), the need for a drug prohibited by the protocol (n=1), death (n=3), and other events (n=2). Among patients receiving MMF 2 g, withdrawal occurred because of adverse events (n=23), unsatisfactory response to therapy (n=7), noncompliance (n=6), the need for a drug prohibited by the protocol (n=4), death (n=3), and other events (n=3). In the AZA group, withdrawal from the study occurred because of adverse events (n=23), unsatisfactory response to therapy (n=11), noncompliance (n=8), the need for a drug prohibited by the protocol (n=5), and death (n=3). By 1 year after transplantation, a total of 28%, 28%, and 33% of the enrolled patients had terminated prematurely in the MMF 3 g, MMF 2 g, and AZA groups, respectively.

DISCUSSION

Treatment with cyclosporine, azathioprine, and prednisone is widely considered to be the most effective combination for prophylactic immunosuppression following cadaveric renal transplantation. Despite this therapy, acute graft rejection occurs in approximately one half of patients. In these patients, rejection requires additional immunosuppressive treatment and results in higher costs of diagnosis and treatment, a greater risk of morbidity and mortality, and an increased rate of graft loss. MMF is a potent immunosuppressant with a different mechanism of action from cyclosporine and prednisone, so that combination of these agents offers the potential to reduce both the incidence and the consequences of acute rejection. However, the use of more intensive immunosuppression may increase morbidity or mortality. Evaluation of therapy must therefore include an assessment of these outcomes in order to evaluate any net clinical benefit. A composite endpoint of treatment failure was therefore used as the primary efficacy analysis in this study and includes the occurrence of biopsy-proven graft rejection, graft loss, death, or withdrawal of therapy. Over 95% of first rejection episodes occurred within the 6-month period selected for the primary efficacy analysis.

The study shows a highly significant and clinically important difference in the rate of treatment failure between the two drugs examined. MMF reduced the incidence of biopsy-proven acute rejection by over one half in patients receiving 3 g/day and by almost one half in those receiving 2 g/day. The incidence of histologically severe rejection was substantially reduced, falling by up to 70% in patients receiving MMF 3 g/day. Graft loss was slightly lower in patients receiving MMF, although the incidence of death was not different between the treatment groups. Study drug was withdrawn at essentially equal rates among the treatment groups. Histological confirmation was requested but proved not to be possible in all cases of presumed acute rejection. Biopsy was either contraindicated or not technically feasible in approximately one half of such patients, while the histology obtained was noncontributory in the remaining patients who experienced presumed rejection. While some of these biopsies may have reflected a sampling effect due to the fact that graft rejection is a nonconfluent process, others indicated uncertainty or failed to substantiate the clinical diagnosis. A subsidiary analysis therefore included within the composite endpoint all episodes of presumed clinical acute rejection, independent of histological confirmation. MMF again showed a significant and clinically important reduction in the incidence of treatment failure over conventional therapy.

The rate of treatment for acute rejection was reduced by half in patients receiving MMF. The number receiving more than one course of treatment for rejection fell by two thirds in patients receiving MMF 3 g/day and by almost one quarter in those receiving MMF 2 g/day: The use of antilymphocyte antibodies for severe or resistant rejection was reduced by 68% and 40%, respectively. Although the study was not powered statistically to assess this outcome, the effect of MMF appeared to be dose dependent, with a lower treatment failure rate, incidence of acute rejection, histologic severity of rejection, requirement for antirejection treatment, and use of antilymphocyte antibodies in patients receiving the higher dose of the drug. The benefit of MMF was sustained throughout the first year of follow-up. The incidence of graft loss was slightly lower in both groups receiving this drug and was consistent with the reduced risk of acute rejection.

Patients receiving MMF reported a greater frequency of gastrointestinal side effects, characterized predominantly by abdominal pain, vomiting, and diarrhea. These symptoms generally occurred after the first posttransplant month. It cannot be established from this study if they were related to the occurrence of CMV in this site or if the increased diagnosis of CMV invasion was attributable to more frequent endoscopic investigation in these patients. The incidence of leukopenia was not perceptibly different among the treatment groups, although a fall in white blood cell count to less than 500/mm3 was reported only in patients receiving the higher dose of MMF.

The overall mortality rate during the first year of follow-up was identical within the three treatment groups. Despite the potency of immunosuppression, MMF did not increase the risk of bacterial or opportunistic infections in patients receiving MMF. The three cases of P carinii infection all occurred in patients receiving AZA, none of whom received prophylactic Bactrim. The overall incidence of CMV infection was comparable in the three treatment groups, although tissue invasion, predominantly confined to the gastrointestinal tract, was slightly more common in those receiving MMF 3 g/day. There was no increase in other viral infections. Malignancy appears slightly more common in patients receiving MMF, although the numbers are currently too small to make definitive statements. Lymphoproliferative disorders occurred in just over 1% of patients receiving MMF, a figure consistent with other forms of therapy (18, 19). No common etiology was identified: Only one patient on MMF received prior treatment with OKT3, and serologic evidence of Epstein-Barr virus infection in the donor and recipient was not systematically captured. Three of the four tumors, which were confined to the brain, resolved following withdrawal of MMF.

Mycophenolate mofetil appears to be an important addition in current clinical immunosuppression, reducing both the incidence and severity of graft rejection following renal transplantation. Treatment for rejection is required less frequently and the use of antilymphocyte antibodies for steroid-resistant rejection is markedly reduced in patients receiving this drug. The benefit of MMF is evident within the first 6 months after transplantation, and the reduction in early acute rejection appears to be reflected by a decline in graft loss by 1 year. It can be anticipated that with longer observation periods, the initial reduction in acute rejection episodes will translate into a significant improvement in graft survival. Whether MMF will prevent the development of chronic rejection either by suppressing subsequent acute rejection episodes or by directly inhibiting smooth muscle proliferation as has been shown in the experimental animal is not yet known (20).

The immunosuppressive effect of MMF was greatest at a dose of 3 g/day, although the net clinical benefit at this dose was offset by a slight increase in gastrointestinal toxicity and CMV tissue invasion. It has therefore been suggested that a more appropriate starting dose of MMF may be 2 g/day. The doses of both study drugs in this trial were controlled according to protocol, however, and only limited adjustments were possible. The use of a more flexible regimen permitting dosage adjustment according to clinical status may enable the dose to be tailored to individual needs and hence improve both the efficacy and tolerability of MMF in clinical practice. Finally, in this study, MMF was used in combination with full doses of both cyclosporine and prednisone. Whether this is necessary, or whether the use of MMF will permit a reduction in dose or elimination of either of these medications, remains to be established by subsequent studies.

Figure 1
Figure 1:
All treatment failures, including biopsy-proven rejection. A = AZA 100-150 mg (n=166); ○ = MMF 2 g (n=173); • = MMF 3 g (n=164).
Figure 2
Figure 2:
All treatment failures, including clinical or biopsy-proven rejection. A = AZA 100-150 mg (n=166); ○ = MMF 2 g (n=173); • = MMF 3 g (n=164).
Figure 3
Figure 3:
Antirejection therapies: speckled bar = MMF 3 g (n=164); striped bar = MMF 2 g (n=171); solid bar = AZA 100-150 mg (n=162).

Footnotes

This study was sponsored by a grant from Syntex (U.S.A.), Inc., Palo Alto, CA.

Abbreviations: AZA, azathioprine; CI, confidence interval; CMH, Cochran-Mantel-Haenszel; CMV, cytomegalovirus; MMF, mycophenolate mofetil; MPA, mycophenolic acid; PRA, panel reactive antibody; PTLD, posttransplant lymphoproliferative disorder.

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