Introduction
Idiopathic nephrotic syndrome (INS) is characterized by severe proteinuria, hypoalbuminemia, dyslipidemia, and thrombogenic tendency. INS affects 2 to 2.7 new children per 100,000 children per year, in Western countries, with a prevalence of 16 cases per 100,000 children (1 2 – 4 5 – 7 7
Prednisone is the cornerstone of therapy for INS, inducing remission within 4 weeks in approximately 90% of cases. However, the risk of clinical relapse can be as high as 85% at 5 years (8 9 , 10 11
Rituximab (RTX) is a genetically engineered chimeric murine/human monoclonal antibody directed against the CD20 antigen on the surface of B lymphocytes that inhibits B cell proliferation and differentiation. Rituximab was first introduced in clinical practice for the treatment of non-Hodgkin's lymphoma and then extended to autoimmune diseases (12 13 14 , 15 16 12 , 17 , 18 19 – 22 versus the standard approach in children with INS dependent on both these agents.
Materials and Methods
Design Overview
Eligible participants entered a 1-month run-in period during which proteinuria was monitored, compliance assessed, calcineurin inhibitors dose maintained constant, and prednisone dose tentatively reduced to the minimum amount of the previous 6 months. During run-in, instructions on urine collection and dipstick readings were carefully reviewed. After run-in, children were centrally allocated to continue standard therapy alone or add RTX independent of the current level of proteinuria. Assignments followed permuted block randomization lists (stratified by center and signs of toxicity) with blocks of variable size. Clinical investigators and study nurses enrolling patients were not blinded to group assignment. However, study staff responsible for facilitating follow-up data measurements were blinded. An independent data safety monitoring board reviewed safety data when half of the participants had been enrolled and at study end. The protocol and consent documents were approved by the ethics committees at each participating center.
Setting and Participants
Participants in this study had to be 16 years old or younger with an estimated creatinine clearance >60 ml/min per 1.73 m2 . They had to have a history of INS responsive to, and dependent on, both prednisone and calcineurin inhibitors for at least 1 year with a remission of at least 6 months (daily proteinuria <4 mg/m2 per hour). INS was diagnosed in the presence of nephrotic range proteinuria (>40 mg/m2 per hour or >1 g/d per m2 , or protein to creatinine ratio [P/C] >4 in a single urine specimen) or between 5 and 40 mg/m2 per hour associated with hypoalbuminemia or dyslipidemia. Genetic testing and renal biopsy were not required as childhood INS is a clinical diagnosis based on the response to prednisone and calcineurin inhibitors. Criteria for exclusion were as follows: infantile onset (<1 year); previous history of macro-hematuria, hepatitis B, hepatitis C, or HIV infection; positivity of any marker of autoimmunity (ANA, nDNA, ANCA); and low C3 levels. Patients requiring diuretics, albumin, or anticoagulant therapy were also temporarily excluded.
Steroid dependence was defined as responsiveness to full doses of prednisone (2 mg/kg) and calcineurin inhibitors (5 mg/kg) with two consecutive relapses occurring during prednisone tapering or within 2 weeks of prednisone withdrawal. Steroid dependence could have been present since the beginning of prednisone therapy or developed after an initial resistance to prednisone monotherapy. In the first case, the addition of a calcineurin inhibitor was required after at least 6 months of prednisone monotherapy to maintain remission. In the other case, calcineurin inhibitors modified the response to therapy. Angiotensin-converting enzyme inhibitors (ACEIs) or angiotensin-receptor blockers (ARBs) were used at the discretion of the investigators but were kept constant during the study. Criteria for toxicity due to steroids and/or calcineurin inhibitors are summarized in Table 1 .
Table 1: Criteria for toxicity to standard medications
Overall, between 2007 and 2008, we screened 150 INS patients, most of whom were excluded because of sensitivity to, or dependency on, low-dose prednisone monotherapy. Children with INS resistant to prednisone and calcineurin inhibitors, or dependent on high prednisone doses (0.7 mg/kg per day), were also excluded (Figure 1 ). Children dependent on steroids and calcineurin inhibitors who showed signs of toxicity were initially enrolled separately (EudraCT 2007-007796-16) from those without toxicity (EudraCT 2008-004486-26) and subsequently treated as separate strata of the same trial.
Figure 1: Number of patients who were screened for the study, who underwent randomization, and who completed the study .
Intervention Strategy and Standard Therapy
The intervention strategy was based on RTX and reduced doses of prednisone and calcineurin inhibitors. Tapering was done following the scheme below that allows drug withdrawal within 45 days. Rituximab (Mabthera; 375 mg/m2 ) was given intravenously once (at randomization in the absence of clinical signs of toxicity secondary to steroids and/or cyclosporine; see Table 1 ) or twice (at randomization and after 2 weeks in the presence of toxicity). The medication was diluted in normal saline (1 mg/ml) and administered at increasing speeds (0.5 to 1.5 ml/min) over approximately 6 hours. The infusion was preceded by 2.5 to 5 mg of intravenous chlorfenamine maleate, 2 mg/kg methyl prednisolone in normal saline, and 8 mg/kg of oral paracetamol. Starting at 30 days, prednisone was tapered off by 0.3 mg/kg per week if proteinuria was <1 g/d. After 2 weeks, calcineurin inhibitors were also decreased by 50% and withdrawn after 2 additional weeks.
The standard strategy was based on prednisone and calcineurin inhibitors alone. Doses of these agents could be tapered off as in the intervention strategy if proteinuria was <1 g/d. In both groups relapses had to be treated with prednisone (maximum dose of 2 mg/kg per day).
Outcomes and Follow-up
Children were seen by the nephrologist responsible for the study at the beginning and at the end of the study, and as many times as necessary in case of complications or relapses. Study coordinators maintained ongoing contact with the children and the families to monitor clinical status and report potential adverse events. BP was measured at regular intervals (2 times per week) by the family pediatrician who contacted the referent nephrologist for data reporting and therapy update.
Urine protein excretion was measured weekly on 24-hour urine collection, or more often in case of dipstick positivity. Determination of proteinuria at baseline and after 3 months was performed at a central laboratory. Dipstick for proteinuria determination was evaluated daily. In case of dipstick positivity, the presence of proteinuria was confirmed with 24-hour urine collection. Kidney function, plasma proteins, and cholesterol were obtained monthly. Counts of white blood cells and lymphocyte populations were monitored monthly in the RTX group. The primary efficacy measure was the percentage change in daily proteinuria at 3 months in children receiving RTX versus those on standard care.
The risk of relapse at 3 months was a secondary outcome. Relapse was diagnosed in the presence of proteinuria >40 mg/h per m2 (P/C >4; full relapse) or of proteinuria of 20 to 40 mg/h per m2 (P/C 2 to 4; partial relapse) and hypoalbuminemia or dyslipidemia.
Statistical Analyses
We estimated that 54 participants were necessary to demonstrate with a power of 90% that RTX was noninferior to standard care in maintaining proteinuria at 3 months as low as baseline levels or lower, or up to 1 g/d greater (noninferiority margin). We assumed a log-normal distribution of the response, with a coefficient of variation of 1.5 on the original scale (mean 0.5 and SD 0.75 g/d), and a geometric mean ratio of 3 as noninferiority margin. The estimation accounted for a 5% risk of withdrawals and multiple comparisons (effect of RTX by presence/absence of toxicity) (23 http://www.R-project.org
Results
Patient Characteristics
Fifty-four patients were randomized. Baseline characteristics are summarized in Table 2 . Children were on average 11 years old and tended to be male. Disease duration was on average 6.7 years. Signs of toxicity were present in 24 children. In these patients, calcineurin inhibitor treatment had been carried out for longer periods than in those without toxicity (6.25 ± 3.3 versus 5.0 ± 3.5 years, P = 0.184) and both prednisone doses and levels of proteinuria tended to be higher (Figure 2 ). All children but two were still on full maintenance doses of calcineurin inhibitors at randomization, defined as the minimum oral amount necessary to achieve trough levels of 50 to 100 and 5 to 10 ng/ml, respectively, for cyclosporine and tacrolimus (for details, see Table 2 ). Average proteinuria was similar by treatment arm at screening and baseline (although overall greater than anticipated), as were average prednisone doses. There were no differences between groups in terms of additional therapies (ARBs and ACEIs), levels of kidney function, serum albumin, and cholesterol levels. ARBs and ACEIs use was limited in patients with hypotension and calcineurin inhibitors toxicity because of their known additive effect (24
Table 2: Baseline characteristics
Figure 2: The plots summarize the distribution of proteinuria (g/d [log-scale]), prednisone [PDN] in mg/kg per day, and proportion of children on full dose of calcineurin inhibitors [CNI, i.e., cyclosporine or tacrolimus] over time in weeks from randomization (time zero) . Dark gray bars refer to patients assigned to RTX-based strategy; light gray bars refer to standard therapy strategy. The plot on the left (all patients) refers to model 1 in
Table 3 ; the middle and right plots refer to model 2 in
Table 3 . The line across the box plots (proteinuria and prednisone plots) is the median, the box hinges are the 25th and 75th percentiles, and the outliers are represented as dots lying beyond 1.5 times the interquartile range.
Effectiveness
Table 3 summarizes the results of regression analysis. Rituximab use allowed the maintenance of remission despite progressive reduction and withdrawal of prednisone. Overall 3-month proteinuria was 70% lower in children who received RTX as compared with controls (95% confidence interval [CI] 35% to 86% lower). Prednisone was withdrawn in all but one child in the RTX arm. Control patients without toxicity had a modest increment of proteinuria during the prednisone reduction at 4 weeks that required resuming previous prednisone dose (Figure 2 ). In children with toxicity, 3-month proteinuria was not significantly different by treatment group (average change −35.66%, 95% CI −78.62% to 93.66%, i.e. , below the noninferiority margin of 3 times). However, the use of RTX made it possible to withdraw prednisone in all but four children with toxicity, two of whom had, however, a 50% and 60% reduction of the initial dose. Overall, the proportion of children in whom calcineurin inhibitors withdrawal was possible without change in proteinuria was also higher in the RTX group (56% versus 4%, P < 0.001). Vice versa , remission was maintained at the cost of unchanged doses of prednisone and calcineurin inhibitors in the standard therapy group. Children with toxicity required overall higher doses of all medications. No other factor (including histology) affected the outcome or modified the effect of RTX.
Table 3: Proteinuria at study end (ANCOVA model of log-proteinuria)
Secondary Outcome and Follow-up Data
The risk of disease relapse at 3 months was 48.1% in the control group (n = 13) versus 18.5% (n = 5) in the intervention group (odds ratio 4.08, 95% CI 1.19 to 13.9; P = 0.029). The probabilities of being prednisone-free and prednisone and calcineurin inhibitors–free at 3 months were 77.8% (n = 21) and 62.9% (n = 17) in the intervention group and 7.4% (n = 2) and 3.7% (n = 1) in the control group (P < 0.001 for both comparisons), respectively. One-year relapse-free survival after RTX therapy is described in Figure 3 . At 6 and 12 months, respectively, 50% and 25% of the children assigned to RTX were still in remission without prednisone or calcineurin inhibitors. Sixteen patients in the control group were switched to RTX after 3 months because of family request and ethical committee approval. Eleven children continued with standard doses of prednisone and calcineurin inhibitors for continuous relapsing episodes (not shown).
Figure 3: Twelve-month relapse-free survival from randomization in children assigned to RTX therapy (n = 27)
Adverse Events
One patient developed bronchospasm and hypotension at the second RTX infusion. Treatment was discontinued with spontaneous recovery. Two other cases required RTX infusion in intensive care for initial bronchospasm, which improved after slowing the infusion rate. Two patients presented fever with migrating skin rash and acute arthritis at the hip joint after 2 and 6 days from RTX infusion. Resolution was rapidly and completely achieved (24 to 48 hours) with nonsteroidal anti-inflammatory medications. CD20 counts were reduced to <1% at the first month in all RTX-treated patients. After 3 months CD20 count was still undetectable in all but three cases (one with toxicity and two without toxicity).
Discussion
The present trial shows that in children with INS responsive to and dependent on prednisone and calcineurin inhibitors, RTX therapy is noninferior to standard therapy in maintaining disease remission with reduced use of standard agents. In our study, disease remission was maintained for 3 months with one single dose of RTX in children without toxicity and with two doses administered 2 weeks apart in children with toxicity despite prednisone and calcineurin inhibitors reduction or withdrawal. This is the first randomized study showing the potential utility of RTX in achieving the dual goal of maintaining disease remission and reducing/withdrawing standard agents in children with INS sensitive to a combination of prednisone and calcineurin inhibitors. In these children, calcineurin inhibitors are often added to prednisone because of development of steroid toxicity or steroid resistance after initial steroid dependence, or because of steroid resistance “ab initio”. Overall, they differ from patients who manifest a clear resistance to any drug and belong to potentially different disease cohorts, including genetically mediated forms of INS (4 , 25
Although responsiveness to therapies makes INS less dramatic in these children, the need for long-term use of prednisone and calcineurin inhibitors exposes them to serious side effects (26 19 – 22
A noninferiority study design was chosen to address the question of whether RTX allowed maintenance of remission in dependent INS while reducing/withdrawing prednisone and calcineurin inhibitors therapy. We hypothesized that RTX and lower/suspended doses of standard therapies were as effective as a combination of standard doses of prednisone and calcineurin inhibitors in maintaining 3-month remission. Although attempts to lower the doses of prednisone and calcineurin inhibitors were possible in the standard strategy arm, only in children who received RTX was disease remission maintained with lower doses of (or without) standard agents. The presence of drug toxicity to prednisone and calcineurin inhibitors and the pathology score did not substantially modify the effect of RTX. Most importantly, prednisone and calcineurin inhibitors withdrawal was rapidly possible in most children who received RTX with a median relapse-free survival longer than 1 year. Importantly, at 6 and 12 months, respectively, as many as 50% and 25% of the children assigned to RTX were still in remission without prednisone or calcineurin inhibitors. On clinical grounds this is a clear benefit that, in case of significant toxicity, is extremely required. Individual and disease-related factors may affect the duration of the response to RTX. Whether additional RTX doses can prolong remission remains to be tested in clinical trials once the safety profile of RTX is confirmed by long-term follow-up data.
The rationale for use of RTX in INS is, unfortunately, based on limited biologic knowledge. Interference of RTX with T helper cells and T regulatory and circulating plasma factors has been proposed (27 – 29 30 31 32
Our study has limitations. In terms of study design, lack of blinding raises the issue of measurement bias and differential cointerventions. However, proteinuria is an objective outcome, staff responsible for patient follow-up were kept blind, the use of medications interfering with the renin-angiotensin system was maintained constant during the study, and prednisone and calcineurin inhibitors dose adjustment was defined per protocol.
Although our study suggests that RTX is effective in achieving the dual goal of maintaining disease remission and reducing the use of toxic agents, several questions remain unaddressed. First, we do not know the extent to which one or two doses of RTX affect the long-term outcomes of the disease including relapse rates, need for additional prednisone and calcineurin inhibitors courses, impairment of kidney function, and management costs (e.g. , 2 RTX doses cost approximately the same as a 1-year treatment with cyclosporine or as 6 months therapy with tacrolimus).
Second, studies with adequate follow-up are necessary to assess the long-term safety of RTX. Potential complications have been described, such as lung fibrosis (33 34 e.g. , JC virus—the etiologic agent of progressive multifocal leukoencephalopathy) in urine and blood cells and data on B cell deprivation are essential requirements for a long-term follow-up program. Finally, kinetic studies are also necessary as proteinuria may affect the metabolism of RTX and its urinary elimination.
In conclusion, our study suggests that RTX is noninferior to prednisone and calcineurin inhibitors in maintaining short-term remission of INS dependent on both these agents. One-year relapse-free survival probabilities of 50% can be achieved with one or two doses of RTX and reduced use of calcineurin inhibitors and prednisone. Longer follow-up studies are necessary to confirm efficacy and safety of RTX in children with INS dependent on both prednisone and calcineurin inhibitors.
Disclosures
None.
Acknowledgments
The present study was investigator-initiated and -driven. All members of the study steering committee are listed as authors of the present report, had access to the study data, and vouch for the accuracy and completeness of the data reported.
The Institute Giannina Gaslini provided financial and logistic support to the trial. This work was also supported by the Italian Ministry of Health “Ricerca Corrente ”, the Renal Child Foundation, Fondazione Mara Wilma e Bianca Querci (project “Ruolo dello stress reticolare nella progressione del danno renale e tumurale ”) , and Fondazione La Nuova Speranza (“Progetto integrato per la definizione dei meccanismi implicati nella glomerulo sclerosi focale ”).
Data Safety and Monitoring Board members included Antonella Trivelli, Giovanni Candiano, Giorgio Piaggio, and Gianluca Caridi.
Published online ahead of print. Publication date available at www.cjasn.org
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