Rituximab Versus Steroids and Cyclophosphamide in the Treatment of Idiopathic Membranous Nephropathy

Idiopathic Membranous nephropathy (IMN) is an immune-mediated glomerular disease characterized by deposition of IgG4 antibodies in the subepithelial area of the glomerular basement membrane (GBM). Proteinuria is the hallmark of the disease. The commonest presentation of IMN is nephrotic syndrome with preserved kidney function. The natural course of the disease can be variable and may be punctuated with spontaneous remissions and relapses. In about 20% of patients, there is spontaneous complete remission of the nephrotic syndrome, and another 15-20% undergo partial remission; about 30% of patients may remain with fluctuating proteinuria and about 30% may progress to end-stage renal disease (ESRD). However, data from natural history studies and placebo arms of intervention studies with follow-up lasting more than 10 years show that about 30-40% of the untreated patients with persistent nephrotic syndrome progress to ESRD.

Complete remission of nephrotic syndrome predicts excellent long-term kidney and patient survival, and partial remission also significantly reduces the risk of progression to ESRD. Therefore, persisting remission of the nephrotic state is an acceptable surrogate end-point to assess efficacy of treatment. The primary aims of treatment, therefore, are to induce a lasting reduction in proteinuria. The best-validated regimen is combination therapy with corticosteroids and cyclophosphamide ("Ponticelli" regimen). This treatment is superior to supportive therapy alone in inducing remissions and preventing long-term decline of kidney function in patients with idiopathic MN and persisting nephrotic syndrome. However, there are concerns about the use of cyclophosphamide, since its use may be associated with adverse events, leading to treatment interruption in about 9% of patients. These adverse events include bone marrow suppression, gonadal toxicity, infections and oncogenic effects.

Thus, the availability of alternative therapies highly effective but with a greater safety profile is desirable.

Recent human studies confirmed that MN is an autoimmune disease, suggesting that the disease may be triggered by isotype specific autoantibodies directed against podocyte enzymes and podocyte receptors that are recognized as antigens, including M-type phospholipase-2 receptors(PLA2R1) and thrombospondin type 1 domain-containing 7A (THSD7A). The podocyte expression of these autoantigens can trigger the production of specific antibodies and in situ deposits of immune complexes, with consequent activation of complement cascade, oxygen radicals, and other inflammatory pathways leading to tissue injury and fibrosis. Additional autoantibodies, directed to podocyte neo-expressed cytoplasm proteins have been described, including aldose reductase (AR), Mn-superoxide dismutase (SOD2) and alpha-enolase (alpha-ENO).

However, the mechanisms eliciting the expression of these neoantigens on podocytes and regulating the deposition of the auto-antibodies on the subepithelial surface of the glomerular basement membrane is not known.

Considering the potential role of IgG antibodies in the pathogenesis of IMN, B cell depletion may favourably impact the glomerular disease as reflected by a reduction in proteinuria. The anti-CD20 monoclonal antibody Rituximab is a selective B cell depleting agent, capable to maintain B cells undetectable for 3-12 months. There is evidence that this strategy is effective in the treatment of other diseases in which B cells play a key role, such as ANCA-related vasculitis and humoral allograft rejection. Preliminary studies in IMN are promising, with observational studies providing encouraging data; in addition, the drug seems well tolerated with minimal adverse events.

Head-to-head comparisons between Rituximab and steroid plus ciclophosphamide in randomized clinical trials are missing.

The investigators propose this study in order to test in a randomized controlled trial the hypothesis that selective B lymphocyte depletion obtained with Rituximab is more effective than cyclical corticosteroid/alkylating-agent therapy in inducing long-term remission of proteinuria in patients undergoing the initial treatment of with IMN and nephrotic syndrome. In addition, since specific assay for the above-mentioned autoantibodies are now available, the levels of these pathogenetic autoantibodies will be measured at baseline and during treatment. Finally, the study will compare the safety profile of steroid plus cyclophosphamide and Rituximab by evaluating the rate and severity of adverse events.

Design and Power Considerations

The investigators hypothesized that the remission probability in the RTX arm will be greater than in the active comparator group (superiority design). Available data (Ponticelli 1998) suggest that the probability of complete remission with standard therapy is 15% at one year.

The investigators plan to enroll 70 patients in this pilot RCT. This sample size will be able to detect with a power of 80% (and a two-sided P of 0.05) an odds ratio of 3, i.e. change in probability from 0.15 to 0.45 - a very optimistic effect. Smaller (and likely more reasonable) effects would require larger studies.

The study will provide an estimate of this true effect, if it exists.

Adverse effects:

Patients will be directly questioned every two weeks during the drug exposure and then at monthly intervals during follow-up. In addition a contact number will be provided to the subjects to call if they experience any adverse affect or if they suspect adverse effect at any time between specific visits

Definition Of Proteinuric Status

UP = urinary protein (g/24h)

Complete remission (CR) UP ≤ 0.3 g

Partial remission (PR): Reduction in UP of > 50% plus final UP ≤ 3.5 g but >0.3g

Non-response (NR): Reduction in UP of < 50% (includes increase in UP <50%)

Neither CR nor PR

Progression: Proteinuria /S. creatinine increases by > 50% over the baseline