New insights into immune mechanisms underlying response to Rituximab in patients with membranous nephropathy: A prospective study and a review of the literature

Idiopathic membranous nephropathy (MN) is a common immune-mediated glomerular disease and the main cause of nephrotic syndrome (NS) in Caucasian adults. Rituximab (RTX) has been reported to safely reduce proteinuria in patients with primary MN and severe NS. However, the effects of RTX treatment on T-cells including regulatory T-cells (Treg) in MN have not been fully determined.Seventeen patients [mean age 67 (29-86) years, 6 women, 11 men] with biopsy-proven MN, and persistent proteinuria >3.5 g/24h were prospectively enrolled and received RTX, 375 mg/m(2) (iv) on days 1, 8, 15 and 22. Changes in circulating B and T cell homeostasis were examined in the peripheral blood by flow-cytometry studies; serum levels of IL-35 were measured using a high-sensitivity ELISA kits (baseline, at month 3, 6, 9 and 12).Patients had been followed-up for a mean of 36.3 months (24-48). Proteinuria decreased from 5.6 (3.5-8) g/24h to 2.4 (0.06-13) g/24h at 6 months (p<0.05) and to 1.3 (0.06-8) at 12 months (p<0.01), respectively after therapy with RTX. Four patients received a 2nd course of RTX (one at 6 months because of persistent NS, and three at 12, 18, or 30 months for relapse). The three relapsing patients became proteinuria-free (<0.5 g/24h) in the following 6 months. Serum creatinine remained stable during the follow-up: median 1mg/dl (0.7-1.6) at 12 months and 1.1 (0.7-1.7) at 24 months as compared to 1 (0.5-2.4) at baseline. At 6 months after RTX, complete remission (CR) was observed in 7 patients, partial remission (PR) in 4, while 6 were non responders (NR) non responder (NR). At the end of the follow-up, 14 patients were in CR, 1 in PR, while 2 were NR. In the T-cell compartment, upon detection of B cell depletion, there was an increase in Treg up to 10-fold when comparing baseline and at month 12 (mean ± SD 1.2 ± 0.6%, and 5.8 ± 0.7% p=0.02, respectively). When stratifying patients in responders (CR+PR) and NRs at month 12, we observed a significant increase in Treg cells from month 6 which persisted till 12 months only in the responder group (5.5 ± 0.6% and 1.1 ± 0.6%, p=0.04, respectively in responders and NRs). A statistically significant decrease in the levels of active T-lymphocytes (HLA-DR+CD8+ cells) was observed, with a maximum reached at 12 months after treatment with RTX [6 ± 1.1% baseline, 4.7 ± 1.7% at 6 months (p=0.043) and 1.5 ± 1.4% at 12 months (p=0.05)]. A marked increase in IL-35 levels [defined as delta >40% (serum values at 6 months minus baseline values)] was seen in 68% of the patients who achieved clinical response (CR or PR) at 12 month, but in none of the patients who failed to respond (p=0.034).Our findings and data from literature support the idea that RTX can be envisaged as a first-line therapy for patients at risk of progression because of persistent NS due to idiopathic MN. Insights into the putative T cell-related mechanisms of action have been discussed.