Effect of Continuous B Cell Depletion With Rituximab on Pathogenic Autoantibodies and Total IgG Levels in Antineutrophil Cytoplasmic Antibody–Associated Vasculitis

Objective: To evaluate the effect of rituximab on pathogenic autoantibodies and total Ig levels, and to identify serious adverse events in patients with antineutrophil cytoplasmic antibody (ANCA)–associated vasculitis (AAV) treated with continuous B cell depletion. Methods: We conducted a retrospective analysis of 239 patients with AAV treated with rituximab-induced continuous B cell depletion. Two treatment cohorts were analyzed: an induction group (n = 52) and a maintenance group (n = 237). Changes in ANCA titers and total Ig levels over time were evaluated using mixed-effects models. Risk factors for serious infections during maintenance treatment were evaluated using Poisson regression. Results: During induction, IgG levels fell at a mean rate of 6% per month (95% confidence interval [95% CI] 4, 8%), while ANCA levels declined at a mean rate of 47% per month (95% CI 42, 52%) and 48% per month (95% CI 42, 54%) for patients with antimyeloperoxidase (anti-MPO) antibodies and those with anti–proteinase 3 (anti-PR3) antibodies, respectively. During maintenance treatment, with a median duration of 2.4 years (interquartile range 1.5, 4.0 years), IgG levels declined a mean of 0.6% per year (95% CI −0.2, 1.4%). New significant hypogammaglobulinemia (IgG level of <400 mg/dl) during maintenance treatment occurred in 4.6% of the patients, all of whom were in the lowest baseline IgG quartile. Serious infections during maintenance therapy occurred at a rate of 0.85 per 10 patient-years (95% CI 0.66, 1.1) and were independently associated with an IgG level of <400 mg/dl. Conclusion: B cell–targeted therapy causes a preferential decline in ANCA titers relative to total IgG levels. Despite prolonged maintenance therapy with rituximab, IgG levels remain essentially constant. Serious infections were rare.