Rituximab-associated Hypogammaglobulinemia in ANCA-associated Vasculitis: Incidence and Time Course

Objective: Rituximab (RTX) is approved for remission induction and maintenance of antineutrophil cytoplasmic antibodies (ANCA)-associated vasculitis (AAV). Observational studies demonstrate decline in immunoglobulin (IgG) in AAV post-RTX. The time course for the onset of hypogammaglobulinemia (Hypo-IgG) post-RTX is unknown. This is a key determinant in deciding whether to continue RTX for reinduction or maintenance of remission for AAV. We evaluated the trends of Hypo-IgG among AAV patients post-RTX therapies. Methods: An observational single-tertiary-center study of AAV patients treated with RTX for remission induction or maintenance (induction therapy, maintenance therapy, and combined induction and maintenance therapy) between 1998 and 2018. Poisson regression was used to compare the incidences of Hypo-IgG: mild (450-700 mg dL(-1)), moderate (200-450 mg dL(-1)), and severe (<= 200 mg dL(-1)). Ig levels were measured every 3-6months after RTX use. Results: Mean (SD) age at last visit was 59 (16) years, 93% were Caucasians, 64% were females, and 71 (63%) had granulomatosis with polyangiitis (GPA). Hypo-IgG occurred in 47 patients: one (2%) severe, 13 (28%) moderate, and 33 (70%) mild. Lower incidences of mild Hypo-IgG post-RTX were seen during induction compared to maintenance (IR 5.04 per 100 000 days vs 5.45 per 100 000 days, incidence rate ratio (IRR) 1.08, 95% CI 0.34, 3.19). Moderate Hypo-IgG occurred at 2.29 per 100 000 days during induction and 1.82 per 100 000 days during maintenance (IRR 0.79, 95% CI 0.08, 4.84). Conclusion: Hypo-IgG is common among AAV treated with RTX, occurring in 42% of patients in this single-center cohort. The nadir IgG levels occur during remission induction, and the IgG levels remain relatively stable or increase over time in those receiving RTX for remission maintenance.