Tailoring Maintenance Therapy to Cluster of Differentiation 5 Positive (CD5+) Regulatory B Cell Recovery in ANCA Vasculitis

ANCA vasculitis is a pauci-immune systemic small vessel vasculitis. The anti-neutrophilic cytoplasmic antibodies (ANCA) are pathogenic and cause disease by activating neutrophils which damage blood vessels. CD means "cluster of differentiation" . CD5 is a type I transmembrane protein found on T cells, thymocytes, and some B cells. Cluster of Differentiation 20 (CD20) is a type III transmembrane protein found on B cells. The investigators previously detected an association between recovery of Interleukin 10 (IL-10)-secreting CD20+ and CD5+ regulatory B cells after immunotherapy (with rituximab and corticosteroids) and decreased risk of subsequent relapse in patients with ANCA-vasculitis. The investigators hypothesize that patients with complete reconstitution of a functional regulatory B cell repertoire after induction therapy are at low risk of relapse and may be monitored conservatively without further immunotherapy. The investigators will test this hypothesis through a proof of concept randomized controlled study. Patients with normalization of CD5+ regulatory B cells will be randomized to maintenance therapy with rituximab vs. close observation without immunosuppression. Patients whose peripheral CD5+ regulatory B cells remain low after induction therapy (who are at higher risk of relapse), will receive maintenance immunosuppression with rituximab. Patients needing or randomized to maintenance therapy who are unable to receive rituximab will receive azathioprine or mycophenolate mofetil, two standard alternative medications for maintenance immunosuppression.