A Phase IIa Study of Intravenous Rituximab in Pediatric Participants With Severe Granulomatosis With Polyangiitis (Wegener's) or Microscopic Polyangiitis

Inclusion Criteria

• Diagnosis of GPA (EULAR/PRINTO/PRES 2008, Ankara criteria for childhood Wegener's granulomatosis) or diagnosis of MPA (according to the Chapel Hill Consensus Conference)
• Newly diagnosed participants or participants with relapsing disease according to the following definition:

The recurrence or new onset of potentially organ- or life-threatening disease (i.e. one or more major Birmingham Vasculitis Activity Score for Wegener's Granulomatosis [BVAS/WG] items or disease severe enough to require treatment with cyclophosphamide)

• For participants of reproductive potential (males and females), use of reliable means of contraception throughout the study participation
• For all eligible participants mandatory prophylactic treatment for Pneumocystis jirovecii infection

Exclusion Criteria

• Diagnosis of Churg-Strauss syndrome, as defined by the Chapel Hill Consensus Conference
• Limited disease that would not normally be treated with cyclophosphamide
• Severe disease requiring mechanical ventilation due to alveolar hemorrhage
• Requirement for plasmapheresis or dialysis at screening
• Incomplete recovery from recent surgery or less than (<) 12 weeks since surgery prior to baseline or planned within 24 weeks of baseline
• Lack of peripheral venous access
• Pregnancy or breast-feeding
• Evidence of other significant uncontrolled concomitant disease, or of disorder or condition that, in the investigator's opinion, would preclude or interfere with participation of participant
• Primary or secondary immunodeficiency (history of or currently active), including known history of human immunodeficiency virus (HIV) infection
• Evidence of active tuberculosis (participants receiving chemoprophylaxis for latent tuberculosis infection are eligible for the study)
• Known active infection of any kind (excluding fungal infections of nail beds), or any major episode of infection requiring hospitalization or treatment with IV anti-infective agents within 4 weeks of baseline or completion of oral anti-infective agents within 2 weeks prior to baseline. Entry into this study may be reconsidered once the infection has fully resolved
• History of deep space/tissue infection within 24 weeks prior to baseline
• History of serious recurrent or chronic infection
• History of cancer (except for basal cell and squamous cell carcinoma of the skin that have been excised and cured)
• Currently active alcohol or drug abuse or history of alcohol or drug abuse
• History of severe allergic or anaphylactic reaction to a biologic agent or known hypersensitivity to any component of rituximab or to murine proteins
• Treatment with rituximab or other biologic B cell-targeted therapy (e.g., anti- Cluster of Differentiation [CD] 19, anti-CD20, anti-CD22, or anti-B-lymphocyte stimulator [BLys]/B-cell activating factor [BAFF]) within 6 months prior to baseline visit
• Previous treatment with an anti-alpha 4 integrin antibody or co-stimulation modulator
• Previous treatment with other cell-depleting therapies, including, but not limited to, investigational agents (e.g., alemtuzumab, anti-CD4, anti-CD5, anti-CD3, and anti-CD11a)
• Receipt of oral or IV cyclophosphamide within the previous 4 months prior to the baseline visit
• Receipt of infliximab within 3 months, adalimumab within 2 months or etanercept within 1 month prior to the baseline visit
• Treatment with any investigational agent within 28 days of baseline or 5 half-lives of the investigational drug (whichever is longer)
• Receipt of any live attenuated vaccine within 28 days prior to baseline
• Intolerance or contraindications to IV glucocorticoids
• Positive serum human chorionic gonadotropin measured at screening or a positive pregnancy test prior to the first rituximab infusion for participants of childbearing potential
• Positive tests for hepatitis B surface antigen (HBsAg), hepatitis B core antibody (HBcAb), hepatitis B virus (HBV), or hepatitis C serology
• Level of Immunoglobulin (Ig