Key Inclusion Criteria:

   - Clinical diagnosis Wegener's granulomatosis or microscopic polyangiitis by Chapel Hill
   criteria.

   - Disease flare in the past 26 weeks requiring treatment with high dose corticosteroids
   and 1 of the following medications: rituximab, oral cyclophosphamide OR IV
   cyclophosphamide.

   - Tested positive for anti-proteinase 3 (anti-PR3) or anti-myeloperoxidase (anti-MPO)
   antibodies at any time prior to enrollment.

   - Achieve remission no more than 26 weeks after first dose of induction treatment.
   Remission is defined as a Birmingham Vasculitis Activity (BVAS) score of 0 and
   receiving less than 10 mg/day of oral prednisone (or equivalent) on 2 consecutive
   visits 21 to 35 days apart.

   - Maintenance therapy on this study must start no more than 2 weeks after confirmation
   of remission.

Key Exclusion Criteria:

   - Pregnant or nursing.

   - Receipt of a B cell targeted therapy (other than rituximab) at anytime

   - Receipt of an investigational biological agent within the past 60 days.

   - Required management of acute or chronic infections within the past 60 days.

   - Current drug or alcohol abuse or dependence.

   - Current or past positive test for human immunodeficiency virus (HIV), hepatitis B, or
   hepatitis C.

   - History of severe allergic reaction to contrast agents or biological medicines.