Inclusion Criteria:

• Clinical diagnosis of granulomatosis with polyangiitis (Wegener's) or microscopic polyangiitis
• Male and female subjects, aged at least 18 years, with newly-diagnosed or relapsed AAV where treatment with cyclophosphamide or rituximab is needed; where approved by Regulatory Agencies, adolescents (12-17 year old) may be enrolled
• Use of adequate contraception
• Positive test for anti-PR3 or anti-MPO
• At least 1 major item, or at least 3 non-major items, or at least the 2 renal items of proteinuria and hematuria on BVAS
• Estimated glomerular filtration rate ≥15 mL/minute/1.73 m^2 at screening

Exclusion Criteria:

• Pregnant or breast-feeding
• Alveolar hemorrhage requiring pulmonary ventilation support at screening
• Any other known multi-system autoimmune disease
• Required dialysis or plasma exchange within 12 weeks prior to screening
• Have a kidney transplant
• Received cyclophosphamide within 12 weeks prior to screening; if on azathioprine, mycophenolate mofetil or methotrexate at the time of screening, these drugs must be withdrawn prior to receiving the cyclophosphamide or rituximab dose on Day 1
• Received intravenous glucocorticoids, >3000 mg methylprednisolone equivalent, within 4 weeks prior to screening
• Have been taking an oral daily dose of a glucocorticoid of more than 10 mg prednisone-equivalent for more than 6 weeks continuously prior to screening
• Received rituximab or other B-cell antibody within 52 weeks of screening or 26 weeks provided B cell reconstitution has occurred (i.e., CD19 count > 0.01x10^9/L); received anti-TNF treatment, abatacept, alemtuzumab, IVIg, belimumab, tocilizumab, or eculizumab within 12 weeks prior to screening
• For patients scheduled to receive cyclophosphamide treatment, urinary outflow obstruction, active infection (especially varicella zoster infection), or platelet count <50,000/μL before start of dosing
• Participated previously in a CCX168 study