Phase 2 Study Evaluating Rapcabtagene Autoleucel in Participants With Severe Active GPA or MPA

This is a Phase 2, randomized, assessor-blinded active controlled study. This study comprises two cohorts: * A lead-in cohort enrolling participants to receive rapcabtagene autoleucel * A randomized cohort with participants receiving either rapcabtagene autoleucel or comparator. After end of study (EOS), participants who received rapcabtagene autoleucel infusion will enter a long-term follow-up (LTFU) period lasting up to 15 years after rapcabtagene autoleucel infusion. This LTFU will be described in a separate study protocol.