A Rollover Study to Evaluate the Long-Term Safety and Efficacy of Atacicept

Eligible participants will receive atacicept 150 mg once weekly (QW) self-administered subcutaneously (SC). Participants will be grouped by whether they are restarting atacicept after cessation in the parent study (Group 1: Atacicept Drug Holiday) or are continuing atacicept with no disruption in treatment (Group 2: Continuous Atacicept Treatment). Long-term safety and tolerability of atacicept is assessed by routine clinical and laboratory tests and adverse events.