**Autosomal Dominant Polycystic Kidney Disease (ADPKD)** is a genetic disease causing cysts in kidneys. This study tests if the new drug **ABBV-CLS-628** is safe and works well for treating ADPKD. The study includes 240 adults and is conducted at about 100 places worldwide. Participants will be split into 4 groups; 3 groups get the drug, and 1 group gets a placebo (a fake treatment, like a sugar pill). The chance of getting the placebo is 1 in 4.

Participants will receive the treatment through an IV (a tube in a vein) every 4 weeks for 92 weeks, with follow-up visits for 15 more weeks. They will have regular hospital or clinic visits for checks like blood tests and answering questions about how they feel.

• The study lasts almost 2 years, with visits every 4 weeks.
• Participants might face more treatment tasks than usual care.
• Regular medical tests and questionnaires are part of the study.