**Study Summary** This study is for people who have had a kidney transplant and are experiencing **antibody-mediated rejection (AMR)**. AMR happens when the body attacks the new kidney, thinking it's a foreign object. The study is evaluating a drug called **ALXN2030** to see if it can help with AMR. It compares ALXN2030 to a placebo (a harmless pill with no medicine) over a period of 52 weeks. Participants will receive their usual immunosuppressive treatment while in the study. **Key Points:** - The study lasts for **104 weeks**, including a 52-week treatment period and a 52-week follow-up. - Participants will need to undergo **biopsies** (a small tissue sample) at weeks 28 and 52. - After the initial study, participants may continue with an **Open-Label Extension** for additional 52 weeks of treatment. Participants must have received their kidney transplant at least 6 months ago, have certain test results, and meet vaccination requirements. The study is **double-blind**, meaning neither the participants nor the researchers know who receives the actual drug or placebo. There are certain health conditions that would prevent participation.