This study is testing a new treatment called **ACE1831** for people with a condition known as **IgG4-Related Disease (IgG4-RD)**, which happens when your immune system attacks your own body. The treatment uses special cells from healthy people to try and help those with this disease. The study is open label, meaning everyone will know what treatment they are getting, and it will take place in multiple locations.

To join, you must be between 18-75 years old, have active symptoms, and have had the disease affect at least two body parts before. You must agree to use birth control during and after the study for safety. You cannot join if you have other serious health issues, infections, or recent cancer.

• The study involves receiving ACE1831 therapy and requires multiple visits to the study center.
• Participants will be monitored for safety, effectiveness, and how long the treatment lasts in the body.
• Potential risks include side effects from the treatment and the requirement to stop certain medications.