RESET-Myositis is a study for people with a rare muscle disease called idiopathic inflammatory myopathy (IIM), which involves muscle weakness and inflammation. The exact cause of IIM is unknown, but it might involve the body's immune cells, like B cells, attacking muscles. This study tests a new treatment called CABA-201, given with drugs cyclophosphamide and fludarabine, to see if it helps people with active IIM or juvenile IIM (JIIM). All participants receive one dose of this new treatment.

Key Points:

• Participants must be 6-75 years old with active IIM or JIIM, even after standard treatments.
• Exclusions include severe heart, lung, or other major health issues, or having had certain prior treatments.
• The study aims to check if CABA-201 is safe and effective, but participating involves medical evaluations and potential risks.