An open-label, multi-center, phase I/II study to assess safety, efficacy, and cellular kinetics of YTB323 in participants with treatment-resistant generalized myasthenia gravis.

The purpose of this research study is to learn more about the safety of YTB323 and how well it works on disease activity in participants with generalized myasthenia gravis (gMG) who have tried other medications to treat gMG, but they did not work. Generalized myasthenia gravis is an autoimmune disease which means the body’s immune system mistakes its own healthy tissues as foreign and attacks them. Current medications that are available for gMG do not effectively target the immune cells that produce the antibodies that damage the NMJ. YTB323 is a type of treatment called CAR T-cell therapy. CAR T-cell therapy uses the participant’s own immune cells which are re-directed (engineered) to fight the cells that are thought to cause the disease. After YTB323 treatment, the symptoms may or may not partially or fully disappear and may or may not come back. This trial is designed to find out if YTB323 can eliminate production of the antibodies that produce these cells and then allow for healing of the damaged NMJ re-establishing a more normal communication between the nerves and the muscles. Because this is an experimental treatment that has not been used in MG before, we will test it in patients who have very active MG disease and who have tried conventional MG treatments that have not worked or led to severe side effects. All participants in this study will receive YTB323. Both the participant and the study doctor will know that the participant is getting YTB323. Participants are in this study for 2 years and will be followed for an additional 13 years in a long-term follow up study. Participants will be given one dose of YTB323 given intravenously.