Muscle-specific tyrosine kinase (MuSK) myasthenia gravis (MG) is a rare but potentially severe disease, in which patients develop pathogenic autoantibodies that specifically target the MuSK protein in the neuromuscular junction. This phase 1 study is being conducted to evaluate the safety of various dosing regimens of an investigational cell therapy, MuSK-CAART, that can be given to patients with anti-MuSK antibody positive Myasthenia Gravis (MuSK MG), who have active disease. Various dosing regimens of MuSK-CAART alone, in combination with cyclophosphamide (CY), and in combination with CY and fludarabine (FLU) will be evaluated. Treatment with MuSK-CAART may potentially lead to complete and durable remission of disease.

Inclusion Criteria:

• Confirmed diagnosis of MuSK-type MG with at least 1 prior positive anti-MuSK antibody test.
• History of a negative anti-AChR (acetylcholine receptor) antibody test.
• Positive anti-MuSK antibody test at screening
• MG severity Class I to IVa on the MGFA (Myasthenia Gravis Foundation of America) Clinical Classification

Exclusion Criteria:

• Rituximab in the last 12 months.
• Prednisone > 0.25mg/kg/day [in Part A]
• Other autoimmune disorder requiring immunosuppressive therapies.
• Investigational treatment for MG in the past 12 weeks.
• Absolute lymphocyte count < 500/µL at screening.