Durability of Response to B‐Cell Maturation Antigen‐Directed mRNA Cell Therapy in Myasthenia Gravis

ABSTRACT Objective We report the 12‐month follow‐up outcomes from a Phase 2 clinical trial (NCT04146051) evaluating Descartes‐08, a BCMA‐directed RNA chimeric antigen receptor T‐cell (rCAR‐T) therapy for refractory generalized myasthenia gravis (MG). These findings provide insight into the potential applicability of BCMA‐targeted rCAR‐T therapy for antibody‐mediated autoimmune diseases. Methods In the Phase 2a part of the study, Descartes‐08 was administered at 52.5 × 10 6 CAR+ cells/kg per infusion with varying dosing frequencies as an outpatient treatment and without lymphodepletion chemotherapy. A subset of participants received Descartes‐08 as six weekly infusions and were followed long term with assessments conducted at 2, 3, 6, 9, and 12 months. Results All seven participants who received six weekly infusions of Descartes‐08 exhibited clinically meaningful improvement in common MG severity scales (MG Composite, MG Activities of Daily Living, Quantitative MG scores, and Quality of Life 15‐revised) at Month 3 without significant toxicity. At Month 9 follow‐up, all participants continued to experience marked clinically meaningful improvements. Five out of seven participants maintained the response at Month 12. A third participant experienced a relapse approximately 6 months after completing on‐study follow‐up. All three participants who experienced loss of clinical effects were retreated. Two had rapid improvement in clinical scores with minimal symptom expression at Week 8, which was maintained through 12 months of retreatment follow‐up. The third participant experienced similar improvement in MG severity scores to their initial treatment. Interpretation These data support continued development of Descartes‐08 in myasthenia gravis and other autoantibody‐associated autoimmune disorders.