What Schett had in mind for his patient: chimeric antigen receptor T-cell (CAR-T) therapy. The treatment involves isolating a patient’s T cells—the sentries of the immune system that strike invaders—and engineering them in a lab to destroy blood cells called B cells that have become cancerous. B cells also help power many autoimmune diseases, and Schett had seen a 2019 study describing mice with lupus restored to good health after CAR-T treatment. He wondered whether the treatment could rescue someone like Thu-Thao.