Progressive multifocal leukoencephalopathy after CAR T therapy.

Progressive multifocal leukoencephalopathy (PML) remains a life-threatening central nervous system infection in immunocompromised patients. Although outcomes have improved in cases that immune reconstitution is feasible with anti-retroviral therapy (ART) in HIV + patients or natalizumab removal in those with multiple sclerosis, in individuals with hematological malignancies, the prognosis is usually dismal. Anti-viral treatments have been largely ineffective, but immunotherapy-based approaches with checkpoint inhibitors and adoptive virus-specific T cells' transfer are currently explored in clinical trials. PML has not been described as a cause of encephalopathy after CAR T therapy. We report the first case of PML 7 months after lymphodepleting chemotherapy with fludarabine/cyclophosphamide and anti-CD19-directed CAR T therapy in a patient with relapsed diffuse large B-cell lymphoma who relapsed fast after a previous autologous hematopoietic stem cell transplant. She remains alive 12 months after diagnosis with stabilization of her symptoms with a combination of therapies targeting viral replication and immunotherapy.