RecruitingPhase 1Biological interventionA Study of MB-CART19.1 Cellular Therapy for People With Central Nervous System Lymphoma (CNSL)This study will test whether MB-CART19.1 is a safe and effective treatment for central nervous system lymphoma (CNSL). This study will test different doses of MB-CART19.1 to find the highest dose that causes few or mild side effects in participants.