Researchers are assessing the cellular therapy lisocabtagene maraleucel (liso-cel) in people with primary central nervous system lymphoma (PCNSL). The people in this study have PCNSL that has not yet been treated. In addition, they cannot have autologous stem cell transplantation (ASCT). During ASCT, a patient's healthy, blood-forming cells are collected before treatment, stored, and returned after treatment with very strong chemotherapy.