RecruitingDrug trialTafasitamab Plus Lenalidomide in Relapsed CNS LymphomaThis is a single arm open-label multicenter phase I/II investigation of combination lenalidomide/Tafasitamab in patients with relapsed central nervous system (CNS) lymphoma. This is the first study to examine a naked anti-CD19 monoclonal antibody in relapsed CNS lymphoma patients as well as the combination of anti-CD19 antibody plus an Immunomodulatory imide drugs (IMiDs) in CNS lymphomas. This study will also test the novel hypothesis that Tafasitamab enhances blood-brain barrier permeability, a potential property that could have broad clinical implications.