Pembrolizumab and Tazemetostat to Overcome Immune Tolerance Following ASCT or CAR T-cell Therapy in Patients With Aggressive B-Cell Non-Hodgkin's Lymphoma

Inclusion Criteria: * Patients must have a histo-pathologically confirmed aggressive B-cell NHL intended for or currently undergoing standard of care ASCT or CAR T-cell therapy. * Note: Patients should have met the Food and Drug Administration (FDA) approved indications for the respective CAR T cell construct being used. Standard of care/FDA approved CAR-Ts for this population include axicabtagene ciloleucel, tisagenlecleucel or lisocabtagene maraleucel, any of which may have been used for this patients and is provider dependent. Out of specification products of these respective CAR Ts may also be utilized if intended for FDA approved indication by way of expanded access if the provider feels that the product offers similar efficacy and safety as compared to commercial product per guidance provided by manufacturer. For the purpose of this study, aggressive B-cell NHL histologies should conform to the label indications for the respective CAR-T being utilized. Accordingly, CAR-T eligible histologies include the following groups according to the 2016 revision of the World Health Organization (WHO) classification of lymphoid neoplasms High-grade B-cell lymphoma, with MYC and BCL2 and/or BCL6 rearrangements * High-grade B-cell lymphoma, Not Otherwise Specified (NOS) * Diffuse large B-cell lymphoma (DLBCL), NOS * Diffuse large B-cell lymphoma (DLBCL), NOS; Germinal center B-cell type\*\* \[Refer note below\] * Diffuse large B-cell lymphoma (DLBCL), NOS; Non-germinal cen…