RecruitingDrug trialAutologous Stem Cell Transplant Followed by Polatuzumab Vedotin in Patients With B-cell Non-Hodgkin and Hodgkin LymphomaPatients will receive one of two conditioning regimens (BEAM or CBV) before receiving an autologous stem cell transplant (ASCT). If patients achieve either complete, partial, or stable response following ASCT, they will receive an IV dose of Polatuzumab Vedotin once every 21 days until they receive 8 doses. After Polatuzumab Vedotin therapy is completed, patients will be followed every 4 months for about 2 years.