Phase 2 Poor Risk DLBCL of TLI and ATG Followed by Matched Allogeneic HT as Consolidation to Autologous HCT

This study tests a tandem transplant approach that starts with transplantation of the participant's own hematopoietic (blood) cells, eg, autologous hematopoietic cell transplant (auto-HCT) as preparation for an subsequent matched-donor allogeneic HCT (allo-HCT). Participants will be have progenitor cells (stem cells) mobilized into the peripheral blood with rituximab, chemotherapy (cyclophosphamide or etoposide), and filgrastim (G-CSF); undergo apheresis to collect autologous peripheral blood stem cells (PBSC, aka hematopoietic cells); and be re-infused with ≥ 3 x 10e6 CD34+ cells/kg (auto-HCT). Subsequently, participants will receive therapeutic, non-myeloablative chemotherapy (carmustine + cyclophosphamide + etoposide), then transplant conditioning \[total lymphoid irradiation (TLI) + anti-thymocyte globulin (ATG)\] followed by ≥ 2 x 10e6 CD34+ cells/kg allogeneic PBSC obtained from a human leukocyte antigen (HLA)-matched or HLA single allele / antigen-mismatched donor (allo-HCT). Donors will be mobilized with 16 µg/kg filgrastim. Participant allo-HCT transplant is to occur within 150 days of auto-HCT. Post-allo-HCT infusion treatment includes cyclosporine and mycophenolate mofetil (MMF) Subject's participation ends if a suitable matched donor is not identified within the 150 days. Pre-medication treatments administered during this study may include acetaminophen; diphenhydramine; hydrocortisone; and methylprednisolone.