Tandem Stem Cell Transplantation for Non-Hodgkin's Lymphoma

Inclusion Criteria * Age 18 to 70 years. * Histologically proven non-Hodgkin's lymphoma * High risk disease including at least one of the following: * Relapsed or refractory disease * Transformed lymphoma * Aggressive T-cell lymphoma * Failure to achieve completed remission (CR) following Auto SCT * Less than a 20% chance of event-free survival from autologous transplant determined by the treating physician and the Principal Investigator * ECOG performance status \< or = 2 * Underwent Autologous SCT 60-120 days prior to registration including: * BEAM conditioning (BCNU: 300 mg/m2 IV day -7, Etoposide: 100 mg/m2 IV BID days -6,-5,-4,-3, Cytarabine: 100 mg/m2 IV BID days -6,-5,-4,-3, Melphalan: 140 mg/m2 IV day -2) * Minimum of 2 x 106 CD34+ cells/kg infused * Full hematologic recovery following Auto HCT including: * Absolute neutrophil count (ANC) \>1000 µl * Platelet count of ≥50,000 µl independent of transfusion for \>7 days * Available matched related or unrelated donor. Selected donor must be a complete match or have only a single antigen mismatch. * Women of child-bearing potential and sexually active males must use an accepted and effective method of birth control. * Bone marrow comprising of \< 10% lymphoma on most recent biopsy/aspiration (within 9 months of Allo transplant; may have been performed prior to autologous transplant). * Serum bilirubin \< or = 2 x the institutional ULN * Serum creatinine \< or = 2 x the institutional ULN and measured or estimated creatinine clearance \> 60 cc/min by the following formula * Estimated Creatinine Clearance = (140 age)X WT(kg) X 0.85 if female 72X serum creatinine(mg/dl). * Patients must be informed of the investigational nature of this study and must sign and give written informed consent in accordance with institutional and federal guidelines. Exclusion Criteria * Prior autologous or allogeneic hematopoietic cell transplantation (other than autologous SCT 60-120 days prior to registration) * Prior radioimmunotherapy * Known or suspected progressive disease following autologous SCT * Additional treatment for NHL administered from time of autologous SCT through registration * Pregnant or breast-feeding women (due to the known birth defects association with the treatments used in this study) * Human immunodeficiency virus (HIV)-positive (the concern for opportunistic infection and hematologic reserve are considered to be significantly greater in this population.) * Any prior malignancy is allowed except adequately treated basal cell or squamous cell skin cancer, in situ cervical cancer or other cancer for which the patients has been disease-free for five years. * Active infection requiring oral or intravenous antibiotics. Inclusion of Women and Minorities -Both men and women and members of all races and ethnic groups are eligible for this trial.