Allogeneic Hematopoietic Stem Cell Transplantation With Reduced Intensity Pre-transplant Conditioning for the Treatment of High-risk Hematological Malignancies (V3)

Inclusion Criteria: * A proven diagnosis of one of the conditions in Table 1. * Prior therapy including blood or marrow transplant will not exclude patients for reduced intensity transplant. * Age \< 75 years. Pediatric patients are eligible from the ages of 1 month to 18 years if the transplant physician believes that co-morbid conditions significantly increase the risk for a standard transplant regimen. * HIV antibody negative. * ECOG performance status 0-3, (or equivalent Karnofsky and Lansky performance scores for patients \<18yrs, see appendix 2) * Availability of an HLA-identical related donor or suitable alternative donor, (≥7/8 allele match at A, B, C and DRB). Syngeneic transplants will not be allowed in this protocol. * Due to the complexity of the study, all patients prior to enrollment will be assessed by the PI or co-PI. * Patient with marrow failure states or immune deficiency syndromes undergoing stem cell transplants must be reviewed by one of the investigators to determine eligibility for study. * Adequate insurance coverage (or financial resources) to cover the costs associated with the patient's transplant and, in the case of patients eligible for cohort C, to cover the costs associated with I 131 Tositumomab treatment. Exclusion Criteria: * Active CNS involvement with malignant disease. * Pregnancy. * Fertile men or women unwilling to use contraceptive techniques during the study period. * Creatinine clearance \< 30 ml/min. * Left ventricular ejection fraction \<30% or clinical cardiac failure uncontrolled by medical therapy. * Pulmonary disease requiring supplemental oxygen therapy. * Patients with estimated life span less than 1 year due to medical illnesses other than the condition being treated on the study. Donor Selection: Inclusion Criteria * Major HLA identical relative or genotypically matched unrelated donor (7-8/8 alleles) . * Donors must meet the selection criteria as defined by the Foundation for the Accreditation of Cell Therapy (FACT) and will be screened per the American Association of Blood Banks (AABB) guidelines. Exclusion Criterion * Positive anti-donor HLA antibody. * Identical twin.