We propose a highly synergistic and innovative program of basic and clinical research to improve treatment of patients with primary immunodeficiency disorders and hemoglobinopathies by allogeneic hematopoietic cell transplantation (HCT) and gene therapy. We seek to accomplish this by introducing safe, non-toxic conditioning regimens and novel ways of averting graft-vs.-host disease (GVHD). The Program consists of three projects supported by four cores. The clinical Project 1 has three aims, the first to be accomplished in recipients of HLA-matched HCT and the remaining two in patients given HLA-haploidentical grafts. Aim one is to avoid toxicities of current conditioning regimens, especially secondary cancer, by using targeted irradiation with the alpha-particle emitting radionuclide astatine-211 (211At) coupled to a monoclonal antibody (MAb) directed at CD45. Aim two is a multicenter trial exploiting suicide gene modified T cells (BPX 501) given along with CD34+ selected HLA-haploidentical stem cells in order to both accomplish engraftment after reduced- intensity conditioning and avert subsequent GVHD. This would assure that virtually every patient with a candidate disease, especially patients from ethnic minority groups, can receive allogeneic HCT. The third aim is to incorporate 211At-anti-CD45 MAb to prevent rejection of HLA-haploidentical grafts, a goal particularly important for patients with sickle cell anemia. The two preclinical projects, using a canine model of HCT, are closely integrated with each other as well as with the clinical project. Specifically, Project 2 focuses on four aims. The first uses a 211At-labeled anti-CD45 radiolabeled MAb as conditioning for HCT in dogs with pyruvate kinase (PK) deficiency as model for human hemoglobinopathies. The second tackles DLA-haploidentical grafts in dogs with X-linked severe combined immunodeficiency (SCID-X1) using the 211At-labeled anti-CD45 MAb in order to assure sustained multi-lineage donor cell engraftment. The third aims to overcome transfusion- induced sensitization and consequently reduce the risk of graft rejection in the DLA-identical setting using 211At-labeled MAb. The fourth aim will study ex vivo-expanded DLA-identical CD34+ stem cells for their ability to achieve sustained engraftment without GVHD. Project 3 will focus on the development of new and less toxic conditioning regimens for gene therapy, expansion of hematopoietic stem/progenitor cells (HSCs) and on in vivo delivery of lentiviral vectors. Three aims will be pursued. The first will evaluate engraftment of gene- modified HSCs following conditioning with busulfan, treosulfan or 211At-labeled anti-CD45 MAb. It will also explore a suicide-gene safety switch and carry out extensive clonal analyses. Aim two will evaluate whether ex vivo expansion of HSCs can improve engraftment after non-myeloablative conditioning. Aim three will evaluate whether expanded and gene-corrected HSCs can correct genetic diseases in the canine SCID-X1 and PK models after minimal conditioning. The highly synergistic Program proposes innovative, practice-changing, basic and clinical research aimed at dramatically improving outcomes of allogeneic hematopoietic cell transplantation (HCT) and gene therapy for inherited nonmalignant blood diseases including primary immunodeficiencies and hemoglobinopathies. The development of successful regimens for grafts from HLA-haploidentical family members would assure that virtually every patient with a candidate disease, especially patients from ethnic minority groups, could become a recipient of allogeneic HCT. (End of Abstract) PROJECT 1: CELL THERAPY FOR CORRECTION OF BLOOD DISORDERS (STORB, RAINER F.)