Haplocompatible Transplant Using TCRα/β Depletion Followed by CD45RA-Depleted Donor Lymphocyte Infusions for Severe Combined Immunodeficiency (SCID)

Infants with severe combined immunodeficiency (SCID) have a profound decrease in number and function of immune cells, and therefore remain highly vulnerable to infection. If not corrected this often leads to death. Hematopoietic cell transplantation (HCT) from matched sibling donor is the standard treatment for these patients, unfortunately though; most SCID patients lack a sibling donor. Building upon experience and existing data, the investigators are proposing a trial the goals of which are: to provide a conditioning regimen that is well tolerated, and provision of immune cells that altogether should establish rapid immune recovery providing protection from life threatening infections without increasing the risk of dangerous Graft-Versus-Host-Disease. Primary Objectives 1. To evaluate the safety of a TCRα/β/CD19-depleted graft with CD45RA-depleted DLI in infants with SCID 2. To estimate overall survival at 1 year post transplantation Exploratory Objectives 1. To evaluate the significant donor T cell reconstitution of a TCRα/β/CD19 depleted graft with CD45RA-depleted DLI at 1 year (+/-2 weeks). 2. To evaluate engraftment at day 30, 100, month 6, and years 1 to 10 post HCT. 3. To evaluate B cell reconstitution at years 1 to 10 post HCT. 4. To evaluate biomarkers of immune reconstitution at day 30, 60 100, month 6 and years 1 to 10; e.g. immunophenotype (including epigenetic profiling) of T, B, and NK cells, and assays to determine their function. 5. To evaluate clinical outcomes, post HCT. 6. To define the incidence and severity of acute (at day 100, month 6), and chronic (month 6, 12, 24) GVHD following HCT.