The study is open to twenty (20) infants and children diagnosed with ADA-deficient SCID who did not have a medically eligible, human leukocyte antigen (HLA)-identical sibling donor for bone marrow transplantation. The EFS-ADA lentiviral vector with the human ADA complementary DNA (cDNA) will be used to transduce autologous CD34+ cells from Granulocyte Colony Stimulating Factor (G-CSF)/Plerixafor mobilized Peripheral Blood (mPB) of these subjects. The subjects will receive pharmacokinetically-adjusted busulfan reduced intensity conditioning prior to re-infusion of their gene-modified cells. Overall survival at two years is the primary endpoint. During the follow-up phase, the investigators aim to determine whether the cells could engraft and produce mature cells that contain and express the corrected ADA gene in the absence of pegylated adenosine deaminase (PEG-ADA) enzyme replacement therapy (ERT), which will be withheld starting on Day +30 following transplant. Efficacy studies to evaluate the level of immune reconstitution, will be performed in the two years of the study. Patients will be asked to enroll into a long-term follow-up study to reach a total of 15 years follow-up after gene therapy.
The aim of this study is to assess the safety and efficacy of autologous transplantation of hematopoietic stem cells (CD34+ cells) from mobilized peripheral blood (mPB) of ADA-deficient SCID infants and children following human ADA gene transfer by the EFS-ADA lentiviral vector. The level of gene transfer in blood cells and immune function will be measured as endpoints.