JSP191 Antibody Targeting Conditioning in SCID Patients

Key Inclusion Criteria: 1. Typical SCID as defined by Primary Immune Deficiency Treatment Consortia including but not limited to the following subtypes: 1. T-, B+, NK-: IL-2Rcγ deficient, JAK3-deficient (no longer enrolling) 2. T-, B-, NK+: RAG1/2 deficient, Artemis-deficient 3. T-, B+, NK+: IL7Rα deficient, CD3 subunit deficient, CD45 deficient (no longer enrolling) OR Variant SCID with absent or low T cell function, Omenn syndrome, Leaky SCID, Reticular dysgenesis, Adenosine deaminase deficiency, and Purine nucleoside phosphorylase deficiency may be included after consultation with the medical monitor. 2. Patients with human leukocyte antigen (HLA) matched related or unrelated donors 3. Adequate end organ function as defined in study protocol 4. Age ≤ 12 years 5. Prior donor of appropriate age (≥ 5 years old) available for re-collection of stem cells 6. Previous allogeneic Hematopoietic Cell Transplantation HCT (≥ 6 months post initial transplant) with poor graft function Key Exclusion Criteria: 1. Patients with any acute or uncontrolled infections 2. Patients receiving any other investigational agents, or concurrent biological, chemotherapy, or radiation therapy 3. Patients with active malignancies 4. Active GVHD within 6 months prior to enrollment, or on immunosuppressive therapy for GVHD