Sponsor Decision - terminated due to changes in company priorities and not related to safety concerns.

A Phase 1/2 study to evaluate the safety, tolerability, and efficacy of an antibody conditioning regimen, known as JSP191, in patients with Severe Combined Immune Deficiency undergoing blood stem cell transplantation

A Phase 1/2 study to evaluate the safety, tolerability, and efficacy of an antibody conditioning regimen, known as JSP191, in patients with SCID undergoing blood stem cell transplantation. Blood Stem Cell transplantation offers the only potentially curative therapy for SCID.

The biological conditioning regimen, JSP191, is an antibody that binds to CD117. CD117 is the receptor for Stem Cell Factor on blood forming cells. CD117 binding to Stem Cell Factor is critical for survival and maintenance of blood forming stem cells. The binding of JSP191 to CD117 blocks CD117 from binding to Stem Cell Factor on blood forming stem cells. In the absence of CD117/Stem Cell Factor binding, hematopoietic stem cells that are currently occupying the bone marrow niches in SCID patients exit from the bone marrow.

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

Data collected is for future publication