A Phase 1/2 Study to Evaluate the Safety, Tolerability, and Efficacy of JSP191 for Hematopoietic Cell Transplantation Conditioning to Achieve Engraftment and Immune Reconstitution in Subjects With SCID

Safety and tolerability will be evaluated by measuring the incidence of Adverse Events (AEs), changes in laboratory values, physical examination, and the frequency and nature of dose-limiting toxicities (DLTs) following JSP191 conditioning. Efficacy will be measured in the proportion of participants achieving adequate donor HSC engraftment and healthy naïve CD4+ T cell production. 

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 are depleted.