As a neonatal source of cells, UCB-derived HSPC (HSPC(CB)) tend to be more immature compared to adult bone marrow (BM) or mobilized peripheral blood, leading to a lower incidence of graft vs. host disease (GvHD), which allows a greater human leukocyte antigen (HLA) mismatch between donors and recipients [1]. The gene discussed is PSMA7; the disease is graft versus host disease.