background: umbilical cord blood (ucb) is an alternative source of hematopoietic stem cell transplantation (hsct), used in leukemia treatment. cd26+ cells, a fraction of cd34 positive cells, are a major population of ucb cells which negatively regulate the in vivo homing and engraftment of hscs. cd26 is highly expressed in various cells such as hscs, immune cells, fibroblasts, and epithelial ce...