Blood cells expand their numbers

cientists in the field of blood cell development have found a protein of expansive abilities. According to two new papers, HoxB4 is able to promote self-renewal of hematopoietic stem cells (HSCs) both in vivo and in vitro. HoxB4 is a homeotic gene whose expression in vivo has been shown previously to enhance HSC regeneration. Now, Jennifer Antonchuk, Guy Sauvageau, and Keith Humphries (Terry Fox Laboratory, Vancouver, BC) demonstrate that the number of adult HSC can be expanded in vitro when bone marrow cells are transduced with HoxB4 . Compared with untransfected cells, the HoxB4expressing cells showed a 40-fold net increase after 14 d in culture. “So far, this [method] stands out uniquely as a means to expand stem cells,” says Humphries. “The stem cells are normal in terms of being able to S