In vitro and in vivo expansion of stem cell populations

Expansion of hemopoietic stem cells occurs in vivo following transplantation of limited numbers of bone marrow cells or of highly purified stem cells. Stem cell expansion can in principle be achieved in vitro and also be promoted in vivo by growth factor treatment, notably with thrombopoietin. Advances in identification of stromal elements, growth factors and culture conditions that stimulate immature hemopoietic stem cell proliferation may result in effective stem cell expansion protocols and contribute to efficient retrovirally mediated gene transfer. In vivo expansion of immature cells by growth factor treatment may both be a valid alternative and an adjuvant to in vitro expansion.