Manipulation of hematopoietic stem cells for regenerative medicine.

Hematopoietic stem cells (HSCs) are defined by their capacity to self-renew and to differentiate into all blood cell lineages while retaining robust capacity to regenerate hematopoiesis. Based on these characteristics, they are widely used for transplantation and gene therapy. However, the dose of HSCs available for use in treatments is limited. Therefore, extensive work has been undertaken to expand HSCs in culture and to produce HSCs from embryonic stem cells (ESCs) and induced pluripotent stem cells (iPSCs) in order to improve the efficiency and outcome of HSC-based therapies. Various surface markers have been characterized to improve the purification of HSCs and a huge number of cytokines and small-molecule compounds have been screened for use in the expansion of HSCs. In addition, attempts to generate not only HSCs but also mature blood cells from ESCs and iPSCs are currently ongoing. This review covers recent approaches for the purification, expansion or production of human HSCs and provides insight into problems that need to be resolved.