Searching for the Key to Expand Hematopoietic Stem Cells

Embryonic stem cells (ESC) are mostly derived from the undifferentiated inner mass cells of a blastocyst. These cells give rise during development of the embryo to all derivatives of the three primary germ layers: ectoderm, endoderm and mesoderm. They do not contribute to the extra-embryonic membranes or the placenta. Ex-vivo, they can be cultured for extended periods of time and under the appropriate conditions, they can be also directed to differentiate into many specialized types of cells. These particular features are being exploited to use ESC as starting material for treatment of degenerative diseases and replacement of damaged organs. Although their potential is great, the promise of ESC-derived therapies will be unfulfilled unless several challenges are overcome. For example, the quite small production of ESCderived cells obtained or the active immune rejection of the ESC-derived graft.