As noted at EurekAlert!: "Scientists now can take embryonic stem cells, the cells that can become any tissue type in the body, and coax them into becoming all the cells in the blood supply ... However, they can't make blood stem cells that [self-renew] and don't differentiate prematurely when transplanted into patients. The only way this currently can be achieved is by manipulating the cell's nuclear regulatory machinery with genes using retroviruses. To generate blood stem cells that are safe for use in patients [scientists must] learn how to generate self-renewing blood stem cells in a more natural way, by providing the correct developmental cues from the environment in which the cells develop. ... This recent study indicates that the first niche for expansion of blood stem cells is the placenta's vascular labyrinth, where oxygen and nutrients are exchanged between the mother and the fetus. The findings show the placenta harbors two different microenvironments, one area where blood stem cells originate and another area, the labyrinth, that nurtures them, allowing them to expand in number. ... The labyrinth is a source of many growth factors and cytokines. We just need to identify what those signaling molecules and cues are that are nurturing those cells when in the placenta."