Embryonic stem cells ( ESCs ) are pluripotent stem cells derived from
the inner cell mass of a blastocyst, an early-stage pre-implantation embryo.
Human embryos reach the blastocyst stage 4–5 days post fertilization, at which
time they consist of 50–150 cells. Isolating the inner cell mass (embryoblast)
using immunosurgery results in destruction of the blastocyst, a process which
raises ethical issues, including whether or not embryos at the pre-
implantation stage have the same moral considerations as embryos in the post-
implantation stage of development.
Researchers are currently focusing heavily on the therapeutic potential of
embryonic stem cells, with clinical use being the goal for many laboratories.