Background
Embryonic stem (ES) cells are continuous proliferating stem cell lines of embryonic origin first isolated
from the inner cell mass (ICM). Two distinguishing features of these ES cells are their ability to be
maintained indefinitely in an undifferentiated state and their potential to develop into any cell within the
body.
ES-D3 was first isolated from day 4 129/Sv blastocysts in 1985 by Doetschmann et al. When injected into
himeric blastocysts, ES-D3 contributed to the germ line. Alkaline phosphatase is routinely used as a
marker of undifferentiated pluripotent stem cells. ES-D3 cells propagated on a feeder layer of irradiated
STO mouse fibroblasts in the presence of recombinant mouse LIF are positive for alkaline phosphatase
activity. Spontaneous differentiation of embryoid body cells can be induced by leukemia inhibitory factor
withdrawal.