Primary human embryonic cells obtained from embryonic blastocysts nodes and a few weeks fetuses. Confirmed their ability to hold more than one year in culture in vitro in undifferentiated state . It was also shown that after transplantation in vivo in mice and in vitro , they can differentiate into tissues derived from all three germ layers . Thanks to these properties, primary human cells carrying a hope for therapeutic applications . In studies of mice primordial germ cells confirmed that it is possible to obtain differentiated therefrom , functional cells ( e.g., neurons , oligodendrocytes ) which transplant recipients to integrate into the corresponding tissue. Interest in stem cells from embryos soon spread to the stem cells of adult tissues . Methods have been developed for isolating and concentrating the cells from different tissues . In the case of blood stem cells , connective tissue , muscle, nerve tissue , and spermatogonial demonstrated their ability to differentiate into the appropriate tissues shortly after transplantation into the recipient . It turned out that stem cells are capable of transdifferentiation in vivo were also observed in recipients of tissue other than the starting material. For example, the stem cells form nerve tissue blood cells , muscles, hepatocytes and intestinal epithelium .