Placental Tissue Found Similar to ESCs

Although it is routinely discarded as medical waste, placental tissue may be an abundant source of cells with the same potential to treat diseases and regenerate tissues as embryonic stem cells (ESCs), according to a study published in the August 4, 2005, online edition of Stem Cells Express.

A part of the placenta called the amnion is comprised of cells that have strikingly similar characteristics of ESCs, reported the study's researchers, including the ability to express two key genes that give embryonic stem cells their unique capability for developing into any kind of specialized cell. The study results suggest that these amniotic epithelial cells could in fact be directed to form liver, pancreas, heart, and nerve cells under the right conditions.

The amnion, derived from the embryo, forms as early as eight days after fertilization, when the fate of cells has yet to be determined, and serves to protect the developing fetus. The new studies using placentas from full-term pregnancies show that amniotic epithelial cells have many of the telltale surface markers of ESCs and also express the Oct-4 and nanog genes known to be required for self-renewal and pluripotency, which is the ability to develop into any kind of cell.

On the other hand, amniotic epithelial cells are not stem cells per se because they cannot grow indefinitely. This may be due to the fact that they do not express telomerase, important for DNA and chromosome replication and, by extension, cell division.

"Perhaps it's to their advantage that the amnion epithelial cells lack telomerase expression, because telomerase is associated with many cancers and one of the main concerns about stem cell therapies is that transplanted stem cells would replicate in the recipient to form tumors,” noted first author, Toshio Miki, M.D., Ph.D., an instructor in the department of pathology at the University of Pittsburgh School of Medicine (PA, USA).

To determine if amnion-derived cells delivered directly to tissues might cause tumors, the researchers conducted studies in immune system-deficient mice and found no evidence that tumors had developed seven months after the cells were injected into multiple sites. One advantage of amniotic epithelial cells is that they can double in population about 20 times over without needing another cell type to serve as a feeder cell layer. Instead, they create their own feeder layer, averting the need for using mice cells.

With the addition of various growth factors, the authors report the amnion-derived cells could differentiate to become liver cells, heart cells, the glial and neuronal cells that make up the nervous system, and pancreatic cells with genetic markers for insulin and glycogen production.