Alternatives to controversial human embryonic stem cells are being explored for creating tissue needed to repair damaged organs.
Adult stems cells are rare, hard to isolate and purify, hard to grow in culture, and may not exist for all tissues. Some success has been achieved with umbilical cord blood and fat sources.
Other cells are created from various sources, such as human embryos (by Anthrogenesis Corporation, which has isolated stem cells from human placentas), foreskins from circumcisions for making artificial skin for wound repair, and neurons obtained from pig fetuses by Diacrin as a treatment for people with brain diseases like Parkinson’s.
Drugs would activate the body’s own stem cells to let the body repair itself. For example, the human protein erythropoietin, when injected, prompts the body to create new red blood cells. However, tissue growth requires not just one growth factor but a carefully orchestrated combination of them. Duplicating that with drugs may be difficult.
Parthenogenesis (in certain species, eggs can turn into embryos without being fertilized by sperm). Some scientists are trying to use chemicals to turn unfertilized human eggs into embryos from which stem cells can be extracted. Such embryos (“parthenotes”) could never become babies, so destruction of them to make stem cells may not raise the same moral issues as destruction of embryos. Since tissue derived from parthenotes would be very similar to that of the egg donor, a woman might donate her own eggs to make tissue for herself that her body would not reject.
Advanced Cell Technology reported the first human parthenotes
De-differentiation (cellular reprogramming) aims at getting specialized body cells to revert to a primordial state, like stem cells, so they can be turned into various types of tissues. PPL Therapeutics, which cloned Dolly the sheep, is pioneering research techniques in this area.
Transdifferentiation aims to turn a cell back to its primordial state in order to turn that primordial cell into another type of cell. Hematech has successfully reprogrammed the nuclei of fibroblasts, which are cells that produce the body’s connective tissue.