Growing human tissues and organs in the lab is no longer science fiction. Researchers have come a long way since stem cells — ‘master cells’ with the ability to become any of the body’s tissue types — were first isolated in in 1998. It’s now possible to generate an endless supply of lab-grown human tissue, which could test potential medicines, treat a range of disorders, and cure afflictions like Parkinson’s and spinal cord injury by rebuilding the nervous system. More exciting still is the possibility of growing new tissue for transplantation into patients.
The main hurdles before organ transplantation are the non-availability of organs and incompatibility of donated organs with the recipient’s body. Usually, the body’s immune response system tries to reject transplanted cells. Early efforts at tissue engineering involved growing tissues on polymer scaffolding. A porous structure, shaped like the organ, is “seeded” with cells that grow and spread along it. Once the finished tissue is in place, the scaffolding degrades. This is unwieldy though, and only embryonic stem cells made from the patient’s own genetic material yield perfectly matched tissue. If genetic material is taken from a cell in an adult’s body and fused with an empty egg, the resulting embryo could be farmed stem cells. A leukemia patient, for instance, can have perfectly matched bone marrow from his own skin cells, skipping a desperate search for the right donor.
But critics are outraged at scientists creating embryos and discarding them after harvesting some cells. Many see even blastocysts — five-day-old embryos of about 140 cells— as human beings. Last week, however, scientists at the Whitehead Institute, Cambridge, Massachusetts, crossed this ethical minefield by culturing embryonic stem cells without eggs. They genetically manipulated skin cells taken from mice back into a pluripotent state —identical to embryonic stem cells. These cells could not only generate every kind of tissue, but also engender live mice by producing egg and sperm cells, and be transmitted down generations. Such use of ‘adult stem cells’ negates the need for embryonic stem cells, and could be just what the doctor ordered for a world constantly running short of donor organs.