Our organs can unfortunately be irretrievably damaged by disease or just wear out with old age. The good news is that many organs can be successfully transplanted, including heart, kidneys, liver, lungs, pancreas, intestine, and thymus. The bad news is that there aren't enough organs to go around, with over 100,000 Americans on waiting lists (organdonor.gov), and more than 6,000 dying every year for lack of a donor.
Despite these dismal statistics, there is cause for hope. Incredibly exciting research from a pair of Japanese research laboratories suggests a new solution. Imagine the following. The doctor takes a skin cell from the patient needing a new organ, and first converts it into a stem cell. The stem cell is then subjected to a series of remarkable procedures that transform it into a fully functional replacement organ. This might sound like science fiction, but this exact scenario is now possible in animal model systems.
As described in detail in the book "DESIGNER GENES: A New Era in the Evolution of Man," Dr. Shinya Yamanaka and his colleagues at Kyoto University made the first giant leap. He showed that it is possible to take adult cells, reactivate four specific genes in them, and by essentially turning back time, transform them into the equivalent of embryonic stem cells. This remarkable discovery shocked the world of biologists, and will surely win him a Nobel Prize. These powerful stem cells can be made straight from adults and since no embryos are destroyed in the process, the ethical concerns are removed -- a truly astonishing achievement.
Stem cells, as the name suggests, are able to branch out in many different developmental directions. Scientists have studied stem cells for years, and have shown it is possible to treat them with different combinations of factors to turn them into many diverse cell types, including those found in the heart, kidneys, liver, lungs, and other organs. However, having some heart cells growing on a plastic dish is not the same as having a replacement heart.
The second breakthrough came from the lab of Dr. Hiromitsu Nakauchi. He showed that stem cells could be used to make organs in interspecies chimeras. The term chimera comes from Greek mythology, and refers to a creature made of the parts of different animals. Real chimeras can be made in the laboratory by mixing the embryonic cells of different species. Dr. Nakauchi used rat-mouse chimeras to produce replacement organs. His lab started with a mouse embryo that had been genetically designed to be unable to make a pancreas. It turns out that a specific gene, named Pdx1, is absolutely required for pancreas formation, so when this gene is inactivated, an embryo develops relatively normally except for the absence of this organ. The researchers then added some normal rat stem cells to the Pdx1 deficient mouse embryo, and only the rat cells were able to make a pancreas. The end result was a mouse with a rat pancreas.
This suggests that animals can be used to make replacement parts for people. The stem cells made from the patient would be placed in an animal embryo genetically engineered to provide the perfect incubator for the formation of the desired organ.
Some thorny issues remain. For example, what animal would we use? A pig might seem a good choice, but interspecies chimeras don't work well when the two species are too distantly related. Chimps, on the other hand, would almost certainly work, but would we be willing to sacrifice chimps to save people? And what if the human stem cells contributed to the formation of the brain? It would clearly be necessary to devise genetic strategies to insure that we aren't inadvertently killing people, trapped in the bodies of animals.
When these and other issues are finally solved then those 100,000 Americans on the waiting list might find it is possible to get replacement organs from their very own stem cells. In addition, the organs would be genetically identical to the patients, a perfect match, and therefore not subject to immune rejection.
This is only one aspect of the ever-changing genetics revolution. As I explain in "DESIGNER GENES," the revolution is ongoing and there may indeed be no stopping it now. The human species is about to undergo an incredible transformation. Not only will we be able to use adult's own stem cells to create replacement organs, but in the future it will likely be routine for parents to eliminate the genes that cause disease for their children and perhaps help choose the genes that will determine traits such as intelligence, appearance, and athletic abilities. The ramifications could be enormous, with each generation smarter, more technologically proficient and better able to design the genes of their offspring.