Researchers are reporting some tantalizing results from efforts to grow new organs and other body parts.
Most of the work is still being done on mice, rats and dogs, where medical advances don't always translate to people, but some transplants and other regenerative therapies have been done on humans -- and more are in the wings.
On Wednesday, a Japanese team reported in the journal Nature that it has been able to grow functional human liver tissue from small clumps of cells transplanted to mice. The cells, first produced in a lab dish from human skin cells reprogrammed as stem cells into an embryo-like condition, then enhanced with two other cell types.
The result -- human "liver buds" about the size and level of maturity found at six weeks of development. The livers appeared to continue to mature and show signs of being functional after they were transplanted into mice.
The liver buds were implanted inside either the head or one of two sites in the abdomen in each mouse.
Takanori Takebe, a stem cell biologist at Yokohama City University and leader of the research team, told reporters the team is are now working to reduce the size of the liver buds to make it easier to transplant them into an existing mouse liver via blood vessels.
He said although the amount of liver tissue was small, the micro-organs performed well enough that they improved survival in mice after liver failure. The researchers estimate it will be another 10 years before something like the liver buds could be transplanted in humans.
Scientists have been working on replacement parts for nearly a decade, bioengineering a bladder, tear ducts, arteries, even windpipes coated with stem cells. The tracheas have been transplanted to at least five human patients. More complex organs, such as a heart, are being made for mice and rats.
Researchers are also learning that organs are able to replenish certain types of cells long after birth. One study at Boston Children's Hospital reported in January found that the hearts of infants, children and even teens are able to generate new muscle cells up until about age 20. It had been thought that heart muscle cells repaired damage only by expanding remaining cells, not through regeneration. The study was published by The Proceedings of the National Academy of Sciences.
Last month, scientists at the Lawrence Livermore (Calif.) National Lab and a group of colleagues from Sweden and elsewhere used data derived from nuclear weapons testing in the 1950s to track changes in the human brain, establishing that a small portion of the human brain involved in memory, the hippocampus, continues to regenerate neurons well into adulthood. The team used carbon 14 dating based on a decline in the element since above ground nuclear testing ended in the 1960s.
The research was published in the journal Cell.
In Japan, a group of dogs "bit the bullet" so-to-speak by undergoing root canals and then a test involving stem cells taken from their teeth. After treating the stem cells with a growth factor, researchers from the National Center of Geriatrics and Gerontology returned the cells to the teeth. The replacement cells all regenerated pulp tissue inside the tooth and completely filled in the root canals in the canines' canines.
The hope is that the procedure can be used to repair cavity damage in human teeth without deep drilling and cleaning of decayed areas. The Japanese team, which reported their work last month in the journal Stem Cells Translational Medicine, has started work on human trials.
Other teams in Korea, the U.S. and Britain have also been working on getting stem cells to grow tooth pulp. One group at Baylor and Rice universities are working with a special protein gel to foster pulp regeneration.