The prospect of using human embryonic stem cells to treat disease appears a small step closer as the result of two new experiments with the cells, which are mired in political controversy because they are derived from human embryos.
In one report released yesterday, researchers showed that the versatile cells can serve as "biological pacemakers," correcting faulty heart rhythms when injected into the failing hearts of pigs.
In another report, scientists demonstrated for the first time that stem cells can become a cell crucial to vision. Many doctors believe that several vision-destroying diseases could be fought by transplanting these cells directly into the eyes.
Human embryonic stem cells, derived from five-day-old embryos, have the biological potential to morph into virtually all of the 200 or so kinds of cells in the body. Researchers are racing to learn how to direct them to develop into specific types of cells that can be transplanted into failing organs. It is an approach that could launch a new era of regenerative medicine -- but only if the cells prove capable of integrating into existing organs and functioning normally there.
Izhak Kehat and Lior Gepstein of the Technion-Israel Institute of Technology in Haifa and their colleagues sought to test that capacity with stem cells that were growing into heart muscle cells.
The team started with masses of stem cells growing in laboratory dishes, from which they isolated those few that were spontaneously developing into heart cells.
They were easy to spot: They were the ones that were pulsing in unison, as heart cells are apt to do.
In one experiment, the scientists isolated small balls of the human cells -- each ball about the size of the head of a pin, or about 1 million cells -- and placed that little mass into a lab dish with rat heart cells.
The cells of each species, rat and human, beat at different rates at first. Within 24 hours of living together, however, the combined masses of cells coordinated their pulsing into a single rhythm.
"At least in the dish, they integrated structurally, mechanically and electrically," Gepstein said.
But could stem-derived heart cells help set the pace of a heart in a live animal?
To find out, the team threaded a probe into the hearts of 13 pigs and made a small burn in the area that regulates the heart beat, causing a permanent severe slowing of those animals' heart rates. The injury mimicked a human heart rhythm disorder that could be caused by disease or a small heart attack.
Then they injected about 100,000 of their human embryo-derived heart cells into the damaged pig hearts. Eleven of the 13 returned to faster heart rates, the team reported in yesterday's advanced online edition of Nature Biotechnology. There was no improvement in control animals that did not receive the cells.
"It's not like tomorrow people are going to be waiting in line for biological pacemakers," Gepstein said. "But we were happy to see after a few days a new rhythm arose," providing what he called "proof of principle."