Nov 9, 2006: Cell Transplants help Blind Mice See!

Scientists have used cell transplants to restore some vision in blind mice, the best evidence yet that similar techniques could one day treat people with degenerative eye disease.

In their experiments, researchers extracted light-sensitive photoreceptor cells from newborn mice and transplanted them into the retinas of mice with eye diseases. Tests showed that the previously blind mice could sense light and that they had some vision. The results appeared in the journal Nature.

Photoreceptor cells are the focus of attention because they are destroyed in some common causes of blindness, including retinal and macular degeneration, that affect millions of people. Past attempts have used retinal transplants with embryonic stem cells, master cells that can eventually turn into all other types of cells in the body. Those attempts failed because the transplanted embryonic cells didn’t turn into well-functioning photoreceptors. Experiments with adult stem cells also haven’t been particularly successful.

“We’ve shown for the first time that photoreceptor transplantation can be done,” said Robert MacLaren, an eye surgeon at the University College London and at Moorfields Eye Hospital , London , and an author of the Nature study. However, he cautioned, “there are still many steps before we do this in patients.” Other authors included researchers from the University of Michigan.

The procedure isn’t immediately applicable to humans because it would require extracting photoreceptor cells from a human fetus. But the authors of the paper are hopeful that they can build on the research to create vast quantities of photoreceptor cells in the lab for transplants into patients.

When it comes to treating disease with stem cells, retinal-cell transplants hold special promise. One reason is that even when photoreceptors are destroyed, the rest of the wiring to the brain initially stays intact. So transplanted cells would need to bridge only one short connection to restore vision.

The latest study suggests that it may be more effective to transplant somewhat mature cells. Thus, researchers in the latest experiments studied “precursor” cells which are programmed to be — but haven’t yet become — mature and functioning photoreceptors. They experimented with precursors that turn into rods, which are photoreceptors that detect dark and light.

After being extracted from newborn mice, the precursor rod cells were transplanted into other mice that were missing the rods in their retinas. The cells correctly developed into rod photoreceptors and properly connected to nerve cells that carry visual signals to the brain. Tests indicated that the mice had some restored vision, though it wasn’t clear how much.

“It may be that the specific time at which the specific cell is harvested will make all the difference in its potential” for transplant therapy, Thomas Reh, a scientist at the University of Washington , wrote in an article accompanying the Nature study. Prof. Reh isn’t an author of the Nature paper.

Dec 19, 2006: RNA interference technology:

Sirna is developing drugs using so-called RNA interference technology. There are at least a half-dozen biotechnology companies developing drugs that silence genes by interfering with the messenger-carrying RNA, a technique discovered by this year’s Nobel winners, Andrew Fire of Stanford University and Craig Mello at the University of Massachusetts.

There are eight U.S and European patents specifically related to the technology. The closest drug Sirna has near market is for the treatment of the eye disorder, macular degeneration, a leading cause of blindness in the elderly. However, that drug is still at least two years from regulatory approval and probably further out because its experimental treatment will require the successful completion of at least two costly, time-consuming and large-scale human trials testing for safety and effectiveness.