A second report -- appearing in the fall issue of the journal Cloning and Stem Cells -- describes the first documented growth of retinal pigment epithelial cells, or RPE cells, from human embryonic stem cells.
RPE cells, which are related to nerve cells, live inside the eye and provide essential "housekeeping" duties for the rods and cones -- the light-sensitive cells in the retina. RPE cells scavenge the retinal area for cellular debris, sucking old material up like little vacuum cleaners. And they secrete substances that aid in tissue repair within the eye.
 
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The loss of RPE cells in middle and old age is a major cause of age-related vision loss, including macular degeneration. That disease is the leading cause of blindness in people older than 60, affecting 30 million people worldwide. Doctors have begun to experiment with RPE cell transplants into people's eyes, but the approach has been plagued by problems -- including an inadequate supply of cells.
In experiments led by Irina Klimanskaya and Robert Lanza of Advanced Cell Technology in Worcester, Mass., human embryonic stem cells grown in lab dishes under certain conditions spontaneously became RPE cells, offering a possible solution to the supply problem.
Moreover, the ACT system involves no animal cells or products -- a feature the Food and Drug Administration has said will be important as it considers granting permission to test stem cell-derived cells in people.
Lanza said the company hopes to complete transplant studies in large animals during the next year, after which it will apply for permission to test the cells' safety and therapeutic value in the eyes of people with RPE-related vision loss.
Not all stem cell colonies worked equally well, Lanza noted, touching on a hot area of political debate. Six of the colonies -- those developed by Harvard researcher Douglas Melton with private funds -- "worked like a charm," Lanza said, as did two colonies developed by ACT.
But the three colonies developed by a Wisconsin team -- among the few approved by President Bush for study with federal dollars -- worked only "very reluctantly," Lanza said. Bush has banned federal funding for research on newly derived stem cell lines in order not to encourage the destruction of human embryos, but Lanza said his work shows that policy is short-sighted.
"It's becoming clear that each colony is different and can do different tricks," Lanza said. "To limit federally funded research to just a handful of lines is a mistake."
