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The first clinical trial of a therapy based on human embryonic stem cells has received the green light from the FDA, marking a scientific and political milestone for embryonic stem (ES) cell research. The biotech company, Geron Corporation, received approval today for a study that would inject neural stem cells into patients suffering from spinal cord injuries. The study will be mainly a test for safety, but functional improvements, which have been observed in animals trials, may be possible. “For us, it marks the dawn of a new era in medical therapeutics. This approach is one that reaches beyond pills and scalpels to achieve a new level of healing,” Geron Chief Executive Dr. Thomas Okarma said [Reuters].
ES cells are taken from embryos a few days after fertilization and have the potential to differentiate into any type of cell in the body. The undifferentiated cells can’t be used directly, because they can form cancers called teratomas. But they can be used in the lab to generate potentially inexhaustible supplies of all other types of cell[s] that might be needed for repair. The type to be used in the trial are neural stem cells called oligodendrocyte progenitor cells. These support other neurons in the brain and nerves by supplying growth factors and by producing the myelin sheaths that protect neurons from damage [New Scientist]. The FDA will allow Geron to implant these neural stem cells directly into the spinal cords of eight to ten paraplegics. The trials are expected to begin this summer, and may be carried out in multiple medical centers. The patients have not yet been recruited because the injections must take place within two weeks of the spinal cord injury, before scar tissue forms.
Researchers hope that the therapy will induce damaged nerve cells to generate new myelin. In experiments on mice with paralyzed hind legs, the therapy was able to restore some mobility and autopsies revealed regenerated myelin.

The patients have not yet been recruited because the injections must take place within two weeks of the spinal cord injury, before scar tissue forms.