For only the second time, the Food and Drug Administration approved a company's request to test an embryonic stem cell-based therapy on human patients. Advanced Cell Technology (ACT), based in Marlborough, Mass., will begin testing its retinal cell treatment this year in a dozen patients with Stargardt's macular dystrophy, an inherited degenerative eye disease that leads to blindness in children. In July, the FDA released its hold on the first trial of an embryonic stem cell based treatment, for spinal cord injury.
ACT's trial will involve injecting retinal pigment epithelium (RPE) cells, which nurture the retina, into volunteers with the most advanced forms of Stargardt's, in an attempt to replace dying and no longer functioning photoreceptor cells. In animals, the infusion of healthy cells improved vision and rescued the function of some diseased cells.
Robert Lanza, ACT's chief scientific officer, is hoping that the company's RPE cells do the same in the patients, since the approval has been a long time coming. The company had initially submitted its request to begin human trials with its RPE cells in November 2009, but has spent the past year addressing the FDA's concerns about the safety of the embryonic stem from which the RPE cells are made.
The protocol involves injecting 50,000 to 100,000 RPE cells into the vitreous cavity of the eye. Because this region is protected from the body's ever-vigilant immune system, the new RPE cells do not have to be immunologically matched to the patients. But since they are made from embryonic stem cells, which can go on to become any of the body's various tissue types as well as form a type of tumor, the FDA was concerned that some pure stem cells would remain in the transplanted RPE population. Lanza says the company's scientists have developed an assay that can detect a single such stem cell from about one million RPE cells, a measure that satisfied the agency and may become a standard for future embryonic stem cell based treatments.
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