Robert Lanza, chief scientific officer at ACT, says that the study is an important step toward bringing the therapy into clinical trials, as it includes more detailed safety studies and uses cells produced under the strict manufacturing conditions that are required for human applications. To ensure the quality and consistency of cell therapies, the FDA has laid out extensive guidelines for preparing cells and testing them for any potential disease-causing pathogens. Lanza says that after completing this and two other animal studies under the guidelines, the company will be set to file an application with the FDA to begin clinical trials in the coming months.

Lanza believes that the RPE treatment is a promising early application for embryonic-stem-cell therapies. Not only does it avoid the problem of immune rejection, but the cells themselves are relatively easy to create, as embryonic cells tend to spontaneously differentiate into RPE cells and can be easily maintained in that state. "This is absolutely one of the perfect first therapies," Lanza says. ACT will focus first on patients with Stargardt's disease, which is an "orphan" disease--a rare disease with no available treatment that qualifies for federal tax incentives for clinical trials. Lanza believes that the therapy is likely to work well because the supporting tissue that RPE cells must attach to is still intact in these patients. The next patient population would be those with age-related macular degeneration, a much more common disease in which gradual deterioration of tissue in the retina leads to vision loss.

Thomas Reh, a neurobiologist at the University of Washington who is unaffiliated with ACT, agrees that the RPE therapy is a promising candidate for translating embryonic-stem-cell therapies to the clinic. However, he cautions that the Stem Cells study does not provide the "slam dunk" that he had expected to see. Although the transplants did restore visual function in the eye, the benefit was not always sustained over time in animals.

Reh says that these experimental therapies rely on the assumption that cells generated from embryonic stem cells will function like their normal counterparts. But the less-than-stellar results suggest that the cells may not represent an exact replacement, he says. Scientists won't know for sure until they see how the cells perform in clinical trials.