Patients with macular degeneration are having their sight partially restored using human embryonic stem cells. As important as the development is for people in danger of going blind, the announcement also marks the first medium-term demonstration of the safety of embryonic stem cells, with implications for a host of other conditions.
Stem cell science is promising to replace everything from hearts to kidneys, with some hopes for diseases like MS as well. However, debate has raged over whether treatments should involve human embryonic stem cells (hESCs) or adult pluripotent stem cells from the patient themselves. The debate is partly about whether the use of hESCs is ethical, but there are also questions of safety.
Many attempts to use ESCs in animals have produced tumors, and rejection by the immune system can also be a problem. So the fact that 18 patients have had hESCs implanted without negative effects an average of 22 months later is big news.
Half the patients have Stargardt's macular dystrophy and the other half have atrophic age-related macular degeneration, two of the most common causes of blindness in the developed world. Doses of 50,000-150,000 cells were applied. By treating one eye in each patient and leaving the other untouched, the researchers had the perfect control to establish the extent to which any changes were the result of the transplanted cells.
Publishing in The Lancet, a team led by Professor Robert Lanza of Massachusetts company Advanced Cell Technology write, “There was no evidence of adverse proliferation, rejection or serious ocular or systemic safety issues related to the transplanted tissue." Unsurprisingly, the surgery itself and the suppression of the immune system did produce negative effects, however, and four patients needed cataract surgery.
Ten of the patients experienced noticeable improvement in the visual acuity of their treated eye, while seven remained the same and only one got worse. On the other hand, none of the untreated eyes showed any improvement, although the researchers admit that one cannot rule out placebo effects since “both examiner and patient were aware of [which] eye underwent surgery.”
Schwartz et al/Lancet. Pigmentation progress after stem cell transplantation in eyes with age-related macular degeneration (A-C) and Stargardt's muscular dystrophy (D-F) and (G-I).
The authors note that the eye's capacity to tolerate foreign antigens make it a particularly attractive target for hESCs, and Lanza says, "As a result, immunoprivileged sites (that do not produce a strong immune response) such as the eye have become the first parts of the human body to benefit from this technology." Nevertheless, they point out, “A central feature of hESCs is that they have the capacity to proliferate indefinitely,” providing a potentially huge resource for treatments such as these.