National Geographic : 2016 Sep
48 national geographic • September 2016 principal investigator, University of Califor- nia, Santa Barbara stem cell biologist Dennis Clegg, call it simply a patch. That patch’s chassis, made of the same stuff used to coat wiring for pacemakers and neural implants, is a thin wa- fer about the shape of this d but twice as large. Onto this speck Clegg distributes 120,000 cells derived from embryonic stem cells. Humayun and Clegg propose to use this patch to treat a condition called age-related macular degeneration (AMD). Going blind from AMD is the reverse of what happens in retinitis pig- mentosa: A blurry spot fogs the middle of one’s vision, then slowly darkens and spreads until you’re functionally blind. It’s the most common untreatable cause of vision loss, accounting for five percent of all blindness. AMD rises from cell decay in the eye’s rear- most layer, the retinal pigment epithelium. The RPE gives key support for the photoreceptor layer lying just in front of it. Humayun and Clegg hope the patch’s stem cell–derived RPE cells will replace these failed RPE cells. The cells can’t just be injected. In animal studies that Humayun and Clegg conducted, the cells integrated most effectively with the photoreceptor layer’s complicated architecture if they were on a well-placed patch. Position- ing the patch in just the right spot will be tricky business—precisely the kind of challenge that surgeons like Humayun crave. The trial just started and should end by 2018. If it works—a big if, as with all these projects—it could be useful in treating AMD and other forms of blindness. Humayun and Clegg also might learn things about how to fuse such cells into biological structures in other organs, paving the way for other cell-patch implants. The untapped potential of stem cells has drawn others pursuing blindness cures, includ- ing Henry Klassen of the University of California, Irvine. Klassen has spent 30 years studying how to coax progenitor cells—former stem cells that have begun to move toward being specific cell types—into replacing or rehabilitating failed ret- inal cells. Having successfully used retinal pro- genitor cells to improve vision in mice, rats, cats, dogs, and pigs, he’s testing a similar treatment in people with advanced retinitis pigmentosa. In a procedure that Klassen calls “Zen-like” in its simplicity, a surgeon uses a needle to quickly inject into the eye a half million to three million progenitor cells meant to play multiple roles in rescuing the failed retina. Some retinitis pig- mentosa patients who’ve had the procedure are seeing significantly more light and shape. Kristin Macdonald, a 50-something California resident who was nearly totally blind from retinitis pig- mentosa, received the treatment in one eye in June 2015. Now she can see more of her furni- ture, a van across a street, and, at a swimming pool, “a pale hue”—the reflected turquoise of the water that once was just black and white. Klassen hopes such gains will prove his premise that if you send the right cells to the right spots, they’ll know what to do.