Progress in Therapies for Retinitis Pigmentosa

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Therapies for several forms of degenerative blindness have been under development for some years. Here is news of progress towards trials for two of them:

Two recent experimental treatments - one involving skin-derived induced pluripotent stem (iPS) cell grafts, the other gene therapy - have been shown to produce long-term improvement in visual function in mouse models of retinitis pigmentosa (RP).
Researchers tested the long-term safety and efficacy of using iPS cell grafts to restore visual function in a mouse model of RP. [The] cells were administered, via injection directly underneath the retina, when the mice were five days old. The iPS cells assimilated into the host retina without disruption, and none of the mice receiving transplants developed tumors over their lifetimes, the researchers reported. The iPS cells were found to express markers specific to retinal pigmented epithelium (the cell layer adjacent to the photoreceptor layer), showing that they had the potential to develop into functional retinal cells. Using electroretinography, a standard method for measuring retinal function, the researchers found that the visual function of the mice improved after treatment and the effect was long lasting.

In the [other] study, the [researchers] tested whether gene therapy could be used to improve photoreceptor survival and neuronal function in mice with RP caused by a mutation to a gene called phosphodiesterase-alpha (Pde6α) - a common form of the disease in humans. To treat the mice, the researchers used adeno-associated viruses (AAV) to ferry correct copies of the gene into the retina. The AAV were administered by a single injection in one eye, with the other eye serving as a control.

When the mice were examined at six months of age (over one-third of the mouse lifespan), photoreceptor cells were found in the treated eyes but not in the untreated eyes, the researchers reported. More important, the treated eyes showed functional visual responses, while the untreated eyes had lost all vision.

Link: http://www.eurekalert.org/pub_releases/2012-12/cumc-tnt122012.php