Human Tissue Transplanted Retinas

There could be hope on the horizon for an untreatable genetic disease: Scientists have successfully grown eye tissue in the lab and transplanted it into monkeys with models of a human degenerative disease that affects the retina. Not only did the graft survive, but it also showed signs of integration with the recipient’s eye cells, forming connections across which information could potentially flow. While this certainly doesn’t mean a cure is close, it demonstrates that the strategy could at least be feasible in humans, and lays the foundations for further studies.

The disease this study is centered on is called retinitis pigmentosa (RP), which actually refers to a group of genetic conditions in which the eye’s light sensitive tissue, the retina, degrades over time. While it rarely leads to complete blindness, affected individuals struggle to see in low light conditions and progressively lose their peripheral vision.

More than 45 genes have so far been implicated in RP, which is why some research efforts have focused on gene therapy as a potential treatment. Among various other strategies currently under scrutiny, with improvements in cell culture techniques another possible avenue that has emerged involves replacing the damaged tissue with cells grown in the lab. Scientists have already demonstrated that it’s possible to create enough retinal tissue to be relevant for clinical use using human stem cells, and studies on rodents have shown that transplants of this tissue can indeed survive in the eye and even integrate with host cells.

Although useful, rodents can only offer us so much information given their physiological and anatomical differences with humans, so in order to progress scientists have to develop more relevant models that could offer a more reliable idea of the viability of such procedures. That’s where the present study comes in, which worked with primates as well as rodents.

Described in the journal Proceedings of the National Academy of Sciences, researchers in Japan began by growing retinal tissue from human stem cells and then transplanting this into rats, with or without degenerated retinas. Encouragingly, the tissue matured in the rodents and formed layers of light-sensitive, or photoreceptor, cells. The team then created monkey models of retinitis pigmentosa and repeated the procedure.

As with the rats, the scientists found that the transplanted tissue successfully survived and turned into both types of photoreceptors – rods and cones. The former are more sensitive to light than the latter, but cones are the ones concerned with color. Importantly, the tissue showed signs of integration with the monkey’s bipolar cells, sensory nerves that relay visual information.

While this isn’t enough to suggest that the procedure will help restore vision in humans, the fact that the graft may have developed functional connections with host cells is encouraging and definitely warrants further investigation. And now scientists have an established model to work with, hopefully it won’t be too long before we know whether human trials are worth pursuing.

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