Human stem cells restore monkey's sight

Researchers have successfully treated a hole in the macula of a macaque monkey, using a sheet of cells derived from human embryonic stem cells. 

A macular hole in the retina can lead to loss of sight in that eye, and while some can be treated with surgery others can be treated only with a retinal transplant. Researchers in Japan have now shown that they were able to close a 1mm macular hole in a macaque, using human embryo stem-cell derived retinal-precursor cells. They found that 200 days after transplantation, rod and cone cells responsible for light perception had developed, though no synapse formation between graft and host was observed. 

'We confirmed for the first time in a non-human primate model that embryonic stem-derived retinal organoid sheet transplantation facilitates the closure of macular holes,' said senior study author Dr Michiko Mandai of the Kobe City Eye Hospital, Japan.

The macaque was trained to undergo an eye test of its right eye which it had received the transplant in, to determine whether it could respond to coloured dots on a screen. Before the transplant it could only fix its gaze on 1.5 percent of the dots, but after the transplant this increased up to 26 percent of the dots.  

Researchers found that there was some rejection of the grafted sheet of cells, which was likely due to the macaque's immune system rejecting human-derived cells. They also say that the period of time between the grafting of the cells into the retina and removing the eyeball to observe results 200 days later, might not have been long enough for synapse formation to occur. Their results are published in Stem Cell Reports. 

'The mild rejection may have limited the functional integration of the transplanted tissue,' Dr Mandai says. 'Additionally, this was a single-case result for one eye, and the model did not exactly replicate the pathology of human refractory macular holes. However, the findings suggest that the surgical technique is feasible for human macular holes.'

Researchers plan on investigating how long it might take for synapse formation to occur, in future research.