How does the treatment work?
The jCyte treatment involves injecting a dose of several million of these cells into the vitreous (jelly) of the eyeball, with a local anaesthetic. This can be done as an outpatient procedure.
Unlike gene therapies, jCell is not designed to overcome a specific genetic fault and its potential beneficial effects do not depend on genetic diagnosis. It could therefore possibly be useful for a relatively large proportion of those living with RP, even those for whom genetic testing has not returned a result.
jCyte do not expect their stem cells to integrate into the retina and replace degenerated photoreceptors. (Some scientists question whether this is even possible.) Instead, their rationale is that jCell will provide nourishment and support, by way of substances called trophic factors, to slow degeneration and improve survival in the remaining retina. It would therefore be expected that this approach would work best when there is still some relatively healthy retina left, and would not be successful if the retina was completed degenerated. People with “very advanced disease” were not included in jCyte’s phase 2 trial.
What did the phase 2 trial show?
In summary, the phase 2 trial showed that:
- On average, trial participants receiving a single 6 million cell dose had an early, sustained, and significant improvement in best corrected visual acuity (BCVA) i.e. the number of letters they could read from an eye chart.
- Other measures, which evaluated different aspects of functional vision in people with RP, were aligned with the significant results in BCVA, with meaningful improvements in peripheral visual field area, contrast sensitivity, and the ability to navigate a maze in low light.
- The best outcomes were seen in people with the greatest retinal thickness, as measured by OCT scans. This basically means that people with more remaining healthy retina experienced the greatest benefit from the treatment, which would make sense given the rationale of supporting surviving retinal cells.
What is the next step?
jCyte now plans to progress to phase 3, or what’s known as a “pivotal” trial, which they hope will produce enough robust data for the company to apply for licensing. The phase 2b findings will be used to help define inclusion criteria for phase 3 participants, which means that the new trial will only recruit people with a certain minimum retinal thickness, who have the best chance of responding to the treatment.
At the moment, we do not have any details, such as trial site locations or a start date, for the phase 3 trial. We would expect most trial sites to be in the USA, but it’s possible that jCyte may select a UK site.
For those with very advanced sight loss, the optogenetics approach, which is also independent of genetic diagnosis, is showing some promise.