Botaretigene sparoparvovec is designed to tackle RPGR-associated sight loss by delivering healthy copies of the RPGR gene, packaged inside a harmless virus, into the back of the eye. The affected retinal cells can then use these genetic instructions to build healthy protein and overcome some of the deficits caused by the disease-causing mutations. This is the same mode of action as Luxturna, the only gene therapy for inherited retinal conditions currently available on the NHS.
The primary aim of a phase 1/2 clinical trial is to establish the safety of the treatment, and botaretigene sparoparvovec was found to be generally safe and well-tolerated. In addition, MeiraGTx has announced that trial participants given the treatment experienced significant improvements in their retinal sensitivity and vision compared to untreated “control” participants. These changes were measured via a number of methods, including static perimetry tests (which examine the visual field and establish how well different areas of the retina are working), letter charts, and functional vision tests that investigate how well people can navigate obstacles in various light conditions.
MeiraGTx will now proceed to a phase 3 trial, which will gather the larger amount of data needed to clearly establish the risk-benefit profile for the treatment and, if the outcome is positive, enable the company to apply to regulators for licensing. This further testing is important, as other treatments that had looked promising in early phase trials have failed to demonstrate sufficient benefit at phase 3.
The phase 3 trial is already recruiting participants in the USA, and four centres in the UK (in London, Leeds, Edinburgh and Glasgow) will begin recruiting soon. These UK sites are not yet active, and will only have capacity for a small number of participants; they may be able to complete recruitment from their existing clinic patients. For up to date information, see https://clinicaltrials.gov/ct2/show/NCT04671433?term=MeiraGTx&cond=X-Linked+Retinitis+Pigmentosa&draw=2&rank=1 .
Potential participants will need to have a genetic test result confirming that their sight loss is caused by mutations in the RPGR gene, and will also need to meet a number of other criteria. Participation in the trial would require regular visits to a trial centre for appointments. If you would like to know more about the clinical trials process, come along to our 2022 Annual Conference on 9 July, where we will hear from a trial centre ophthalmologist and a trial participant.