In the current study, Dr MacLaren’s collaborators at Oxford, the NHS, University College London, Imperial College London, and other institutes reported the outcomes of 14 total participants – including the initial six – who had been followed for at least two years after receiving the gene therapy injections.
Overall, the patients’ treated eyes showed remarkable improvements over their control eyes, even the two who experienced adverse reactions early on.
"The early results of vision improvement we saw have been sustained for as long as we have been following up these patients and in several, the gene therapy injection was over 5 years ago. The trial has made a big difference to their lives,” Dr MacLaren said in a statement.
The median visual gain was 4.5 letters on the chart, and six patients were able to read more than 5 additional letters, aka more than an entire line. Untreated eyes lost a median of 1.5 letters during follow-up.
“The results suggest that retinal gene therapy can sustain and improve visual acuity in a cohort of predominantly late-stage choroideremia patients in whom rapid visual acuity loss would ordinarily be predicted,” the authors concluded.
A phase three clinical trial – the last step before a drug can be approved by the FDA – is already underway. The first gene therapy to be approved for an inherited disease, Luxturna, treats a similar progressive retinal disease that is mediated by mutations in a gene called RPE65. It was given the green light for US distribution in December 2017.