Objective Measurement of Human Gene Therapy

Palo Alto, CA — Gene therapy has become a viable option for people with inherited eye disease, but because it is still a novel treatment, patient progress following gene therapy often relies on subjective measurements like walking through a maze in dim light or reading letters on a board. 

Researchers wanted to know if there was an objective way to measure the effects of gene therapy and whether that measurement could determine the durability of the treatment. Vinit Mahajan M.D., Ph.D., Stanford professor and vice chair of ophthalmology research, is a co-author on a case report that successfully answers both of these questions. 

Mahajan performed gene therapy on a patient referred to him by his longtime collaborator Stephen Tsang M.D., Ph.D., Columbia University Laszlo Z. Bito Professor of Ophthalmology and Professor of Pathology and Cell Biology, as part of the Spark Gene Therapy trials. Mahajan replaced the RPE65 gene to treat one form of Leber’s congenital amaurosis. It became the first FDA approved gene therapy trial after patients underwent subjective testing that showed improved vision. 

Senior author on the report, Janet Sparrow Ph.D., Columbia University Anthony Donn Professor of Ophthalmic Science and Professor of Pathology and Cell Biology, was able to identify the biochemical markers that verified the patient’s improved vision demonstrated during their subjective testing. Quantitative autofluorescence imaging made it quite obvious that the gene was now functioning. 

One of the ways ophthalmologists clinically diagnose patients with Leber’s Congenital Amaurosis is to take an autofluorescence image to see if there is a normal fluorescent pattern. Normally, the retina “glows” because of lipofuscin. If the RPE65 gene is not functioning, it does not make the lipofuscin metabolite and there is no glow. 

Mahajan said, “This study clearly shows that those cells that had the gene replaced are now functioning because we can clearly see the reemergence of the normal fluorescent pattern. This noninvasive way to measure their function is truly amazing. It gives us another really important diagnostic tool to validate gene therapy.”

Quantitative autofluorescence imaging can also reveal if gene therapy wears off after a certain length of time, which could determine if a patient needs another round of treatment. The images in this case report show durability of the gene therapy for six years. 

Mahajan said, “A subjective measurement makes it difficult to know if there has really been a change in the patient’s retina. Autofluorescence images can help us to see if the retina is functioning at the molecular level. Dr. Sparrow's work to make autofluorescence quantitative turns this technology into something very important and useful clinically.” 

Authors of Quantitative Autofluorescence Following Gene Therapy with Voretigene Neparvovec. published in JAMA Ophthalmology include: Levi SR, Oh JK, de Carvalho JRL, Mahajan VB, Tsang SH, Sparrow JR.