Bilateral distribution of the transgene seen with unilateral injection
Alfred A. Sadun, MD, and colleagues conducted an international post-mortem study of human eyes treated with adeno-associated virus (AAV) 2-based gene therapy for Leber’s hereditary optic neuropathy (LHON).
The study takeaway, according to first author Dr Sadun, was that the results provided the first evidence of successful gene transfection of retinal ganglion cells. This effect, interestingly, was seen in both patient eyes despite unilateral injection. He is from Doheny Eye Institute, UCLA School of Medicine, Los Angeles.
The results were reported at the American Academy of Ophthalmology annual meeting in San Francisco.
LHON is a maternally inherited blinding mitochondrial genetic disease caused by the m.11778G>A mutation in the ND4 gene. The treatment with AAV2-based gene therapy compensates for the m.11778G>A mutation in affected retinal ganglion cells, the investigators explained.
The study under discussion included 2 patients from the RESCUE clinical study. The patients were treated within 6 months following bilateral visual loss with an intravitreal injection of lenadogene nolparvovec (AAV2-ND4) at 9x1010 vg in one eye and a sham injection in the fellow eye.
The investigators conducted post-mortem histopathologic and molecular analyses of the eyes using retinal laser microdissection and droplet digital polymerase chain reaction.
Patient 1 was a 29-year-old man and patient 2, a 22-year-old man. Both had LHON caused by the m.11778G>A ND4 mutation. Patient 1 died as the result of acute alcohol toxicity and patient 2 of cardiac arrest.
In patient 1, the AAV2-ND4 transgene was distributed in both eyes but mostly in the right retina. In the non-injected eye, a minimal amount of transgene was found (1:200). At 1 and 2 months after treatment, the right eye had moderate anterior chamber and vitreous intraocular inflammation; at 6 months and 1 year no intraocular inflammation was seen. The anterior chamber contained a few old pigmented keratitis precipitates and pigmented cells. At 6 months, the right eye had intermittent throbbing that resolved with sleep; at 1 year, both eyes burned constantly and were photosensitive.
The investigators explained that the transgene in the inner half of the retina was about 100 times more concentrated than in the outer retina and was most abundant on the temporal retina. Transgene was not found in the retinal pigment epithelium, choroid and optic nerve.
In contrast, in patient 2 no focal areas of inflammation were seen in the retina or optic nerve head in both eyes. At 2 months and 1 year after injection, the left eye had mild intermediate intraocular inflammation (no concomitant treatment).
In commenting on the findings, the authors said, “The efficiency of DNA quantity for patient 2 was much higher than for patient 1. As in patient 1, AAV2-ND4 transgene was found in the retinas of both eyes.
The key points gleaned from the 2 patients are as follows:
“Taken together,” the investigators said, “this study provides the first evidence of successful gene transfection of retinal ganglion cells. It is intriguing that this occurred in both eyes after unilateral injection and further experiments at the optic chiasm and other parts of the brain of patient 2 are underway to determine the route of transfer.”