First-of-its-kind transplant injects a blind patient's own mitochondria into her eyes

Scientists have extracted mitochondria from a woman's leg muscles and injected them into her eyes in an attempt to treat near-total blindness, reporting the first such transplant performed in human eyes (Nature). The procedure caused no inflammation or side effects, but produced only a limited effect on light responses and did not restore her vision. The findings were posted as a preprint on 10 August that has not been peer reviewed.

The woman had suffered a brain bleed in February that injured her optic nerve and retina, leaving her nearly completely blind, with no pupil response to light. After the injections, carried out under emergency approval from the US Food and Drug Administration granted in May, her pupils showed a response to light again — though the effect was temporary, subsiding after about four weeks. In a post-transplant low-vision assessment she was noted to be perceiving shapes and shadows in her left eye, co-author David Putrino, a neuroscientist at the Icahn School of Medicine at Mount Sinai in New York, told Nature.

Transplanting healthy mitochondria — the organelles that generate energy in cells — is being explored as a treatment for diseases that damage these structures in tissue, on the theory that damaged cells can take up healthy mitochondria and partially regain function. Previous human trials have transplanted mitochondria into the heart and brain; this is the first attempt in the eye. Rodent studies have shown that delivering mitochondria into the vitreous fluid increased the survival of retinal ganglion cells remaining viable after optic-nerve injury.

Safety was the primary goal rather than efficacy. "We can't prove efficacy at all, nor are we trying to," Putrino said, adding that "we saw a significant effect on physiological changes in the eye." The main concern going in was triggering an immune attack on the injected material, but tests found no signs of inflammation or damage in either eye.

Independent experts urged caution about the therapeutic signal. Temurkhan Ayupov, a mitochondria biologist at the Institute of Molecular and Clinical Ophthalmology Basel in Switzerland, told Nature the study shows it is "relatively safe" to inject a person's own mitochondria into the eyes, "but it does not confirm the therapeutic effect of a mitochondrial transplant."

**Sources:** Nature