Leg-Derived Mitochondria Injected into Human Eyes: Case One

Imagine borrowing a set of tiny batteries from your thigh and placing them into your eyes. It sounds like science fiction. Yet a research team has just reported the first known attempt to do something close to that in a human patient.

A tiny battery with a giant job

Mitochondria are the microscopic powerplants inside almost every cell, converting food and oxygen into usable energy. Some cells are especially hungry for that energy. Retinal ganglion cells, the neurons that ferry visual signals from the eye to the brain, rank among the most energy-demanding in the nervous system. When oxygen and blood flow stop, mitochondria falter. Cells can go dark, and vision can fade.

In animal experiments, researchers have shown that transplanting healthy mitochondria into injured tissue can sometimes revive struggling cells and slow degeneration. The leap from animals to people, however, is large. Which is why the new case report matters: doctors extracted mitochondria from a patient’s leg muscle and injected them directly into the vitreous, the jelly-like fluid filling each eye.

The patient was a 26-year-old woman who had suffered a severe brain hemorrhage and arrived at hospital roughly 18 hours after the event. She survived emergency surgery, but the prolonged period without adequate blood and oxygen left the optic nerves damaged and her sight near total loss. Conventional therapies offered no meaningful recovery over months, but imaging hinted at one critical detail: some retinal nerve fibers and ganglion cells remained, albeit thinned. Brain recordings also suggested that faint visual signals still reached the visual cortex. Could fresh mitochondria re-energize those half-alive neurons?

To minimize immune reactions, the team used the patient’s own tissue. A thigh biopsy yielded muscle cells, from which tens of millions of mitochondria were isolated, kept fresh, and injected into each eye. The procedure itself was uneventful. No severe adverse effects, no alarming immune response. That safety signal alone is notable for a first-in-human attempt, the authors reported in a preprint led by neuroscientist David Putrino from the Icahn School of Medicine at Mount Sinai and posted to Research Square.

Brain and eye imaging showing damage to the patient's optic nerves and retinal ganglion cells before the mitochondrial transplant. 

Unexpected flickers of response

Before treatment, clinicians had measured pupillary responses to light 45 times over 71 days without a single normal result. Then, within days of the mitochondrial injections, both pupils began to show normal constrictions to light in some tests. In addition, cortical recordings taken at three separate sessions—days 3, 44, and 45 after the treatment—revealed organized visual responses that had not been detectable earlier.

Important caveats apply. The patient’s visual acuity did not improve beyond light perception. The pupillary improvements were temporary: the left eye showed the last normal response on day 11, and the right eye’s sporadic normal responses ceased by day 39. There was no direct evidence in this report that the injected mitochondria entered retinal ganglion cells and took over energy production. The study included a single patient and no control group; the authors explicitly say the case cannot prove causation.

Still, the pattern is intriguing. A procedure that is tolerable for a patient, and that coincides with transient physiological changes in the eye and brain, is a signal worth following. It suggests a testable hypothesis: perhaps cells that remain viable but energy-starved could benefit from periodic doses of healthy mitochondria.

Next steps and what to watch for

Before anyone can speak of therapies, several questions must be answered. Did the transplanted mitochondria integrate into retinal neurons, or did they trigger other processes that temporarily altered physiology? If mitochondria did enter target cells, how long do they survive and function? Would repeated injections be required to sustain an effect? And crucially, how reproducible and safe would this approach be across patients with different causes of vision loss?

Putrino and colleagues are pursuing those questions. As reported by Nature, Putrino said, "Now that we've shown that we can do this safely, we are working with the FDA to come up with a protocol for repeated serial mitochondrial injections." That statement highlights the pragmatic path ahead: safety trials, controlled studies, and careful tracking of both functional outcomes and any immunological consequences.

Related technologies also matter. Methods to purify mitochondria more efficiently, to label them for tracking, and to deliver them with greater precision inside the eye would strengthen future trials. Parallel research is exploring whether mitochondria taken from stem cells or other autologous sources could provide more robust benefits. Additionally, advances in retinal imaging and electrophysiology will help determine whether treatments restore cellular energy or merely produce short-lived physiological shifts.

Expert Insight

"This case is an important first step," says Dr. Elena Morales, a neuro-ophthalmologist who was not involved in the report. "We should not conflate a transient physiological signal with functional recovery. But the fact that the intervention was tolerated and that cortical responses briefly reappeared gives us a foothold. The next studies must combine imaging, electrophysiology, and molecular tracking so we can see where the mitochondria go and what they do."

Dr. Morales emphasizes realistic aims. "The goal is incremental: establish safety, then explore dosing and timing, then test efficacy in carefully controlled cohorts. If mitochondria therapy proves viable, it could complement other approaches like gene therapy or neuroprotective drugs, especially for conditions where energy deficiency is central to cell death."

The road from a single-case preprint to a validated clinical therapy is long. But the experiment opens a conceptual door: rather than replace cells, we may one day boost the energy supply of cells on the brink. For ocular diseases in particular, where retinal ganglion cells demand vast amounts of energy, that strategy could be especially relevant.

Researchers and clinicians will watch for follow-up studies that address integration, durability, and functional benefit. Meanwhile, this first human attempt provides both a caution and a spark: a caution because the evidence is preliminary and a spark because safe, targeted mitochondrial delivery has become a testable possibility.