University of Pittsburgh scientists have turned a harmless eye-dwelling bacterium into a “living eye drop” that speeds corneal healing in mice. The early-stage work hints at future one-time treatments that could protect and repair the eye from within.
A team of University of Pittsburgh School of Medicine scientists has engineered a “living eye drop” that helps the surface of the eye heal itself, pointing toward a future where a single treatment could protect and repair vision for the long term.
In an early-stage study in mice, researchers turned a harmless bacterium that naturally lives under the eyelid into a tiny drug factory. The microbe was reprogrammed to release an anti-inflammatory molecule that sped up healing after corneal injury, according to findings published in Cell Reports.
Senior author Anthony St. Leger, an associate professor of ophthalmology and immunology at Pitt and the UPMC Vision Institute, noted the work marks a turning point in how scientists think about treating eye disease.
“This is the first demonstration that a microbe that lives on the ocular surface could be engineered to deliver a therapeutic that improves eye health,” St. Leger said in a news release. “It opens the door to the idea of ‘living medicine’ for the eye—something you apply once, and it stays, protects and helps the tissue heal.”
The cornea — the clear, dome-shaped surface at the front of the eye — is essential for sharp vision. It is also vulnerable. Everyday scratches from contact lenses, dry eye, infections or trauma can be painful and, in severe cases, threaten sight. Current treatments often rely on eye drops that must be applied several times a day because tears quickly wash medications away.
That constant rinsing makes it hard to keep drugs on the eye long enough to do their job. Patients may struggle to stick to frequent dosing schedules, and even when they do, the medicine does not stay put for long.
To get around this problem, the Pitt team focused on Corynebacterium mastitidis, a benign bacterium that naturally colonizes the eye. Instead of adding more and more drug from the outside, they asked whether they could turn this resident microbe into a built-in delivery system.
Using genetic engineering, the researchers modified C. mastitidis so it continuously secreted interleukin-10, or IL-10, a small protein that helps regulate inflammation. In a mouse model, the scientists gently scratched the cornea to mimic injury, then treated the eyes with either the engineered bacteria, unmodified bacteria or a simple saline solution.
Mice that received the IL-10–secreting microbes healed faster than those given regular bacteria or saline. When the team blocked the receptor that IL-10 uses to signal, the healing benefit disappeared. That result showed the effect depended on IL-10 and not just on the presence of bacteria.
To begin exploring whether the approach might one day work in people, the researchers also built a version of the microbe that releases human IL-10. In lab experiments, that engineered strain improved wound closure in cultured human corneal cells and reduced inflammatory signaling in human immune cells. Those tests are only an early indication, but they suggest the strategy could potentially be adapted for human use with further development.
Beyond IL-10, St. Leger and colleagues designed their system to be flexible.
“What makes this exciting is that the system is modular,” St. Leger added. “We built it so you can swap in different genes—different cytokines, growth factors or other proteins—to tailor the therapy to specific eye diseases.”
That modular design raises the possibility of custom “living medicines” for a range of conditions that affect the ocular surface, from severe dry eye and inflammatory disorders to traumatic injuries. Instead of repeated drops or injections, a single application of engineered microbes might one day provide a steady, long-lasting supply of helpful molecules right where they are needed.
The concept fits into a broader movement in medicine toward live biotherapeutics — living cells or microbes that deliver treatment from within the body. Similar strategies are being explored for gut, skin and cancer therapies. The eye, with its delicate tissues and constant tear flow, presents unique challenges but also a clear need for more durable treatments.
The researchers stress that their work is still at an early, proof-of-concept stage. Before any clinical trials in people, they will need to show that the engineered bacteria are safe, stable and controllable over time.
One key priority is building in reliable ways to turn the microbes off when they are no longer needed. The team notes that future versions will likely need genetic “off switches,” along with methods to remove or deactivate the bacteria on demand.
Regulatory testing, manufacturing standards and careful studies in larger animal models would also be required before the approach could move toward human patients.
Still, for the scientists behind the project, seeing their engineered microbe actually improve healing in a living system was a powerful moment.
“In my lab, we don’t typically build tools from the ground up,” added St. Leger. “Seeing a measurable improvement in healing in an animal model using something we engineered was incredibly rewarding, and it points us toward intriguing possibilities for future research.”
The study was led by Jackie Shane, with contributions from Matthew Evans, Yannis Rigas and Robert Shanks, all of Pitt. Their work lays a foundation for future efforts to harness the eye’s own microscopic residents as partners in protecting sight.