Researchers at the University of Pittsburgh School of Medicine have developed an early-stage experimental therapy known as a “living eye drop,” which uses naturally occurring eye bacteria to promote corneal wound healing. The proof-of-concept study, published in Cell Reports, demonstrates that the harmless eye-dwelling bacterium Corynebacterium mastitidis can be genetically engineered to release therapeutic molecules that support healing after corneal injury in a mouse model.
According to senior author Anthony St. Leger, Associate Professor of Ophthalmology and Immunology at the University of Pittsburgh and the UPMC Vision Institute, this study marks the first time scientists have engineered a naturally occurring ocular microbe to deliver a therapeutic agent directly on the eye’s surface.
“This is the first demonstration that a microbe living on the ocular surface can be engineered to deliver a therapeutic that improves eye health,” he explained. “It introduces the concept of ‘living medicine’ for the eye—something applied once that can remain in place, protect the tissue and support healing.”
Challenges With Conventional Eye Drop Treatments
Treating ocular surface diseases often presents challenges because tears continuously wash medications away. As a result, patients frequently need to apply eye drops multiple times a day. This limitation reduces treatment effectiveness for conditions such as Dry Eye Disease and Corneal Abrasion.
To overcome this challenge, the researchers explored whether naturally occurring bacteria on the eye could function as long-term delivery systems for therapeutic molecules.
Engineering Bacteria to Deliver Anti-Inflammatory Therapy
To test this approach, scientists genetically modified Corynebacterium mastitidis, a benign bacterium that naturally lives beneath the eyelid. The engineered microbe was designed to continuously produce the anti-inflammatory cytokine Interleukin‑10, which plays a key role in regulating immune responses and inflammation.
In mouse experiments, corneas that were gently scratched and treated with the engineered bacteria healed significantly faster than those treated with unmodified bacteria or saline. Moreover, when researchers blocked the receptor for Interleukin‑10, the healing benefit disappeared. This result confirmed that the improved healing depended specifically on the cytokine.
Promising Results in Human Cell Studies
In addition, the team developed a modified version of the bacterium capable of producing human Interleukin‑10. Laboratory tests showed that this engineered microbe improved wound closure in cultured human corneal epithelial cells—the cells forming the outermost layer of the cornea. It also reduced inflammatory signalling in human immune cells.
Although these findings remain preliminary, they suggest that the approach could eventually be adapted for human therapies.
A Modular Platform for Future Eye Treatments
Researchers also emphasised that the technology is designed to be modular. As Anthony St. Leger explained, scientists can potentially replace the therapeutic gene with others that encode different cytokines, growth factors or healing proteins.
As reported by medicalxpress, this flexibility could allow the platform to treat a variety of ocular conditions, including inflammatory eye diseases, corneal injuries and chronic ocular surface disorders.
Next Steps Before Clinical Use
Despite its promise, the therapy remains in the early stages of development. The research team must address several challenges before human trials become possible. These include creating built-in safety “off switches” and developing reliable methods to remove or deactivate the engineered bacteria when treatment is no longer required.
Conditions such as severe Dry Eye Disease, inflammatory ocular disorders and traumatic corneal injuries affect millions of people each year. While the current study does not yet establish a clinical therapy, it lays the groundwork for exploring whether engineered living microbes could deliver sustained anti-inflammatory or regenerative treatments directly to the eye.