People who suffered blinding eye injuries have had their sight restored using a new form of stem cell therapy.

American surgeons took stem cells from the patient’s healthy eye and transplanted them into the injured eye, successfully repairing previously “irreversible” damage.

The experimental procedure safely restored corneal surfaces in 14 patients who were followed for 18 months.

Researchers say this clinical trial shows that the experimental treatment for injuries to the cornea is both “feasible and safe.”

Called cultivated autologous limbal epithelial cells (CALEC), the treatment was developed at Massachusetts Eye and Ear, a specialty hospital located in Boston, and became the first stem cell therapy for the eye ever trialed in the United States.

The research team explained that the ground-breaking procedure consists of removing stem cells from a healthy eye with a biopsy, expanding them into a cellular tissue graft in a new manufacturing process that takes two to three weeks, and then surgically transplanting the graft into the eye with a damaged cornea.

“Our first trial in four patients showed that CALEC was safe and the treatment was possible,” said Principal investigator Professor Ula Jurkunas.

“Now we have this new data supporting that CALEC is more than 90% effective at restoring the cornea’s surface, which makes a meaningful difference in individuals with cornea damage that was considered untreatable.”

The team showed CALEC “completely restored” the cornea in 50% of participants at their three-month visit and that rate of complete success increased to 79% and 77% at their 12- and 18-month visits, respectively.

With two participants meeting the definition of partial success at 12 and 18 months, the overall success of CALEC was 92% at 18 months. Three participants received a second CALEC transplant, one of whom reached complete success by the study end visit.

Prof Jurkunas said CALEC displayed a high safety profile, with no serious events occurring in either the donor or recipient eyes. The only major adverse event, a bacterial infection, occurred in one participant, eight months after the transplant due to “chronic” contact lens use.

Other adverse events were minor and resolved quickly following the procedures.

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The researchers say the study shows the “promise” of cell therapy for treating incurable conditions.

One limitation of the approach is that it is necessary for the patient to have only one involved eye so a biopsy can be performed to get starting material from the unaffected normal eye. Study team members said that an allogenic manufacturing method would, in the future, allow for CALEC to be possible in patients with two damaged eyes rather than just one.

CALEC remains an experimental procedure and is currently not offered at Mass Eye and Ear or any other hospital, and research team says additional studies will be needed before the treatment is submitted for federal approval.

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“We feel this research warrants additional trials that can help lead towards FDA approval,” said Jurkunas.

“While we are proud to have been able to bring a new treatment from the lab bench to clinical trials, our guiding objective was and always will be for patients around the country to have access to this effective treatment.”