Stem cell-based CALEC therapy achieves 90% corneal surface restoration in clinical trial

(Image Credit: AdobeStock/Siarhei)

An expanded clinical trial found a high proportion of complete or partial success in experimental stem cell treatment for blinding cornea injuries.¹ The results of the Phase 1/2 trial, which evaluated 14 patients that were treated with cultivated autologous limbal epithelial cells (CALEC) and followed them for 18 months, was published in Nature Communications, according to a news release.

The CALEC procedure consists of removing stem cells from a health eye with a biopsy, expanding said cells into a cellular tissue graft in a 2-3 week novel manufacturing process, and then surgically transplanting the graft into the eye with a damaged cornea. CALEC was developed at Mass Eye and Ear, a member of the Mass General Brigham healthcare system. The CALEC trial is the first human study of a stem cell therapy to be funded by the National Eye Institute.¹

“Our first trial in four patients showed that CALEC was safe and the treatment was possible,” said Principal Investigator Ula Jurkunas, MD, associate director of the Cornea Service at Mass Eye and Ear and professor of Ophthalmology at Harvard Medical School, in the release. “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.”

According to study findings, 50% patients treated with CALEC had cornea completely restored at their 3-month visit, with a rate of complete success increasing to 79% and 77% at their 12- and 18-month visits, respectively. The definition of partial success at 12 and 18 months was met for 2 of the study participants, with an overall success of CALEC at 93% and 92% at 12 and 18 months. A second CALEC transplant was received by 3 participants, with 1 patient reaching complete success by the study end visit.¹ An additional analysis of CALEC’s impact on vision showed varying levels of improvement of visual acuity in all 14 patients, according to the release.

Additionally, the study demonstrated that CALEC displayed a high safety profile, with no serious events occurring in either the donor or recipient eyes. One adverse event in the form of a bacterial infection occurred in 1 patient 8 months after the transplant due to chronic contact lens use.¹ Other adverse events were minor and resolved quickly following the procedures, according to the release.

While CALEC is still an experimental procedure and is not currently offered at Mass Eye and Ear or any US hospital, Jerome Ritz, MD, of Dana-Farber Cancer Institute’s Connell and O’Reilly Families Cell Manipulation Core Facility and research collaborator in the CALEC trial, believe in the promise that cell therapy holds for treating incurable conditions.¹

“Our future hope is to set up an allogeneic manufacturing process starting with limbal stem cells from a normal cadaveric donor eye,” said Ritz in the release. “This will hopefully expand the use of this approach and make it possible to treat patients who have damage to both eyes.”

For now, future CALEC studies are anticipated to include larger numbers of patients at multiple centers with longer follow ups and a randomized-control design.¹

“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.”

Reference:

1. Novel stem cell therapy repairs irreversible corneal damage in clinical trial. News release. Mass General Brigham. March 4, 2025. Accessed March 17, 2025. https://www.massgeneralbrigham.org/en/about/newsroom/press-releases/calec-stem-cell-therapy-clinical-trial-repairs-corneal-damage