Cultivated epithelial stem cells may repair acute corneal damage

Limbal and oral tissue grafts are options, depending on indications such as age and degree of tissue damage.

LISBON – Repair of inflamed tissues in Stevens-Johnson syndrome or after chemical trauma may be possible with the use of cultivated epithelial stem-cell sheets, according to a researcher speaking here.

Radical surgery during the acutely inflamed phase of ocular surface disorders may be accomplished with engineered ocular tissue, using either sheets of limbal allograft tissue or autografts cultivated from patients’ buccal mucosal cells, said Shigeru Kinoshita, MD, PhD.

“Most doctors think that radical surgery at the acute phase is a contraindication, but if we could use this kind of cultivated epithelial cell sheet, maybe we could make some sort of paradigm shift,” Dr. Kinoshita said at the European Society of Cataract and Refractive Surgeons meeting.

Dr. Kinoshita, of the Kyoto Prefectural University of Medicine, discussed a number of cases in which epithelial stem-cell sheets were created to treat corneal damage from chemical burn scarring and tissue damage from Stevens-Johnson syndrome.

Dr. Kinoshita said the technique involves growing cells on a layer of amniotic membrane for 2 weeks and then cutting out the grafts using a trephine that is 19 mm in diameter.

In an interview with Ocular Surgery News, Dr. Kinoshita explained that with these cultivated epithelial cell sheets, ophthalmologists might be able to avoid the pitfalls of limbal transplantation, known for a high rate of failure due to inflammation and the inability to effectively regenerate epithelial cells.

“The ocular surface can be covered by these epithelial cells, and once the epithelial cells heal, the underlying tissue thinks it has already finished the wound healing process, so the inflammation goes away quite rapidly,” he said.

He explained that for the grafts to be successful, the epithelial cell sheet must have proliferative activity in the basal cells and must maintain a tight adhesion to the most superficial cell layers.

Scientists can ensure this tight adhesion by using what Dr. Kinoshita called an air-lifting technique to promote epithelial cell differentiation.

According to Dr. Kinoshita, the technique involves decreasing the amount of culture medium at the end of cultivation in order to expose the most superficial layer to the air. As this promotes differentiation, it also produces a tight bond at the cell junction border.

“If we didn’t use the air-lifting technique, we would not have much good surface,” he said.

Acute phase surgery

According to Dr. Kinoshita, surgical grafts at the acute phase of corneal damage could at least help repair surface damage in the underlying corneal stroma.

He discussed the case of a patient with scarred corneal tissue as the result of a chemical injury. Researchers applied an allogeneic cultivated corneal epithelial graft to the cornea. After 2 years, the cornea had cleared up, and clarity remained stable almost 6 years postoperatively.

“This cornea is pretty clear with some superficial punctate keratitis but no major corneal epithelial problems,” he said.

Dr. Kinoshita emphasized the repeatability of this procedure by discussing the case of a man in the acute phase of Stevens-Johnson syndrome who experienced graft rejection.

In this patient, an initial graft of allogeneic cultivated corneal epithelial cells remained stable for 3 years but then underwent immunological rejection. This necessitated a second operation, which also failed within a year, followed by two more procedures.

“The interesting thing is that when we remove this sheet and then put it under a new cultivated epithelial cell sheet, still the cornea returns to the relatively normal or clear cornea, so the stripping of this epithelial cell sheet with amniotic membrane is so easy it’s like the flat printing of the basic procedure,” he said.

At their maximum capabilities, these grafts can potentially promote corneal wound healing and restore good visual acuity because there is no scarring on the corneal stroma once the epithelial cell layer has healed, Dr. Kinoshita said.

Varying indications

Autografts using small amounts of limbal tissue from the contralateral eye or buccal mucosal tissue from the oral cavity are options in acute cases depending on the indication, Dr. Kinoshita explained.

He said that allogeneic grafts would be best used in elderly patients with bilateral disease or in patients in an acute phase of a disease such as Stevens-Johnson syndrome.

He said autografts can be used in unilateral cases, and in young patients with bilateral disease, it is feasible to use oral epithelial stem cell transplantation because young patients do not require immunosuppressive drugs as much as older patients.

“I think there could be a trend from allograft to autograft, so that’s why in bilaterally affected ocular surface disorders we selected oral mucosal epithelial cells,” he said.

Dr. Kinoshita discussed the case of a 14-year-old girl in the acute phase of Stevens-Johnson syndrome. The patient was grafted with cultivated oral mucosal epithelial cells on the diseased eye, and she recovered corneal clarity at 1.5 years postop. He said that while some vessel ingrowth occurred, the epithelial cells stabilized.

“These [cells] are quite similar to those of the corneal epithelial cells but not identical,” he said.

He told the audience that the clinical success rate in 15 such cases was 87%.

Overall, corneal epithelial stem-cell sheets are preferable because they are more transparent than the oral mucosal epithelial cell sheets, he said.

“We have some chance to get a 20/20 vision after the operation using the cultivated cornea but not the oral,” Dr. Kinoshita said. “[With the oral stem-cell sheets], usually the visual acuity is about 20/60 or 20/200.”

He also said that the cultivated allogeneic sheets can be available more readily than oral mucosal sheets, which take 2 weeks to prepare.

Future work

Work on these cell sheets is still in an investigational phase, Dr. Kinoshita said, and more clinical work is needed before the technique could be widely used.

According to Dr. Kinoshita, researchers are in the process of switching from fetal cow serum to autograft serum in the cultivation process in order to enhance their progress. However, they are still using mouse fibroblasts as feeder cells, which are not optional.

“This is a kind of starting point in terms of tissue engineering or regenerative medicine in ophthalmology, so our technique is kind of open,” he said. “We can make remarkable progress in this field, so we are quite happy about that.”

For Your Information:

• Shigeru Kinoshita, MD, PhD, can be reached at 465 Kajii-cyo, Agaru, Hirokoji, Kawaramachi, Kamigyo-ku, Kyoto 602-0841, Japan; 81-75-251-5577; fax: 81-75-251-5663; e-mail: skinoshi@ophth.kpu-m.ac.jp.

• Jared Schultz is an OSN Staff Writer who covers all aspects of ophthalmology. He focuses geographically on Europe and the Asia-Pacific region.