Bioengineered corneal surface replacement found to be successful in two small studies

Technique varies on ex vivo expansion of stem cells for severe ocular surface disease.

SACRAMENTO, Calif. — Transplantation of a bioengineered composite corneal surface in patients with severe ocular surface disease from limbal stem-cell deficiency has resulted in restored or improved vision in two recently published small studies. The two research teams, one from the University of California here and the other from Taiwan, used slightly different techniques to achieve ex vivo expansion of stem cells.

In the California study, which appeared in Cornea, 14 patients who were unresponsive to standard medical and surgical treatments were chosen for transplantation. Ten patients received autologous grafts, and four received allogenic grafts. “The procedure was successful in 10 out of the 14 patients, restoring a clear corneal surface and markedly improving their sight,” said coauthor R. Rivkah Isseroff, MD, a professor of dermatology and cell biology at the University of California, Davis. The four failures were all from autologous grafts.

The Taiwanese study, which was printed in the New England Journal of Medicine, involved taking specimens of limbal epithelial cells from the healthy contralateral eyes of six patients with severe unilateral corneal disease. “An advantage of this technique is that only a small amount of tissue is necessary from the normal fellow eye,” said first author Ray Jui-Fang Tsai, MD, chair of the Department of Ophthalmology at Chang Gung Memorial Hospital, Chang Gung University, Taoyuan, Taiwan.

The epithelial cells were cultured and expanded on amniotic membrane for 2 to 3 weeks. Complete re-epithelialization of the corneal surface occurred within 2 to 4 days of transplantation in all six eyes. After a mean follow-up period of 15 months, the mean visual acuity also improved from 20/112 to 20/45. “Because only autologous cells are transplanted, immunosuppression is not required,” Dr. Tsai said.

Varied approach

The two new approaches differ in the way limbal epithelial cells are treated and the way the graft is made. The Taiwanese group seeds harvested corneal stem cells directly onto an amniotic membrane, rather than first expanding the corneal cells in laboratory dishes. “Because we expanded the cell numbers before we made the graft, we have extra cells for freezing,” Dr. Isseroff said. Therefore, “if the technique fails, we can always go back to the freezer and take out more cells to make a new graft.”

The size of the harvested limbal tissue containing epithelial cells was 1 mm by 2 mm in the Taiwanese group and 2 mm by 2 mm in the California group. These small sizes are “not believed to compromise the integrity of the eye,” Dr. Isseroff said. No complications from harvesting were reported in either study.

Dr. Isseroff and Ivan R. Schwab, MD, a professor of ophthalmology at the University of California, Davis, and a specialist in corneal surface disease, wrote an editorial in the New England Journal of Medicine that underscored the significance of the Taiwanese study. The two doctors noted that theoretically an allograft from a cadaveric donor should be successful. However, despite the promise of bioengineered corneas, “we need a better way of characterizing the stem cells of the cornea,” Dr. Isseroff said. “A second challenge is to find a laboratory-engineered scaffolding that would release us from the need to use amniotic membrane.”

Challenging problem

Edward J. Holland, MD, director of cornea services at the Cincinnati Eye Institute in Ohio, said that severe ocular surface disease “is one of the most challenging problems we face in all of ophthalmology. These patients have severe visual loss. Standard approaches of corneal transplantation have failed.” The two recent studies “build on our previous techniques and offer a newer and potentially better technique, although they are very new and certainly have to be evaluated critically. We need to look at more long-term results from these reports.”

Nonetheless, Dr. Holland is intrigued by the novelty of the new approach. “At the present time, we either take a significant number of cells from a cadaveric donor or remove 50% of cells from healthy eyes.

This new technique takes a small amount of cells that are expanded in the laboratory,” he said. With a keratolimbal allograft, “we’re transplanting limbus only. We’re not transplanting a large sheet of cells.” Harvesting cells from a living donor, on the other hand, “allows us the opportunity to remove some conjunctival tissue along with limbus. Some of these diseases have marked inflamed conjunctiva and benefit from the transplanted conjunctiva.”

But there is a theoretical long-term risk to the standard procedure of harvesting so many stem cells from a living donor eye. “You are subjecting this eye to loss of some stem cells. Who knows what can occur 20 to 30 years from now?” said Dr. Holland, a clinical professor of ophthalmology at the University of Cincinnati. The new technique also poses a potential problem down the road. “You are taking only a small number of cells for expansion. We simply don’t know if that small number of cells will be sufficient to sustain a healthy epithelium over the lifetime of a patient,” Dr. Holland said. In essence, “the small number of cells harvested is an advantage to the donor eye but is a potential disadvantage to the recipient eye.”

Fellow eye best source

Gary S. Schwartz, MD, a clinical assistant professor of ophthalmology at the University of Minnesota in Minneapolis, has collaborated with Dr. Holland on research in ocular surface disease from limbal stem-cell deficiency. “Standard modalities of therapy are rarely effective,” said Dr. Schwartz, including penetrating keratoplasty, tarsorrhaphy and artificial tears. “The only treatment available to these patients is to replace the limbal stem cells.”

Dr. Schwartz said the best source of limbal stem cells is from the patient’s fellow eye. “You avoid the whole problem of systemic immunosuppression,” he said. However, “until this new technique was invented, we had to take this tissue from almost half of the other eye. Many patients have bilateral disease and cannot afford to give up 50% of the stem cells in their fellow eye.”

It is amazing, Dr. Schwartz said, “that we can now take a 2-mm square of stem cells from the other eye and within 1 month grow it roughly 100-fold before transplantation. In 5 years, I could see this becoming one of the standard treatment modalities as a source of cells to repopulate the diseased eye.”

For Your Information:

• R. Rivkah Isseroff, MD, can be reached at the University of California, Davis, Department of Dermatology, TB 192, One Shields Avenue, Davis, CA 95616; (530) 752-9767; fax: (530) 752-9766; e-mail: rrisseroff@ucdavis.edu. Dr. Isseroff has no direct financial interest in bioengineered corneas.
• Ray Jui-Fang Tsai, MD, can be reached at the Department of Ophthalmology, Chang Gung Memorial Hospital, Chang Gung University, Taoyuan, Taiwan; (886) 2 2795 5513; fax: (886) 2 2795 5534; e-mail: raytsai@ms4.hinet.net. Dr. Tsai has filed a provisional patent in the United States for his transplantation method.
• Edward J. Holland, MD, can be reached at the Cincinnati Eye Institute, 10494 Montgomery Rd., Cincinnati, OH 45242; (513) 984-5133, ext. 3151; fax: (513) 984-4870; e-mail: eholland@isco.net. Dr. Holland has no direct financial interest in bioengineered corneas.
• Gary S. Schwartz, MD, can be reached at 8650 Hudson Blvd., Ste. 110, Lake Elmo, MN 55042; (651) 702-0436; fax: (651) 702-7333. Dr. Schwartz also has no direct financial interest in bioengineered corneas.

References:

• Schwab IR, Isseroff RR. Bioengineered corneas — the promise and the challenge. N Engl J Med editorial. 2000;343:136-138.
• Schwab IR, Reyes M, Isseroff RR. Successful transplantation of bioengineered tissue replacements in patients with ocular surface disease. Cornea. 2000; 19(4):421-426.
• Tsai RJF, Li LM, Chen JK. Reconstruction of damaged corneas by transplantation of autologous limbal epithelial cells. N Engl J Med. 2000;343:86-93.