Purpose: To evaluate the potential efficacy for autologous and allogeneic expanded corneal epithelial cell transplants derived from harvested limbal corneal epithelial stem cells cultured in vitro for the management of ocular surface disease.
Methods: Human Subjects. Of the 19 human subjects included, 18 (20 procedures) underwent in vitro cultured corneal epithelial cell transplants using various carriers for the epithelial cells to determine the most efficacious approach. Sixteen patients (18 procedures on 17 eyes) received autologous transplants, and 2 patients (1 procedure each) received allogeneic sibling grafts. The presumed corneal epithelial stem cells from 1 patient did not grow in vitro. The carriers for the expanded corneal epithelial cells included corneal stroma, type 1 collagen (Vitrogen), soft contact lenses, collagen shields, and amniotic membrane for the autologous grafts and only amniotic membrane for the allogeneic sibling grafts. Histologic confirmation was reviewed on selected donor grafts. Amniotic membrane as carrier. Further studies were made to determine whether amniotic membrane might be the best carrier for the expanding corneal epithelial cells. Seventeen different combinations of tryspinization, sonication, scraping, and washing were studied to find the simplest, most effective method for removing the amniotic epithelium while still preserving the histologic appearance of the basement membrane of the amnion. Presumed corneal epithelial stem cells were harvested and expanded in vitro and applied to the amniotic membrane to create a composite graft. Thus, the composite graft consisted of the amniotic membrane from which the original epithelium had been removed without significant histologic damage to the basement membrane, and the expanded corneal epithelial stem cells, which had been applied to and had successfully adhered to the denuded amniotic membrane. Animal model. Twelve rabbits had the ocular surface of 1 eye damaged in a standard manner with direct removal of the presumed limbal stem cells, corneal epithelium, and related epithelium, followed by the application of n-heptanol for 60 seconds. After 6 weeks, all damaged eyes were epithelialized and vascularized. Two such treated eyes were harvested without further treatment, to be used for histologic study as damaged controls. The remaining 10 rabbits received composite grafts (consisting of amniotic membrane with expanded allogeneic rabbit corneal epithelial cell transplants) applied to the ocular surface in a standard manner followed by the application of a contact lens. At 16 days following transplantation, 5 of the rabbits were sacrificed and the corneal rims were removed for histologic study. At 28 days, the remaining rabbits were sacrificed and the previously damaged eyes were harvested for histologic and immunohistochemical study.
Results: Human subjects. Of the 19 total patients admitted to the study, the presumed corneal epithelial stem cells of 1 patient did not grow in vitro. Of the remaining 18 patients (20 procedures, 19 eyes), 3 patients had unsuccessful results (3 autologous procedures), 1 patient had a partially successful procedure (allogeneic procedure), and 1 patient had a procedure with an undetermined result at present (allogeneic procedure). One unsuccessful patient had entropion/trichiasis and mechanically removed the graft and eventually went into phthisis. The other 2 unsuccessful patients suffered presumed loss of autologous donor epithelium and recurrence of the ocular surface disease (pterygium). The partially successful patient receiving an allogeneic transplant had infectious keratitis delay of his re-epithelialization; he has only minimal visual improvement but has re-epithelialized. The patient receiving the second allogeneic graft lost his donor epithelium at day 4. Additional donor epithelium was reapplied, but the result is undetermined at present. Amniotic membrane as carrier. The in vitro preparation of the amniotic membrane with corneal epithelial stem cell graft overlay was successful. Histology documented removal of the amniotic epithelium and reapplication of corneal epithelial cells. Animal model. The 2 rabbits that had no reparative surgery following standard ocular surface injury had histology and immunopathology consistent with incomplete corneal epithelial stem cell failure with vascularization and scarring of the ocular surface. Light microscopy and immunohistologic staining with AE5 confirmed the conjunctival phenotype of the ocular surface repair but also documented the incomplete model. The allogeneic stern cell transplants had varying results. One rabbit had a suppurative infection and lost the graft. Reparative surgery failed in 2 of the rabbits, failed partially in 3 of the rabbits, was partially successful in 3 others, and was successful in 1 rabbit at 28 days. Histologic and immunopathologic study documented successful growth of corneal epithelium onto the recipient surface.
Conclusions: 1. Presumed corneal epithelial stem cells can be harvested safely from the limbus and expanded successfully in vitro. 2. Expanded corneal epithelial cell cultures can be grown onto various carriers, but currently denuded amniotic membrane seems to be the best carrier for ocular surface repair. 3. Expanded corneal epithelial cell transplants appear to resurface damaged ocular surfaces successfully, but cellular tracking and further confirmation are required. 4. Expanded allogeneic corneal epithelial cell transplants are technically possible and may represent alternative treatment modalities for selected ocular surface problems. 5. These techniques potentially offer a new method of restoring a normal ocular surface while minimizing the threat of damage or depletion to the contralateral or sibling limbal corneal epithelial stem cells. 6. The rabbit model was probably incomplete and should be interpreted with caution. The complete eradication of all corneal epithelial stem cells from any eye is difficult, making confirmation of such work challenging. 7. The results of the rabbit model suggest that allogeneic grafts may restore a nearly normal ocular epithelial surface to certain ocular surface injuries.