Effect of immunosuppression on survival of allograft limbal stem cells

To examine whether the application of immunosuppression enhances the survival of limbal allograft stem cells. Wistar (allograft) or Fischer 344 (isograft) rat limbal tissue was transplanted into superior lamellar excision sites in Fischer 344 rats. Allograft-recipient rats received an immunosuppressive agent or vehicle for 8 weeks. Graft-recipient rats were examined by slit-lamp microscopy for clinical signs of rejection, and some recipients were killed for immunohistochemical analysis during rejection. One month from the time of transplantation, other (five in each group) recipients received daily injections of 5-bromo-2-deoxyuridine (BrdU) at a dose of 5 mg/100 g for 2 weeks, followed by a 1-month BrdU-free period before death. After the rats were killed, limbal allograft eyes were removed for BrdU staining to identify label-retaining cells. The labeling index of transplanted limbal basal epithelial cells was determined. In nonimmunosuppressed allograft recipients, clinical rejection occurred between days 5 and 10 after transplantation (median, 7 days). In contrast, rejection was suppressed for more than 60 days (median value) when the immunosuppressive was administered. Numerous MHC class II(+), CD4(+), and CD8(+) T cells were identified with acute rejection. Immunosuppressive-treated allografts had significantly less inflammation compared with untreated controls. Furthermore, immunosuppressive-treated allografts showed more label-retaining basal cells in transplanted limbal epithelium compared with untreated allograft controls ( P < 0.01). The survival of limbal allograft stem cells can be improved by immunosuppression. The limbal allograft procedure described here provides a useful model for evaluating a suitable alternative means of sustaining the survival of corneal stem cells.