Dynamics of donor cell persistence and recipient cell replacement in orthotopic corneal allografts in mice

To determine the extent to which donor cells persist and recipient cells repopulate each of the three cell layers of orthotopic corneal grafts in mice.

BALB/c, C57BL/6, and enhanced green fluorescence protein (EGFP) transgenic mice (B6 background) were used as donors and recipients for orthotopic syngeneic and allogeneic corneal grafts. Graft-bearing eyes were harvested at 5, 10, 15, 28, and 56 days, stained with propidium iodide, and observed (layer by layer) by confocal microscopy. Bone marrow-derived cells in the grafts were assessed immunohistochemically.

Donor epithelium was totally replaced by recipient epithelial cells within 15 days in both syngeneic and allogeneic grafts, whereas donor stromal keratocytes and endothelial cells were retained virtually intact in syngeneic grafts and in accepted allografts. In rejected allografts, neither donor-derived keratocytes nor endothelial cells were detected, and, instead, recipient-derived stromal fibroblasts, neovessels, and infiltrating leukocytes were heavily represented. The posterior surface of rejected grafts was devoid of corneal endothelium and was covered incompletely with bone marrow-derived cells of recipient origin.

Whereas in mice graft-derived epithelium is largely irrelevant to corneal allograft outcome, persistence of donor-derived endothelium and keratocytes correlates perfectly with graft acceptance. Recipient endothelium is incapable of covering the posterior surface of accepted or rejected corneal grafts, whereas bone marrow-derived cells of recipient origin come to occupy this site in rejected grafts.