Cross-matches on donor cadaver retinal pigment epithelial cells in corneal risk patients

Background: Allografts can be rejected either through the antibody-mediated or cellular pathways. The objective of this study was to look at the extent of antibody formation in patients awaiting re-keratoplasty using cross-matches on cadaver retinal pigment epithelial (RPE) cells. Methods: Cadaver RPE cells were derived by trypsin digestion from donor eyes (n=1200). After 3 days of cell cultivation: the cells were adherent and began to lose their pigment. By day 7 most cells were clear and grew as a polygonal monolayer. MHC class I expression by RPE cells was studied by the W6/32 (anti-HLA-A, B, C) monoclonal antibody (MoAb) and that of class II (HLA-DR) by the 136 MoAb. Normal RPE cells express few class I and no detectable class II antigens. For the induction of MHC expression, cells were subsequently stimulated with 250 U/ml of recombinant gamma-interferon for 5 days. Cells were used for tissue typing and also for cross-matches with recipient serum. Cross-matches were subsequently performed and measured by flow cytometry. Results: Both class I and class II antigens were strongly enhanced, as could be shown by immunohistochemical staining. Some 20% of those patients awaiting rekeratoplasty (n=60) were positive for anti-HLA antibodies. In one case anti-DR3 antibodies were detected in a recipient who had had several rejection episodes after keratoplasty. Conclusions: RPE cells are not only useful for cadaver post-mortem HLA typing but also for donor-specific crossmatches. The degree of antibody formation after keratoplasty in rejecting patients was, however, low. This may imply that anti-HLA antibodies are not the major cause of corneal graft loss after keratoplasty.