Immunogenicity of Human Amniotic Membrane in Experimental Xenotransplantation

Purpose: The immunogenic characterization of amniotic membrane is still unknown. This study was designed to examine the immunogenicity of human amniotic membrane, by using experimental xenotransplantation models.

Methods: Anti-human class I, class II, and Fas ligand monoclonal antibodies were used against cryopreserved amniotic membrane and cell viability tested for cryopreserved amniotic membrane. Amniotic membranes were then transplanted to the limbal area, intracorneal space, and under the kidney capsule. The scores of transparency and neovascularization after transplantation were recorded by slit lamp microscopy. Host cell infiltration was examined by hematoxylin-eosin or immunohistochemical staining. Control grafts were transplanted human cryopreserved skin grafts.

Results: Strong class I expression was observed in amniotic epithelium, mesenchymal cells, and fibroblasts in cryopreserved amniotic membrane. Some fibroblast cells unexpectedly expressed class II antigen. Fas ligand-positive cells were also detected in mesenchymal cells of amniotic stroma. Approximately 50% of epithelial cells of amniotic membrane cryopreserved for several months were still viable. In limbal transplantation, although some CD4(+) and CD8(+) T cells surrounded the amniotic graft, the response was mild. In intracorneal transplantation, all grafted amniotic membranes were accepted and clear, without host cell infiltration. In contrast, all skin grafts were rejected within 3 weeks after intracorneal transplantation. In amniotic membrane transplantation under the kidney capsule, extremely few host vessels and cells infiltrated the amniotic membrane; however, more host cells infiltrated the skin tissues under the kidney capsule.

Conclusions: Amniotic membrane seems to be immune-privileged tissue and to contain some immunoregulatory factors, including HLA-G and Fas ligand. The amniotic membrane may be useful to supplement corneal collagen, and it may be applied not only to the ocular surface but also intracorneally.