Minimal immune response after transplantation of a cryopreserved human amniotic membrane on the ocular surface

Human amniotic membrane (hAM) is considered to have low immunogenicity since Akle et al. reported no anti-HLA antibodies (Abs) in four volunteers after subcutaneous grafting of fresh hAM in 1981. But the sensitivity of the detection methods has significantly improved since then. Furthermore, hAM graft is a massive local input of allogenic HLA-G whose potential immunogenicity has never been assessed. The objective of this study was to look for the presence of anti-HLA class I, II, and anti HLA-G Abs at 1 and 3 months after hAM transplantation on the ocular surface.

Twenty-three patients who required a hAM graft on the ocular surface (cornea and/or conjunctiva) for any indication were enrolled in this prospective clinical study. Sera were collected on the day of transplantation and at 1- and 3-months post-transplantation (M0, M1, M3). Anti-HLA class I, and II Abs were assessed using the Luminex® Single Antigen technique. Anti HLA-G Abs were assessed using an in-house ELISA-based detection assay, derived from the Monoclonal Antibody specific Immobilization of Platelet Antigen (MAIPA) assay.

Only one patient showed de novo Ab apparition after transplantation. Six patients showed a significant increase of preformed Abs MFI (>50 %) during follow up although transient in one out of six. No anti-HLA-G Abs were identified before or after hAM transplantation.

This is the first study to investigate anti-HLA class I, II, and anti HLA-G Abs in a clinical setting after cryopreserved hAM transplantation. The main finding of this study is the minimal humoral immune response in our patients, supporting the immunological safety of the procedure and the excellent clinical tolerance reported across various indications over decades of use.