Developing Universal ABO Blood Type Donor Lungs with Ex Vivo Enzymatic Treatment: A Proof of Concept Feasibility Study

Purpose This study explores feasibility and safety of using enzymes (FpGalNAc deacetylase & FpGalNase) to remove ABO-A antigens from donor lungs during ex vivo lung perfusion (EVLP). The enzymes have been reported to efficiently convert ABO-A blood to O (Withers, Nat Microbiol, 2019). Methods Human lungs (ABO-A1, n=5), declined for transplant, were treated with the enzymes during EVLP. Tissues were sampled before and after. The distribution and expression level of ABO antigens were analyzed by immunohistochemistry and flow cytometry. Lung function was monitored for side-effects. Immediate post-transplant immune response was simulated in an ex vivo model of hyperacute lung rejection, with introduction of ABO-O plasma (carrying ABO antibodies) as the surrogate for the recipient circulation (Fig.1H, n=1). The physiology and histology of lungs were analyzed for anti-A-induced immune responses. Results The histo-blood type A (BTA) antigens in the A1 lungs are observed primarily on endothelial and epithelial cells. BTA were cleared remarkably well from treated lungs (Fig.1A). The enzymes convert vascular BTA to the blood group H (BTH) antigens found in ABO-O tissue (Fig.1B). Over 97% of endothelial BTA antigens were removed within the typical 4h clinical EVLP timeframe using very low dose (1 µg/mL) enzymes (Fig.1C). No acute side-effects were seen (Fig.1D-G). The rejection model showed that the 3-hour treatment of human lung with low dose enzymes prevented the damage triggered by type O plasma (presumably due to anti-A antibodies) as observed in the physiology and histology of the control lung (Fig.1I-J). Conclusion Ex vivo enzymatic treatment can efficiently remove ABO-A antigen in donor lungs without acute side-effects. Preliminary results show that the treatment can prevent ABO mismatch-induced early damages. The treatment can potentially allow expansion of ABO-incompatible lung transplantation, leading to significant improvements in logistics and fairness of organ allocation.