Enzymatic blood group conversion of human kidneys for transplantation

Abstract

ABO blood group antigens present an immunological barrier in transplantation, restricting organ donor-recipient matches to blood group compatible pairings only. Due to the chronic shortage of donor organs worldwide, novel strategies to remove ABO blood group restrictions are desperately needed to increase the number of kidney transplants. This thesis describes the first example of enzymatic blood group conversion as a strategy to create “universal” blood group kidneys for transplantation. The principle of this strategy involves the cleavage of blood group antigens on the vascular surface of human kidneys by glycoside hydrolase enzymes, resulting in the conversion of blood group A or B substrates to a core H antigen structure found in the universal donor blood group O. This work involved optimising the delivery of these enzymes to human kidneys with ex vivo normothermic and hypothermic machine perfusion technologies to produce enzyme converted (ABOe) blood group O kidneys. Firstly, an a-galactosidase enzyme from Bacteroides fragilis was used to remove blood group B antigens from human tissue in vitro and ex vivo in Chapter 4, successfully converting three human kidneys during normothermic perfusion. Secondly, a pair of enzymes from Flavonifractor plautii were used to remove blood group A antigens from human kidneys in Chapter 5. Here, both hypothermic and normothermic machine perfusion were used to successfully remove blood group A antigens from nine human kidneys ex vivo, reflecting the flexibility of this strategy. To explore cellular responses to blood group incompatible conditions, an ABO-incompatible model of kidney transplantation was established in Chapter 6, demonstrating how ABOe kidneys can evade early immunological interactions associated with hyperacute rejection. More research is still required to pursue the ABOe strategy clinically, with antigen re-emergence kinetics remaining an unknown in the field. Overall, the work presented in this thesis reflects a simple and novel approach to the ABO problem in transplantation. The method described here uses clinically approved perfusion technologies to achieve rapid antigen removal of both A and B blood group antigens in whole human kidneys. This reflects how the ABOe strategy would easily translate to clinical practice, potentially heralding a new era of organ allocation without blood group restrictions in transplantation.