Enzymatic removal of cell surface antigens as a route towards universal O type blood and organs

Abstract

Mammalian cell surfaces are coated in specific sugar structures, many of which function as antigens and are involved in cellular recognition. Important examples are the oligosaccharide A, B, and H antigens present on red blood cells that differentiate the A, B and O blood types. Enzymatic cleavage of the GalNAc and Gal residues from the cell surface would allow conversion of A and B red blood cells, respectively, to O type. Since Type O blood can be universally donated to patients with the same Rh factor, access to efficient enzymes would greatly broaden and simplify blood supply. We have sought such enzymes in metagenomic libraries derived from the human gut microbiome.Total DNA was extracted from feces samples, fragmented into pieces containing ~30‐40 genes (40‐50 kB) and transformed into E. coli. After picking colonies into 384 well plates we screened them for enzymes that can be used to remove the Gal or GalNAc residues that function as the antigenic determinants from A and B type red blood cells, thereby generating “universal” O type blood. A set of efficient enzymes of a new class has been identified and characterized and used to convert whole units of A blood to O. These enzymes work approximately 30 times faster than any previously characterized and with high specificity. Further, they function well in whole blood thus can be hopefully integrated into the current blood processing process.1These enzymes also function well on tissue surfaces and, when perfused through donated human A‐type lungs successfully cleared A‐antigen from surfaces exposed to the blood. Subsequent perfusion of the lungs with O‐type plasma to mimic an ABO‐incompatible transplant showed that antigen removal minimized antibody binding and antibody‐mediated injury relative to the control lung, thus may greatly temper the acute rejection phase.2 This could allow expansion of ABO‐incompatible lung transplantations, leading to significant improvements in logistics and fairness of organ allocation. Rahfeld, P. et al. “An enzymatic pathway in the human gut microbiome that converts A to universal O‐type blood” (2019) Nature Microbiology 4, 1475‐1485. Wang et al Conversion of blood type A donor lungs into universal blood type lungs using ex vivo ABO enzymatic treatment” (2022) Science Translational Medicine In Press, Scheduled Feb 2022