Conversion of ABO blood groups

Progress is being made toward producing erythrocytes similar to native group O cells from A and B donors. Blood group A and B antigens are known to be carbohydrate in nature. The antigenicity is conferred by different terminal sugars. Removal of these sugars by specific exoglycosidases produces the H antigenic structure that is the determinant found on group O cells. Conditions have been developed that allow for the removal of these antigens while maintaining the metabolic and membrane viability of the red cell. Following successful autologous transfusions with gibbons, appropriately treated human group B erythrocytes are now being used in preclinical studies with normal healthy human volunteers. Results indicate that such treated cells have normal in vivo life spans in both group A and O recipients. However, the latter exhibit a transitory increase in anti-B antibody titer, the significance of which is not yet known. Similar exoglycosidic treatment of group A erythrocytes does not remove all serologically detectable A antigens. This is probably due to the presence of a second internal A antigenic site adjacent to the usual terminal A antigen on some structures. Several approaches are being used to address this problem, including projected treatment with a combination of pertinent exoglycosidases and a search for an endoglycosidase that will cleave the polysaccharide chain at a site upstream from both A antigens.