The four primary human blood types--A, B, AB, and O--arise from differences in molecules called antigens that dot the surface of red blood cells and provoke responses from the body's immune system. Individuals with the type A antigens make antibodies to type B antigen, which causes their bodies to attack and reject transfused type B blood as foreign. The same grim scenario unfolds for type B individuals who get type A blood. Blood from type O individuals lacks both antigens and can be safely transfused into people with all four blood types. Type O individuals can receive only type O blood, however, which means that during blood shortages, they may want for blood that’s been donated to patients with other blood types.
To alleviate type O blood shortages, Henrik Clausen, a glycobiologist at the University of Copenhagen in Denmark, and a team of scientists at ZymeQuest, a biotechnology company based in Beverly, Massachusetts, hunted for enzymes that convert other blood types to type O. The A and B antigens consist of similar branched carbohydrate molecules that differ in the sugars that cap their tips. The researchers searched for enzymes that would snip the sugars off the two antigens without damaging red blood cells. The company had previously isolated a coffee-bean enzyme that stripped the B antigen that worked, but too inefficiently. To identify and mass-produce more efficient enzymes, they tested extracts of 2500 kinds of bacteria and fungi. They focused on two enzymes: One, from a bacterium that causes infant meningitis, converted type A blood into type O, while another, from a human gut bacterium, converted type B to type O. (The two enzymes together convert type AB to type O.)Each enzyme stripped so much of its target antigen from red blood cells that the antigen could not be detected by a U.S. Food and Drug Administration-approved blood-typing test and by a subsequent chemical test, the researchers reported online yesterday in Nature Biotechnology. ZymeQuest is testing the type-A-converting enzyme for effectiveness in blood clinics and hopes to conduct a clinical trial of the type-B-converting enzyme beginning later this year, Clausen says.:
"I was impressed" by the study, says transfusion scientist Geoff Daniels of the Bristol Institute for Transfusion Sciences in Bristol, U.K. Type O blood runs short any time blood is in short supply, Daniels says. If the technology proves safe and effective in humans and financially viable for blood banks, he concludes, in a few years the new enzyme technology "would be able to reduce the pressure on [type] O."
