Enzymes convert all donor blood to group O

You're rushed into hospital and need a blood transfusion – but what is your blood group? In future, it may not matter, thanks to enzymes that scrub antigens from red blood cells, turning all donated blood into group O – which can be given safely to anyone.

The A and B antigens, which give blood groups their name, are sugars carried on the surface of red blood cells. Human red blood cells can carry one of these antigens, both, or neither; giving four blood groups: A, B, AB and O, respectively. Receiving mismatched blood can cause a life-threatening reaction, and errors are made in 1 in every 15,000 transfusions, on average.

In the 1980s, a team in New York, US, showed that an enzyme from green coffee beans could remove the B antigen from red blood cells. It proved too inefficient for practical use, but Henrik Clausen at the University of Copenhagen in Denmark and colleagues have now screened bacteria and fungi for more powerful enzymes. "The diversity you get in the bacterial kingdom is much higher," Clausen explains.

The researchers homed in on two enzymes. One, from a gut bacterium called Bacteroides fragilis, removes the B antigen. The other, from Elizabethkingia meningosepticum – which causes opportunistic infections in people – targets the A antigen. The purified enzymes are highly efficient. For example, the B. fragilis enzyme is used up at only one-thousandth the rate of the coffee bean enzyme.

Clausen's team is working with a company called ZymeQuest in Beverly, Massachusetts, US, which plans clinical trials to test whether the treated blood is safe and effective. If so, the technology should be in hot demand, because group O blood – the only safe option if there is any doubt about the recipient's blood group – is a precious commodity.

"We're always in a shortage," says Richard Benjamin, chief medical officer with the American Red Cross in Washington DC, US.

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