Blood shortages may soon be a thing of the past. Newly discovered bacterial enzymes in the human gut have been used to turn type A blood into the universally accepted type O much faster than previous methods.
“This technique could broaden the utility of the current blood supply because O type blood can be donated to anybody,” says Steve Withers at the University of British Columbia, who presented this work on 21 August at a meeting of the American Chemical Society. He says it may prove especially useful in remote communities, emergencies situations or armed conflicts if O type blood is in short supply.
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Our blood comes in four main types: A, B, AB and O. The red blood cells in each type are similar in shape but they have different sugars on their surfaces. Red blood cells in type A host a particular set of these sugars; type B has its own as well. AB blood cells carry both A and B sugars, and type O cells have none.
These sugars can act as antigens, which means if the immune system doesn’t recognise them, it will attack the cells they are attached to. So transfuse type B blood into someone with type A blood and a potentially fatal immune reaction may result. That’s what makes anyone with type O blood a universal donor – there are none of these antigens. So rapidly stripping these sugars from A, B and AB type blood would be helpful, effectively making it useable in transfusions for all.
Similar sugars
“We knew that those same sugars that are on our red blood cells are also produced on the lining of the gut wall,” says Withers. So he and his colleagues started their search for sugar-stripping enzymes in bacteria in human faeces that they thought might feed on gut wall sugars.
They extracted the genetic sequence for bacterial enzymes within the faeces and inserted those genes into Escherichia coli to see which would show sugar-related enzyme activity. They found a new family of enzymes that live in gut bacteria that help them harvest sugars from proteins called mucins that line the gut wall.
The sugars on mucins have a similar structure to red blood cell antigens. When the team combined these enzymes with type A blood, they found that the sugars were removed from the blood cells, resulting in type O blood. The process is 30 times faster than enzymes already used for this and it works with whole blood, which wasn’t previously the case. One caveat: Type A blood can also have a non-sugar antigen, usually rhesus D, so to make truly universal blood you’d have to start with type A  blood that lacks this, known as rhesus negative.
These enzymes will have to go through more safety testing before they can be used in blood destined for human transfusions, but it’s a promising step, Withers says. “We know for sure it removes the antigens. We don’t know yet if there are unintended consequences,” he says.
