After reading the article “Type A Blood Converted to Universal Donor…” tell me your thoughts on the current challenges in blood transfusions today? What are the advantages of this new process, and pot
Gut bacteria provide a new way to increase the type O blood supply. ISTOCK.COM/ARINDAM GHOSH
Type A blood converted to universal donor
blood with help from bacterial enzymes
By Elizabeth Pennisi Jun. 10, 2019 , 11:00 AM
On any given day, hospitals across t he United States burn through some 16,500 liters (35,000
pints) of donated blood for emergency surgeries, scheduled operations, and routine transfusions.
But recipients can’t take just any blood: For a transfusion to be successful, the patient and donor
blood types must be compatible. Now, researchers analyzing bacteria in the human gut have
discovered that microbes there produce two enzymes that can convert the common type A into a
more universally accepted type. If the process pans out, blood specialists suggest it could
revolutionize blood donation and transfusion.
“This is a first, and if these data can be replicated, it is certainly a major advance,” says Harvey
Klein, a blood transfusion expert at the National Institutes of Health’s Clinical Center in
Bethesda, Maryland, who was not involved with the work.
People typically have one of four blood types — A, B, AB, or O — defined by unusual sugar
molecules on the surfaces of their red blood cells. If a person with type A receives type B blood,
or vice versa, these molecules, called blood antigens, can cause the immune system to mount a
deadly attack on the red blood cells. But type O cells lack these antigens, making it possible to
transfuse that blood type into anyone. That makes this “universal” blood especi ally important in emergency rooms, where nurses and doctors may not have time to determine an accident
victim’s blood type .
“Around the United States and the rest of the world, there is a constant shortage,” says Mohandas
Narla, a red blood cell physiologist at the New York Blood Center in New York City.
To up the supply of universal blood, scientists have tried transforming th e second most common
blood, type A, by removing its “A -defining” antigens . But they’ve met with limited success, as
the known enzymes that can strip the red blood cell of t he offending sugars aren’t efficient
enough to do the job economically.
After 4 years of trying to improve on those enzymes, a team led by Stephen Withers, a chemical
biologist at the University of British Columbia (UBC) in Vancouver, Canada, decided to lo ok for
a better one among human gut bacteria. Some of these microbes latch onto the gut wall, where
they “eat” the sugar -protein combos called mucins that line it. Mucins’ sugars are similar to the
type -defining ones on red blood cells.
So UBC postdoc Pete r Rahfeld collected a human stool sample and isolated its DNA, which in
theory would include genes that encode the bacterial enzymes that digest mucins. Chopping this
DNA up and loading different pieces into copies of the commonly used lab
bacterium Escher ichia coli , the researchers monitored whether any of the microbes subsequently
produced proteins with the ability to remove A -defining sugars.
At first, they didn’t see anything promising. But when they tested two of the resulting enzymes at
once — adding th em to substances that would glow if the sugars were removed — the sugars
came right off . The enzymes also worked their magic in human blood. The enzymes originally
come from a gut bacterium ca lled Flavonifractor plautii , Rahfeld, Withers, and their colleagues
report today in Nature Microbiology . Tiny amounts added to a unit of type A blood could get rid
of the offending sugars, they found. “The findings are very promising in terms of their prac tical
utility,” Narla says. In the United States, type A blood makes up just under one -third of the
supply, meaning the availability of “universal” donor blood could almost double.
But Narla says more work is needed to ensure that all the offending A antig ens have been
removed, a problem in previous efforts. And Withers says researchers need to make sure the
microbial enzymes have not inadvertently altered anything else on the red blood cell that could
produce problems. For now, the researchers are focusing on only converting type A, as it’s more
common than type B blood. Having the ability to transform type A to type O, Withers says,
“would broaden our supply of blood and ease these shortages.”
Posted in:
• Health
doi:10.1126/science.aay3386