Researchers at the University of British Columbia have found a potential way to turn type A blood into universal type O blood, a development which could massively increase the supply of blood for those in need of a transfusion.
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So far, the researches have only achieved this using petri dishes in a lab and a lot more research would be needed before the technique could benefit patients in hospitals. However, potentially, the development could be revolutionary in terms of increasing the supply of blood for life-saving transfusions.
Currently, around 117 million pints of blood are donated annually worldwide. Although this sounds like a lot, incompatibility between the blood types (A, B, AB, O) that each person is born with means a person cannot always receive a transfusion. Transfusing a non-matched blood type could trigger a fatal reaction and kill them.
However, type O blood is compatible with anyone who has Rhesus (Rh) positive blood. It is therefore considered the universal blood type because it can be used for anyone who has A+, B+, AB+, or O+ blood – which is about 75% of the population.
This means type O blood is considered incredibly valuable and now postdoctoral researcher Peter Rahfeld and colleagues have found a way to use enzymes to transform type A red blood cells into universal type O blood cells. The development could potentially double the supply of blood available for transfusions.
The authors write:
Access to efficient enzymes that can convert A and B type red blood cells to ‘universal’ donor O would greatly increase the supply of blood for transfusions.”
Converting one blood type into another using bacteria
A person’s blood type is determined by the type of antigens that are presented on the surface of red blood cells and the type of antibodies present in plasma. Simply put, people with type A blood have A antigens and anti-B antibodies, while those with type B have B antigens and anti-A antibodies.
Now, if a person with type A blood was given type B blood during a transfusion, the B antigens in the transfused blood would trigger the anti-B antibodies to induce a potentially life-threatening immune attack on the blood cells. However, type O red blood cells have neither A nor B antigens on their surface; they have a neutral “H” antigen instead and anyone can receive a transfusion of these.
Now, Rahfeld and team have used a bacterial enzyme present in the human gut to effectively eliminate A antigens by converting them into H antigens.
After isolating the bacteria Flavonifractor plautii from human stools, they identified genes that encode two enzymes capable of removing important components of the A antigen.
“We [identified] an enzyme pair from the obligate anaerobe Flavonifractor plautii that work in concert to efficiently convert the A antigen to the H antigen of O type blood, via a galactosamine intermediate,” explain the authors.
When these enzymes were added to type A blood, they stripped the blood cells of their antigens and essentially converted them to the universal type O blood cells.
Blood type A that has these modified antigens would no longer trigger an immune response in the recipient, just as type O would not, meaning it could be transfused to any patient with blood of the same Rhesus type.
Their ability to completely convert A to O of the same rhesus type at very low enzyme concentrations in whole blood will simplify their incorporation into blood transfusion practice, broadening blood supply."
Replenishing blood stocks
Given that type A is the second most common blood type next to O, this development could be revolutionary in terms of saving and changing lives through increased supply and access to transfusions.
Commenting more generally on the findings, Rahfeld says that in recent years, the research community has started to recognize the importance of the human microbiome in the context of human health. However, its importance may be even greater, given that the microorganisms residing within us also harbor enzymatic activities we do not even know about yet, he adds: "I am keen to see what kind of other activities will be discovered within the human gut microbiome in the future."
Next, the team is planning to carry out further research to ensure that the enzymes do completely convert all of the antigens on the blood cell surface. If this is the case, the availability of converted type A blood would almost double the supply of universal donor blood for transfusions – all courtesy of the human gut.
An enzymatic pathway in the human gut microbiome that converts A to universal O type blood. (2019). Nature Microbiology. doi.org/10.1038/s41564-019-0469-7.