Around 117 million pints of blood are donated each year across the world. While that sounds like lake-loads of blood, incompatibility between blood types – the main ones being A, B, AB, and O – means that a transfusion isn’t always straightforward. Type O, however, is compatible with anyone who has Rhesus (Rh) positive blood, so is deemed a "universal" blood type as it can be freely accepted by anyone with A+, B+, AB+, or O+, which is three-quarters of the world's population.
Now, a new study has shown how enzymes can be used to covert A type red blood cells to “universal” donor O type blood cells. While the science is still in its early days, it has the potential to pave the way towards greatly increasing the supply of, and access to, blood for life-saving transfusions.
Your blood type depends on the different types of antigens, the structures that spark an immune response, on the surface of red blood cells (as well as antibodies in the plasma). In the simplest terms, blood group A has A antigens on the red blood cells with anti-B antibodies, while blood group B has B antigens with anti-A antibodies. So, for example, if you pumped a recipient with type A blood with a pint of type B blood, their anti-B antibodies will become fired up by the B antigens, triggering a potentially life-threatening immune response.
On the other hand, blood group O is compatible with both as it doesn’t contain A or B antigens but has “neutral” H antigen. Reporting in the journal Nature Microbiology, researchers at the University of British Columbia have found an effective way to remove the “awkward” A antigens by converting it to the H antigen. This means that the modified blood group A won’t trigger an immune response to its receiver, just like blood group O, and could be universally transfused to patients of the same Rhesus type.
Considering that A is the second most common blood type, after O, this trick could be revolutionary in increasing the supply of universal donor blood.
Perhaps most intriguingly of all, the method actually uses enzymatic pathways found in the bacteria that live in the human gut. After obtaining Flavonifractor plautii bacteria from human poop, they isolated its specific genes that code for two bacterial enzymes that are capable of removing key components of the A antigen.
Simply by adding small amounts of the two enzymes to type A blood, they were able to strip it of its A antigens, creating a sample that could be used as a “universal” blood type. So far, this has only be carried in a petri dish in the comfort of a lab, so there’s still a lot of work to do before we see this is in hospitals. Nevertheless, this work undoubtedly holds a lot of life-changing and life-saving promise.
"In recent years the research community has started to realize the importance of the human microbiome in the context of human health. However, it may prove to be even more important since the microorganisms within us also harbor enzyme activities we do not even know about yet," lead author Peter Rahfeld, a postdoctoral researcher at the University of British Columbia, wrote in an accompanying article.
"I am keen to see what kind of other activities will be discovered within the human gut microbiome in the future," he added.