Scientists believe they have found a reliable way to transform donor blood into the universal type needed for safe emergency blood transfusions.
The discovery is enzymes of intestinal bacteria that can efficiently change human blood of type A into type-O.
Type-O-blood is special because it can be given to anyone without the risk of a bad mismatch reaction.
The researchers, from the University of British Columbia, say that clinical trials with the treatment could begin soon.
The intestinal bacteria remove markers from the surface of the donor red blood cells present in type A but not in type O.
Runaway means that the recipient's immune system thinks the donor type-A is blood type-O and will not attack because it is "strange".
Giving someone blood from the wrong group can be life-threatening.
While type O patients can only receive type-O red cell transfusions, type O donations are compatible with all other ABO types.
- The four main blood groups in the ABO system are: O, A, B and AB
- Which group you belong to is determined by the genes that you inherit from your parents
In an emergency situation, there may not be time to perform a full check to get a good match. That is why having sufficient type O blood is so important for health services.
About 7-8% of the British population has type-O Rhesus-negative blood, but the demand for this special group accounts for about 13% of all hospital requests, according to NHS Blood and Transplant.
Beth Johnson, 18, from Irlam, Lancashire, is a blood donor and her donation was used to help people who were injured on the night of the attack on the Manchester Arena, May 22, 2017.
"I am O negative and know how rare and valuable this blood type is for the NHS," she said.
"I am so glad that my blood may have been used to save the life of someone who is involved in something so horrific."
The idea of changing the blood group with enzymes is not new – other scientists and the British Columbia team have been exploring it for a while.
But researcher Stephen Withers, who presents his findings at the National Meeting of the American Chemical Society in Boston, said the intestinal enzymes were the most promising treatment to date.
He said: "I am optimistic that we have a very interesting candidate to adapt the donated blood to a normal type.
"Of course it will have to go through many clinical paths to ensure that it does not have any adverse effects, but it looks promising.
"It works in full blood, so you could see that this was put in the bag at the time of collection and just sitting down doing his job while this stuff was being stored."
In laboratory tests, the enzymes were able to completely convert blood group A into O.
With the help of the Canadian Blood Service, the researchers now want to test more blood samples before they try the treatment in the clinic.
"Obviously, the next stages are all about safety, to ensure that this does not cause unintended effects," said Mr. Withers.