An Austrian physician, Karl Landsteiner, first discovered the four basic human blood groups — A, B, AB and O — in 1900. Since then, scientists have learned a lot more about them, including the fact that blood types are complicated and researchers still don’t know why they evolved. But one thing doctors know for sure is that they play an important role in blood transfusions. Get the wrong type of blood and you can die as the antibodies specific to your blood attack the red blood cells from the foreign donor. Only type O blood, which carries no antigens to trigger that attack, is safe for everyone. Which puts type O blood at a premium. Those who are so called "universal donors" are often particularly encouraged to donate, since their blood is so valuable.

But now researchers have figured out how to make all blood resemble type O. The approach simply uses an enzyme to snip the antigens off type A, B and AB blood cells. For Popular Science, Alexandra Ossola writes:

This isn’t the first time that researchers have produced blood with fewer antigens in the lab, but this attempt has worked better than any other. The researchers used a technique called directed evolution; they used bacteria to create the enzyme and inserted particular mutations in the bacteria’s DNA to make the enzyme even more powerful. After cultivating the bacteria over five generations, the enzyme became 170 times more effective.

The researchers published the results in the Journal of the American Chemical Society. However, though the enzyme works better than any created in the past, it still doesn’t catch and clean 100 percent of the donor blood cells. Scientists are still working to make it even more effective so that it can help patients.

If they succeed, the enzyme-treated blood may become the norm. It does still require human donors, unlike the artificial blood other researchers are working on, but it could help make life-saving blood transfusions easier to get.