Blood flows around the body all the time, yet we barely see it unless we suffer from an accident. If this were the case, and we lost too much of it, we’d need a blood transfusion. But it is not as easy as just putting blood from one individual into another: you need to test it and make sure the blood is compatible.
This occurs because human blood can be divided into many categories. The most common one is the ABO group classification, which divides blood into four types: A, B, AB and O. In each, red blood cells (those cells specialised in carrying oxygen around the body) have a specific antigen depending on the blood type. For example, if you have group A blood, you will have A antigens; if you have AB blood, you will have A and B antigens; and most importantly, if you have O blood, you will have no antigens.
Each antigen stimulates a response from our immune system to produces antibodies against the other antigens. So if you have blood group A, you will produce antibodies that will destroy cells with antigen B, and vice versa. This is potentially very dangerous, because if you give someone of type A blood from a person of type B, the antibodies can attack each other’s red blood cells and wreck havoc in our bodies.
When it comes to transfusing blood, the best one is group O- since it has no antigens, so there is no way your body can attack it. That is why we call it universal, since it works for anyone, no matter their blood type. This makes it very sought after for blood transfusions, but there isn’t always plenty of it available.
But what if we could convert all blood into O type blood? We can’t change the genotype of adults so that their body produced it, but we can change the blood itself after the blood has been donated. The most successful way to do this would be to insert bacterial enzymes into the blood which can recognise antigens in the red blood cells and cut them off so they are just like red blood cells from O group blood.
In the experiment which created this mechanism, the original enzyme worked mostly with cells from group B only, so to make it effective on cells from group A too they used a very interesting method called directed evolution. It’s just as it sounds: they grew the bacteria that produce this type of enzyme, and slowly mutated their genome (by adding bases to their DNA) so that every generation produced a better enzyme. At the end of the experiment, after 5 generations of bacteria, the final enzyme was produced, which not only could severe A antigens, but was also an impressive 170 times more efficient than the original one.
Yet this method is still not perfect: the enzyme can’t modify all the thousands of red blood cells in a sample of blood and therefore can’t make it completely safe, as there will still be some red blood cells with antigens present. But with enough time, the scientists hope to perfect it and make the technique available so blood transfusions are easier to carry out.