Blood that has been grown in a laboratory has been put into people in a world-first clinical trial, UK researchers say.
Tiny amounts – equivalent to a couple of spoonfuls – are being tested to see how it performs inside the body.
The bulk of blood transfusions will always rely on people regularly rolling up their sleeve to donate.
But the ultimate goal is to manufacture vital, but ultra-rare, blood groups that are hard to get hold of.
These are necessary for people who depend on regular blood transfusions for conditions such as sickle cell anaemia.
If the blood is not a precise match then the body starts to reject it and the treatment fails. This level of tissue-matching goes beyond the well-known A, B, AB and O blood groups.
Prof Ashley Toye, from the University of Bristol, said some groups were “really, really rare” and there “might only be 10 people in the country” able to donate.
At the moment, there are only three units of the “Bombay” blood group – first identified in India – in stock across the whole of the UK.
The process takes about three weeks and an initial pool of around half a million stem cells results in 50 billion red blood cells.
These are filtered down to get around 15 billion red blood cells that are at the right stage of development to transplant.
The first two people have taken part in the trial, which aims to test the blood in at least 10 healthy volunteers. They will get two donations of 5-10mls at least four months apart – one of normal blood and one of lab-grown blood.
The blood has been tagged with a radioactive substance, often used in medical procedures, so scientists can see how long it lasts in the body.
It is hoped the lab-grown blood will be more potent than normal.
Red blood cells normally last for around 120 days before they need to be replaced. A typical blood donation contains a mix of young and old red blood cells, whereas the lab-grown blood is all freshly made so should last the full 120 days. The researchers suspect this could allow both smaller and less frequent donations in the future.
However, there are considerable financial and technological challenges.
The average blood donation costs the NHS around £130. Growing blood will cost vastly more, although the team will not say how much.