Volunteers have received a blood transfusion of laboratory-grown red blood cells in a world-first clinical trial in the UK.
As part of the University of Bristol trial, volunteers received manufactured blood cells that were grown from stem cells from a blood donor.
The control participants in the trial received a standard blood transfusion of red blood cells from the same donor.
Researchers hope the lab-grown cells will last longer in the recipients' bodies than the standard donated cells, which are of varying ages.
Longer-lasting blood could mean patients who regularly need blood many not need transfusions as often, reducing iron overload from frequent transfusions.
"If our trial, the first such in the world, is successful, it will mean that patients who currently require regular long-term blood transfusions will need fewer transfusions in future, helping transform their care," co-chief investigator Cedric Ghevaert said.
The trial is the first step towards lab-grown blood cells becoming a clinical product.
But even if it is successful, researchers say the majority of transfusions would still come from standard blood donations.
"This research offers real hope for those difficult-to-transfuse sickle cell patients who have developed antibodies against most donor blood types," chief executive of the Sickle Cell Society, John James, said.
The amount of lab-grown cells transfused into the volunteers was around 5-10 millilitres, or about two teaspoons.
