For decades researchers have been trying to make fake blood to feed shortages, treat people with diseases like sickle cell anemia and even study diseases carried by bloodsucking mosquitoes. Now a candidate for synthetic blood will be tested in the United Kingdom in the first trial of its kind, as James Gallagher reports for BBC.

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The U.K.’s National Health Service announced plans on June 25 for a small safety trial of 20 people that will begin in 2017. Nick Watkins, a physician on the NHS’s blood and transplant team, said in a statement:

“Scientists across the globe have been investigating for a number of years how to manufacture red blood cells to offer an alternative to donated blood to treat patients. We are confident that by 2017 our team will be ready to carry out the first early phase clinical trials in human volunteers.”

Blood substitutes don’t aim to replace real blood, they simply fill one of bloods’ roles: transporting oxygen. Some do this by just mimicking hemoglobin. Others are entirely novel, synthetic oxygen carriers. To do that, researchers will need to scale up the technology, as Colin Barras notes for New Scientist.

As Barras explains, the NHS has created lab-grown red blood cells. These can be made from bone marrow or umbilical cord stem cells. Some groups working on stem cell-based approached have had success injecting a few milliliters their substitutes into a human patient, though none have been tested in full scale human trials. The key obstacle, as Barras frames it, will be whether scientists can produce enough red blood cells from stem cells to do a full transfusion.