One team of researchers has created red blood cells that are ready to go into human study volunteers. When the clinical trial testing the cells’ safety starts, it will be the first time humans have ever received red blood cells made from adult cells, according to the Wellcome Trust, the project’s funder. The cells are made from skin cells taken from a human donor.

Researchers have long been interested in making red blood cells in lab. The man-made cells could ensure that a steady supply of fresh cells is available for transfusions. Donated blood must be used within 42 days, so the donated supply isn’t always steady… or available for sudden surges in demand. Engineered red blood cells would also be designed to be of the universal donor type, so they would be safe for almost all potential recipients. You can even imagine that, if the blood-making works exceptionally well, it would eliminate the need for human donors altogether—but that’s a long way away yet.

This U.K. effort represents the first time anybody has engineered red blood cells that meet safety and quality standards for transfusion into humans, the cells’ lead creator, Marc Turner of the University of Edinburgh, told The Telegraph. The university is working with other U.K. schools, the Scottish National Blood Service, and other private and public U.K. organizations to develop the lab-made blood cells.

Turner and his colleagues plan to test their cells by giving them to volunteers who have thalassemia, a blood disorder that gives people abnormal red blood cells. People with thalassemia must get regular blood transfusions. The research team hopes to start a clinical trial by late 2016, according to the University of Glasgow, one of the participating schools.

Beyond just making the cells, one of the biggest challenges will be making enough of the cells. “Every single bag of transfused blood has about two trillion red blood cells in it. It’s a ludicrously high number to make in the lab.” Joanne Mountford, a researcher working on the project at the University of Glasgow, said in a statement. “We use two million of those bags every year in the U.K. alone. Ensuring that any industrially produced blood can be made economically viable is quite a task.”

[The Telegraph, University of Glasgow, Wellcome Trust]