The British researchers have overcome a major barrier that has plagued many scientists: creating  red cells to fill a blood bag. Their findings are published in the journal Nature Communications. 

The latest study "is a dramatic step forward because it gives us the view that we can actually scale up to whole units of blood," said Dr. Harvey Klein, chief of the NIH Clinical Center's Department of Transfusion Medicine. 

Two to three drops of blood may contain a billion red cells, according to the American Red Cross.

To ramp up production, the UK researchers infected stem cells with cervical cancer genes.

As the red blood cells mature, they spit out the nucleus -- the core that houses their DNA - giving the cells a signature round, dimpled shape. 

http://edition.cnn.com/2017/03/28/health/stem-cells-synthetic-blood-study/index.html