Human blood have been grown from embryonic stem cells for the first time during research that promises to provide an almost limitless supply suitable for transfusion into any patient. This could lead to trials of the blood within two years, and ultimately to an alternative to donations that would transform medicine.

If such blood was made from stem cells of the O negative blood type, which is compatible with every blood group but is often in short supply, it could be given safely to anybody who needs a transfusion. Stem-cell-derived blood would also eliminate the risk of transmitting the pathogens that cause hepatitis, HIV and Creutzfeldt-Jakob disease (CJD) through transfusions.