A human recombinant haemoglobin designed for use as a blood substitute

THE need to develop a blood substitute is now urgent because of the increasing concern over blood-transmitted viral and bacterial pathogens 1 . Cell-free haemoglobin solutions 2,3 and human haemoglobin synthesized in Escherichia coli 4 and Saccharomyces cerevisiae 5 have been investigated as potential oxygen-carrying substitutes for red blood cells. But these haemoglobins cannot be used as a blood substitute because (1) the oxygen affinity in the absence of 2,3-bisphosphoglycerate is too high to allow unloading of enough oxygen in the tissues 6 , and (2) they dissociate into αβ dimers 7 that are cleared rapidly by renal filtration 8–10 , which can result in long-term kidney damage 7–9 . We have produced a human haemoglobin using an expression vector containing one gene encoding a mutant β-globin with decreased oxygen affinity and one duplicated, tandemly fused α-globin gene. Fusion of the two α-globin subunits increases the half-life of this haemoglobin molecule in vivo by preventing its dissociation into αβ dimers and therefore also eliminates renal toxicity.