Engineering a new generation of blood substitutes

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Patients with blood loss suffer acute hypotension and a drop in oxygen content; oxygen delivery to tissue then falls with a catastrophic clinical outcome. Blood transfusions are therefore a major element of treating patients suffering blood loss through trauma or surgery. Globally around 85 million units of red blood cells are transfused annually in an industry worth ~$16Bn. However, there are inherent problems with transfusions of packed red blood cells. The need for blood group typing and the short shelf life limits the ability to stockpile the supplies necessary for major disasters. It also precludes routine transfusion support in ambulances and in population centres distant from major hospitals (including use by the military). Homologous blood transfusions are not always benign: they can result in acute transfusion reactions, either by mistyping accidents or in immune compromised individuals. Hence immune compromised individuals, as well as certain religious groups, are unable to benefit from blood transfusions.Blood is a biological agent; it cannot be sterilised and therefore always has the potential for contamination with bacteria and blood-borne infectious agents such as HIV, hepatitis, vCJD and West Nile virus. Not all viruses are screened for in all countries, and in some cases (vCJD) no validated tests are currently available. New blood borne viruses are discovered on a regular basis; for those that are infectious and induce pathology, there will always be a pathological window prior to the introduction of a new screening test. Increased screening raises the cost of blood products as well as decreasing supply; the increasing age of populations adds to this problem by increasing the number of people requiring transfusions, whilst decreasing the fraction of the population able to donate blood. The combination of these factors limits the use of "safe" blood transfusions to those countries with a funded and developed medical system able both to manage a blood transfusion service and having a population that is relatively free of infectious blood borne viruses. In many counties, notably in Africa, these factors preclude the use of blood transfusions in trauma.There is a clear global medical need for a long life, pathogen free "blood substitute" able to augment the use of red blood cells. A great deal of effort has been expended into producing products based on chemical or genetic modification to haemoglobin, the red cell oxygen carrying protein. Although several haemoglobin-based oxygen carriers (HBOC) have been shown to deliver oxygen they have failed to get approval for use in the major healthcare markets due to safety concerns. Three major mechanisms have been proposed for HBOC toxicity. One is a lack of product stability. The other two relate to molecular mechanisms: (i) outside the protective environment of the red cell HBOC can scavenge nitric oxide (NO) that controls blood pressure and blood flow (ii) HBOC can create toxic free radicals. All these problems can be addressed by genetic engineering techniques. At Essex we have been funded by BBSRC and the EU to investigate the basic science of toxic free radical production by haemoglobin. We have been able to develop novel modified haemoglobin molecules that are more readily detoxified by the body's antioxidants, and so induce less free radical damage.We now wish to apply this knowledge to directly address clinical issues. Previous researchers have developed haemoglobin mutants that do not scavenge nitric oxide. We intend to combine these mutations with our own optimised mutations that decrease free radical production. Our base protein will be human foetal haemoglobin, which is a far more stable protein than the adult form. Solving these three issues (product stability, NO scavenging and free radical production) will form a basis for the next generation of blood substitute products, accessible to all countries and useable in all environments.