An advance report that will soon be published in Nature Biotechnology describes progress toward artificially creating type O blood from A, AB, and B blood donors. The advantage is that type O blood can be given to any patient who needs a blood transfusion. If you can convert all donated blood to the universal donor then the blood supply becomes much more flexible.The ABO blood types are determined by the presence or absence of sugar groups on proteins bound to the outer surface of red blood cells [ABO Blood Types]. A single gene is responsible for the different blood types [Human ABO Gene] and the genetics is well understood [Genetics of ABO Blood Types].
Liu et al. (2007) screened 2,500 fungus and bacterial species for enzymes that could remove the A antigens and B antigens from red blood cells.
The rationale is illustrated in this figure from their paper.All red blood cells have H antigen. In people with type A blood the H antigen is converted to A antigen through the action of the enzyme α1,3-N- galactosaminyl transferase (GTA). GTA adds N-acetyl- galactosamine (GalNAc) to the H antigen structure. If you have blood type B then a different version of the enzyme (GTB) adds galactose (Gal) to make B antigen [see ABO Blood Types]. If neither version of the enzyme is present then H antigen will not be modified and you will have blood type O.
The authors discovered several enzymes (A-zyme) that remove GalNAc converting type A blood back to type O blood. They decided to characterize an enzyme from the flavobacterium Elizabethkingia meningoseptum that had previously been identified—and patented—in 2002. Liu et al. constucted recombinant versions of the E. meningoseptum gene and expressed it in Escherichia coli. They were able to make large quantities of active enzyme which led to crystallization and solving the structure.
A version of B-zyme was identified in the common gut bacterium Bacteroides fragilis. The gene for this enzyme was also cloned and expressed in E. coli. A modified version with high activity was selected for further study.
The two purified enzymes were used to treat blood from A, AB, and B donors. All traces of A- and B-antigens were removed as demonstrated by the lack of reactivity against anti-A and anti-B antibodies. Thus, the treated blood was effectively type O and was suitable to use as universal donor. The authors are confident that the process can be scaled up.
Accordingly, we believe that automated cost-effective processes can be developed for practical use in transfusion medicine.Several of the authors are associated with ZymeQuest Inc. of Beverly MA (USA) and the project was funded, in part, by ZymeQuest. The authors declare their competing interest in a statement that can only be accessed from the full text version of the paper on the website. Here's the statement,
Declaration: Authors (except for G.S., J.M.N., W.S.L. and Y.V.) are employees, consultants and/or shareholders in Zymequest Inc., which holds patents covering the described technologies.
Liu, Q.P., Sulzenbacher, G., Yuan, H., Bennett, E.P., Pietz, G., Saunders, K., Spence, J., Nudelman, E., Levery, S.B., White, T., Neveu, J.M., Lane, W.S., Bourne, Y., Olsson, M.L., Henrissat, B. and Clausen, H. (2007) Bacterial glycosidases for the production of universal red blood cells. Nature Biotechnology Published online: 1 April 2007; | doi:10.1038/nbt1298.
5 comments :
This is really interesting and seems a lot more promising than the synthetic blood substitutes that they've been trying to develop. Would there be an efficient way to extract the necessary enzymes from the bacteria without introducing the bacteria into the blood? It seems like this would be a costly/time-consuming process. We also have to worry about the potential for contamination from exogenous protein, otherwise there is the potential that these proteins could cause an immune reaction in the recipient.
am I missing something? The converted blood will still contain antibodies to other blood types. for instance, type A blood contains antibodies to the type B antigen, so even if you remove the type A sugars from the donor blood, won't it still contain the type B antibodies and therefore be useless to give to type B recipients?
Or is there a method of removing those donor antibodies? or maybe there isn't a sufficient amount in the donated blood?
ryan asks,
am I missing something? The converted blood will still contain antibodies to other blood types. for instance
The red blood cells are separated from the fresh blood by centrifugation and it's the packed RBC's that are treated. Then they're washed several times before being resuspended in buffered saline for transfusions.
In answer to matt's question ... The enzymes are purified from the bacterial cultures. That was part of the proof of principle that was published in the Nature Biotechnology paper. In fact, one of the pure enzymes was crystallized and its structure was published in the paper.
Would something like this work on transplants of organs and tissues with mostly non-diving cells (like the heart) or would cells like cardiac myocytes still be manufacturing antigens even if they do not divide? (obviously the blood vessels would still be a problem, but there might be other ways around that)
ZYMEQUEST see www.progressnow.ch
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