Pigs' hearts could be available for transplanting into humans by 2010 and mechanical hearts by 2005. A mechanical heart would not be rejected by a human host because its immune system would not recognise any of its materials. To produce the genetically-modified pigs' hearts, scientists tried to engineer human 'identity' tags onto the surface of the pig organs to 'fool' the immune system into accepting the organs. They did this by inserting human genes into the genetic material of pig embryos.
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