The piglets have human proteins on the surface of their organs which would - in theory - enable surgeons to carry out the first heart transplant from pig to human without serious tissue rejection.
It is the first time scientists have bred pigs from genetically engineered sows carrying a human gene that makes it feasible for animal organs to be used in transplant surgery.
If pig organs could be designed for use in human surgery it would dramatically alleviate the worldwide shortage of suitable hearts, kidneys and other organs for seriously ill patients.
The current pace of research indicates the first pig-to-human organ transplant could take place in two or three years, said David White, a lecturer in immunology at Cambridge University who has co- founded a company called Imutran to develop the research.
Dr White and colleagues injected human genes into nearly 2,500 pig eggs. Out of 311 piglets that were born, 49 proved to carry the human genes. Thirty-eight survived.
The next stage is to cross-breed from these piglets to produce a second generation which should have two copies of the human gene and therefore double the amount of human protein on the surface of their organs. Dr White said: 'If you get double the gene you get double the protection.'
Dr White said that Imutran has received financial backing from Warburg Pincus, an American venture capital company and Sandoz, a Swiss drug company. 'We applied for funds from the British Government and we were rejected,' he said.
The human gene bred into the pigs disables a protein in the human immune system called 'complement' which is involved in tissue rejection, Dr White said. 'If you think of complement as the bomb of the immune system, it literally blows holes out of cells.'
A heart from a normal pig would turn black and begin to dissolve within minutes of being transplanted into the human body without the complement protein being disabled, he said.
John Wallwork, a Cambridge heart surgeon and the second co- founder of Imutran, said the current shortage of organs for transplants means 'we are essentially waiting for well people to die in order for sick people to live'.