Using genetic engineering techniques, biologists have developed pigs that produce human hemoglobin, the essential oxygen-carrying component of blood.
Experts called the achievement a milestone in the effort to find a substitute for blood that could be used in all types of transfusions and might offer advantages over the donated blood now used.
A blood substitute could be stored for months instead of weeks, would be free of any risk of human infection and could be transfused into anyone without the need for blood typing and matching.
Officials of a small biotechnology company, DNX Inc. of Princeton, N.J., said they had developed three pigs that produce human hemoglobin, the substance in the red blood cells that transports oxygen throughout the body.
When the pigs were day-old embryos, the scientists injected sets of two genes that make human hemoglobin, and now, about 15 percent of the pigs' hemoglobin is human.
It is one of a very few times that scientists have put human genes into large animals and seen them function successfully.
The company's officials will outline the work today at a scientific meeting in Anaheim, Calif., and will describe what they regard as equally important: the discovery of a method of purifying the human hemoglobin produced.
The extracted hemoglobin has not been tried in humans, and it might not succeed. But DNX has given research data to the Food and Drug Administration and plans to apply this year for approval of human trials.
The company said it would take at least five years to complete research and testing of pig-produced hemoglobin, and there are also serious questions that will have to be overcome about the safety of using hemoglobin extracted from animals for human FTC transfusion.
But experts nevertheless praised the achievement.
"I think this is an exciting development," said Dr. Robert Winslow, chief of the blood research division of the Army's Letterman Institute of Research in San Francisco.
"Military doctors believe a solution to this problem of making a blood substitute that can carry oxygen would have saved the lives of 10,000 soldiers in Vietnam," he said. "Soldiers bleed to death on the battlefield, where you can't get blood to them, and before you can get them back to where they can be transfused."
Among the safety questions are whether some animal viruses might escape the purification process and cause illness in humans and whether cellular debris missed in purification could cause kidney damage or allergic reactions.
