"Transplant too early and the risk is [that] embryonic tissue can develop into undesirable and possibly malignant tissue, a type of tumor known as teratoma," Reisner said. "Transplant too late and the risk is that the tissues will have reached the stage where they have been marked with certain identifiers that trigger rejection by the new host."
To identify when to harvest the embryonic cells, the scientists took embryonic pig tissue that had begun to form particular organs at various developmental stages and transplanted them into mice.
They studied three types of organsliver, pancreas, and lungand found optimal time windows for transplantation for each organ.
"What he has shown is that there's a window of opportunity," said Bernhard Hering at the Diabetes Institute for Immunology and Transplantation at the University of Minnesota.
"If you obtain this tissue at a very defined point in time, then you can see development into islets [portions of the pancreas that secrete hormones like insulin] without risks such as teratoma formation," Hering said. "That's clearly something that makes us feel very strongly that this could be a real opportunity, one that can be translated into tangible benefits much faster than other technologies."
Reevaluating the Past
The findings could help enhance the chances for successful implementation of embryonic pig tissue in the treatment of a wide spectrum of human diseases, particularly diabetes. The findings may help in part to explain the failure of previous transplantation trials of pancreatic islets in diabetic patients.
"Early studies that attempted to cure diabetic patients by implantation of pig embryonic pancreas made use of late-gestation tissue, which is now shown to be inferior, compared to the optimal six-week gestational time," Reisner said.
Embryonic liver transplants also have a curative potential for enzyme deficiencies and for hemophilia.
The new findings may now allow scientists to go back to their previous work and look at it in a different light.
"Previous failures may have had to do with the timing of the tissue as opposed to it not being able to accomplish appropriate transfer of embryonic tissue to allow it to develop into specific organ type," said Kenneth Chavin, an assistant professor of surgery, microbiology, and immunology at the Medical University of South Carolina in Charleston.
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