Scientists Graft Pigs' Hearts to Sheep

February 8, 2003
by Jow Ruff, Associated Press Writer

Scientists have successfully grafted pigs' hearts to sheep by manipulating the immune systems of the animals.

Details of the experiment conducted on 13 pairs of pigs and sheep at the University of Nebraska Medical Center appear in the February issue of the journal Annals of Surgery.

First, researchers took bone marrow cells from the sheep and transferred them to a pig fetus. After the pig was born, they took disease-fighting white cells from the pig's spleen and transferred them back to the sheep. These cells contained genetic material from both animals.

When the pig matured, the pig's heart was grafted onto the outside of the sheep and connected to blood vessels located below the sheep's neck.

The sheep retained their own hearts.

Modest amounts of immunosuppression drugs were given to the sheep to avoid organ rejection, but the doses were lower than those normally given to humans receiving heart transplants, said the study's senior author, William Beschorner.

Of the 13 sheep with grafted pig hearts, one rejected the new heart. Five more showed milder rejection signs, and were successfully treated with anti-inflammatory medications. The remaining sheep showed no signs of organ rejection for as long as 70 days.

In contrast, all 12 control sheep rejected the attached hearts within eight days. None of them were inoculated with pig cells before the procedure, said Beschorner, who also is president of Ximerex, an animal-to-human transplant company.