Within the next few weeks scientists will attempt a uterus swap between two sheep in what they hope will be the first successfully transplanted uteruses in a large animal. Already, four ewes that had their uteruses removed and then reattached later to a different artery in their bodies are nearing the end of their pregnancies, the same team has announced. They plan to deliver the lambs from these ewes via caesarean section by the end of April 2007. Mats Brannstrom at the Sahlgrenska Academy in Gothenburg, Sweden, and colleagues removed the uteruses of 14 female sheep. Each five-hour surgical procedure involved delicately detaching the uterus and the ovary from the artery that supplies it with blood. The organ was preserved outside of the body and completely detached for about four hours, including at least an hour on ice.
Researchers then returned each uterus to the ewe from which it came in a seven-hour surgical operation. This ‘auto-transplantation’ avoids the possibility that the animals will reject the organ due to an immune reaction. Because the artery that supplies the uterus with blood is so delicate, Brannstrom’s team instead reattached the uterus to the artery that partly supplies blood to the legs. This involved stopping the flow in the artery temporarily and suturing the uterine vessels to it. Of the 14 ewes that underwent this auto-transplantation, five had complications as a result of the surgery and a further two developed severe intestinal problems. Those seven were euthanized. Researchers mated five of the remaining seven ewes with two rams, towards the end of 2006. Four of these ewes became pregnant as a result of this natural mating. The animals are now four-months-pregnant – one month away from full term, at which point they will undergo a caesarean section delivery.
Brannstrom’s team-mate Pernilla Dahm-Kahler is presenting details of the experiment this weekend at the first annual symposium of uterine transplantation taking place in Sweden. The team previously showed that mice that receive uterine transplants can successfully become pregnant and give birth. They say that the pregnancies in sheep represent a significant advance as the animals are larger, making the transplantation procedure more similar to one that might work in humans. Their next step will be to swap the uterus organs of two sheep in the next few weeks. These sheep will have to receive drugs that suppress the immune system, to prevent their bodies rejecting the foreign transplants. A successful outcome of this follow-up experiment could bolster hopes that uterine transplants will become a viable option for humans.
Women who suffer from a condition called Rokitansky syndrome are born without a uterus, while some women must have theirs removed due to cancer, fibrous growths or rupturing during childbirth. Some women who lack a womb hope that a transplant procedure may restore their ability to become pregnant. Kutluk Oktay at Weil Medical College of Cornell University in New York, US, says the sheep pregnancies are impressive and, he believes, unique. But he cautions that a non-vital procedure in humans can carry potentially fatal risks, including blood clotting complications. And the drugs patients must take to protect against tissue rejection puts them at higher risk of cancer later in life. Even if the womb recipients do become pregnant, these drugs could result in lower birth weight or premature delivery of their babies, he warns. In 2000, for example, surgeons transplanted a uterus into a 26-year-old woman. But a few months later the organ had to be removed because of the formation of a dangerous clot. Still, surgeons at the New York Downtown Hospital have received approval from the hospital’s review board to carry out a womb transplant and say they are interviewing women who would like to receive a donated uterus.
April 17, 2007
Original web page at New Scientist