Scientists have successfully transplanted sperm-making cells between species, raising the possibility someday of using animals to produce sperm for infertile men.
They have also found that the sperm-making cells can be frozen for a long time, which could one day enable men made sterile by chemotherapy to regain their fertility.
With further improvement, the techniques could also be a boon to conservation of endangered animals, livestock breeding and studies of human genetic diseases, said researcher Ralph Brinster.
Sperm from humans and some animals is already routinely frozen for later use. But those samples capture only a tiny fraction of the genetic combinations a male can produce.
The latest research involves what are known as stem cells, from which all sperm spring. Freezing stem cells could confer a sort of biological immortality because they “really embody the essence of the individual,” Brinster said.
“If you freeze the stem cell, you’ve really frozen the individual,” said Brinster, a researcher at the University of Pennsylvania’s School of Veterinary Medicine. “That individual, the fast race horse, the high-producing bovine, that’s in the freezer … forever.”
Brinster and colleagues reported their findings on freezing in the June issue of the journal Nature Medicine. They froze sperm-making cells from mice for up to 156 days, thawed them, implanted them in other mice and found that the cells produced sperm.
In a second study, published in today’s issue of the journal Nature, Brinster and colleagues reported that when they transplanted rat stem cells into mice, the mice made rat sperm.
Brinster said previous studies make him confident that sperm would produce normal offspring after the freezing or transplant process.
Stem cell transplants might someday help infertile men who can’t make sperm or prepubescent boys who are about to undergo chemotherapy that will sterilize them permanently as a side effect, Brinster said.
The infertile man’s stem cells may need only a new environment to start producing sperm, so a transplant to another man or possibly an animal could make the cells productive, he said.
As for a boy, his cells could be frozen until he matured, and then either transplanted back into him or into an animal if he didn’t want to undergo the transplant operation, Brinster said.
It’s not clear what animal could be a suitable recipient, he said. He also said he doubted such treatments would be common.