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. Last Updated: 07/27/2016

New Sperm-Freezing Method Reported

A new technique for freezing sperm-producing tissues can provide "biological immortality" for males, a finding that researchers say could have a major impact on conserving endangered species, protecting valuable research animals and preserving the reproduction ability of males who undergo intensive chemotherapy for cancer.

The technique may even make it possible for men with abnormally low sperm production to reproduce.

Fertility specialists now routinely freeze sperm itself, but the freezing process is tricky and unique for each species. In addition, frozen sperm has a relatively short lifetime and researchers are limited to the amount of sperm originally frozen.

Veterinarian Ralph Brinster, a pioneer in genetic engineering of animals, and his colleagues at the University of Pennsylvania report in Thursday's journals Nature and Nature Medicine that spermatogonia -- the tissues that produce sperm -- can be easily frozen and stored for long periods.

When the tissue is thawed out, it can be transplanted into the original donor or a host, where it begins making unlimited quantities of fresh sperm. Although Brinster has not yet attempted to fertilize eggs with the sperm, he has every confidence that it can. "I would be very surprised, closer to amazed, if it didn't fertilize an egg," he said.

Sperm are routinely frozen today for a variety of purposes, including breeding of cattle and artificial insemination of humans, but results can be variable. Bull sperm freezes easily, while human sperm, is variable in its ability to survive the process.

"Sperm from some men survives very well, while sperm from other men does not survive at all, for reasons we don't understand," biologist George Seidel Jr. of Colorado State University said.

Brinster has circumvented those problems by focusing on the incredibly productive spermatogonia.

Surprisingly, he said, people have not really attempted to freeze these tissues before. But his team found that they could readily freeze and thaw the cells using standard techniques.

"I don't want to denigrate my own work, but this was incredibly easy," Brinster said.

Brinster reported in Nature that they also froze rat spermatogonia, then transplanted the thawed tissue into mice, which began producing apparently healthy rat sperm.

Brinster is now working on achieving the same feat with larger animals. After that, the team will proceed to human tissues.