Well, all the transhumanists should be very interested in this one:
<http://www.newscientist.com/news/news.jsp?id=ns99992677>
>Cross-species testes transplant successful
>19:00 14 August 02 NewScientist.com news service
>Testis tissue from goats and pigs has been grafted onto the backs of mice
>and shown to produce normal sperm, capable of fertilising eggs.
>It is the first time testis tissue from such distant species has produced
>mature sperm when grafted in mice. "It might work for primates or even
>humans," claims Ina Dobrinski of the University of Pennsylvania, one of
>the co-authors of the study.
>If so, the technique could be used to preserve the reproductive potential
>of male cancer patients about to undergo therapies that would destroy
>their ability to make sperm.
>Men often freeze sperm samples before receiving chemotherapy, but young
>boys cannot do this because they do not produce mature sperm. If it works
>in humans, the technique would allow testis tissue grafted from boys to
>mature and produce sperm.
>
>Infectious particles
>The mouse grafting technique also has an advantage over another option for
>preserving fertility - testicular transplants. These involve re-implanting
>preserved germ cells into the testes after cancer remission.
>But the grafting approach "would eliminate any possibility of passing
>cancer cells back to the patient," says reproductive biologist Michael
>Griswold from Washington State University.
>However, it is possible that the grafting procedure could introduce
>mouse-derived infectious particles into human embryos, making some
>scientists wary of the idea. "I would very much hesitate to say that it's
>something we should be doing," says reproductive biologist Roger Gosden of
>the East Virginia Medical School.
>
>Castrated mice
>In the study, Dobrinski and colleagues placed small pieces of testis
>tissue from newborn goats or pigs just under the skin on the backs of
>castrated mice. Two to four weeks later, they found that more than half of
>the 477 grafts had survived and were producing normal-looking goat or pig
>sperm.
>When they injected the graft-derived sperm directly into eggs they saw
>clear signs of fertilisation, indicating that the sperm function normally.
>The researchers also found that the procedure worked just as well with
>testis tissue that had been refrigerated for two days or frozen for
>several weeks.
>Gosden has tried transplanting human testes tissue into mice, but was not
>successful. However, Dobrinski believes the technique could soon be used
>to preserve the germ lines of endangered species, including rare animals
>that usually die in captivity before reaching sexual maturity. "We think
>that's a very real application," she says.
>She adds that mice with human testis tissue grafts would also be useful to
>scientists who want to test the effects of toxic substances and new
>contraceptives on human sperm production.
>Journal reference: Nature (vol 418, p 778)
>Robin Orwant