WAY FOUND TO TRANSFER SPERM CELLS TO OTHER SPECIES.

Byline: Gina Kolata The New York Times

A discovery to be announced today could make possible some strange new modes of reproduction. It would allow the cells that make sperm to be put on ice and cultivated in another species many years later.

Thus a woman wanting artificial insemination could take her choice from a vast array of sterling candidates. Once she made her selection, those frozen cells of a man who might have died long before she was born might be implanted into the testes of a mouse, where they would grow and develop into human sperm.

Ethicists say this is a scenario for the future. But, they add, hard as it is to believe, the pieces are falling into place, based on the newly announced discovery, by Dr. Ralph Brinster of the University of Pennsylvania's School of Veterinary Medicine.

``It's the kind of research that sends shivers through people,'' said John Robertson, an ethicist and law professor at the University of Texas in Austin.

Dr. Arthur Caplan, director of the Center for Bioethics at the University of Pennsylvania, called the work ``staggering and flabbergasting and amazing.'' Caplan has frequently consulted with Brinster as the implications of his work emerged.

Brinster's studies are being published today in the journals Nature and Nature Medicine. In one paper, Brinster showed that he could freeze the cells, known as spermatogonial stem cells, from which all sperm cells arise, then thaw them and grow them in another animal's testes. These experiments were with mice.

In a second paper, Brinster showed that the stem cells could grow and produce sperm even if they were transplanted to the testes of an animal of another species. In this case, he put rat stem cells into the testes of mice where they generated rat sperm.

Unlike ordinary sperm banks, where deposits once used are gone for ever, sperm stem cells can replenish themselves, providing in principle an inexhaustible source of an individual's sperm.

Brinster, a professor of veterinary medicine, said the first applications might be in animals.

A champion racehorse, for example, or a prize bull might become essentially immortal, his sperm progenitors developing in the testes of another horse or even a laboratory mouse, harvested whenever a veterinarian needs some valuable semen.

The studies also might help infertile humans.