Sperm may one day become a surprisingly renewable resource, thanks to work reported last May by Ralph Brinster of the University of Pennsylvania School of Veterinary Medicine. Brinster and his colleagues cut into a rat testicle, removed spermatogonia--the cells from which sperm arise--and injected them into mouse gonads. The transplants took, and within months Brinster’s mice were producing up to one rat sperm for every 39 of their own. The result was greeted by some researchers as offering new hope for endangered species. If you are worried about, say, the survival of the Florida panther, it becomes possible to think of transplanting panther spermatogonia into a related cat species, thus protecting the future supply of panther sperm.
What worried some ethicists about Brinster’s experiment, though, was simply his success at manipulating spermatogonia. Brinster showed not only that they could be transplanted but also that they could survive being frozen and thawed--which brings geneticists one step closer to being able to alter the genes that fathers pass on to their offspring. Right now gene therapy for medical purposes is restricted to body cells, and such changes are not handed down to the next generation. The barriers to manipulating germ cells--sperm and eggs--have been technical as well as moral. Just in terms of scientific methods, says Thomas Murray, director of the Center for Biomedical Ethics at Case Western Reserve University in Cleveland, Brinster’s work makes what was once technically impossible more possible.
Of course, enormous technical hurdles remain before researchers can alter the genes in spermatogonia--for instance, they must figure out how to keep the cells alive in a petri dish. And Murray is quick to point out an immediate benefit to Brinster’s research: it suggests that male cancer patients may someday be able to avoid being rendered infertile by chemotherapy, if they freeze their spermatogonial tissue before the treatment and then have it reinjected afterward.
Brinster’s own interests are more academic: he wants to understand how germ cells develop. There was no reason, he says, to expect that the process would be similar enough in different species for a transplant to work--but now that he knows it does, he plans to test the limits by transplanting dog, pig, and bull spermatogonia into mice. Brinster is also alive, though, to the social implications of his work. His procedures, he predicts, will change the way that people look at male germ-line cells. They won’t be left alone now.