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PHILADELPHIA—The political fight over the use of human embryonic stem cells rages in this country. So much so, that the political
and ethical debate about government-funded embryonic stem cell research often overshadows its much more moderate cousin, adult
stem cell research, without the political baggage.
A stem cell has been described simply as having a unique capacity to renew itself and give rise to specialized cell types.
It is this distinction that has made stem cell research so alluring to medical researchers. It ushers in an entirely new weapon
in the war against inherited disease. Ralph Brinster, VMD, PhD, is a chief architect.
In an interview with DVM Newsmagazine, Brinster, the Richard King Mellon Professor of Reproductive Physiology at the University of Pennsylvania talked about his
National Institutes of Health-funded research in identifying the growth factors essential to allow spermatogonial stems cells
to exist in culture, which is considered a major step in an ultimate quest to understand infertility in humans and agriculture.
The resulting benefits from Brinster's work with colleagues Hiroshi Kubota and Mary R. Avarbock will have "profound consequences
to future fertility therapies and offer a source of stem cells that will make it possible to modify genes from males before
they are passed on to the next generation," Brinster says.
"In 1998, I published the first paper on culture, but the cells eventually died out over three months. So, we spent a lot
of time in the laboratory studying cultures."
Eventually, Kubota went into the laboratory armed with information about enriching stem cells and other empirical observations.
The result? Kubota developed a very rich population of stem cells. He came up with a serum-free media. The last ingredient
to the successful culture was the use of simple feeder cells known as STOs.
"So now the cells can be cultured, and I believe they will proliferate for a very long time, perhaps forever," Brinster says.
"We now already have a way that we can freeze these cells, so basically it makes any male germline immortal because you can
freeze it, put it back into a recipient and make sperm. That is very different than freezing sperm. You are limited with all
of the offerings a male can make. If you freeze 1 million spermatozoa, you have a million spermatozoa."
Divide and conquer
Adult stem cells "are capable of making identical copies of themselves for the lifetime of the organism. Adult stem cells
usually divide to generate progenitor or precursor cells, which differentiate or develop into "mature" cell types that have
characteristic shapes and specialized functions. (Stem Cells: Scientific Progress and Future Directions; Winslow, 2001.)
"With the ability to culture these cells, you can do a lot of experiments, biology and just manipulate them in any way you
want. More specifically you can add or delete genes in a stem cell. It's just a matter of applying already known techniques
to introduce these genes or go make a mutant."
The implications? "For research, this opens up a wonderfully robust diagnostic system for analyzing the function of individual
genes. For medicine, it opens up a new chapter in fertility medicine," he says.
Brinster also believes these results will also be applicable to other species, although the research has primarily focused
on mice.
While the female germ cell stops dividing before birth, the spermatogonial stem cells continue to divide throughout life.
So, it's possible to modify the male germ line between generations by manipulating the spermatogonial stem cells in culture.
Theoretically, it will be possible to harvest the male spermatogonic stem cells, correct the gene in culture and implant the
stem cells back into the male to produce normal sperm.
Brinster also theorizes that it might be possible to convert spermatogonial stem cells to totipotent cells, capable of becoming
almost any other cell type and similar to embryonic stem cells.
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