Sperm Stem Cells Are Grown Outside Body
November 4, 2004
By NICHOLAS WADE
A male achievement that is perhaps insufficiently
celebrated is that with every heartbeat a man generates
1,000 sperm, each of which has taken two months to produce.
In a step that brings closer the possibility of making
inheritable genetic changes in humans, scientists have
succeeded in growing outside the body the special stem
cells that direct the remarkably prolific process of sperm
Although the method now works just for mice, it may well
apply to human cells, since they use the same genetic
signals as mouse cells.
Cultivation of the sperm production cells has been a
10-year goal of Dr. Ralph L. Brinster, a reproductive
biologist at the University of Pennsylvania School of
Veterinary Medicine. The ability to culture the cells is a
first step that leads in a number of possible directions.
One is correcting the sperm of infertile men. Another, if
ethically acceptable, would be genetic engineering in
humans. A third is generating embryonic stem cells without
the controversial step of making an embryo.
The new method was developed by Dr. Brinster and his
colleagues Hiroshi Kubota and Mary R. Avarbock and is
reported in the current issue of Proceedings of the
National Academy of Sciences.
The ability to cultivate the sperm production cells in
large numbers would make it possible to try swapping
mutated genes in the cells for normal or improved versions.
With infertile men, the sperm production cells could be
removed, genetically treated, and put back in the testis,
where they should produce normal sperm.
Dr. Brinster said he hoped to learn how to make the sperm
production cells produce sperm outside the body.
Genetically altered sperm could then be used directly for
in vitro fertilization. The technique could be useful in
animal breeding; whether it would be considered ethical in
human reproduction is likely to be a matter of debate.
The technique may also provide an alternative route for
generating embryonic stem cells for use in repairing the
body's tissues. The sperm production cells are adult stem
cells, which are specialized, self-renewing cells, each
type of which is dedicated to repairing or maintaining a
specific body tissue. All are descended from embryonic stem
cells, the all-purpose cells from which the body is made.
At present, embryonic stem cells are taken from the surplus
embryos generated in fertility clinics. The sperm
production cells have many of the same characteristics of
embryonic stem cells and, Dr. Brinster believes, are only a
couple of developmental steps away from them. It may be
possible to walk them backward into being embryonic stem
cells. These could then be converted into the specialized
cell types needed to repair damaged organs.
The new technique "will fuel a major advance in genetic
modification for farm animals, endangered species and
primates, including humans," Martin M. Matzuk, a
reproductive biologist at the Baylor College of Medicine,
said in a written commentary.
John Gearhart, a stem cell biologist at Johns Hopkins
University, said Dr. Brinster's achievement lay in showing
how to grow sperm production cells in a reproducible way.