Can Stem Cells Become Sperm Cells?

July 9, 2009 — -- The face of infertility -- in literature, in the media, in advocacy groups -- is so predominantly female that many often forget about the other part of the equation. But more than a third of infertility cases, which affect 7.3 million people in the United States, can be attributed to the male partner, according to a 2002 National Survey of Family Growth from the Centers for Disease Control and Prevention.

Now, new research may provide a glimmer of hope that infertile men may one day be able to contribute to the gene pool.

"We have a system which enables us for the first time to produce human sperm from stem cells," said Dr. Karim Nayernia, a professor of stem cell biology at Newcastle University in the United Kingdom and the lead researcher on this study, published July 8 in the journal Stem Cells and Development.

Skeptics are unconvinced that the researchers have gone as far as creating viable sperm -- sperm that could someday stand in for a male. But the researchers note that the study's data is too premature to consider writing men out of the reproductive picture.

In fact, Nayernia said the study may lead to treatments that could keep men squarely in the picture, even when they have problems with fertility.

"Studying sperm maturation is not accessible in vivo [in a body]. You cannot follow the system," Nayernia said. "Now we have a system to monitor the stages of male infertility."

Growing Sperm Cells From Stem Cells

Nayernia and his team developed XY (male) stem cells into haploid gametes -- sex cells with half the normal number of chromosomes. These new cells were able to grow into mature sperm, called In Vitro Derived sperm (IVD sperm).

Nayernia attempted to create sperm cells using XX (female) stem cells, but their development arrested, showing that the genes on the Y chromosome are necessary for sperm maturation.

The researchers had used this technique to produce viable sperm that were used to create offspring in mice and are currently developing a new system in which the stem cells are derived from human skin instead of an embryo.

A Long Way for Test-Tube Sperm

But the test-tube sperm are abnormal. The baby mice born of the sperm died shortly after birth and it is certain that the test-tube sperm would not be able to support a human embryo. British law bans researchers from even trying.

"I would be very skeptical at this point and really look at what they define as sperm. An actual moving sperm cell or just a haploid cell that can be used to implant into an egg cell?" said Byron Petersen, associate professor in the Department of Pathology at the University of Florida. "The devil is in the details and it will be how they define their cell phenotype and whatnot."

Real Baby Einsteins?

And there are ethical concerns about Nayernia's research as well as viability concerns.

"What's most concerning about this potential technology, is that anyone, young or old, fertile or infertile, straight or gay, could potentially pass on their genes to a child from just a few cells," said Dr. Robert Lanza, chief scientific officer at Advanced Cell Technology and adjunct professor at the Institute of Regenerative Medicine at the Wake Forest University School of Medicine.

"For instance, if you had a few skin cells from Albert Einstein -- or perhaps even a hair follicle from the pope or Queen Elizabeth -- you could generate pluripotent stem cells," he said. "Any couple could go to an IVF clinic and have a child that is half, say Albert Einstein or perhaps Brad Pitt or Elizabeth Taylor."

But Nayernia said any clinical applications derived from his research were at least five years away, after significant vetting by further experiments.

Right now, he said, his research offers a proof of principle -- that it is possible to create sperm cells, even if they are not fully viable yet, using his technique. And it is the process of how sperm forms, not the sperm themselves, that can show how a variety of factors may contribute to infertility.

"With those techniques, we can then model the individual situation of the patient and then see.. why those men are infertile," Nayernia said. "Once we have this factor -- it could be genetic, it could be environmental -- we will be able to offer the proper clinical application."