Can Stem Cells Become Sperm Cells?

A study published in the Medical Journal Stem Cell and Development (Nayernia et al. In Vitro Derivation of Human Sperm from Embryonic Stem Cells. Stem Cells Dev. 2009 Jul 7) addresses an issue that influences the lives of approximately 7.3 million Americans: infertility.

In a report by the 2002 National Survey of Family Growth from the Centers for Disease Control and Prevention, it is stated that one third of infertility cases are the result of the male. Accordingly, the generation of brand new sperm would have great implications for this segment of the population.

The publication, in which the lead author is Professor Karim Nayernia, from Newcastle University and the NorthEast England Stem Cell Institute, in Newcastle, England, describes the generation of sperm cells from embryonic stem cells. Most strikingly, the sperm was able to mimic many of the properties of functional human sperm.

While the current study used embryonic stem cells, thus would not be possible for practical use in treatment of infertility, the scientists are now trying to generate sperm from inducible pluripotent stem cells (iPS), a type of stem cell derived from skin that mimics embryonic stem cells. More information about iPS cells can be seen on the video available at this link: iPS cells video.

Creation of sperm from frozen non-sperm cells offers some far reaching possibilities. Dr. Robert Lanza, of the stem cell company ACT, Michael West's former company, stated:

"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,"

He continued:

"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." While this may sound like science fiction, the generation of iPS stem cells has previously been performed with many types of tissues that can easily be stored across decades if not centuries. While the fact that iPS cells have not yet been made into sperm cells is a barrier, to date, every cell type that has been generated from an embryonic stem cell has also been generated by iPS cells. Accordingly, the ethical questions of using such technology should be addressed now, since scholars believe it will be relatively soon (less than a decade), when frozen cells such as skin cells, will be useful for the brand new generation of sperm.

On the other hand, the findings of Nayernia et al, although exciting, still have several drawbacks. For example, while sperm cells that "look and feel" like normal sperm cells, have been created, these cells have not been able to successfully fertilize an egg and generate offspring. This is actually the vital test, which from what we understand, has not been successfully performed.

In the news article that we are commenting on (RADHA CHITALE, ABC News Medical Unit, July 9, 2009), the statement is made that "The researchers had used this technique to produce viable sperm that were used to create offspring in mice", although in the scientific publication we could not find any reference to creation of viable offspring, nor could we find mention of mouse embryonic stem cells.

Perhaps an even more important paper to the area of male infertility, which did not receive as much media exposure, was a paper by Swerdloff's group from Los Angeles (Lue et al. Fate of bone marrow stem cells transplanted into the testis: potential implication for men with testicular failure. Am J Pathol 2007 Mar;170(3):899-908). In this paper the administration of bone marrow, adult stem cells, was performed into testicles of mice. It was found that the administered bone marrow stem cells could generate cells that looked and acted like sperm cells. The important part about this paper is that conceptually some types of infertility may be addressed by injection of the patient's own bone marrow cells into the testis.

An independent Germen group (Dursenheirmer et al. Putative human male germ cells from bone marrow stem cells. Soc Reprod Fertil Suppl. 2007;63:69-76) reported that bone marrow stem cells can be induced to become the cells that give rise to sperm cells based on expression of specific proteins.

In conclusion, the prospects for developing therapies for infertility using stem cells is very bright these days, with advances being made in the areas of both bone marrow derived adult stem cells, as well as in embryonic stem cells.