Recent headlines tout that it may be possible for same-sex couples to have biological children thanks to stem cell technology. Using skin stem cells, scientists from the University of Cambridge and the Weismann Institute found that it is possible to make primordial germ cells, the cells that eventually form into egg and sperm (gametes), from induced pluripotent stem cells created from a donor’s skin.
The opportunity for same-sex couples to have biological children may take over the headlines, but it is not the only, or necessarily the primary reason, scientists are interested in this research. One thing scientists hope to do is to use this technique to study age-related diseases. As we go through our lives, we accumulate epigenetic messages that tell genes when to turn on or off, when to make more cells, or when to stop making cells. Recent research shows that certain cancers and age-related diseases are likely due to these epigenetic factors going awry. These epigenetic factors are “reset” in germ cells, meaning scientists can start over and see how these factors develop at the cellular level. There is still much research that needs to be done in this area, including questions as to which epigenetic factors are passed on and which ones are actually reset in germ cells (See Nature’s recent issue on the results of the NIH’s Roadmap Epigenetics Project here).
While the epigenetic research is interesting, the headlines emphasize the reproductive possibilities. This technique could be another option for infertile couples who want to have biological children, including same-sex couples who want children that are biologically related to both of them. However, what is not touted as loudly is that, for now, the technology only works for male same-sex couples.
The why this technique can be used for two men but not two women has to do with how the cells are made. Primordial germ cells are made from skin cells are taken from each person to be converted into induced pluripotent stem cells. Those stem cells are then converted into primordial germ cells by turning on or off certain genetic factors involved in converting pluripotent stem cells to particular cell types.
Female cells have XX chromosomes and male cells have XY chromosomes, but in order to make primordial germ cells that are precursors to sperm, researchers need a Y chromosome. Lead researcher, Dr. Hannah pointed out, that it is easier to take away a chromosome than to insert one. Women don’t have any Y chromosomes to contribute, meaning that making primordial germ cells from women “is a long way off.”
Finally, one of the more troubling factors in this research is that little has been said about the health and well-being of the children that would be produced from this technique. A key point in the original research article in Cell is that SOX17 is a key factor in the process of making primordial germ cells and likely plays an important role in gene regulation. This was surprising to scientists because SOX17 does not play a key role in mouse development. This means that even though mice have been used in prior studies on creating primordial germ cells, they may not be a good model system for creating the subsequent sperm and egg cells. Often before a procedure or a drug makes it to human trials, it is first tested in mice and then in primates. When it comes to human development, though, things do not translate from animal models to human models as easily.
Once scientists are able to take the primordial cells and advance them to egg and sperm cells, they will be able to create an embryo. However, because the mouse models are different, this is a case in which we have no way of knowing whether these embryos or the children will be healthy until the experiment is actually done.
It is unclear from the interviews or the article if the assumption is that “unhealthy” embryos will die off before they implant in the uterus or how exactly researchers are expecting to test whether this technique work as another reproductive technology. If unhealthy embryos die, this poses an ethical problem for those that assume embryos should be granted dignity in their own right. But even if one does not accept that embryos are accorded a certain level of dignity, what about babies and children? What do scientists plan to do if the children born from this procedure are unhealthy or deformed?
Finally, it is worth mentioning that this technique would provide a source of eggs, which are needed for various other reproductive techniques and research endeavors. For example, The UK just passed legislation permitting what has been dubbed “three-parent IVF” in which scientists transfer the nucleus from one woman’s egg to another woman’s enucleated egg that will then be used in IVF. The hope is to prevent mitochondrial disease which is genetically passed down to offspring from the mother. Obtaining skin cells from a donor is much less invasive and poses less of a risk to the donor than obtaining her eggs after inducing hyperovulation.
This research is rife with ethical concerns, most notably the fact that it amounts to human experimentation on people who did not have the opportunity to choose to be the product of experimentation, but must live with the consequences, if they live at all.