07 March 2016
ByAppeared in BioNews 842
A recent press release from the Chinese Academy of Sciences announced the publication of research showing that scientists had created functioning spermatozoids from mouse embryonic stem cells in the laboratory (see BioNews 841). This made quite a splash in the media who suggested this new technology could allow infertile men to have children. I cannot blame the media; this is what both the press release and the actual article in Cell Stem Cell suggested (Zhou et al., 2016). However, one key point seemed to be overlooked – adult infertile men do not have embryonic stem cells; these cells exist only in embryos.
Apparently it must have been automatically assumed that the technology would work with iPSCs (induced pluripotent stem cells) too. But, although reprogramming technology has been advancing at tremendous speed, we cannot ignore that mutations in adult cells accumulate over the lifetime of the donor. And, the older a donor is, the higher the number of the mutations present.
A clinical trial in Japan, in which patients with age-related macular degeneration were treated with their own iPSC-derived retinal pigment epithelial cells, had to be halted because reprogrammed cells from one patient were found to contain a novel mutation that was not present in the original cells. Therefore, to assure success in creating sperm cells this way, we would have to generate and analyse multiple iPSC clones from several rounds of reprogramming using the cells from different biopsied sites in the donor.
The Japanese scientists are circumventing the problem by avoiding autologous transplantation. Instead they are making a bank of iPSC lines with the most common HLA types using cells from umbilical cord blood, which are as genetically naïve as cells can be. Such cells will be used as an allogeneic therapy. The Japanese strategy has been adapted worldwide and iPSC-based personalised treatments now look further away than they did a couple of years ago.
Another obstacle is that reprogramming involves erasing and remodelling epigenetic marks such as DNA methylation in adult somatic cells in order to bring them back to embryonic level. The remodelling of the epigenetic signature during reprogramming is never complete and there is a possibility that any un-erased methylation sites could be linked with susceptibility to diseases. For example, there is evidence of involvement of DNA methylation in the aetiology of autism and psychosis. Quality control would have to be quite strict and, although we have the technology in our hands, is fairly complex and too costly to be routine.
Furthermore, even if the previous two obstacles were not there, not all infertile men could benefit from this technology. The causes of male infertility are of either genetic or physical nature. If the cause is genetic, the chances that this technology could help are quite slim.
For example, abnormalities in the azoospermia factor (AZF) locus on the Y chromosome cause varying degrees of spermatogenic failure, which are unlikely to be fixed without additional genetic manipulation. A group from Stanford University in California derived iPSC from infertile men with deletions in the AZF regions, associated with production of few or no sperm but normal somatic development (Ramathal et al., 2014).
They transplanted iPSCs directly into murine seminiferous tubules. The testicular microenvironment induced differentiation of the iPSCs into germ cell-like cells, which were indistinguishable from fetal germ cells. But iPSCs with mutations in the AZF region generated significantly fewer germ cell-like cells and they had distinct defects in gene expression when compared with normal controls. Therefore, the 10-20 percent of infertile men carrying a deletion on the Y chromosome with no sperm in ejaculate would not be able to benefit from this technology. The mutations that prevented formation of sperm in their bodies would interfere with sperm production in vitro too.
Finally, the costs of iPSC-based personalised treatment would be reasonably steep and it is unlikely any health insurance company would cover it. Thus, if this ever came to fruition, the patient will have to pick up the tab and pay from his own pocket.
Keeping all these obstacles in mind, I do not see clinical applications coming any time soon, even though further development of technology for iPSC-derived gametes could benefit men with non-genetic causes of infertility, as well as same-sex couples. It could allow these people to have children that are genetically theirs, a truly exciting prospect. But, as it is, the report is a significant achievement and major step forward in understanding the molecular mechanisms governing gametogenesis, and nothing more.