Gene Editing Sperm and Eggs (not Embryos)

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Heritable, human genome editing constitutes one of the most contentious issues facing science policy. This was starkly illustrated by Dr. He’s unsafe, unethical, and irresponsible editing of twin girls’ embryos in an attempt to confer HIV immunity. The hubris of those experiments stands in contrast to calls for a regulated pathway from the U.S.’s National Academies and the U.K.’s Nuffield Council. But in all of the public discussion of the topic, the focus has been on editing embryos. What about editing sperm or eggs? Weighed down by technical, statutory, as well as sectarian challenges, the prospect of editing a human embryo’s genome at fertilization still remains a long-term goal. Mindful of this reality, the 2015 International Summit on Human Gene Editing reported the editing of mouse spermatogonial stem cells followed by testicular transplantation, resulting in the repair of a cataract-causing mutation. Further experimental work in this area, however, has proven limited. Similarly limited efforts have characterized editing eggs, although the editing of gametes is likely to flourish as the prospect of stem cell-derived gametes becomes reality. This outcome is bound to shift the focus from genome editing the embryo to its antecedent gametes. This will likely increase control of the genome editing process, including eliminating problems of embryonic mosaicism. In this paper we discuss how the editing of sperm and eggs differs from embryos from a bioethical and U.S. legal perspective.