This 2015 study describes an experiment that utilized CRISPR/Cas9 to modify human embryos in vitro. These embryos were pre-implantation and nonviable, and the study identified technical difficulties with embryonic CRISPR modification, including poor DNA repair and off-target effects. Nonetheless, the publication of this research prompted the US National Academies of Sciences and Medicine to organize the first International Summit on Human Gene Editing later that same year.

Japanese bioethicists and scholars defend the 14-day rule, pointing out that it was a promise and compromise that helped secure public trust in biomedicine. They also draw attention to concerns raised by others in the wake of the ISSCR’s 2021 revised guidelines. First, the ISSCR made its decision without sufficient public debate. Second, the ISSCR did not set a new limit for embryo culture in vitro. Overall, the authors “get the impression that the ISSCR’s justification does not give enough consideration to moral concerns vis-à-vis scientific merits” (2021:e53726).