This paper was rejected by both Nature and Science partly for "ethical objections." When published it immediately triggered worldwide controversy among scientists and the public. This was the first application of the CRISPR gene-editing tool to human embryos. The authors used human embryos from fertility clinics which had been created for in vitro fertilization but had an extra set of chromosomes (tripronuclear) which was the result of anomalous fertilization by two sperm instead of one. Such  embryos could undergo only a few stages of development but could not result in a live birth. Of 84 initial embryos, 71 went on to the early stages of division and 54 were chosen for genetic evaluation, leaving 28 of them acceptable. However, a surprising number of "off target" mutations were introduced by the CRISPR/Cas complex acting on other parts of the cell's genome with catastrophic results. This led the authors to stop the experiment.

Open access: available from link.springer.com at this link.

(Thanks to Juan Weiss for this reference and its interpretation.)