FRIDAY, 1 MAY 2015Last week, a group from China led by Pupin Liang reported the testing of a gene-editing method in human tri-pronuclear zygotes (published in Protein & Cell). The zygotes are eggs fertilised by two sperms and therefore non-viable; a common waste product of clinics that cannot develop into human embryos. The method they used is called CRISPR/Cas9 (clustered regularly interspaced short palindromic repeat-associated system), a technique that has revolutionized genetics and developmental biology over the last two years since its inception, because it is the most accurate in vivo genome editing method known to date. It is regularly used to insert or delete genes in laboratory animals and has impressed researchers with its accuracy. It has previously been reported that CRISPR/Cas9 had very little off-target effects in human pluripotent stem cells and mouse zygotes, meaning that it usually only edits the target gene and does not cause unwanted trouble anywhere else in the genome, making it an interesting candidate for human gene editing. However, the present study importantly shoes that the method is not quite there yet, as it has produced very low efficiency, with only 4 out of 54 of the eggs showing the intended changes and all of them showing off-target effects. Furthermore, after cell division, only some of the cells retained the changes (“mosaic” effect), making it impossible to predict the outcome over the course of development of an organism.
The study raised ethical concerns that have divided the scientific community. A spokesman for the US National Institute of Health (NIH) claims that such a study could not have been funded by the federal government under current US legislation, while a bioethicist at the University of Manchester told Nature News that he has no concerns about the study, since the embryos used were non-viable. It may be just as unethical towards patients who suffer from, or are carriers of, genetic diseases not to at least experimentally consider new possibilities of treatment.
Written by Laura-Nadine Schuhmacher.