Highly efficient ssODN-mediated homology-directed repair of DSBs generated by CRISPR/Cas9 in human 3PN zygotes

Ma et al. (2017) published data in Nature Journal using human zygotes that showed that double-strand breaks (DSBs) generated by CRISPR/Cas9 could be repaired by homology-directed repair (HDR) using the wild-type allele as a template, by inter-homologue recombination. This result received great attention from the scientific community, however, in a recent publication, researchers have raised some concerns about Ma's interpretation of their results (Egli et al., 2017). Our previous work showed that ssODN-mediated HDR could repair 75% of DSBs generated by CRISPR/ Cas9 at G6PD mutant alleles (Tang et al., 2017), while no ssODN-mediated HDR repair was reported in Ma's work. Thus, we set out to repeat Ma's work using clinically discarded human tripronuclear (3PN) zygotes to exclude the influences of external experimental conditions, such as injected mixture preparation, injection equipment, or injection procedure.