Junjiu Huang is back. Two years later, Protein & Cell publishes another study by the team which first edited human embryos in 2015 sparking uproar. They targeted the gene responsible for beta thalassemia, once again. This time, however, in place of using embryos discarded by fertilization clinics, they resorted to cloning. Furthermore, Huang and colleagues employed a CRISPR variant called base editor changing a single DNA letter without even cutting the double helix. The news is circulating among experts but has not yet attracted the media spotlight. Stem cell specialist Alessandro Bertero has brought it to the attention of CRISPeR Frenzy. According to the researcher involved in the British experiment just published in Nature, the latest paper from China is far from perfect but it’s quite interesting anyway (see his technical comment below).
“Briefly, they used a modified Cas9 that edits a single base via cytidine deamination, and tested it in the context of a homozygous mutation that causes beta thalassemia. For the experiments they generated surrogate human embryos by somatic cell nuclear transfer (SCNT, the procedure behind human cloning, although in this study they do not go as far to formally demonstrate cloning since they did not try to obtain blastocysts nor they isolated human embryonic stem cells). The reported efficiency of gene editing appears good, albeit still not high enough for practical applications (23% corrected blastomeres, of which only 6% were homozygous). They did not examine specificity genome-wide, but based on in vitro data on a few loci it seems it could be sufficient. On the other hand the study went through an unusually rapid peer-review (less than a week), so we should wait and see how this will be received by the scientific community. Overall despite these limitations, I find it a very interesting study. In particular, the use of surrogate embryos for pre-clinical tests could be less controversial from an ethical perspective than using supernumerary IVF embryos or those created ad hoc for research. However, this might be less relevant for studies of early human development, as it remains to be established whether cloned embryos behave identically to normal ones during these early phases.”