Chinese scientists recently genetically modified human embryos in an experimental effort to repair or eliminate mutations that cause a particular disease. While the results proved that this field of study is still in an extremely early stage of development, their experiment has received widespread attention in the scientific community for the potential ethical implications of tampering with the human genome. Regardless, the experiment is noteworthy in that it demonstrates the first step in human genome modification.
Junjiu Huang, a researcher at Sun-Yat Sen University in Guangzhou, and his research team attempted to modify the hemoglobin-B gene (HBB), which, when mutated, can cause the blood disorder β-thalassaemia. According to Nature.com, Huang’s group used a gene editing technique known as CRISPR/Cas9. CRISPR/Cas9 is a relatively new and simple method of gene editing that relies on the base pairings of RNA and DNA, as opposed to other methods which involve engineering proteins that can bind onto DNA sequences. The CRISPR enzyme can be programmed to target a mutated gene, which can be fixed or replaced by another molecule introduced at the same time.
Huang and his team conducted their test on 86 “non-viable” human embryos, which were donated from an in vitro fertilization (IVF) clinic. The embryos contained an extra set of chromosomes and would not have been born alive. Huang injected the CRISPR enzyme and, after two days, tested 54 of the 71 surviving embryos. According to Science Insider, they found that while 28 of them successfully spliced, only four carried the desired genetic alterations.
“If you want to do it in normal embryos, you need to be close to 100 percent,” Huang said, regarding the results of the study. “That’s why we stopped. We still think it’s too immature.”
In addition, the team also found that the CRISPR injection caused a number of other unwanted mutations in the embryos, which could be potentially harmful. The rate of the mutations they observed post-procedure was much higher than the naturally-occurring mutation rate in mouse embryos or even human adult cells. The researchers also only looked at a particular portion of the genome, called the exome—so, there could be a number of other possible mutations that they had failed to account for.
The study has demonstrated that any viable modification of the human genome may be years away, but that has not stopped a significant response from the scientific community over the experiment’s implications in human genetics. A recent article by Nature argued that research is at too early of a stage to be modifying “germ,” or human reproductive cells and that for the time being, research should continue to focus on somatic non-reproductive cell modification. Furthermore, the article calls for a moratorium on germ modification among the scientific community until there could be a meaningful discussion about the future of genome editing.
Indeed, both Science and Nature refused to publish Huang’s work out of ethical considerations. The study was only reported in the less prestigious, Protein and Cell.
On the other hand, many scientists are defending Huang’s work. Harvard molecular geneticist George Church explains that experimenting on discarded IVF embryos are nothing new, but the CRISPR technique is what “makes it noteworthy.” Similarly, George Q. Daley of Science explains that experiments with human embryos are acceptable under international guidelines as long as the cells are not allowed to grow for more than 14 days. Huang’s work itself was reviewed by the Sun-Yat Sen University’s’ ethics board and complied with national and international ethical standards given that the researchers were using these non-viable embryos.
Still, the study indicates that this research remains far from anything viable. “Further investigation of the molecular mechanisms of CRISPR/Cas9-mediated gene editing in human model is sorely needed,” the researchers reported.
Regardless of the response and the results, Huang stands by his work.“We wanted to show our data to the world so people know what really happened with this model, rather than just talking about what would happen without data.”