For the first time in the United States, researchers have used CRISPR technology to edit genes in human embryos.
The U.S. is not the first country to perform such tests. CRISPR technology has already been used in China to edit genes in human embryos. However, regulations covering the use of CRISPR on human embryos has prevented experiments from being conducted until now.
Researchers from Oregon Health and Science University used dozens of single-celled embryos for their experiments, although the cells were discarded after a few days, before development progressed too far. The embryos were never intended to be implanted.
The aim of the experiments was to investigate the potential for using the CRISPR gene editing tool for the treatment of inherited disorders very early in development – preventing symptoms for diseases from developing.
CRISPR – or CRISPR-Cas9 to give it its full name – is a method of performing precise edits to genes. Scientists can use the technology to remove, add or edit genes. CRISPRs are sections of prokaryotic DNA that are used as a defense mechanism against viruses. However, they have been shown to allow scientists to make very precise cuts to stretches of DNA in animals and humans. The cuts are performed by the Cas9 component. Since CRISPRS bind to a very specific section of DNA, they can be used for very precise editing.
CRISPR has already been used to create tuberculosis-resistant cattle, although experiments on humans have been limited. CRISPR has been used in China to perform gene editing on a small number of patients suffering from terminal cancer, with promising results. However, the use of CRISPR in embryos by Chinese researchers was not successful. While gene edits were made, they did not occur in all cells and in some cases, incorrect edits were made.
The researchers at Oregon Health and Science University, led by Shoukhrat Mitalipov, believe they have developed a technique that avoids the problems experienced by the Chinese researchers, allowing edits to be made more accurately. The key appears to be performing the edits early, injecting CRISPR at the same time that eggs are fertilized by sperm.
For the study, the team took sperm from a man with a single mutant gene called MYBPC3 which causes hypertrophic cardiomyopathy (HCM), which causes a thickening of the heart wall. HCM is one of the leading causes of cardiac arrest in young people, with the condition affecting one in 500 individuals.
As expected, fertilizing eggs with the mans sperm caused approximately half of the embryos to carry the mutant gene. However, treatment with CRISPR-Cas9 resulted in 42 out of 58 embryos being free from the mutation – 72%. MIT Technology Review has reported the team has been able to demonstrate the technology can be used without causing mosaicism – the failure to perform edits in all cells – or off-target effects.
However, for the time being at least, genetically modified embryos will not be implanted at IVF clinics. Congress has blocked the use of the technology and the U.S Food and Drug Administration has been forbidden from authorizing any clinical trials.
The study – Correction of a pathogenic gene mutation in human embryos – has recently been published in Nature.