A research group in China has attempted to genetically edit human embryos to be resistant to HIV. The second group within a year to have announced such research, it shows proof of concept that the powerful gene-editing technique CRISPR/Cas 9 can be used to modify human embryos. There are, however, a multitude of scientific and ethical issues to iron out before the widespread editing of human embryos could ever take place.

The team, from the Guangzhou Medical University in China, used CRISPR/Cas 9 to genetically modify a specific gene that codes for a protein found on the surface of cells. This protein, CCR5, is what the Human Immunodeficiency Virus recognizes and uses to latch on to their host cell. People who naturally carry a mutation in their CCR5 gene are immune to HIV, and so the team was aiming to artificially modify the gene in embryos to get the same result. The research is published in the Journal of Assisted Reproduction and Genetics.

This is the second time that a research group from China has published their research on editing human embryos. The first happened about a year ago, when scientists reported their attempts to remove a gene that causes a dangerous blood disorder. This new study confirms many of the obstacles faced by the original, highlighting the difficulties that are present in editing the human embryo.

In the latest research, the team started with over 200 embryos, fertilized in vitro, and donated from a fertility clinic. None of the embryos were viable, and all would have been destroyed anyway if the researchers had not used them for the experiment. Out of these, 26 were targeted for modification, but genetic analysis showed that only four of the embryos showed successful alterations to their DNA. None of the embryos were allowed to live for longer than three days. These low levels of success are in a similar ballpark to the earlier experiment, and show that despite widespread success in using CRISPR to edit other genomes, using it on human DNA is still in its infancy.

Not only that, but this new experiment also exposed another, potentially more controversial problem, which again was seen in the earlier study. While CRISPR was able to add in the modifications desired, it also can cause random alterations to other sections of DNA. The researchers of the latest study didn’t find any of these changes, but are certain they occurred. “The embryos likely carried off-target mutations undetected by our genotyping, and the off-target effects thus merit further inquiry,” write the researchers.

These issues have meant that some experts are calling for more research to be carried out on non-human primates before other groups start editing human embryos. The last year has seen a scramble to set some limits on human embryo editing around the world, from the U.K. to the U.S. In fact, the authors of the recent study are seemingly in agreement. “We believe that any attempt to generate genetically modified humans through the modification of early embryos needs to be strictly prohibited until we can resolve both ethical and scientific issues,” they write. 

But it could be that the flood gates have already opened. According to Nature, who originally found the most recent paper, there are hints and whispers that other groups within China have already been editing human embryos. The fact that this recent study began back in 2014 shows that teams have been working on human embryo editing in secret for quite some time, and Nature predict that more papers will be published from other groups in the coming months.