Science - February 2, 2016

Genetically modified human embryos

Koen Guiking

British scientists are going to apply ‘genome editing’ on human embryos. ‘It is good news that this research has been approved’, John van der Oost reacts, ‘but the application needs to be reviewed critically.’

Human embryo after three days. Photo: RWJMS IVF Program

Van der Oost has been working for over ten years on the CRISPR-technology that is now being used to alter the human embryos. Two weeks ago, in the publication The Heroes of CRISPR in the renowned scientific journal Cell he was praised as one of the pioneers of CRISPR. What does he think of the fact that the technique is now being used in human embryos?

‘The great promise of this technique is that one can repair a defect in a genetic code really precisely. If this can prevent the passing of terrible diseases to offspring, then for me this is a great development. But of course it is really important that there are strict rules of what is acceptable and what is not. With gene editing you can restore a point mutation, but you can also remove or replace multiple genes. Of course you also have the ghost stories about how people with a lot of money will order babies that can play piano like Mozart and play football like Cruijff. Personally I do not believe in this. Talent is a combination of many genes that we do not fully understand yet. But it is good that we look critically at the applications of the technique.’

The technique is relatively new. Isn't it unusual that it is now already used for research on human embryos?

‘In the United States they are really reluctant to get involved in these developments. Recently there was talk about a moratorium for research on genome editing of embryos. On the other hand, in China the technique was already applied on human embryos last year. I find it really positive that in Europe we don't immediately apply the brakes, but that we say: under strict conditions we allow such research. For example, the scientists in the United Kingdom are not allowed to implant the embryos into a woman. Also, they may only keep the embryos alive for a couple of days and study their development in the earliest stages.’

Can you explain how the CRISPR-technique works in layman’s terms?

‘We have been working on the CRISPR system for ten years. It is an immune system of bacteria against viruses. When we had obtained some fundamental insights in the CRISPR mechanism, we managed to specifically make a bacteria resistant to a certain virus. We did this by linking a small piece of RNA to a CRISPR-associated (Cas) enzyme of a bacterium. Then if a virus enters this bacterium, this piece of RNA will guide the enzyme to a specific DNA sequence in the virus, where it subsequently cuts the DNA. Because of this the virus is made harmless. A comparable enzyme, Cas9, can be programmed with a different RNA molecule to make a cut in human DNA, precisely on the location where it needs to, and then replace that cut out piece with a different piece of DNA. This allows for very accurate repairs of mutated DNA sequences in human cells.’

It sounds like a really difficult operation that can easily go wrong.

‘At least 99,99 percent of the time the 'operation' is successful. The question is, whether we consider this a good enough success rate if we are talking about actually repairing damaged DNA in human embryos. Combined with the ethical aspects, these are questions that science has to find answers to, in consultation with various groups in society.’

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