Humans have long sought to improve themselves through technology.
On Nov 25th 2018 Dr He Jiankui announced, via youtube, that he had decided to push humankind across a controversial threshold. This announcement was, of course, that his work had resulted in the birth of twins who had both been subject to genetic engineering using CRISPR.
This was a threshold widely considered to be off limits.
In 2015 two of the foremost journals in research, Science and Nature, both made similar statements stating that modification of human germ cells, that is sperm and egg, should be avoided.
The scientific community seemed to have come to an agreement not to experiment with this technology until we could agree how and when to apply it to humans, but Dr He Jiankui has unceremoniously dragged us across this line in the sand, whether we like it or not.
Now, more than ever, there is an urgent need to stop and ask what the outcomes of this work are for the individual who have been subject to it and also how the rest of society may be affected.
To understand all this we are going to need to understand how CRISPR technology works and what the intrinsic shortcomings of this technology are.
DNA is made of nitrogen and carbon-based rings which form 4 distinct chemical codes. Adenine (A), Guanine (G), Cytosine (C) and Thymine (T).
These codes form an easily reproducible double-stranded molecule which is read in group of threes, called codons, which are contained within structure called genses. These genes are simply the parts of the DNA that code for the more structurally complex proteins, which in turn, form the biological machines and structure that are required for all life on earth.
Due to DNA’s ability to copy itself, until now the code in the DNA of all humans can be traced faithfully to the first cells on earth.
Dr He’s work changed all of this by employing the use of the CRISPR-CAS9 technology to purposefully change the DNA code in the two twins referred to as Lula and Nana.
As its name suggests, the CRISPR/CAS9 methodology is dependent on two key parts: CRISPR and CAS9.
CRISPR is a kind of repeating DNA structure that was first discovered accidentally in bacterial DNA by the Japanese scientist Yoshizumi Ishino in 1987. For 17 years following this discovery, the exact function of these DNA repeats went undiscovered until it was identified as the means by which bacteria identify and protect themselves against invading viral DNA.
It turned out that these strange DNA repeats actually came from viruses. Bacteria have the ability to cut up invading viral DNA, store it in their own DNA, and then subsequently use it as a guide system for the enzymes CAS9, which destroys the viral DNA sequence should it invade again in the future.
In order to do this, CAS9 uses the stored DNA to make something called a guide RNA. This guide RNA is usually coded for by a CRISPR repeat and guides CRISPR to DNA it should cut.
There are two conditions for CRISPR’s binding to its target.
First CAS9 must bind to the target sequence and a specific 3 code variation in DNA which is called a PAM (Protospacer Adjacent Motif). Most PAMs can be recognized by CAS9 as they contain the code: *GG. These recurring patterns are targeted by a bacteria’s CAS9 system as they identify the DNA of invading viruses. This gives the bacteria an ability to target and destroy the viral DNA.
However, in the last 5 years, we have learned to leverage this ability to direct CAS9 with guide RNA’s of our own design to alter the genome of other organisms. This guide RNA binds to a part of CAS9 called the alpha-helical lobe. In turn, another domain of CAS9, the nuclease lobe, binds to any flanking part of the DNA strands that match with the guide RNA, causing the double helix structure of the DNA to unwind.
This process is facilitated by the proximity between the DNA and the CAS9 complex and electrostatic interactions that occur between the RNA and DNA.
At this point, 2 specific domains of the nuclease lobe cut the DNA. Although we are not yet fully sure how this mechanism occurs, comparative studies suggest that the most likely way is that the two separate part of CAS9 are able to rip protons from water molecules, and in turns weaponize the deprotonated water molecule to break the DNA apart.
This is done at two sites in the DNA, one which cleaves the DNA at the target site (HNH) and another which cleaves the DNA at a non-target site (RuvC). At this point a number of things can happen depending on which approach is needed:
CAS9 can be modified to include a deaminase enzyme which can target specific bases of mutation, leading to brand new mutations. A process known as homology-directed repair can be used to insert new DNA at the cutting site. Or the targeted piece of DNA can be simply cut out and removed if it is deemed to be undesirable.
DR He Jankui opted for the latter option and simply cut a section out a gene called CCR5.
This section that was cut corresponded to a mutation known as delta32, that confers its owners with protection to certain strands of HIV. Dr He’s data seems to suggest he may have artificially induced a mutation, similar to, but not identical to the delta 32 mutation in these twins.
In order to do this, Dr He had to first optimize the gene-editing protocol in mice, monkey and human cells. The reason for this is to make sure the protocol has high specificity — simply put, that the gene-editing technique was editing the target DNA and not some other sequence. This claim is of course key to the validity of the experiment.
Unedited embryos can be thrown away after all-but for obvious reasons, making unspecific alternations to a human’s genetic code would be a major red flag, and Dr He’s work raises major red flags for this exact reason.
Their check for specifically of gene editing used parental genetics as a reference point, an inadequate approach due to the fact that a parent’s genetic material is a subject to a certain degree of randomization every time a sperm or egg is produced.
It’s further complicated by the fact that no two sperm or eggs will be the same and that their methodology did not account for the possibility that larger sections of the genetic code could be deleted by their implementation of the CRISPR/CAS9 system.
Further to this, from the data released so far, we can tell that the mutation-induced in the twins does not exactly mirror the delta32 population that He is attempting to induce in the twins.
Although the protein produced should in theory largely mirror the naturally occurring mutation, we cannot tell that for sure because it has not been tested. Standard practice at this point is to test these mutations in an animal model in order to assess unexpected effects of the experiment.
This is perhaps the most troublesome part of this experiment. Lulu and Nana are test subjects for a genetic mutation that we have not even taken the time and care to test in animals.
Nonetheless, the mutation was induced in a total of 31 human embryos. These embryos were grown for a period of 5–8 days and the 19 that were deemed “normal” were taken forward.
Out of these 19 embryos, 2 were implanted in the mother to give rise to the twins.
These concerns over Lulu’s and Nana’s well being are only one of myriad of issues. Perhaps most critically there was no medical need for this treatment in the first place. It has been claimed that the biological father of the twins is HIV positive. Given that the couple used IVF, and that there is no evidence that HIV would be passed on from father to child using this method of conception.
The procedure was medically unnecessary.
Furthermore, He claims to have induced this mutation completely into at least one of the twins.
To do this, He and his group would have had to check the DNA in every cell in the growing blastocyst, a group of cells that exist from days 5–9 post-fertilization that eventually becomes the embryo.
Given that they would have to destroy the blastocyst to test all the cells, a clear logistical problem exists in trying to qualify that the mutation exists in all the cells. Accordingly, He and his group only checked a number of cells from the blastocyst. This means both twins might have a condition called mosaicism, where the deletion only occurs in a subset of their cells. This means that different cells in their body, have different DNA.
In this context, the effects of this condition are completely unstudied.
Finally, the gene that He took aim at has also been reported to have a role in learning. A link between the activity of the CCR5 gene product and the dampening down of the brain’s ability to form a new neural connection has been previously described in mice models.
Theoretically, there is a possibility that the induced deletion could have a positive effect on the twin’s ability to learn.
Right now there are far too many unkowns to make an accurate prediction on what if any effect this experiment will have on the two twins and there’s an even bigger question about what effect the announcement will have on the progress of the field.
Complicating this mess is the fact that this study did not go in front of an adequate ethics approval board and default Chinese law prohibits any kind of follow up with the twins.
Because of this, we will likely never know what will become of Lulu and Nana.
Dr He has stated that he plans to publish the work in a peer-reviewed journal, but given that he has gone M.I.A for almost 2 months now, the scientific community may never have an opportunity to properly review and digest the impact of this work.
So where do we go from here?
There is no doubt that genetic engineering is a valuable tool that can potentially safely increase human wellbeing and productivity. It’s not unlikely that plunging into these uncharted waters unaccounted and without approval may have a chilling effect on the proper utilization and development of this technology though. Perhaps, until a consensus on the way forward is established this is a good thing.
Thankfully, the World Health Organization has stepped up to take a moderating role in the process and are establishing a working group to establish clear guidelines. We need these guidelines because we have stepped into a new era of medicine.
One where the genetic modification of humans is not only a possibility but an increasingly realistic option.