A scientific article argues the virus could not have been genetically engineered – but not all scientists are convinced. Claire Robinson reports
Since the COVID-19 pandemic took off, speculation has been rife about its origins. The truth is that nobody knows for certain how the virus first took hold. But despite that uncertainty, suggestions that the virus may have been genetically engineered, or otherwise lab-generated, have been rejected as “conspiracy theories” incompatible with the evidence.
Yet the main evidence that is cited as ending all speculation about the role of genetic engineering and as proving the virus could only have been the product of natural evolution turns out to be surprisingly weak. Let’s take a look at it.
The authors of a recently published paper in the journal Nature Medicine argue that the SARS-CoV-2 virus driving the pandemic arose through natural mutation and selection in animal (notably bats and pangolins) or human hosts, and not through laboratory manipulation and accidental release. And they say they have identified two key characteristics of the virus that prove this: the absence of a previously used virus backbone and the way in which the virus binds to human cells.
Not the "ideal" design for infectivity?
As you would expect of a virus that can cause a global pandemic, SARS-CoV-2 is good at infecting human cells. It does this by binding with high affinity (that is, it binds strongly) to the cell surface membrane protein known as angiotensin-converting enzyme 2 (ACE2), which enables it to enter human cells. But, basing their argument on a computer modelling system, the authors of the Nature Medicine paper argue that the interaction between the virus and the ACE2 receptor is “not ideal”.
They say that the receptor-binding domain (RBD) amino acid sequence of the SARS-CoV-2 spike protein – the part of the spike protein that allows the virus to bind to the ACE2 protein on human cell surfaces – is different from those shown in the SARS-CoV family of viruses to be optimal for receptor binding.
They appear to argue, based on their and others’ computer modelling data, that they have identified the “ideal” CoV spike protein RBD amino acid sequence for ACE2 receptor binding. They then seem to imply that if you were to genetically engineer SARS-CoV for optimal human ACE2 binding and infectivity, you would use the RBD amino acid sequence predicted by their computer modelling. But they point out that SARS-CoV-2 does not have exactly the same computer program-predicted RBD amino acid sequence. Thus they conclude that it could not have been genetically engineered, stating: “This is strong evidence that SARS-CoV-2 is not the product of purposeful manipulation.”
To put it simply, the authors are saying that SARS-CoV-2 was not deliberately engineered because if it were, it would have been designed differently.
However, the London-based molecular geneticist Dr Michael Antoniou commented that this line of reasoning fails to take into account that there are a number of laboratory-based systems that can select for high affinity RBD variants that are able to take into account the complex environment of a living organism. This complex environment may impact the efficiency with which the SARS-CoV spike protein can find the ACE2 receptor and bind to it. An RBD selected via these more realistic real-world experimental systems would be just as “ideal”, or even more so, for human ACE2 binding than any RBD that a computer model could predict. And crucially, it would likely be different in amino acid sequence. So the fact that SARS-CoV-2 doesn’t have the same RBD amino acid sequence as the one that the computer program predicted in no way rules out the possibility that it was genetically engineered.
Limits to computer modelling
Dr Antoniou said that the authors’ reasoning is not conclusive because it is based largely on computer modelling, which, he says, is “not definitive but only predictive. It cannot tell us whether any given virus would be optimized for infectivity in a real world scenario, such as in the human body. That's because the environment of the human body will influence how the virus interacts with the receptor. You can’t model that accurately with computer modelling as there are simply too many variables to factor into the equation.”
Dr Antoniou added, “People can put too much faith in computer programs, but they are only a beginning. You then have to prove whether the computer program’s prediction is correct or not by direct experimentation in a living organism. This has not been done in the case of this hypothesis, so it remains unproven.”
It is even possible that SARS-CoV-2 was optimized using a living organism model, resulting in a virus that is better at infecting humans than any computer model could predict.
More than one way to engineer a virus
The authors of the Nature Medicine article seem to assume that the only way to genetically engineer a virus is to take an already known virus and then engineer it to have the new properties you want. On this premise, they looked for evidence of an already known virus that could have been used in the engineering of SARS-CoV-2.
And they failed to find that evidence. They stated, “Genetic data irrefutably show that SARS-CoV-2 is not derived from any previously used virus backbone.”
But Dr Antoniou told us that while the authors did indeed show that SARS-CoV-2 was unlikely to have been built by deliberate genetic engineering from a previously used virus backbone, that’s not the only way of constructing a virus. There is another method by which an enhanced-infectivity virus can be engineered in the lab.
A well-known alternative
A well-known alternative process that could have been used has the cumbersome name of “directed iterative evolutionary selection process”. In this case, it would involve using genetic engineering to generate a large number of randomly mutated versions of the SARS-CoV spike protein receptor binding domain (RBD), which would then be selected for strong binding to the ACE2 receptor and consequently high infectivity of human cells.
This selection can be done either with purified proteins or, better still, with a mixture of whole coronavirus (CoV) preparations and human cells in tissue culture. Alternatively, the SARS-CoV spike protein variants can be genetically engineered within what is known as a “phage display library”. A phage is a virus that infects bacteria and can be genetically engineered to express on its exterior coat the CoV spike protein with a large number of variants of the RBD. This preparation of phage, displaying on its surface a “library” of CoV spike protein variants, is then added to human cells under laboratory culture conditions in order to select for those that bind to the ACE2 receptor.
This process is repeated under more and more stringent binding conditions until CoV spike protein variants with a high binding affinity are isolated.
Once any of the above selection procedures for high affinity interaction of SARS-CoV spike protein with ACE2 has been completed, then whole infectious CoV with these properties can be manufactured.
Such a directed iterative evolutionary selection process is a frequently used method in laboratory research. So there is little or no possibility that the Nature Medicine article authors haven't heard of it – not least, as it is considered so scientifically important that its inventors were awarded the Nobel Prize in Chemistry in 2018.
Yet the possibility that this is the way that SARS-CoV-2 arose is not addressed by the Nature Medicine article authors and so its use has not been disproven.
No proof SARS-CoV-2 was not genetically engineered
In sum, the Nature Medicine article authors offer no evidence that the SARS-CoV-2 virus could not have been genetically engineered. That's not to say that it was, of course. We can’t know one way or the other on the basis of currently available information.
Dr Antoniou wrote a short letter to Nature Medicine to point out these omissions in the authors’ case. Nature Medicine has no method of submitting a simple letter to the editor, so Dr Antoniou had to submit it as a Matters Arising commentary, which the journal defines as presenting "challenges or clarifications" to an original published work.
Dr Antoniou's comments were titled, "SARS-CoV-2 could have been created through laboratory manipulation". However, Nature Medicine refused to publish them on the grounds that “we do not feel that they advance or clarify understanding” of the original article. The journal offered no scientific argument to rebut his points.
In our view, those points do offer clarification to the original article, and what’s more, there is a strong public interest case for making them public. That’s why we reproduce Dr Antoniou’s letter below this article, with his permission.
Not genetic engineering – but human intervention
There is, incidentally, another possible way that SARS-CoV-2 could have been developed in a laboratory, but in this case without using genetic engineering. This was pointed out by Nikolai Petrovsky, a researcher at the College of Medicine and Public Health at Flinders University in South Australia. Petrovsky says that coronaviruses can be cultured in lab dishes with cells that have the human ACE2 receptor. Over time, the virus will gain adaptations that let it efficiently bind to those receptors. Along the way, that virus would pick up random genetic mutations that pop up but don't do anything noticeable.
“The result of these experiments is a virus that is highly virulent in humans but is sufficiently different that it no longer resembles the original bat virus,” Petrovsky said. “Because the mutations are acquired randomly by selection, there is no signature of a human gene jockey, but this is clearly a virus still created by human intervention.”
Dr Antoniou agrees that this method is possible – but he points out that waiting for nature to produce the desired mutations is a lot slower than using genetic engineering to generate a large number of random mutations that you can then select for the desired outcome by a directed iterative evolutionary procedure.
Because genetic engineering greatly speeds up the process, it is by far the most efficient way to generate novel pathogenic viruses in the lab.
So why do some experts – and non-experts for that matter – seem so determined to put a stop to any speculation about whether SARS-CoV-2 could have been genetically engineered?
One explanation might be fear of a backlash against such research from the victims of the pandemic. Virologists, for example, who may want as much freedom as possible to study and manipulate viruses in their labs, won’t want their research restricted because of public concern. Others using genetic engineering in their work may also fear it will damage the general reputation of the technology and encourage tighter regulation.
And if concerns that SARS-CoV-2 may have been developed in a lab were to gain traction, the consequences in such a heavily commercialised area as biotechnology might not just be reputational but also financial.
In this context it is worth noting that one of the authors of the Nature Medicine piece is Robert F. Garry, who lists his “competing interest” as being “co-founder of Zalgen Labs, a biotechnology company that develops countermeasures to emerging viruses”. Heavier restrictions on genetic engineering or laboratory virus research might be considered counter to the interests of Zalgen Labs.
It is clear that there is no conclusive evidence either way at this point as to whether SARS-CoV-2 arose by natural mutation and selection in animal and/or human hosts or was genetically engineered in a laboratory. And in this light, the question of where this virus came from should continue to be explored with an open mind.
SARS-CoV-2 could have been created through laboratory manipulation
Dr Michael Antoniou
Kristian Andersen and colleagues (“The proximal origin of SARS-CoV-2”, Nature Medicine, 26: 450–452, 2020) argue that their amino acid sequence comparisons and computational modelling definitively proves that SARS-CoV-2 has arisen through natural mutation and selection in animal or human hosts, and not through laboratory manipulation and accidental release. However, although the authors may indeed be correct in how they perceive SARS-CoV-2 to have arisen, the data they present does not exclude the possibility that this new coronavirus variant could have been created through an in vitro, directed iterative evolutionary selection process (see https://en.wikipedia.org/wiki/Directed_evolution). Using this method, a very large library of randomly mutagenized coronavirus spike proteins could be selected for strong binding to the ACE2 receptor and consequently high infectivity of human cells. The power of such directed evolution to select for optimal enzymatic and protein-protein interactions was acknowledged by the award of the Nobel Prize in Chemistry in 2018 (see https://www.nobelprize.org/prizes/chemistry/2018/summary/).