There Is Something to Be Gained From Gain of Function Experiments

by Gertrud U. Rey

In recent years, the phrase “gain of function” and its abbreviation “GoF” have attained a sinister connotation that is coupled with a general mistrust toward scientists who engage in this type of experimentation. This public perception is grounded in a basic misunderstanding of what constitutes GoF and a lack of appreciation for how such work can further scientific advances. In this post, I wish to clarify what motivates scientists to do GoF experiments and why such research is important.

The expression originated in the field of genetics but is frequently used in virology, where it describes experimental outcomes involving viruses that have acquired one or more new functions with respect to transmissibility, pathogenicity, immunogenicity, and/or host range. There are several ways to investigate gene function. One is to introduce mutations into the viral genome or directly insert new or foreign genes to see which genes control a particular functional property. Another way is by infecting animals or cells with a virus and using the viruses isolated from those animals/cells to infect new animals or cells. After ten or more such “passages” in the experimental animals/cells, the final progeny viruses are analyzed for changes in activity. This passaging may lead to the selection of viruses that have new properties, or, a gain of function. Although presumed GoF experiments regarding transmission and pathogenesis are typically based on hypotheses that are meant to predict specific functional outcomes, it is difficult to accurately foretell such results because it is currently unclear which factors control viral transmission and pathogenesis. In other words, one cannot be sure whether a certain experiment will result in a gain of function, loss of function, or neither. Results may also vary greatly depending on the type of animal or cell that is used in an experiment, meaning that a virus may gain a new function in one animal or cell type, but not in another.

What motivates scientists to do such experiments? The truth is that most experiments in the life sciences involve some form of GoF approaches. For example, the virus passaging technique typically produces a weakened version of a virus, so it is often used to generate attenuated virus vaccines. Although most people would view this attenuation in virulence as a loss of function, it is also a gain of function because attenuated viruses have a new use – they prevent disease by eliciting a more focused immune response.

GoF experiments can also lead to new and/or optimized antiviral drugs. For instance, efforts aimed at addressing resistance of hepatitis C virus (HCV) to certain antivirals involved repeatedly culturing HCV in the presence of those drugs to screen for viruses that were resistant to the drugs. Once these resistant viruses were identified, scientists were able to optimize the drugs until they were also effective against the resistant HCVs.

Furthermore, some viruses that naturally infect cancer cells can be manipulated using GoF procedures to enrich their oncolytic properties and produce more efficient tumor-killing viruses. This approach has led to improved oncolytic viruses that effectively target and shrink tumors and are slowly becoming a powerful new tool in the field of oncology.

Yet another motivation for engaging in GoF research is the desire to understand the mechanisms that increase the transmissibility and infectibility of viruses. The current COVID-19 pandemic is the result of a “spillover” of an animal virus into humans, an event that happens when the virus has acquired the mutations needed to infect humans and allow for sustained human-to-human transmission. One of the most effective ways to explore the molecular mechanisms that drive such evolution in viruses is to introduce mutations into genomic sites that are thought to be important for transmission and infection and then analyze the effects of these mutations on viral function. Whether or not such experiments result in one or more gains of function for the virus, they often provide critical new insights into which viral factors might be implicated in spillover, thus further enhancing our understanding of how spillover events happen and enabling us to predict and prevent future pandemics.

In deciding whether a potential GoF experiment is justified, one must weigh the possible benefits of that experiment against any potential dangers. Judging from the countless advances in science, medicine, standard of living, and life expectancy that have resulted from GoF experiments, most of the time the benefits far outweigh the dangers. GoF research has led to new vaccines, improved cancer therapies, bacteriophages for treatment of antibiotic-resistant bacterial infections, synthetic insulin and other hormones, drought- and salt-resistant plants, freeze-resistant plants and animals, dengue virus-resistant mosquitoes, improved insect control, plants with reduced need for fertilizers, enhanced lithium batteries, and faster computers. In contrast, the potential dangers associated with GoF procedures are actually very low because this type of work is always carried out under high containment and by rigorously trained professionals. Virological research in general is subject to many layers of federal and institutional regulations, and the policies surrounding the funding, authorization, and monitoring of GoF-type work are particularly exhaustive and redundant.

When one takes all the above factors into consideration, there is a clear scientific rationale for allowing scientists to follow their curiosities and do the experiments they need to do, even if they appear to be unjustified or risky.

[For an extensive list of GoF experiments that have proven useful, check out Table 2 of this recent Commentary in the Journal of Virology.]