A perfect iFITm to fight viruses

There are an estimated 7 billion humans worldwide. That's 7,000,000,000, a huge number. However, 7 billion pales in comparison to the estimated 10 to the power 31 viruses living alongside us - that's 10,000,000,000,000,000,000,000,000,000,000. Put another way, for every predicted star in the universe there are 10 million viruses on Earth. Closer to home, within each of us there are approximately 4 trillion viruses; yet for the majority of our lives we will be healthy and free of viral disease. There are many reasons for this, not least because most viruses have no interest in humans. But another major factor is a set of cells and molecules to which we are deeply indebted: these are the components that make up our immune system.

The immune system can be broadly divided into two interlinked halves. There are the front line, rapid responders comprising the innate immune system; cells and molecules that are evolutionarily "designed" to react rapidly and broadly, controlling invasion from any foreign organism. The second half is the adaptive immune system. This has the big guns, taking longer to mobilize but with the power to fully clear invading organisms following the initial suppression from the innate system. Together these two halves co-ordinate a response that effectively removes almost all infectious agents we encounter. Every once in a while we will get briefly sick as the system kicks into full force, but largely, we will never notice the silent protection it provides. The halves are inseparable. However, without the rapid response of our innate system many viruses and other pathogens would be able to gain a foothold and potentially overwhelm us. Furthermore, the adaptive immune system cannot be triggered unless the innate system warns it of an invasion, making the innate immune system paramount for our survival.

Possibly the most important players in the innate response to viral infection are a group of proteins known as interferons (IFNs). Following an infection, IFNs trigger the expression of 200-300 genes, producing effector proteins that function as part of the innate immune response to block viral infection. It is known that these IFN stimulated genes protect us, however, very little is known about the function of individual proteins produced from these genes. In 2009 a major new component in the IFN response was discovered that is now known as InterFeron-Induced TransMembrane protein 3 (IFITM3). This protein was found through its ability to protect cells from influenza virus infection. Influenza virus, or flu, annually causes 3-5 million cases of clinical disease worldwide, and has the major potential for pandemic spread. It was subsequently found that IFITM3 is present in the cells of our lungs (the site of influenza infection) and that these cells can be stimulated to express even more of this protective protein following infection.

 

Influenza virus particles

Most importantly for the story of IFITM3, it was found not only to protect cells in a laboratory, but also to protect us on a regular basis. Usually flu is a minor illness, you simply get over it after a couple of weeks. However, certain people can be hospitalized, or worse. In a study of patients hospitalized by influenza, it has been found that a mutation in IFITM3 was over-represented. To put it another way, it seems that people who carry a mutation in IFITM3 are at an increased risk of severe flu infection.

What makes IFITM3, and its close relatives IFITM1 and IFITM2, even more exciting is that they don't just protect against influenza. At the time of writing, the list of viruses the IFITMs protect against is in double figures and includes some of the most notorious known to infect humans. Dengue virus, a mosquito borne virus that threatens around 3 billion people, is sensitive to IFITMs. Similarly, Ebola virus that can kill up to 90% of the people it infects is restricted by the IFITMs. HIV may even be kept in check by the IFITM proteins. This is to name but three. Obviously these viruses still cause infections and still kill on a daily basis. However, without protection provided by the IFITMs it is possible these viruses could be even greater killers.

Currently, we still do not completely understand how the IFITM proteins work. If this is fully elucidated we may be able to produce drugs that mimic their protective properties. Better yet, we may be able to regulate expression of the IFITMs or improve on their function and provide even greater levels of protection. Imagine if we could make a single drug that protected against infection by the four viruses already mentioned and a whole host of others! This may be slightly blue-sky thinking, but as someone at the start of a PhD in the field, that sky looks pretty bright and appealing to me. 


(NB. This article was entered into the Max Perutz Science Writing Competition run by the MRC by myself and is my own work in both cases)

Adding some culture (and history) to the blog

As someone starting a career in a biological field of science I find it hard to imagine a world in which it wasn't possible to do experiments using human cells, it's pretty much all I do. However, until the 1950s the use of human cells in a lab was only done in a few places that had the expertise. Following the establishment of techniques to grow cells in a lab, and the discovery of immortal cell lines that grow forever, biological science exploded! Almost all of the major breakthroughs of the last 60 years will have at some point used cells in a lab. So I though I'd make a post talking about the history of cell culture (as it is known).

A cell culture hood used to grow cells in sterile environment

To start with an important question - why do we want to work on cells? A cell is the building block of life; humans are made of close to 10 trillion of them, each containing the genetic code that turns to us into who and what we are. Since cells underpin all of life they are of the upmost interest to sciences studying any biological question. However, studying cells within a living being is pretty difficult. Human experimentation is largely frowned upon, so we look to animals and more simple organisms to guide or understanding. Even then you're looking at a whole system made up of hundreds of different cell types all interacting and maintaining life. The ability to look at a single type of cell provides much more useful information - if you were trying find when a specific person was born, you wouldn't want to have to deal with a whole city of people. 

This desire to look at single cells outside of a living being was the spark that set scientists on the road to develop cell culture. It all began in 1885 when Wilhelm Roux managed to keep cells from an embryonic chicken alive in a laboratory. They didn't last long, but it was a start. Not for want of trying, but it wasn't until 1907 that the next major breakthrough was made by Ross Harrison who managed to actually grow cells in his lab, rather than just keep them alive. Similarly to Roux, Harrison did not use human cells, instead opting for nerve cells from a frog, and his cells didn't last long.

Another big gap ensued. It wasn't until a period through the 1930s-1950s that cell culture, and particularly that of human cells, really took off and set the foundations for almost all biological science to this day. To a large extent this work was dictated by the hunt for a polio vaccine. To produce a vaccine it is necessary to produce virus particles, which can then be injected into a recipient to produce a protective immune response. There was however a hurdle for this at the time. Viruses need cells in which to grow, and a vaccine needs lots of virus particles. In the early 1930s, the best way to grow virus was to infect an animal and collect samples. This was indeed done under the guise of vaccine development by infecting monkeys and collecting extracts from the nervous system. However, the collected viral particles were contaminated with monkey nervous system extract, which was found to cause paralysis when injected into humans, the very syndrome a polio vaccine should prevent. This approach was rapidly binned as you can imagine.

Following the failure of this monkey grown virus, attention shifted to growing virus in the safer and more controlled environment of a laboratory, using human cells. This has many advantages of which safety is a huge one. But additionally, there is a huge economic benefit - it is much cheaper to look after cells in a lab than a whole collection of animals. This desire led to work in 1936 by Albert Sabin and Peter Olitsky, at the Rockefeller Institute in America, who grew poliovirus in cultures of human brain tissue. While this was an achievement, they were concerned that using brain tissue might have similar issues to those seen with monkeys. As such, they attempted to recapitulate their results in other cell extracts - but to no avail.

Cartoon of poliovirus

It wasn't for another 13 years that the aim of growing poliovirus using human cells in a lab was realized. This advancement was a complete accident by John Enders, Thomas Weller and Franklin Robbins. At the time, these eventual Nobel Laureates were attempting to grow varicella virus (chicken pox). They had managed to grow human skin and muscle cells in a lab and infected these cells with varicella. As a control virus, used because they thought it wouldn't grow, so acted as a point of comparison, they used poliovirus. In a huge stroke of luck, or mis-fortune depending how you see it, their original experiment failed. Varicella failed to grow, however, poliovirus did! Following this, these men moved on to grow the virus in multiple different extracts of human cells and eventually managed to get a high level of production of the virus (earning them their Nobel Prize). This work paved the way for Jonas Salk to produce the first polio vaccine.

The science of growing human cells in a lab had advanced a long way by the start of the 1950s. From a point of relying entirely on live animals, it was now possible to grow cells extracted from humans and use these to produce the viruses needed for vaccines. However, these cells still had issues. The way these cells were produced was largely from biopsies of human tissues. In a biopsy, a small chunk of tissue is taken from the body, such as the skin. These chunks of human material were then broken up into individual cells and grown in a lab. The issue comes from the fact that biopsies take all the cells that reside in a certain area, giving a very mixed population of cells. This limits the reproducibility of experiments since different tissue samples will be made up of highly variable cell types. Reproducibility is a bedrock of the scientific enterprise so this was hardly ideal. Additionally, the cells only lasted for a short amount of time when grown in a lab, meaning there was a need for lots of biopsies.

HeLa cells

In 1951 (and over the following years) these issues with human cell culture were overcome when the first ever immortal cell line was produce - biological science hasn't looked back since. 1951 saw the birth of the HeLa cell line which is still the most commonly used cell line in the world with an estimated 60,000 scientific articles published using these cells as of 2009. HeLa is taken from the name Henrietta Lacks from whom these cells were extracted. Lacks died in 1951 from an aggressive adenocarcinoma of the cervix, from which the cells were taken in the form of a biopsy. Lacks’ physician gave the extracted cancerous cells to George Otto Gey, who set up the cells as any other biopsied tissue to grow in a lab. To his surprise the cells survived with ease, and continued to grow indefinitely - they are still growing. These cells were taken like any other biopsy (as discussed above), but what made them truly special was that they came from cancer instead of healthy tissue. Cancers are a clonal diseases, meaning that all cancerous cells are (essentially) exactly the same. This clonality gave the all-important reproducibility so craved by scientists since everyone could work on cells that were exactly the same. What’s more, these cancer cells had a mutation that made them immortal (given the right treatment), meaning they can grow indefinitely outside of a body.

Sadly, HeLa cells are shrouded in controversy. Lacks' physician did not ask for her, or her family's permission to donate the cells to Gey. By the time they were made aware, the cells had been patented and commercialized and had taken over science. Companies had made millions of dollars selling the cells and the Lacks family didn't see a dime. In America this is still allowed, there is no need for a physician to obtain permission to use cells extracted from a patient. However, in the UK there is a need for ethical approval and patient consent.

While there are certainly some injustices surrounding the development of HeLa cells, the contribution of Henrietta Lacks to science is unparalleled. To his credit, Gey freely gave away the cells to anyone who wanted them for the "advancement of science". Tying things together – shortly after their development the cells found their way to Jonas Salk who used them to test the safety of his polio vaccine.

The cells have since been used for the testing and production of many other vaccines; they have also been used for the production of drugs to treat cancer and HIV (and many other viruses). They have gone to space and have been subject to Chernobyl-esque levels of radiation. Since we can't test most things on a human straight away, having humans cells growing in a lab that you can throw everything but the kitchen sink at (there’s an issue with proportions there) gives a fantastic way to test out how safe (or dangerous) something is to humans.

Plates in which cells can be grown

The ability to grow and study cells in a lab has contributed an incredible amount to science. Being able to grow cells extracted from humans lead to early discoveries in virology that paved the way for numerous vaccines. With the discovery of immortalized cells, such as HeLa, the whole thing became even easier and more uniform, giving the reproducibility scientists crave. The story of HeLa is one of controversy as well as being a world-changing discovery. I've attempted to give a taste of the HeLa history here, but for anyone wanting more, I highly recommend "The Immortal Life of Henrietta Lacks" by Rebecca Skloot. This is not to advertise the book (and there is no conflicting interest - in the desire for full disclosure), but reading that gave me the impetus to write this blog and I feel credit should be given where it is due. 

With all this written, it's time I go back and look after my cells.