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She is a biologist, and he is a physician and biophysicist. Together they are investigating cell vesicles, and especially the role of these in cancer. This has been a booming business for twenty years, and Utrecht is one of the world leaders in this field. An interview with Marca Wauben, immunologist and Professor of Cell Biology at Utrecht ľ�ϸ���Ӱ�� and , Professor of Medical Cell Biophysics at the ľ�ϸ���Ӱ�� of Twente. ‘To be honest, we don’t really understand how cells communicate with each other. Until we know that, we will not understand how biological systems work.’

Marca Wauben and Leon Terstappen have been working together for more than five years on research into cell vesicles in cancer. They both come from the province of Limburg in the south of the Netherlands, know each other well, and they share their passion for extracellular vesicles. What do these biologically important vesicles do in the communication between cells? Which kinds of vesicles are there, and what is their function? Wauben mainly looks at their role in controlling the immune system, whereas Terstappen focuses on vesicles excreted by cancer cells. The more of those you find in a cancer patient’s blood, the worse the prognosis, the biophysicist discovered years ago. But more about that later.

What exactly are cell vesicles?

‘Extracellular vesicles are “tiny sacs” that are excreted by cells’, explains Wauben. ‘Extracellular means outside the cell. Therefore cell vesicles not only regulate transport mechanisms in the cell, but they also transfer messages between cells. They ensure that biochemical processes work well. That transport system in the cell has already been described in biology and was also awarded a Nobel Prize.’

I am the apostle for the extracellular vesicles.

Are they like tiny balloons that transfer messages from A to B?

‘Yes, they are effectively tiny spheres surrounded by a layer of fat. These spheres contain proteins, genetic material and sugars; all of the building blocks a cell needs for biochemical processes. Via vesicles, these building blocks are transported from A to B inside the cell, but also outside of it.’
In her lectures, Wauben often compares the function of the vesicles to the car industry. ‘If you want to produce a car, then the parts are often made in separate factories specialised in one of those parts. Such a semi-finished product then goes to the next factory and, eventually, everything comes together. Cell vesicles play a role in transporting semi-finished products in one factory in the cell – an organelle – to another factory. They pack the products well to protect these, attach an address code and sender’s address and send the vesicle to the next factory. It’s a highly efficient transport system to get stuff to the right place in good condition.’

You talk about transport mechanisms in the cell, but extracellular means outside the cell?

‘That’s correct, these vesicles are mainly known for transport in the cell, but since the 1960s we have also learned that vesicles can be excreted by cells into the surrounding environment. They then become extracellular. For a long time it was thought that this only happened in culture dishes or that vesicles were merely tiny waste containers from the cell. It took a very long time before the biological activity of the vesicles came to light. That is what makes this research new.’

‘There are indeed many vesicles that neatly tidy up waste, just like in dustbin bags’, adds Terstappen. ‘The problem is that at present we cannot see which is which. Which vesicles are there exactly and what is their function? That is what we want to investigate now.’ There are also cells that tidy up the dustbin bags. ‘If you put dustbin bags outside and these are not collected, then you do not have a sustainable system’, says Wauben. ‘And in biology, systems are always set up in such a way that they seek to achieve a balance. We call that homeostasis; keeping an organism’s internal environment in balance.’

If you can keep the system in balance, then you can turn cancer into a chronic disease

So there are basically two categories: transporters and dustbin bags?

‘No, far more’, they both answer at once. ‘And it is anybody’s guess how many. You can see that now with COVID-19 as well’, says Terstappen. ‘People are dying because the immune system gets knocked off balance and can no longer regulate itself. These vesicles probably play an important role in that too. So there are cell vesicles that disrupt the balance of the system, but also vesicles that restore the balance of the system again.’

In fact, you could say that they have a vital role for the cell and organism?

‘Yes, for both people and animals’, says Wauben. ‘But plants and bacteria excrete these vesicles too. All living organisms make use of communication via extracellular vesicles. I see it as a new dimension in cell biology. That insight is missing in many textbooks, but it is a new field that yields knowledge about how biological systems communicate with each other. And it is now booming business worldwide.’

Terstappen: ‘Hormones are relatively simple and do not need to be packaged in vesicles to ensure they survive. But RNA, such as micro-RNA, is immediately destroyed in the blood. Similarly, some medicines also need to be given a thick coating to prevent them from being destroyed in the stomach. Not all particles can be transported without taking protective measures. The problem is that we do not know which messages are contained in which vesicles. And there is such a large diversity that we do not know which vesicles do what.’

How did you discover that some vesicles transfer messages from cancer cells?

‘I come from the field of cancer research and was busy working on detecting tumour cells in blood’, says the oncologist. ‘I observed a lot of small vesicles, and when I examined these more carefully, I discovered that these vesicles exhibited a very strong correlation with the outcome for the patient. If the blood contained a lot of these vesicles, then the person usually died very quickly; the more vesicles, the more aggressive the tumour. Therefore the number of vesicles is an indicator for the severity of the disease.’

‘Blood normally only contains blood cells, no epithelial or cancer cells’, continues Terstappen. ‘However, our markers exhibited cells that had to have come from a cancer cell because I could see that from their membrane proteins. However, they were too small to measure. At that time, we started a Perspectief research programme from Technology Foundation STW (now NWO Applied and Engineering Sciences) to develop techniques that would allow us to study the vesicles better and to understand what these look like. Now we want to examine exactly how they are formed, to which cells they are transported and which function they have in cancer.’

Differently coloured marbles

‘You need to see it as follows’, adds Wauben. ‘In the blood, you have a bag with differently coloured marbles. These marbles are the different types of vesicles, and these all come from different cells. On the vesicles are markers that you could use to determine which cell each vesicle comes from: a sort of sticker of origin. Leon has identified several characteristic molecules on tumours that are also found in some vesicles in the blood. Of the millions of vesicles in the blood, a few therefore originate from the tumour. If the technique can be made accurate enough, then we can examine these individually.’

People travel here from around the world to sort and distinguish vesicles using this facility

Which technique do you need for this?

‘At the faculty of veterinary medicine, we have a very good system for measuring individual vesicles: high-resolution flow cytometry’, says Wauben. ‘People travel here from around the world to sort and distinguish vesicles using this facility. I can honestly state that we are one of the few labs in the world that has this expertise. But we are always working on improving our system. We are also increasingly aware that there are still even smaller vesicles that we cannot yet identify properly. Therefore, we need to continuously hone the existing techniques and develop new techniques to properly describe the allocation and composition of these particles. They contain very complex messages; nature is so ingenious that it does not communicate with a single molecule. So there are an infinite number of variables. That makes the field extremely complex.’

What is your dream?

Terstappen: ‘I hope to be able to prevent cancer, at least its spread. That’s what I want to work on. If you can prevent metastasis, then people will no longer die from cancer. People with AIDS are also not cured, but they do still live. That is what matters the most. Then cancer would become a chronic illness.’

Wauben: ‘My big dream is that I understand how extracellular vesicles control the biological system. As a biologist, I want to understand how homeostasis works in a system. If you can keep the system in balance, then you can turn cancer into a chronic disease. But you can also deal with infection pressure such as during a COVID-19 pandemic, or problems in your environment due to pollution. In all these cases, you need to know how the system keeps itself in balance. My motivation is to gain insight into that. I am the apostle for the extracellular vesicles.’

This is an article from Vetscience no. 9