Developing vaccines with NeCEN
Tuberculosis causes 2 million deaths every year and the current vaccines are inadequate. Nicole van der Wel works in a research team at the Netherlands Cancer Institute- Antoni van Leeuwenhoek Hospital (NKI-AVL). In order to develop a better vaccine, they study a crucial protein complex that the bacteria need to cause the disease. The scientists need the resolution and power of the NeCEN microscopes to understand exactly what this protein complex looks like and how it works.
The group of Nicole studies the interaction between the bacterium and the human macrophage cell. This cell can eat up bacteria and Nicole explains that after this happens “the macrophage usually breaks down bacteria.” However, the tuberculosis bacterium survives “because this bacterium is very resistant; it survives in very acidic environments, and is hardly affected by enzymes.”
Left: electron microscopy image of a human tuberculosis bacterium (M.tub) inside a human cell. Right: BCG vaccine bacteria (BCG) inside a human cell. The BCG vaccine bacteria are inside a body in the cell (light area around BCG) together with enzymes that can break them down (black dots). The human tuberculosis bacterium (M. tub) is free inside the cell. Different processing phases show the effect of improving resolution from 17Ǻ to 9.4 Ǻ for the protein studied by NKI-AVL. An even higher resolution is needed to fully understand the function of the protein. Nicole emphasizes the importance of making small structures visible. “In order to find the balance for the vaccine, you have to be able to understand it. And in order to understand it, you have to be able to see it.” She also mentions that it is “unique to combine the knowledge and expertise of a whole country in one centre. In this way you prevent that everyone reinvents the wheel. Now we can make progress.”
BCG is the best available vaccine right now and is made of weak bacteria that cause tuberculosis in cows. In human host cells, BCG bacteria remain enclosed inside a membrane and are not pathogenic. Human tuberculosis bacteria on the other hand can destroy these membranes and kill the human host cell. Scientists do not know how this mechanism works, but “it is clear that one protein complex makes the difference.” If you give this protein complex to the BCG bacteria, they can also break down the membrane. This can be dangerous as this means the modified BCG vaccine may become pathogenic. At the same time it results in better protection against human tuberculosis. Nicole tells “It is crucial to find a balance in this system, and that is why we have to understand exactly what is going on.”
The protein complex that makes the difference is a secretion system that transports virulence factors from inside bacteria to the outside. Scientists know that the system involves thirteen proteins, but that is all they know of the mechanism. The NKI-AVL research group currently studies a protein that is secreted by this system. The scientists have already taken many cryo-EM images with their in house microscope in Amsterdam, but the results did not give enough detail. Using a microscope in Groningen, they got the resolution down to 9.4 angström (Ǻ) but Nicole says this “simply isn’t good enough. With the NeCEN microscopes we can get the resolution needed to understand how it really works.” She hopes the microscopes will give a resolution of 4-5 Ǻ.
It is not just the resolution that will give a boost to this research project. “The microscope also gives much more power, so we can really see right through the bacteria.” Nicole explains that if you can look through whole bacteria and know what a protein looks like, you can try to find this protein inside the bacterium. This is called ‘template matching’ “and in this way we can find the location of the proteins.”
