by Louise Muller
If you’ve ever had a cold sore or the flu, I can almost guarantee that you don’t have much time of day for viruses. But what if I told you that viruses are not just annoying little bugs that make you ill? How about if we took that one step further and said that they could actually cure cancer?! The very same virus that causes those irritating cold sores (herpes virus) has recently been approved as a treatment for skin cancer.
So how is this possible? With a little background knowledge about viruses, all will become clear. In their simplest form, viruses are genetic material (such as DNA) protected by a protein coat. Because they are non-living organisms, they need to infect dividing cells to be able to multiply and survive. When a virus infects a cell, it can hijack the machinery that the cell uses to divide. Using this machinery, the virus can create many copies of its own genetic material, and create a little virus army inside the cell. Eventually, there are so many viruses inside the cell that the cell bursts. This releases the virus army, which can then infect any surrounding cells, making the infection spread really fast. However, most healthy cells have developed immunity against virus infection, which stops the virus hijacking the cell machinery.
When cells transform into cancer cells, they often lose their anti-virus defense. This leaves the cancer cell unprotected, providing the virus with an easy target – and this is the weakness that is being exploited by scientists for ‘oncolytic virotherapy’. When encountering a cancer cell, the virus has free range to infect it, then it multiplies, and eventually makes the cancer cell explode. While it’s great that the infected cancer cell dies, there’s also the added bonus that the released viruses spread to neighbouring cancer cells (e.g. in a tumour) and kill them too. In this way, researchers have created a treatment that only affects cancer cells, not the healthy cells in your body, and is also self-amplifying! The more cancer cells killed by the virus, the more viruses are made, leading to more cancer cell death… a beautifully virtuous cycle.
In addition to this, there’s a second strategy that can be deployed to combat cancer cells with viruses. Because viruses are naturally detected by the immune system, a number of different immune cells can be activated and recruited by the virus to help in the fight against the cancer. The immune system is always working to protect us from cancers arising in the first place, but sometimes particularly aggressive cancer cells escape this protection and start forming a tumour. These tumours have often developed mechanisms to resist attacks from the immune cells, as well as suppressing their activity. By introducing a virus, the immune cells can be woken up from their suppressed state and be persuaded to start attacking the cancer cells again.
One of the particularly useful immune cells in this scenario are the natural killer cells. They have specific methods for recognizing cells that have undergone transformation to cancer cells. Once they recognize and decide to kill a target cell, they release toxic granules which perforate and destroy the cancer cell. Viruses can also act as a kind of cancer vaccine. When the cancer cells burst as a result of virus multiplication, little remnants of them can be picked up by immune cells which results in the formation of an immunological “memory”. In the same way that a vaccine protects the body against infection with for examples measles, this immunological memory can stop the cancer from returning again, as the white blood cells are more alert to this kind of threat.
While a lot of research is needed to adapt virus treatment to more types of cancer, this field has grown immensely in the last few years. Many different types of viruses are now being tested in humans as part of clinical studies to confirm their safety and efficacy, both alone and in combination with other treatments. So, next time you find yourself with a cold sore, just think that you are host to a potential cancer cure… pretty cool, right?
Find more articles from Louise on her website, Synovia Science Studios.