In online forums and social media, people often make erroneous claims that the human body itself will fight and eradicate cancers on its own if it’s healthy enough to do so in the first place. While that opinion might be a bit short-sighted it’s not entirely wrong, the immune system can shrink tumors if you trigger it correctly.
The international scientific community has known for a while now that activating the immune system can help tackle cancer. A few years back, some researchers even found a way to use viruses to target cancer. Several viruses can explode the cancer cells once they infect them – all of course so that they can spread to new cells. The researchers engineered such viruses to grow only in cancer cells, leaving healthy cells alone.
Many promising preliminary tests showed massive tumors nearly vanishing. However, the results were unpredictable, and there was the complication that once the immune system knew about the virus, it would interfere by attacking it. Meaning, the technique could only be used once.
The researchers also noticed that some of the tumors were destroyed by the immune system, not the virus. This led them to the idea that activating an immune response at the site of cancer could re-engage the immune system to attack the tumor.
Now, a team of investigators from the Rush University Medical Center has found an effective way of doing just that! And by using an inactive flu virus; the flu vaccine. They tested the idea in mouse model experiments and found it worked quite well to shrink tumors.
They got the idea to do so by studying data from the National Cancer Institute. The analysis revealed that patients with lung cancer who were also hospitalized due to influenza-related lung infections tended to live longer than those who had not gotten the flu.
Injecting a tumor with a flu vaccine works because the immune system is not a collection of diffuse cells that wander the bloodstream. It’s more like a coordinated team of cells that “communicate” and organize at the site of infections – or in this case, tumors – where they systematically interact with each other to attack – but limit the attack so that healthy tissue is spared.
The reason why the immune system has a problem eliminating tumor cells on its own is that the cancer cells are similar to healthy cells, and the signaling networks that help the immune system by averting it from attacking healthy cells have been activated.
While there are several drugs in development that release this self-imposed limit, not everyone’s body responds to them. These drugs work by converting a “cold” immune response (dominated by signaling that shuts things down) into a “hot” one (one that can attack a tumor). Nevertheless, the method works, so researchers like the ones at Rush University kept investigating things that naturally rev up the immune system – infectious agents.
The Mouse Experiments
Testing Phase 1
- Melanoma cells that can form tumors were transplanted into the lungs of mice.
- Using melanoma cells served a dual informative purpose – since the influenza virus cannot infect melanoma cells, the researchers would know if the tumor had to be affected by the illness for the system to work.
The Results
- The active influenza virus infection reduced the ability of melanoma cells to establish themselves in the lungs.
- The tumor cells themselves do not have to be infected for the immune system to have an increased response to them.
- The vaccine did not have to be injected into the tumor to work. Other tumors that had not been infected in the lungs were also inhibited.
- The infection must take place in the organ that has cancer. If there is an infection elsewhere in the body, it directs the immune response there instead, and the tumor grows.
Testing Phase 2
- To find out if the immune response to a tumor requires an actual infection, the researchers did a follow-up experiment where they used a flu virus that had been inactivated.
The Results
- The inactive virus worked just as effectively as the live virus to shrink tumors.
Immediate Response Required
Not all types of flu vaccines worked. Some contain chemicals that facilitate a long-term response to pathogens – meaning they enhance the immune system’s memory to work for many years. In the case of killing tumors, this feature inhibits the process, and the chemicals made it so the immune system wasn’t stimulated to limit the tumors’ growth. This discovery suggests that the immune system has to be triggered to attack immediately for the method to work. Future studies will focus on this as well as the location of stimulation.
The study has been published in the journal PNAS.
