Now, some researchers have focused on the immune response, inducing it at the site of the tumor. And they do so by a remarkably simple method: injecting the tumor with the flu vaccine. As a bonus, the mice it was tested on were successfully immunized, too.
Revving up the immune system
This is one of those ideas that seems nuts but had so many earlier results pointing toward it working that it was really just a matter of time before someone tried it. To understand it, you have to overcome the idea that the immune system is always diffuse, composed of cells that wander the blood stream. Instead, immune cells organize at the sites of infections (or tumors), where they communicate with each other to both organize an attack and limit that attack so that healthy tissue isn’t also targeted.
From this perspective, the immune system’s inability to eliminate tumor cells isn’t only the product of their similarities to healthy cells. It’s also the product of the signaling networks that help restrain the immune system to prevent it from attacking normal cells. A number of recently developed drugs help release this self-imposed limit, winning their developers Nobel Prizes in the process. These drugs convert a “cold” immune response, dominated by signaling that shuts things down, into a “hot” one that is able to attack a tumor.
To check whether something similar might be happening in humans, the researchers identified over 30,000 people being treated for lung cancer and found those who also received an influenza diagnosis. You might expect that the combination of the flu and cancer would be very difficult for those patients, but instead, they had lower mortality than the patients who didn’t get the flu.
the researchers obtained this year’s flu vaccine and injected it into the sites of tumors. Not only was tumor growth slowed, but the mice ended up immune to the flu virus.
Oddly, this wasn’t true for every flu vaccine. Some vaccines contain chemicals that enhance the immune system’s memory, promoting the formation of a long-term response to pathogens (called adjuvants). When a vaccine containing one of these chemicals was used, the immune system wasn’t stimulated to limit the tumors’ growth.
This suggests that it’s less a matter of stimulating the immune system and more an issue of triggering it to attack immediately. But this is one of the things that will need to be sorted out with further study.