Cancer immunotherapies use the body’s own immune system to fight off cancer. Despite some remarkable success stories, many patients only see a temporary improvement before the immunotherapy stops being effective and the tumors regrow. It is unclear why this occurs, but it may have to do with how the immune system attacks cancer cells.
Immunotherapies aim to activate a special group of cells known as killer T-cells, which are responsible for the immune response to tumors. These cells can identify cancer cells and inject toxic granules through their membranes, killing them. However, killer T-cells are not always effective because cancer cells are naturally good at avoiding detection, and during treatment, their genes can mutate, giving them new ways to evade the immune system.
It has been shown in mouse models that tumors stop responding to immunotherapy after initial treatment. Examining cells from these tumors revealed that when the immune system attacks, cancer cells reorganize by getting inside one another. This allows some cancer cells to hide under many layers of cell membrane. As a result, killer T-cells can identify and inject the outer cell with toxic granules, but cannot reach the cells inside.
This new explanation for how cancer cells escape the immune system could guide future research and lead to new cancer treatments or approaches to boost existing treatments. It is even more important that our cancer registries capture all important information when patients are treated with immunotherapy regimens. Data from our registries will drive important clinical research in this field.