Cancer cells can neutralize part of our defenses simply by removing molecules from their environment that are needed to attack them.
To understand this mechanism, we need to look at T lymphocytes. These immune system cells recognize certain abnormal cells and can contribute to their destruction. Their activation relies on a succession of chemical signals. Among them are small oxygen-containing molecules, often associated with cellular damage.
Breast cancer cell observed under a scanning electron microscope.
Credit: National Cancer Institute / NIH, public domain.
These molecules are called "reactive oxygen species." At low levels, they contribute to the body's normal functioning. T lymphocytes use them in particular to correctly transmit the signal that triggers their activation.
Researchers from the University of Cambridge, Oregon Health & Science University, and other institutions have discovered how some tumors exploit this dependence. They analyzed the fluid present between the cells of a tumor. It showed strong antioxidant activity, involving an enzyme called peroxiredoxin 1, or PRDX1.
Specifically, PRDX1 neutralizes reactive oxygen species around T lymphocytes. Deprived of these molecules, immune cells transmit their activation signal less effectively. Their ability to attack the tumor then decreases. The cancer cell therefore does not need to destroy the lymphocyte directly: it alters its chemical environment.
The researchers then modified cancer cells so that they no longer produced PRDX1 normally. In several experimental mouse models, the immune response became stronger and tumor growth decreased. In a melanoma model, tumors lacking PRDX1 were even spontaneously eliminated by the immune system.
The study relies mainly on preclinical models and does not justify any change in treatment or diet at this stage.
The next step is to determine how to exploit this mechanism medically. Several approaches are being studied: blocking PRDX1 activity, neutralizing the antioxidants released by the tumor, or making immune cells less sensitive to this environment. Their effectiveness and safety will still need to be verified before considering treatment in humans.