How cancer hijacks your immune system's 'off' switches

Science · Published 20 October 2026 Swipe more like this →

In short: Cancer cells are masters of disguise. They don't just hide from your immune system; they actively sabotage it by hijacking the body's natural regulatory proteins. By understanding these molecular brakes, scientists have unlocked a way to strip cancer of its invisibility cloak.

The human immune system relies on a sophisticated balance of activation and regulation. To prevent the body from attacking its own healthy tissue, it uses 'immune checkpoints'—proteins that act as brakes to prevent overblown immune activity. However, cancer cells have evolved to exploit these very mechanisms. They can block immune activity, interfere with antigen recognition, or exhaust T cells, causing them to lose their ability to destroy the tumor. Tumor-specific antigens are often altered versions of normal self-antigens that the body perceives as foreign. These substances appear only on the surface of malignant cells. This deception allows the disease to evade detection by the body's natural defenses.

Japanese immunologist Tasuku Honjo was instrumental in identifying the mechanisms behind these interactions. His work led to the discovery of programmed cell death protein 1 (PD-1). By identifying these specific proteins, researchers developed 'immune checkpoint inhibitors.' These drugs work by blocking the checkpoint proteins, effectively cutting the brakes and enabling immune cells to mount a more powerful response against cancer cells than they would naturally be able to achieve. Honjo also identified the cytokines IL-4 and IL-5 during his career. Additionally, he discovered activation-induced cytidine deaminase, a protein vital for somatic hypermutation. These findings helped establish the conceptual framework for how antibodies undergo rearrangement.

The impact of this research is profound. Various malignancies, such as renal cell carcinoma, non-small cell lung cancer, and melanoma, can be successfully managed using these inhibitors. Honjo's contributions to understanding these proteins were recognized with a share of the 2018 Nobel Prize in Physiology or Medicine. His work represents a shift toward immunotherapy, which leverages the body's own cells and chemicals to fight disease, contrasting with traditional treatments like chemotherapy. Beyond these inhibitors, other immunotherapies include CAR T-cell therapy and monoclonal antibodies. These treatments can address conditions like lupus erythematosus and rheumatoid arthritis. Such diverse strategies highlight the broad utility of Honjo's foundational research.

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