Immunotherapy

Immunotherapy is any treatment that works through the immune system. In oncology, the word usually means therapies that help the body's defenses recognize and destroy cancer cells. The immune system removes many abnormal cells on its own, but tumors escape by hiding their antigens, by displaying surface proteins that switch immune cells off and by making their surroundings hostile to attack.

Several kinds are in use. Immune checkpoint inhibitors are monoclonal antibodies that block brake molecules such as PD-1, PD-L1 or CTLA-4, freeing T cells to attack the tumor; they have transformed the outlook for cancers such as melanoma and some lung cancers. In CAR T-cell therapy, a patient's own T cells are genetically engineered to carry a receptor aimed at the cancer, multiplied in the laboratory and infused back, mainly for leukemias, lymphomas and myeloma. Other approaches include antibodies that tag cancer cells for destruction, therapeutic cancer vaccines, cytokines such as interleukin-2 and interferons, and BCG bacteria placed in the bladder. Responses can last for years, but only some patients benefit, and an unleashed immune system can attack healthy organs, causing side effects such as colitis or thyroid inflammation.

Outside cancer, the term also covers allergen immunotherapy, which gradually desensitizes people to substances they react to, and immunosuppressive treatment that prevents transplant rejection.