The immune system is a complex network of cells and proteins that defends the body against infection. The immune system keeps a record of every germ (microbe) it has ever defeated so it can recognise and destroy the microbe quickly if it enters the body again.Immunotherapy is a type of cancer treatment that helps your immune system fight cancer. The immune system helps your body fight infections and other diseases. It is made up of white blood cells and organs and tissues of the lymph system. Immunotherapy is a type of biological therapy.,Immunotherapy or biological therapy is the treatment of disease by activating or suppressing the immune system. Immunotherapies designed to elicit or amplify an immune response are classified as activation immunotherapies, while immunotherapies that reduce or suppress are classified as suppression immunotherapies,In a study led by UCLA investigators, treatment with the immunotherapy drug pembrolizumab helped more than 15 percent of people with advanced non-small cell lung cancer live for at least five years—and 25 percent of patients whose tumor cells had a specific protein lived at least that long,Other therapies you have, like chemotherapy, may work better if you also have immunotherapy. It causes fewer side effects than other treatments. This is because it targets just your immune system and not all the cells in your body. Your cancer may be less likely to return.