You’ve probably seen news articles about breakthroughs in immunotherapy for cancer patients. But the word “immunotherapy” can be used to describe many different kinds of treatment. Some immunotherapy drugs help a specific part of the body’s immune system—often white blood cells such as T cells, B cells, or natural killer (NK) cells—to attack a specific type of cancer cell; other treatments promote a more general immune response.
Below we describe some common types of immunotherapy. Please note that these are general descriptions only, and the side effects of these treatments are not discussed. If you have questions about a particular drug, please talk to your doctor.
Antibodies, a natural part of the immune system, are proteins that bind to other proteins called antigens that are found on the surface of some cancer cells or pathogens (invading agents such as bacteria or viruses). Monoclonal antibodies are drugs created to work like natural antibodies.
Most monoclonal antibodies used in cancer treatment bind to specific antigens on cancer cells. This binding either neutralizes the cancer cells to prevent the cancer from spreading or signals the immune system to find and kill the cancer cells. For example, the monoclonal antibody rituximab binds to certain types of leukemia and lymphoma cells to help the body’s NK cells destroy them.
Immune checkpoint inhibitors
A special type of monoclonal antibody is the new class of drugs called immune checkpoint inhibitors. These drugs block the action of immune checkpoint proteins, which are found on the surface of many T cells. The purpose of immune checkpoints is to stop T cells from attacking healthy cells in the body. But some types of cancer can activate these immune checkpoints to protect themselves from T cells.
The U.S. Food and Drug Administration (FDA) has approved drugs that target the immune checkpoints CTLA-4 (cytotoxic T lymphocyte antigen 4) and PD-1 (programmed cell death protein 1). The CTLA-4 inhibitor ipilimumab is approved to treat melanoma, and the PD-1 inhibitors pembrolizumab and nivolumab both are approved to treat non–small cell lung cancer and other cancers. Other immune checkpoint inhibitors target PD-L1, the ligand (a protein molecule that binds to another protein) on some normal or cancer cells that binds to PD-1 on T cells. The PD-L1 inhibitor atezolizumab is approved to treat bladder cancer. And new immune checkpoint inhibitors are being studied in clinical trials to treat various cancers.
Therapies made from immune cells
Some promising cancer treatments are made from a patient’s own immune cells. Blood is drawn from the patient and sent to a laboratory, where certain immune cells are removed and in some cases genetically modified. The number of cells is then expanded in the laboratory, and the cells are infused back into the patient’s bloodstream.
The first such treatment to be approved by the FDA was sipuleucel-T for prostate cancer. Sipuleucel-T is made from the patient’s dendritic cells, which help T cells find cancer cells or pathogens. Clinical trials of other dendritic cell–derived cancer therapies are ongoing. Also under way are clinical trials of modified T cells for the treatment of various cancers. These newer treatments are not yet approved by the FDA.
The problem with treatments made from a patient’s own cells is the time and expense required to custom-make the treatment for each patient. Sipuleucel-T, for example, takes about 3 days to prepare and costs about $93,000 per patient. Experimental therapies using NK cells from donated umbilical cord blood, which could be stored for use in any patient rather than being custom-made, are in the early stages of testing.
Cytokines such as interleukins and interferons are chemicals that the body produces to control the immune system. Synthetic versions of certain cytokines can be injected into patients to stimulate the immune response against cancer or other diseases. For instance, interleukin-2 is approved to treat kidney cancer and melanoma, and interferon-alfa is approved to treat various cancers.
Although immunotherapy has had impressive results against some types of cancer, it’s important to remember that no one therapy works against all kinds of cancer and that most cancers require a combination of treatments—multiple drugs, often combined with surgery and/or radiation therapy. As promising as immunotherapy drugs are, they are only one piece of the cancer treatment puzzle.
– B. Tutt
For more information, ask your physician, call askMDAnderson at 877-632-6789, or visit www.mdanderson.org.
OncoLog, April 2017, Volume 62, Issue 4