Monoclonal Antibodies and Their Side Effects
One way the immune system protects the body is by making antibodies—proteins that stick to specific antigens on germs and other foreign substances. Antibodies circulate throughout the body until they find and attach to their target, helping the immune system destroy harmful cells. Monoclonal antibodies (mAbs) are a type of cancer treatment designed to mimic this natural process.
What are monoclonal antibodies (mAbs)?
Monoclonal antibodies (mAbs or Moabs) are lab-made antibodies (a type of immune protein) designed to that specifically target a certain antigen, such as one found on cancer cells. They are made from a single clone of a B cell, a type of white blood cell and part of the immune system. This makes them different from polyclonal antibodies that are developed from many different clones and can target multiple antigens.
How are monoclonal antibodies used?
Monoclonal antibodies are used to treat many diseases, including some types of cancer. To make a monoclonal antibody, researchers first have to identify the right antigen to attack. Finding the right antigens for cancer cells isn’t always easy, and so far, mAbs have proven to be more useful against some cancers than others.
Are monoclonal antibodies immunotherapy or targeted therapy?
Different monoclonal antibodies can act as targeted therapy, immunotherapy, or both, depending on how they work.
- Some monoclonal antibodies are considered targeted therapy because they attach to a specific target on a cancer cell and stop it from functioning.
- Others act as immunotherapy because they help the immune system find and attack cancer cells more effectively.
Other uses for monoclonal antibodies
In addition to treating some types of cancer, monoclonal antibodies can be used to treat other diseases and conditions, such as:
- Asthma
- Autoimmune disorders
- High cholesterol
- Infection
- Inflammatory bowel disease
- Myasthenia gravis
- Organ rejection after transplantation
- Osteoporosis
Monoclonal antibodies are also used to help diagnose certain diseases or conditions. In cancer, they’re used as part of immunohistochemistry testing that looks for patterns in cancer cells. They can also be used to detect certain infections and pregnancy.
What are monoclonal antibodies made of?
Monoclonal antibodies are lab-made proteins. There are 4 different ways they can be made, and they are named based on what they are made of.
- Murine: Made from mouse proteins, with drug names in -omab
- Chimeric: A combination of mouse and human proteins, with drug names ending in -ximab
- Humanized: Made from small parts of mouse proteins attached to human proteins, with drug names ending in -zumab
- Human: Fully human proteins, with drug names ending in -umab
Types of mAbs used to treat cancer
Naked monoclonal antibodies
Naked mAbs are antibodies that have no drug or radioactive material attached to them. They work by themselves. These are the most common type of mAbs used to treat cancer.
Most naked mAbs attach to antigens on cancer cells, but some work by binding to antigens on non-cancerous cells or even free-floating proteins. Naked mAbs can work in different ways, such as:
- Boosting the immune response against cancer cells by attaching to them and acting as a marker for the body’s immune system to destroy them. Rituximab (Rituxan), used to treat some types of non-Hodgkin lymphoma (NHL), is an example.
- Improving the immune response by targeting immune system checkpoints. Pembrolizumab (Keytruda), used to treat some types of non-small cell lung cancer, is an example.
- Attaching to and blocking proteins on cancer cells (or other nearby cells) that help cancer cells grow or spread. Trastuzumab (Herceptin), used in some types of breast cancer, is an example.
Conjugated monoclonal antibodies
Conjugated mAbs are connected to a chemotherapy drug or a radioactive particle. These mAbs act as a homing device to take one of these substances directly to the cancer cells. The mAb circulates throughout the body until it can find and hook onto the target antigen. It then delivers the toxic substance where it is needed most. Conjugated mAbs are also sometimes referred to as tagged, labeled, or loaded antibodies.
Antibody-drug conjugates (ADCs): These mAbs have powerful chemotherapy (or other) drugs attached to them. Examples include:
- Brentuximab vedotin (Adcetris), an ADC made up of an antibody that targets the CD30 antigen (found on lymphocytes), attached to a chemo drug called MMAE
- Ado-trastuzumab emtansine (Kadcyla, also called TDM-1), an ADC made up of an antibody that targets the HER2 protein, attached to a chemo drug called DM1
Radiolabeled antibodies: Radiolabeled antibodies have small radioactive particles attached to them. The antibody delivers radioactivity directly to cancer cells. Treatment with this type of antibody is sometimes known as radioimmunotherapy (RIT). The drug and radiation are delivered directly to the target cells because the mAb looks for the target, and then the radiation affects the target and nearby cells to a certain extent.
Bispecific monoclonal antibodies
These drugs are made up of parts of 2 different mAbs, meaning they can attach to 2 different proteins at the same time.
T-cell engagers (TCEs): In these drugs, 1 part attaches to a protein on cancer cells, and the other sticks to a protein on immune cells called T cells. This brings the immune cells into contact with the cancer cells, which helps the immune system mount a more effective response against them.
Side effects of monoclonal antibodies
Monoclonal antibodies are most often given as an infusion into a vein (IV). The antibodies themselves are proteins, and giving them can sometimes cause an infusion reaction, which is something like an allergic reaction. This is more common while the drug is first being given. Possible symptoms can include:
- Fever
- Chills
- Weakness
- Headache
- Nausea and vomiting
- Diarrhea
- Low blood pressure
- Skin changes such as rashes
Compared with chemotherapy drugs, naked mAbs tend to have fewer serious side effects. But they can still cause problems in some people.
Some mAbs can have side effects that are related to the antigens they target. For example:
- Bevacizumab (Avastin) is an mAb that targets a protein called VEGF that affects tumor blood vessel growth. It can cause side effects such as high blood pressure, bleeding, poor wound healing, blood clots, and kidney damage.
- Cetuximab (Erbitux) is an antibody that targets a cell protein called EGFR, which is found on normal skin cells (as well as some types of cancer cells). This drug can cause serious rashes in some people.
Your cancer care team will watch you closely during treatment and will check you often. Side effects can and should be treated as early as possible. It’s important that you tell your cancer care team about any changes in how you feel or anything you notice that’s new or unusual. Tell them right away so they can treat any problems and try to keep them from getting worse.
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- References
Developed by the American Cancer Society medical and editorial content team with medical review and contribution by the American Society of Clinical Oncology (ASCO).
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National Cancer Institute (NCI). Immunotherapy to treat cancer. Cancer.gov Updated September 24, 2019. Accessed at https://www.cancer.gov/about-cancer/treatment/types/immunotherapy on August 7, 2025.
National Cancer Institute (NCI). Monoclonal antibodies. Cancer.gov Updated September 24, 2019. Accessed at https://www.cancer.gov/about-cancer/treatment/types/immunotherapy/monoclonal-antibodies on August 7, 2025.
Last Revised: July 7, 2025
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