Types of monoclonal antibodies
Naked Monoclonal Antibodies: There is no drug or radioactive material attached to them. These are the most common type of mAbs used to treat cancer. Most of them attach to antigens on cancer cells, but some work by binding to antigens on other, non-cancerous cells, or even free-floating proteins.
These sorts of antibodies boost the immune system of an individual by various ways such as targeting the immune system checkpoints, attaching to cancerous cell and acting as marker for body’s immune system to destroy them [E.g. Alemtuzumab (Campath®) used for the treatment of chronic lymphocytic leukemia]. Some of them also bind to the antigens on cancer cells and blocks them which stops the cancerous cells from activation. [E.g. Trastuzumab (Herceptin®) binds HER2 protein, active in breast and stomach cancerous cells and inactivates them.]
Conjugated Monoclonal Antibodies: Monoclonal antibodies joined to a chemotherapy drug or to a radioactive particle are called conjugated monoclonal antibodies. It is used as a homing device to take one of these substances directly to the cancer cells. Antibody circulates on body until it binds to target antigen where it then transfers the drug or particle attached to it. It can be either radiolabeled or chemolabelled.
Radiolabeled antibodies have radioactive particles attached to them [E.g. Ibritumomab tiuxetan (Zevalin®), an antibody against the CD20 antigen of B cells. The antibody delivers radioactivity directly to cancerous B cells and can be used to treat some types of Non-hodgkin lymphoma. Method of treatment is sometimes termed as Radioimmunotherapy.
Chemolabelled antibodies have some chemical or drug attached to them [E.g. Brentuximab vedotin (Adcetris®), antibody against CD30 antigen of lymphocytes. This antibody is used to treat hodgkin lymphoma and anaplastic large cell lymphoma.]
Fig: Chemolabelled Monoclonal Antibody binding to Cancer cell
Bispecific Monoclonal Antibodies: These drugs are made up of parts of 2 different monoclonal antibodies, and they can attach to 2 different proteins at the same time. [E.g. Blinatumomab (Blincyto), used in treatment of some types of acute lymphocytic leukemia. One part of it attaches to the CD19 protein, which is found on some leukemia and lymphoma cells. Another part attaches to CD3, a protein found on immune cells called T cells. Through binding of these proteins, this antibody brings the cancer cells and immune cells together, which is thought to cause the immune system to attack the cancer cells].
Monoclonal antibodies can also be classified as following:
- Murine (-omab): entirely derived from a murine source. They can lead to an allergic reaction in humans.
- Chimeric (-ximab): the variable regions are of murine origins whereas the constant regions are human. These can also cause an allergy.
- Humanized (-zumab): mostly derived from a human source except for the part of the antibody which binds to its target.
- Human (-umab) : entirely derived from a human source.