Monoclonal antibodies (MABs) are a type of biological therapy which have an ability to bind to selective molecules found on the cell surface of lymphocytes. (‘Monoclonal’ just means all one type.) Monoclonal antibody therapy uses antibodies that are made in the lab rather than by a person's own immune system. This type of treatment is used in inflammatory conditions such as MS, rheumatoid arthritis, or malignant diseases such as leukemia and lymphoma.
The first monoclonal antibodies (MABs) were made entirely from mouse cells. One problem with this is that the human immune system will see these antibodies as foreign (because they're from a different species) and then will mount a response against them. In the short term, this can sometimes cause allergic-type reactions. In the long term, it means that the antibodies may only work the first time they are given; after that, the body's immune system is primed to destroy them before they can be helpful.
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Monoclonal Antibodies: What are they?