Alemtuzumab (Campath®) is a prescription drug used primarily as a treatment for B-cell chronic lymphocytic leukemia (B-CLL), which is a type of cancer affecting the blood cells. It works by binding to CD52, a specific antigen found on the surface of a variety of white blood cells, including leukemia cells. As a result, alemtuzumab signals the immune system to attack leukemia cells.
Sometimes, drugs are used to treat conditions other than the ones for which they are approved. For example, people with multiple sclerosis may be given alemtuzumab in this "off-label" fashion. This is not an illegal practice, as medications are often prescribed in this way.
(Click What Is Alemtuzumab Used For? to learn more about how this drug works, whether it can be given to children and older adults, and other off-label uses.)