monoclonal antibody

A monoclonal antibody is a custom-built protein that acts like a guided missile, sticking tightly to one chosen target and nothing else. Your immune system naturally makes antibodies, Y-shaped proteins that recognize invaders; a monoclonal antibody is a laboratory version where every single molecule is identical and aimed at exactly the same spot on the target.

The word 'monoclonal' means the antibodies all descend from one clone of cells, so they share an identical structure and bind the same precise feature, called an epitope. By engineering which epitope they recognize, scientists can make an antibody neutralize a toxin, block a receptor, flag a cancer cell for the immune system, or carry a payload to a tumor.

Antibodies are large proteins, so they must be injected or infused rather than swallowed, and they generally cannot cross into cells or into the brain easily. Their great strength is exquisite selectivity and a long half-life in the blood; their limits are cost, the need for refrigeration, and the fact that they mostly reach targets on cell surfaces or floating in the blood.