bispecific antibody

How is it different from a standard antibody?

A natural antibody is shaped like the letter Y, and both arms of the Y recognize the same target. A laboratory-made monoclonal antibody copies that plan exactly, which is why one monoclonal binds one thing. A bispecific antibody deliberately breaks the symmetry. Its two arms come from different parent antibodies, so the finished molecule recognizes two things at once.

How does it work in the body?

The most familiar design is the T cell engager. One arm grips a protein carried on the surface of a tumor cell. The other grips CD3, a protein found on T cells, the immune cells that destroy infected and abnormal cells. Holding the two cells together triggers the T cell to attack, without waiting for the recognition steps it normally requires. That is a different mechanism from ordinary antibody therapy, where the antibody marks a cell and leaves the immune system to respond in its own time.

Other designs never involve a cell at all. One arm can block a growth signal while the second arm blocks a different signal the tumor might switch to, closing off an escape route. A bispecific can also act as a bridge between two clotting proteins, standing in for a clotting factor that is missing.

What are the drawbacks?

Pulling immune cells hard against target cells releases a burst of signaling chemicals. A large release produces cytokine release syndrome, with fever, low blood pressure and breathlessness, which is why the first doses are usually small, stepped upward, and given under close observation. Nerve-related effects such as confusion and tremor are also recognized. Manufacture is demanding in its own right, because a molecule assembled from two mismatched halves tends to pair incorrectly, and the correctly built product has to be separated out. Some formats are cleared from the blood quickly, so they are given as a continuous infusion rather than a single injection.