A normal antibody binds to one target like a lock fitting one key. A bispecific antibody is made to fit two keys. This means it can:

• Connect two different cells (for example, a cancer cell and an immune cell),
• Block two signals in the body that are involved in disease,
• Improve targeting by recognizing two proteins found only in diseased tissue.

This makes bispecific antibodies very flexible and powerful in treating complex problems in the body.

Making bispecific antibodies is not easy. Each antibody has two arms made from heavy and light chains. In a bispecific antibody, these arms must be from two different antibodies, and they have to fit together correctly.

To help the parts connect in the right way, scientists use smart design tricks:

• “Knobs-into-holes” technology: One heavy chain is shaped like a knob, the other has a hole — they only fit together one way.
• Linkers: Flexible protein chains that connect variable regions from different antibodies.
• Single-chain formats: These fuse parts of antibodies together into one long chain.

These designs help prevent the wrong chains from mixing and make sure the antibody behaves properly in the body.

Bring Immune Cells to Disease Cells

One side of the antibody binds to an immune cell, like a T cell, and the other side binds to a target cell (such as a cancer cell). This brings the immune cell close to the target, helping it kill the cell more effectively.

Block Two Disease Signals

Some diseases are driven by more than one signal in the body. A bispecific antibody can block both at once which might work better than using two separate antibodies.

Improve Safety

By requiring two markers to be present at the same time, bispecific antibodies can reduce off-target effects. This means they may avoid healthy cells and only act where both targets exist — like a double safety lock.

There are several shapes and formats of bispecific antibodies, including:

• IgG-like bispecifics: These look like normal antibodies but are made of mixed chains.
• BiTEs (Bispecific T-cell Engagers): Small, flexible antibodies made from two single-chain fragments.
• Tandem scFv antibodies: Two single-chain variable regions connected in one long protein.

Each format has its own strengths depending on the goal — whether it's fast action, long half-life, or easy manufacturing.

Even though bispecific antibodies are powerful, they come with challenges:

• Harder to manufacture: Two types of binding regions must be stable and work together.
• Complex structure: Makes them harder to purify and test.
• Risk of immune response: Some designs may trigger unwanted effects if not carefully built.

To solve these issues, scientists use better design tools, screening methods, and expression systems.