Narrator: This is Science Today. People who get organ transplants, such as a heart or kidney, are given drugs to prevent their immune systems from rejecting the new organs. A few years ago, a new class of drugs called monoclonal antibodies showed promise as anti-rejection drugs. Monoclonals are created in mice and genetically engineered for use in humans. But Dr. Flavio Vincenti of the University of California, San Francisco says the drug's rodent origins betrayed it.

Vincenti: The antibody, although it's effective initially, ultimately it induces in humans a response that we call HAMA - human anti-mouse antibodies.

Narrator: In other words, our bodies reject the anti-rejection drugs, making them useless. But researchers have come up with a new approach.

Vincenti: We're entering now into a new technology that's called humanization of these monoclonal antibodies.

Narrator: Humanized monoclonals are ten percent mouse and ninety percent human. Our bodies recognize only the human part, leaving the mouse part free to prevent rejection. For Science Today, I'm Steve Tokar.