Intracellular antibodies: a revolution waiting to happen?

Antibodies and their derivatives play a key role in modern drug development, as both research tools and therapeutic entities in their own right. The combination of high-affinity binding and exquisite specificity makes them ideal agents for controlled intervention in biological processes. Evolution has designed antibodies to function in the circulation and interstitial spaces of a tissue or organism, but many potentially valuable drug targets are intracellular and therefore beyond the reach of standard antibodies. Some of the recent advances and current pitfalls in attempts to adapt antibodies for intracellular use are described, and the ultimate potential of this powerful but underused technology is discussed.