Intrabodies: Targeting scFv Expression to Eukaryotic Intracellular Compartments

Molecular techniques for inhibiting the expression of specific genes represent a highly refined approach to the analysis and manipulation of microbial and cellular pathways. The specific and high affinity binding properties of antibodies (Abs), combined with their ability to be stably expressed in precise intracellular locations inside mammalian cells, have provided a powerful new family of molecules for gene therapy. These intracellular Abs are called “intrabodies.” A key factor contributing to the success of this approach has been the use of single-chain Abs (scFvs) in which the heavy- and light-chain variable domains (V_H and V_L , respectively) are synthesized as a single polypeptide, and are separated by a flexible linker peptide, generally (GGGGS)₃ . The result is a small molecule of approx 28 kDa. Examples of Fab intrabodies have also been reported, but only where an internal ribosomal entry site has been used to allow stoichiometric amounts of heavy- and light-chain fragments to be expressed simultaneously (1,2 ).