Receptor-targeted gene delivery using multivalent phagemid particles.

Although growth factor- and antibody-targeted filamentous phage have recently been demonstrated to transduce mammalian cells, there is a significant need to increase transduction efficiency so as to improve the usefulness of targeted phage vectors for gene therapy and ligand discovery. Here, we describe the use of multivalent phagemid vectors that are specifically designed for ligand-targeted mammalian cell transduction. This phagemid system has certain advantages over phage vectors, such as larger insert size and vector stability, and it retains the multivalent display necessary for efficient cell binding and internalization. Immunoblotting revealed that the most efficient multivalent display (exceeding that of a phage vector) was achieved in the phagemid system when epidermal growth factor (EGF) was fused to the C-terminal domain of the pIII coat protein. We compared phagemid particles displaying EGF at high or low valence by rescuing the vector with R408d3 (pIII deleted) or wild-type R408 helper phage, respectively. More efficient display of EGF correlated with increased internalization, vector potency, and transduction efficiency ( approximately 9%). The findings described here support our original hypothesis that phage-based vectors can be modified for more efficient gene transfer and suggest that directed evolution may be applied to increase their potential even further.