Ligand-targeted receptor-mediated vectors for gene delivery

Abstract

Gene therapy promises to cure human genetic diseases. One of the main obstacles to fulfilling this promise is in the ability to target a gene to a significant population of cells and express it at adequate levels for a long enough period of time. Viral methods for gene delivery have been studied for a number of years and are effective vectors for gene transfer. The great majority of gene therapy clinical trials currently in progress use retroviruses or adenoviruses. However, there are concerns for their clinical use because of possible risks of mutagenesis, immunogenic side-effects and toxicity. In addition to this, there are other limitations, including the size of gene that can be transferred. Over the last ten years, a new approach has emerged that has increasingly gathered speed thanks to advances in receptor cell biology and antibody production. This method involves ligand-targeted receptor mediated endocytosis (RME) of ‘polyplexes’. Here, synthetic complexes are composed of a cell-specific targeting ligand, coupled to a DNA binding element and endosmolytic function. These complexes are able to deliver genes to cells in a receptor-specific manner, without any viral DNA sequences or packaging constraints. There are now many ligand/receptor systems under investigation, each one demonstrating successful gene transfer with a higher level of tissue specificity than viruses can offer. This review describes most of these systems and looks ahead to an era where cell-specific gene delivery may be a main stream gene therapy, treatment modality.

• polyplexes
• receptor-mediated endocytosis
• targeted gene delivery
• vectors