Phage φC31 integrase-mediated site-specific integration for gene therapy

For most genetic disorders, long-term correction is necessary. Integration of a therapeutic gene into a patient's genome is an obvious route to achieving such permanent correction. Several technologies have been applied to the goal of achieving integration, including viruses and transposases. While these techniques are effective at some level, they each have drawbacks that can be improved upon. A novel integration system based on a phage integrase can address some of the previous limitations. The integrase from the Streptomyces bacteriophage C31 catalyzes site-specific, unidirectional integration into the genomes of higher eukaryotes. This integrase has the ability to recognize a limited number of native genomic sequences and integrate introduced plasmid DNA into them. These native sequences, termed pseudo att sites, resemble the wild-type phage attachment site enough to support integrase-mediated integration. Molecular evolution holds the promise of creating custom integrases that preferentially recombine at particular pseudo att sites. Furthermore, the system has no apparent size limit on carrying capacity. These features make the C31 integrase system extremely appealing for gene therapy applications. The system has been successfully employed in several model gene therapy studies to date. Here we review the development of this novel integration system and its current and potential applications to gene therapy.