Safe delivery of therapeutic genes into specific chromosomal sites using engineered retroviral integrase

Abstract

Gene therapy approaches that involve the permanent insertion of therapeutic genes into host chromosomal DNA have many desirable features and show considerable promise for success in the clinic. One major drawback of these approaches is that any unintended insertion events from the therapy can potentially have detrimental effects in patients, as demonstrated by the development of malignancies in both animal and human studies. Therefore, directing the integration of foreign genes into "safe sites" within the genome is highly desirable for these approaches. In retroviral-based vector systems, the viral enzyme integrase (IN) catalyzes the insertion of a desired transgene nonspecifically into the host cell genome. Efforts to engineer IN to recognize specific target DNA sequences within the genome, and thereby improve the safety of future generations of retroviral-based vectors, are described. Recent results using fusion protein constructs of IN and E2C, a designed polydactyl zinc-finger protein that specifically recognizes an 18-base pair DNA sequence, are highlighted in this review. Encouraging results have been generated in vitro, and additional studies are ongoing in mammalian cell systems. The long-term goal of these efforts is the development of effective retroviral vectors that can safely deliver therapeutics in a gene therapy setting.