Nonintegrating Gene Therapy Vectors

Gene delivery vectors that do not rely on host cell genome integration offer several advantages for gene transfer, chiefly the avoidance of insertional mutagenesis and position effect variegation. However, unless engineered for replication and segregation, nonintegrating vectors will dilute progressively in proliferating cells, and are not exempt of epigenetic effects. This article provides an overview of the main nonintegrating viral (adenoviral, adeno-associated viral, integration-deficient retro-lentiviral, poxviral), and nonviral (plasmid vectors, artificial chromosomes) vectors used for preclinical and clinical cell and gene therapy applications. Particular emphasis is placed on their use in hematologic disease.

Key points

•

Host cell genome integration of first-generation gene therapy vectors may result in various effects on cellular genes (knockout, overexpression, altered splicing), variegated levels of transgene expression, or transcriptional silencing, as well as clonal expansion and oncogenic transformation.
•

Nonintegrating gene therapy vectors can be viral and nonviral. Viral vectors can be nonintegrating like their parental organisms (adenovirus, herpesvirus, poxvirus, Sendai) or engineered to minimize integration (adeno-associated virus, retro-lentivirus).
•

Nonintegrating vectors can provide stable transgene expression in quiescent cells and transient or stable expression in proliferating cells.
•

Variants of nonintegrating vectors carrying suitable payloads (transposons, site-specific recombination cassettes, genome editing cassettes) are suitable platforms for genetic modification of the cellular genome by transposition, site-directed integration, and genome editing.
•

Successful clinical trials have already been reported using adenoviral vectors (genome editing of CCR5 for AIDS), herpesvirus vectors (cancer), and adeno-associated virus vectors (hemophilia).