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The correction of genetic mutations by homologous recombination is an attractive approach to gene therapy. We used the DNA double-strand breaks introduced by the site-specific endonuclease I-Sce1 as a means of increasing homologous recombination of an exogenous DNA template in murine hematopoietic stem cells (mHSCs). To develop this approach, we chose an Artemis knockout (Art−/−) mouse in which exon 12 of the Artemis gene had been replaced by an I-Sce1 recognition site. The I-Sce1 enzyme and the Artemis correction template were each delivered by a self-inactivating (SIN)-integrase-defective lentiviral vector (SIN-IDLV-CMV-ISce1 and SIN-IDLV-Art, respectively). Transduction of Art−/− mHSCs with the two vectors successfully reverted the Art−/− phenotype in 2 of our 10 experiments. Even though the potential for genotoxicity has yet to be evaluated, this new approach to gene editing appears to be promising. Improving the efficacy of this approach will require further technical work. [ABSTRACT FROM AUTHOR]

The immune system is the site of intense DNA damage/modification, which occur during the development and maturation of B and T lymphocytes. V(D)J recombination is initiated by the Rag1 and Rag2 proteins and the formation of a DNA double-strand break (DNA dsb). This DNA lesion is repaired through the use of the non-homologous end-joining (NHEJ) pathway, several factors of which have been identified through the survey of immunodeficient conditions in humans and mice. Upon antigenic recognition in secondary lymphoid organs, mature B cells further diversify their repertoire through class switch recombination (CSR). CSR is a region-specific rearrangement process triggered by the activation-induced cytidine deaminase factor and also proceeds through the introduction of DNA dsb. However, unlike V(D)J recombination, CSR does not rely strictly on NHEJ for the repair of the DNA lesion. Instead, CSR, but not V(D)J recombination, requires the major factors of the DNA damage response. V(D)J recombination and CSR thus represent an interesting paradigm to study the regulation among the various DNA repair pathways.Oncogene (2007) 26, 7780–7791; doi:10.1038/sj.onc.1210875 [ABSTRACT FROM AUTHOR]