Zinc Finger nucleases (ZFNs) have been used to create precise genome 
modifications at frequencies that might be therapeutically useful in gene 
therapy. We created a mouse model of a generic recessive genetic disease to 
establish a preclinical system to develop the use of ZFN-mediated gene 
correction for gene therapy. We knocked a mutated GFP gene into the ROSA26 locus 
in murine embryonic stem (ES) cells and used these cells to create a transgenic 
mouse. We used ZFNs to determine the frequency of gene correction by gene 
targeting in different primary cells from this model. We achieved targeting 
frequencies from 0.17 to 6% in different cell types, including primary 
fibroblasts and astrocytes. We demonstrate that ex vivo gene-corrected 
fibroblasts can be transplanted back into a mouse where they retained the 
corrected phenotype. In addition, we achieved targeting frequencies of over 1% 
in ES cells, and the targeted ES cells retained the ability to differentiate 
into cell types from all three germline lineages. In summary, potentially 
therapeutically relevant frequencies of ZFN-mediated gene targeting can be 
achieved in a variety of primary cells and these cells can then be transplanted 
back into a recipient.