Targeted introduction and effective expression of hFIX at the AAVS1 locus in mesenchymal stem cells

Hemophilia B occurs due to a deficiency in human blood coagulation factor IX (hFIX). Currently, no effective treatment for hemophilia B has been identified, and gene therapy has been considered the most appropriate treatment. Mesenchymal stem cells (MSCs) have homing abilities and low immunogenicity, and therefore they may be potential cell carriers for targeted drug delivery to lesional tissues. The present study constructed an adeno-associated virus integration site 1 (AAVS1)-targeted vector termed AAVS1-green fluorescent protein (GFP)-hFIX and a zinc finger nuclease (ZFN) expression vector. Nucleofection was used to co-transfect the targeting vector and the ZFN expression vector into human MSCs. The GFP-positive cells were selected using flow cytometry. Site-specific integration clones were obtained following the monoclonal culture, subsequent detections were performed using polymerase chain reaction and Southern blotting. Following the confirmation of stem cell traits of the site-specific integration MSCs, the in vivo and in vitro expression levels of hFIX were detected. The results demonstrated that the hFIX gene was successfully transfected into the AAVS1 locus in human MSCs. The clones with the site-specific integration retained stem cell traits of the MSCs. In addition, hFIX was effectively expressed in vivo and in vitro. No significant differences in expression levels were identified among the individual clones. In conclusion, the present study demonstrated that the exogenous gene hFIX was effectively expressed following site-specific targeting into the AAVS1 locus in MSCs; therefore, MSCs may be used as potential cell carriers for gene therapy of hemophilia B.