Biosafety assessment of site-directed transgene integration in human umbilical cord-lining cells

Biosafety and efficacy considerations that impede clinical application of gene therapy could be addressed by nonviral ex vivo cell therapy, utilizing transgenic cells that have been comprehensively pre-evaluated for genotoxic potential and transgene expression. We evaluated the genotoxic potential of phiC31 bacteriophage integrase-mediated transgene integration in cord-lining epithelial cells (CLECs) readily cultured from the outer membrane of human umbilical cords, by sequencing and mapping integration sites, spectral karyotyping, high-resolution genome copy number, transcriptome, and transgene copy number analyses and in vivo tumorigenicity. Of 44 independent integration events, <5% were exonic and 85% of modified cells had integrated