Recombinant AAV8 viral vectors were produced using a helper virus-free system with some modifications [47] . Low-passage human HEK 293 cells were cotransfected by linear polyethylenimine (Polysciences) with three plasmids: the AAV cis-plasmid pTRUF encoding the human mAb gene expression cassette flanked with ITRs; the AAV-packaging plasmid p5e18 (2/8) containing AAV2 rep and AV8 cap genes; and the Ad helper plasmid pXX6-80 containing the VA RNA, E2, and E4 genes required for AAV propagation (obtained from Dr. Jim Wilson, University of Pennsylvania) [48] . At 48 h post-transfection, the cells were harvested, and the AAV virus extracted by freezing and thawing the cells. Subsequently, AAV was purified by two sequential iodixanol density gradients, concentrated, then desalted by centrifugation through Biomax 100-K filters (Millipore) according to the manufacturer's instructions. Viral titers were determined as genome copy titers (vg), by quantitative real-time PCR using primers and probe speicific for AAV vector pTRUF [49] . Forward primer (59-TCTGAGTAGGTGTCATTC-TATTCTGGG-39) is located at the end of the 39-poly(A), and reverse primer (59-CACTAGGGGTTCCTAGATCTCTCCC-39) is at the beginning of the 39 inverted terminal repeat (ITR). The probe (59-TCTTCCCAATCCTCCCCCTTGCTGTC-3; FAM/TAMRA) is located in between.