FIGURE 4

Persistence of transgene expression is induced by transposase-dependent gene insertion. (A) Comparison of long-term stability of hAAT expression in mice (n = 4 mice per group) injected with SB HITT vectors harboring active (SB) or inactive (mSB) transposase. Animals received 30 g of HITT vectors indicated. Mean values standard deviation are shown. (B) Serum hAAT levels after induced liver cell division in HITT-vector-treated mice. Mice (n = 5 per group) treated with 24 g pT/hAAT, 30 g pT/hAAT.PGK-SB, or 30 g pT/hAAT.MTH-SB either were subjected to partial hepatectomy (PHx) at day 70 after DNA injection (n = 2, symbols marked with +) to facilitate loss of extrachromosomal DNA or did not undergo surgery (n = 3). The persistent high serum hAAT levels even after partial hepatectomy demonstrate that integrated copies of the hAAT gene and not putative episomal hAAT-encoding DNA account for the persistence of gene expression. In the absence of transposase (pT/hAAT), we could detect a significant reduction in serum hAAT, indicating loss of a significant portion of episomal pT/hAAT due to hepatocyte cell division. Mean values standard deviation are shown for groups that did not undergo surgery, mean values are shown for pairs of animals subjected to partial hepatectomy. Black arrow indicates time of partial hepatectomy.