These data together strongly suggested that rSV40 vectors integrate and that they do so in both cycling and non-cycling cell populations, both in vitro and in vivo. We then tested directly whether rSV40 DNAs were incorporated into cellular DNA. PCR analyses of genomic DNA in a transduced lymphocyte line yielded the predicted PCR product. That vector DNA inserted into the cell genome was demonstrated directly by two types of studies. Southern blot analysis of restricted and unrestricted high-molecular weight DNAs from cells transduced in vitro showed that almost all vector DNA was incorporated into chromosomal DNA within a few days of delivery. The detection of very small amounts of unintegrated vector DNA underscores the fact that practically all SV(BUGT) DNA integrated into the genome. Comparable Southern blot analyses performed on restricted DNA from livers transduced in vivo yielded a similar interpretation: rapid incorporation of rSV40 DNA into high-molecular weight cellular DNA (J.R.C. and D.S.S., unpublished data). A degree of incomplete digestion of the DNA notwithstanding, there is no other explanation for the observed release of SV(BUGT) restriction fragments from the genomic DNA, as seen in the smear obtained using NotI and in the patterns and sizes of bands obtained with NotI + Eco RI, other than that SV(BUGT) DNA integrated into the cellular genome.
full paper: Durability of Transgene Expression and Vector Integration: Recombinant SV40-Derived Gene Therapy Vectors
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