pEPito: a significantly improved non-viral episomal expression vector for mammalian cells

Background: The episomal replication of the prototype vector pEPI-1
depends on a transcription unit starting from the constitutively
expressed Cytomegalovirus immediate early promoter (CMV-IEP) and
directed into a 2000 bp long matrix attachment region sequence
(MARS) derived from the human beta-interferon gene. The original
pEPI-1 vector contains two mammalian transcription units and a
total of 305 CpG islands, which are located predominantly within
the vector elements necessary for bacterial propagation and known
to be counterproductive for persistent long-term transgene
expression. Results: Here, we report the development of a novel
vector pEPito, which is derived from the pEPI-1 plasmid replicon
but has considerably improved efficacy both in vitro and in vivo.
The pEPito vector is significantly reduced in size, contains only
one transcription unit and 60% less CpG motives in comparison to
pEPI-1. It exhibits major advantages compared to the original
pEPI-1 plasmid, including higher transgene expression levels and
increased colony-forming efficiencies in vitro, as well as more
persistent transgene expression profiles in vivo. The performance
of pEPito-based vectors was further improved by replacing the
CMV-IEP with the human CMV enhancer/human elongation factor 1 alpha
promoter (hCMV/EF1P) element that is known to be less affected by
epigenetic silencing events. Conclusions: The novel vector pEPito
can be considered suitable as an improved vector for
biotechnological applications in vitro and for non-viral gene
delivery in vivo.