The Functionality of Minimal PiggyBac Transposons in Mammalian Cells

Minimal piggyBac vectors are a modified single-plasmid version of the classical piggyBac delivery system that can be used for stable transgene integration. These vectors have a truncated terminal domain in the delivery cassette and thus, integrate significantly less flanking transposon DNA into host cell chromatin than classical piggyBac vectors. Herein, we test various characteristics of this modified transposon. The integration efficiency of minimal piggyBac vectors was inversely related to the size of both the transposon and the entire plasmid, but inserts as large as 15 kb were efficiently integrated. Open and super-coiled vectors demonstrated the same integration efficiency while DNA methylation decreased the integration efficiency and silenced the expression of previously integrated sequences in some cell types. Importantly, the incidence of plasmid backbone integration was not increased above that seen in nontransposon control vectors. In BALB/c mice, we demonstrated prolonged expression of two transgenes (intracellular mCherry and secretable Gaussia luciferase) when delivered by the minimal piggyBac that resulted in a more sustained antibody production against the immunogenic luciferase than when delivered by a transient (nontransposon) vector plasmid. We conclude that minimal piggyBac vectors are an effective alternative to other integrative systems for stable DNA delivery in vitro and in vivo.