Purification of polyethylenimine polyplexes highlights the role of free polycations in gene transfer.

Background: Nonviral vectors based on polyethylenimine (PEI) usually contain an excess of PEI that is not complexed to DNA. Since unbound PEI contributes to cellular and systemic toxicity, purification of polyplexes from unbound PEI is desirable.

Methods: Size exclusion chromatography (SEC) was used to purify PEI polyplexes of free PEI.