Polyethylenimine-Mediated CpG Oligodeoxynucleotide Delivery Stimulates Bifurcated Cytokine Induction

CpG oligodeoxynucleotides (CpG ODNs) bind to toll-like receptor 9 (TLR9) and activate the immune system. Thus, CpG ODNs have attracted considerable interest as immunotherapeutic agents or adjuvants for many diseases. Herein we report that polyethylenimine (PEI) functions as a multifunctional vector for both enhancing and regulating the immunostimulatory activity of CpG ODNs. PEI and CpG ODNs formed nanopolyplexes (NPs), which possessed good biocompatibility. PEI-CpG ODN NPs facilitated the internalization of CpG ODNs and induced increasing amounts of cytokines. Most importantly, PEI-CpG ODN NPs induced interleukin-6 (IL-6) and interferon-α (IFN-α) simultaneously, while class B CpG ODNs induced only IL-6. In contrast to class C CpG ODNs, which also simultaneously induce IFN-α and IL-6, the ratio of IFN-α and IL-6 induced by PEI-CpG ODN NPs could be regulated by changing the N/P ratio. This flexible bifurcated cytokine is promising for treating diseases such as cancer that require IL-6 and IFN-α simultaneously. Our findings propose a regulatory effect of PEI on the immunostimulatory activity of CpG ODNs, which will shed light on the development of highly efficient nonviral vectors for CpG ODN-based immunotherapy.