| Cationic lipid vectors, including lipoplex (liposome-DNA complex) and LPD (liposome-polycation-DNA), are able to transfect the lung via systemic administration and have potential in treating pulmonary diseases. However, systemic administration of these vectors triggers a dose-dependent inflammatory toxicity, including the induction of cytokines TNF-α and IFN-γ. The inflammatory cytokines inhibit transgene expression from lipoplex or LPD carrying an expression plasmid. This toxicity was a limiting factor for gene therapy application of cationic lipid vectors. The goals of the studies summarized in this dissertation are to elucidate the mechanism underlying the cationic lipid vector induced inflammatory toxicity, and to develop strategies to overcome the toxicity in systemic gene delivery using these vectors.; To identify the cause of this inflammatory toxicity, especially the role of DNA sequence, a series of oligodeoxynucleotides (ODNs) containing different CpG sequences were formulated in LPD and delivered intravenously to mice. The level of stimulated TNF-α was monitored as an indicator of the inflammatory toxicity. The presence of a CpG motif was essential for the induction of TNF-α. Flanking sequences greatly influence, and methylation decreases >80% the TNF-α induction potency of a given CpG motif.; Several strategies were taken to overcome the inflammatory toxicity. One approach was to use immune suppressive agents. Both a general immune suppressant dexamethasone and a NF-κB targeted decoy phosphorothioate ODN successfully reduced the inflammatory toxicity in systemic gene delivery of LPD, and both substantially increased transgene expression. The other approach was to use a sequential injection protocol to replace liposome-DNA complexes. With several cationic liposome formulations, sequential injection of cationic liposome and plasmid DNA at 1–2 minutes apart leads to significantly lower levels of inflammatory cytokines and higher level of transgene expression compared to those in the complex injection. Other toxicities associated with complex administration, such as adverse changes in hematological and liver function parameters were also significantly reduced in sequential injection.; These studies have elucidated the role of CpG in causing the inflammatory toxicity of cationic lipid vectors. Furthermore, different strategies have been developed for reducing the toxicity, which promote the application of cationic lipid vectors for treatment of pulmonary diseases. |
