Bacterial DNA is implicated in the inflammatory response to delivery of DNA/DOTAP to mouse lungs

Phase 1 clinical trials of liposome-mediated gene therapy for cystic fibros is have been completed and in all cases the expression level achieved has b een low and transient. Clearly, improvements in the efficiency of gene tran sfer are required. It is now being recognised that delivery of high doses o f DNA/liposomes to the mouse airway epithelium can achieve reproducible evi dence of transgene, but is often associated with an unacceptable level of i nflammation/ toxicity. It has recently been shown that instillation of bact erial DNA causes inflammation in the lower respiratory tract of rodents. Th e increased number and unmethylated status of CpG motifs, particularly when present in a particular base context, was identified as an important facto r in this response. It was suggested that the immune system recognises this molecular pattern as 'foreign' thus activating appropriate immune response s, We have found that methylation of DNA decreases the level of several inf lammatory cytokines in lavage fluid and surprisingly has a differential eff ect on expression of the plasmids pCMV CFTR-int6ab and pCMV CAT which only differ in the actual transcription cassette. The severe lung pathology obse rved did not show a corresponding decrease with methylation suggesting that these cytokines are not the only contributors to the observed.