Gene Ther. 2000 Mar;7(5):384-92.
Phase 1 clinical trials of liposome-mediated gene therapy for cystic fibrosis have been completed and in all cases the expression level achieved has been low and transient. Clearly, improvements in the efficiency of gene transfer are required.
It is now being recognised that delivery of high doses of DNA/liposomes to the mouse airway epithelium can achieve reproducible evidence of transgene, but is often associated with an unacceptable level of inflammation/ toxicity.
It has recently been shown that instillation of bacterial DNA causes inflammation in the lower respiratory tract of rodents. The increased number and unmethylated status of CpG motifs, particularly when present in a particular base context, was identified as an important factor in this response. It was suggested that the immune system recognises this molecular pattern as 'foreign' thus activating appropriate immune responses.
We have found that methylation of DNA decreases the level of several inflammatory cytokines in lavage fluid and surprisingly has a differential effect on expression of the plasmids pCMV CFTR-int6ab and pCMV CAT which only differ in the actual transcription cassette.
The severe lung pathology observed did not show a corresponding decrease with methylation suggesting that these cytokines are not the only contributors to the toxicity/inflammation observed.