Persistent transgene expression following intravenous administration of a liposomal complex: role of interleukin-10-mediated immune suppression.

Studies conducted in non-tumor-bearing, immunocompetent mice have shown that intravenous administration of liposome-DNA complex elicits an inflammatory response that results in a failure to sustain adequate transgene expression. In the present study, however, we investigated the effects of a cationic liposomal DOTAP:cholesterol (DOTAP:Chol)-DNA complex on cytokine production and transgene expression in both experimental lung tumor-bearing (TB) mice and non-tumor-bearing (NTB) syngeneic mice and nude mice. Intravenous injection of DOTAP:Chol-luciferase (luc) DNA complex resulted in tumor necrosis factor-alpha levels that were 50% lower and interleukin-10 levels that were 50-60% higher in TB mice than in NTB mice. Furthermore, a significant increase in luc expression (P = 0.001) that persisted for 7 days was observed in TB mice. In contrast, luc expression decreased significantly from day 1 to day 2 in NTB mice. Also, luc expression was two- to threefold higher in TB mice that were given multiple injections of DOTAP:Chol-luc complex than in mice who received a single injection. In contrast, luc expression was significantly suppressed following multiple injections in NTB mice (P = 0.01). Further analysis revealed IL-10 protein expression by the tumor cells in TB mice. Injection of anti-IL-10 antibody in TB mice resulted in a significant decrease in luc expression (P = 0.01) compared with that in mice injected with a control antibody. Based on these findings, we conclude that transgene expression persists in TB mice and is partly mediated by IL-10. Additionally, multiple injections of liposome-DNA complex can increase transgene expression in TB mice. These findings have clinical applications in the treatment of cancer.