Abstract
In this study, we have developed a novel method to monitor transgene expression in tissues by blood sampling. We administered plasmid DNA (pDNA) encoding non-secretory form of firefly luciferase as a reporter gene and pDNA encoding secretable Gaussia princeps luciferase as a monitor gene simultaneously into mice. Good positive correlations were found between log-transgene expression of the reporter gene and the monitor gene in the treated muscle, between the monitor gene in the treated muscle and plasma, and consequently between the reporter gene in the treated muscle and the monitor gene in plasma after naked pDNA transfer into the muscle of mice. Such positive correlations were also found with gastric serosal surface instillation of naked pDNA, intravenous injection of lipoplex, and hydrodynamics-based injection of naked pDNA. We developed monitoring method of transgene expression in tissues by blood sampling, which was named 'Therapeutic transgene monitoring (TTM)', after 'Therapeutic drug monitoring (TDM)'.