Immune response to firefly luciferase as a naked DNA

Firefly luciferase (Fluc) has been widely used as a reporter gene. The aim of this study was to investigate immune response to luciferase protein after an intradermal injection of pcDNA3.1-Fluc in immunocompetent BALB/c mice. We observed bioluminescence at injection sites from one to seven days post-injection when pcDNA3.1-Fluc was intradermally injected into ear-pinnae. To observe induced immune response, the percentages of CD8+IFN-γ+ cells in the draining lymphoid cells of immunocompetent BALB/c mice immunized by pcDNA3.1-Fluc were measured. And the tumor growths of CT26/Fluc in pcDNA3.1-Fluc group were monitored by observing bioluminescent signals and measuring tumor mass, and these were compared with those of the pcDNA3.1 group in immunocompetent BALB/c mice and immunodeficient Nu/Nu mice. In the immunocompetent BALB/c mice, percentages of CD8+IFN-γ+ cells in the pcDNA3.1-Fluc group were higher than those in the pcDNA3.1 group. Ten days after tumor inoculation, tumor growth inhibition was found in the pcDNA3.1-Fluc group, but not in the pcDNA3.1 group in the immunocompetent BALB/c mice. No significant difference in tumor growth inhibition was observed when CT26/Fluc was injected into immunodeficient Nu/Nu mice. In terms of cytokine profiles of draining lymphoid cells of immunized mice, IFN-γ protein levels in the pcDNA3.1-Fluc group were higher than in pcDNA3.1 group animals among the immunocompetent BALB/c mice. In conclusion, Fluc induced a Th1 immune response to Fluc protein delivered by injecting pcDNA3.1-Fluc into immunocompetent BALB/c mice. We suggest that immune response to the Fluc gene is cautionary in preclinical or clinical trials involving the Fluc gene, and that the immunologic potential of firefly luciferase as a naked DNA may be useful in cancer immunotherapy.