Damping of luciferase expression from a plasmid DNA vaccine construct is FasL-mediated. (A) SIV-gag AL11 epitope-specific CD8⁺ T-cell responses in vaccinated wild-type and FasL KO mice. Epitope-specific CD8⁺ T-cell responses were measured by D^d/AL11 tetramer staining of CD8⁺ T cells at the indicated times after plasmid DNA vaccine inoculation. (B) Photo images overlaid with visualized infrared signal readouts of wild-type and FasL knockout (FasL KO) mice. Wild-type and FasL knockout mice were inoculated with plasmid DNA-Luc (n = 4), and the in vivo expression of luciferase was measured by IVIS imaging. Comparison of luciferase antigen expression between wild-type and FasL KO mice. (C) Representative infrared signal images of luciferase activity are shown as relative light units (RLU) at 0.2, 2, 7, 21, and 28 days after plasmid DNA inoculation. The line graphs represent mean values; error bars represent SEM. Statistically significant differences at specific times were determined by the Mann-Whitney test. *Significant difference (P < .05).