Luciferase-induced immune activation prevents orthotopic K7M2luc osteosarcoma establishment in BALB/c mice

Use of murine orthotopic tumor models dictates utilization of luciferase-expressing cells for in vivo bioluminescence imaging. However, luciferase may trigger immune responses that impair tumor establishment.

We transduced K7M2 cells wild-type (wt) with luciferase gene and evaluated their growth in vitro. We then implanted cells orthotopically in BALB/c mice and upon unsuccessful tumor establishment assessed systemical and local mechanism for tumor growth suppression.

All investigated cell lines had a comparative doubling time in vitro at 24 and 48h. Despite that, K7M2luc E5 differed from K7M2luc A7 and K7M2 wt by having a much higher proliferation rate at 72h (35x, 15x and 17x). In vivo, both luciferase-expressing cell lines failed to establish tumors, whereas K7M2 wt had a 100% success rate. To investigate the underlying mechanism, we assessed systemic and local cell-mediated immunity. Mice in groups K7M2luc A7 and K7M2luc E5 had a higher fold change (5 ± 0.8 and 6 ± 1.05) of GrB secreting splenocytes than naïve mice (1 ± 0.2). In the bone microenvironment, luciferase groups exhibited elevated numbers of GrB-secreting cells and CD8⁺ T cells relative to K7M2 wt and naïve mice.

These findings indicate that luciferase activates cytotoxic T-cell responses capable of eliminating implanted cells. Tumor establishment was restored in immunodeficient mice lacking CD8⁺ cells, confirming the immunemediated rejection.