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

Abstract

Background. 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.

Materials and methods. We transduced K7M2 wt cells 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.

Results. 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.

Conclusions. 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 immune-mediated rejection.