Hyperbaric oxygen inhibits production of CD3+ T cells in the thymus and facilitates malignant glioma cell growth

OBJECTIVE: Hyperbaric oxygen (HBO) is an emerging complementary alternative medical approach in glioma treatment. However, its mode of action is unknown, so this was investigated in the present study. METHODS: We constructed an intracranial glioma model of congenic C57BL/6J mice. Glioma growth under HBO stimulation was assessed by bioluminescent imaging and magnetic resonance imaging. Flow cytometry assessed direct effects of HBO on reactive oxygen species (ROS) signaling of transplanted glioma cells and organs, and quantified mature T cells and subgroups in tumors, the brain, and blood. RESULTS: HBO promoted the growth of transplanted GL261-Luc glioma in the intracranial glioma mouse model. ROS signaling of glioma cells and brain cells was significantly downregulated under HBO stimulation, but thymus ROS levels were significantly upregulated. CD3+ T cells were significantly downregulated, while both Ti/Th cells (CD3+CD4+) and Ts/Tc cells (CD3+CD8+) were inhibited in tumors of the HBO group. The percentage of regulatory T cells in Ti/Th (CD3+CD4+) cells was elevated in the tumors and thymuses of the HBO group. CONCLUSION: HBO induced ROS signaling in the thymus, inhibited CD3+ T cell generation, and facilitated malignant glioma cell growth in vivo in the intracranial glioma mouse model.