Abstract
INTRODUCTION: In recent years, the tumour immunosuppressive mechanism has attracted attention as a cause of tumour chemoresistance. Although chemoresistance and immunosuppression of tumours have been reported to be associated with a hypoxic environment, effective treatments to improve hypoxia in tumours have not yet been established. We have previously applied carbon dioxide (CO(2)) to squamous cell carcinoma and have shown that improvement in local oxygenation has an antitumour effect. However, the effects of local CO(2) administration on tumour immunosuppression, chemoresistance, and combination with chemotherapy are unknown. In this study, we investigated the effects of local CO(2) administration on squamous cell carcinoma and the effects of combined use with chemotherapy, focusing on the effects on tumour immunosuppressive factors. METHODS: Human oral squamous cell carcinoma (HSC-3) was transplanted subcutaneously into the back of a nude mouse, and CO(2) and cisplatin were administered. After administration twice a week for a total of 4 times, tumours were collected and the expression of tumour immunosuppressive factors (PD-L1, PD-L2, and galectin-9) was evaluated using real-time polymerase chain reaction and immunostaining. RESULTS: Compared with the control group, a significant decrease in the mRNA expression of PD-L1 was observed in both, CO(2)-treated and combination groups. Similarly, the expression of PD-L2 and galectin-9 decreased in the CO(2)-treated and combination groups. Furthermore, immunostaining also showed a significant decrease in the protein expression of tumour immunosuppressive factors in the CO(2)-treated and combination groups. CONCLUSION: It was confirmed that the tumour immunosuppressive factors decreased due to local CO(2) administration to the mouse model. CO(2) administration has the potential to improve the hypoxic environment in tumours, and combined use with chemotherapy may also improve tumour immunosuppression.