Transcutaneous Carbon Dioxide Decreases Immunosuppressive Factors in Squamous Cell Carcinoma In Vivo

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 (CO₂) to squamous cell carcinoma and have shown that improvement in local oxygenation has an antitumour effect. However, the effects of local CO₂ administration on tumour immunosuppression, chemoresistance, and combination with chemotherapy are unknown. In this study, we investigated the effects of local CO₂ administration on squamous cell carcinoma and the effects of combined use with chemotherapy, focusing on the effects on tumour immunosuppressive factors.

Human oral squamous cell carcinoma (HSC-3) was transplanted subcutaneously into the back of a nude mouse, and CO₂ 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.

Compared with the control group, a significant decrease in the mRNA expression of PD-L1 was observed in both, CO₂-treated and combination groups. Similarly, the expression of PD-L2 and galectin-9 decreased in the CO₂-treated and combination groups. Furthermore, immunostaining also showed a significant decrease in the protein expression of tumour immunosuppressive factors in the CO₂-treated and combination groups.

It was confirmed that the tumour immunosuppressive factors decreased due to local CO₂ administration to the mouse model. CO₂ administration has the potential to improve the hypoxic environment in tumours, and combined use with chemotherapy may also improve tumour immunosuppression.