Recent progress in bioactive gas delivery for cancer immunotherapy.

Tumors with high mortality rates are still a major threat to human survival and health worldwide. In recent years, cancer immunotherapy has made rapid clinical progress in eliminating cancers by activating the host's own immune system. Particularly, the use of physiological bioactive gas molecules such as nitric oxide, carbon monoxide and hydrogen sulfide have been developed as novel immunotherapeutic strategies. In this review, we have summarized the current strategies for antitumor immunotherapy via bioactive gas molecules, targeting delivery to the tumor microenvironment. We summarize the biofunctions of bioactive gases to the immune system, then gas delivery nanocarriers for antitumor immunotherapy and the current status of the platform are presented. Furthermore, since gas could specifically respond to the ultrasound, ultrasound-assisted gas delivery is generalized as a promising potential pathway for enhanced immunotherapy. Finally, we have discussed the challenges and opportunities for bioactive gas delivery and the effects of acoustic enhanced immunotherapy in future developments and possible clinical applications.