Antitumor immune responses induced by photodynamic and sonodynamic therapy: a narrative review

The immune system has the function of immune surveillance to resist the occurrence and development of tumors, and is essential for inhibition of tumor metastasis. Nevertheless, tumor cells can still suppress immune responses through multiple mechanisms to escape recognition and elimination. Photodynamic and sonodynamic therapy involve systemic or local use of sensitizers followed by light or ultrasound treatment of the affected area, leading to tumor cell death by various mechanisms. The capability of the immune system is essentially affected by photodynamic and sonodynamic therapy. To understand the tumor therapeutic mechanisms of photodynamic and sonodynamic therapy and to explore the use of these modalities for improvement of the antitumor immune effect, extensive preclinical and clinical studies have been carried out. Besides direct killing of tumors, photodynamic and sonodynamic therapy also cause inflammatory reactions, achieve antitumor immune responses, and potentially prevent tumor recurrence, thereby treating both primary and metastatic tumors. In this review, we summarize the antitumor immune responses induced by photodynamic and sonodynamic therapy, describe the processes of the antitumor immune responses in detail, and discuss the clinical applications of the resulting antitumor immunity.