Injectable Oxygen Microparticles Boost Radiation–Mediated In Situ Vaccination and Systemic Antitumor Immune Responses

The aim of this work was to determine whether intratumoral injections of a liquid oxygen solution are effective at boosting radiation-induced abscopal effects. A liquid oxygen solution, comprising slow-release polymer-shelled oxygen microparticles, was fabricated and injected intratumorally to locally elevate tumor oxygen levels before and after treatment with radiation therapy. Changes in tumor volume were monitored. In a subset of studies, CD8-positive cells were depleted and the experiments were repeated. Histologic analyses of the tumor tissues were performed to quantify the concentration of infiltrating immune cells. Daily intratumoral injections of oxygen-filled microparticles significantly retarded primary and secondary tumor growth, boosted infiltration of cytotoxic T cells, and improved overall survival when used as an adjuvant to radiation therapy. The findings also demonstrated that efficacy requires both radiation and oxygen, suggesting that they act synergistically to enhance in situ vaccination and systemic antitumor immune responses. This study demonstrated the potential advantages of intratumoral injections of a liquid oxygen solution as a strategy to boost radiation-induced abscopal effects, and the findings warrant future efforts toward clinical translation of the injectable liquid oxygen solution.