Photothermal therapy synergizes with CD47 blockade by inducing calreticulin exposure and remodeling the tumor extracellular matrix in oral squamous cell carcinoma.

BACKGROUND: Oral squamous cell carcinoma (OSCC) overexpresses CD47, enabling immune evasion via a "don't eat me" signal to macrophages. Although CD47 blockade shows promise, its efficacy is limited due to a lack of "eat me" signal and contact between macrophages and tumor cells. OBJECTIVES: This study aimed to evaluate the synergistic anti-tumor effect of combining photothermal therapy (PTT) with CD47 blockade in OSCC and elucidate the underlying mechanisms. METHODS: In vitro phagocytosis was assessed by flow cytometry. In vivo anti-tumor efficacy was measured by tumor growth inhibition. Mechanistic studies included detection of immunogenic cell death (ICD) markers (ATP, HMGB1, calreticulin (CRT)), confocal microscopy for CRT-macrophage co-localization, analysis of ECM component expression, and immunofluorescence for macrophage infiltration. RESULTS: The combination of PTT and CD47 blockade significantly enhanced macrophage phagocytosis in vitro and strongly inhibited tumor growth in vivo. PTT induced ICD, as evidenced by the release of ATP and HMGB1, and the exposure of CRT on the cell membrane. Confocal microscopy confirmed co-localization of CRT-expressing tumor cells with macrophages. Furthermore, PTT down-regulated ECM components at transcriptional and protein levels, which correlated with increased macrophage infiltration into tumors. CONCLUSIONS: PTT synergizes with CD47 blockade primarily by inducing CRT-dependent pro-phagocytic signaling to provide the "eat me" signal. In parallel, PTT downregulates ECM components, enabling the essential "come near me" process that facilitates macrophage infiltration into tumors. This dual approach significantly improves the macrophage based anti-tumor efficacy of CD47 blockade.