Synergistic strategy based on mild phototherapy and deep tumor hypoxia reversal comprehensively remodels the tumor microenvironment for improved immunotherapy

•A synergistic nanosystem was constructed to enhance anti-tumor immunotherapy.•A positive feedback loop was created for synergistic therapeutic effects.•The nanosystem sensitized PDT therapy and achieved reversal of deep hypoxia.•The nanosystem strengthened the activation, infiltration and efficacy of T cells.•Combination therapy inhibited primary, distant, and metastatic tumor growth.