Multifunctional nanocomposite hydrogel coordinates immunogenic cell death and active species scavenging for effective preoperative in situ vaccination against breast cancer recurrence

In situ immunomodulation prior to surgery represents a promising strategy to elicit potent antitumor immunity and prevent postoperative recurrence, yet it faces the fundamental challenge of balancing sufficient immunostimulation against local hyperinflammation. To address this, we developed a multifunctional nanocomposite hydrogel that synchronizes immunogenic cell death (ICD) induction with multi-target active species regulation. Upon peritumoral co-injection of gallic acid-grafted chitosan (CS-GA), N-aminoethyl-N'-benzoylthiourea-functionalized oxidized hyaluronic acid (OHA-BTU), and allomelanin nanoparticles (pDHN NPs), near-infrared irradiation triggers photothermal ablation and generates reactive oxygen species (ROS), leading to tumor ICD and in situ antigen release. Simultaneously, OHA-BTU sequesters extracellular Cu²⁺ released from ROS-disrupted copper-associated proteins, while pDHN NPs capture cfDNA liberated from damaged nuclei and mitochondria (capture capacity = 258.4 μg mg⁻¹), thereby suppressing M1 macrophage hyperactivation and pro-inflammatory cytokine secretion. The catechol groups in CS-GA further scavenge extracellular ROS via redox cycling. This coordinated modulation of active species alleviates local hyperinflammation while preserving the viability and function of tumor-infiltrating T cells. After 14 days of treatment, significant tumor downstaging was achieved, with a volume reduction rate > 60.2% and a mitotic index of 4.2 per high-power field. In a contralateral rechallenge model, elevated infiltration of CD8⁺ T cells and CD8⁺ effector memory T cells correlated with 72.5% recurrence inhibition and 86.8% metastasis suppression. By integrating in situ vaccination with precise regulation of the immunoinflammatory microenvironment, this hydrogel-based platform functions as an effective preoperative in situ therapeutic vaccine, eliciting robust immune memory that prevents postsurgical recurrence and metastasis in breast cancer. STATEMENT OF SIGNIFICANCE: In situ immunomodulation prior to surgery faces the fundamental challenge of balancing sufficient immunostimulation against local hyperinflammation. Insufficient release diminishes immune stimulation, excessive release triggers local hyperinflammation and negative feedback inhibition of adaptive immunity. To address this, allomelanin nanoparticles were employed to induce photothermal immunogenic cell death under NIR irradiation and capture extracellular cell-free DNA to block TLR-9-mediated pro-inflammatory signaling in macrophages. N-aminoethyl-N'-benzoylthiourea-functionalized oxidized hyaluronic acid captures extracellular Cu²⁺ to inhibit CD44-accelerated metal uptake and subsequent pro-inflammatory metabolic reprogramming. Gallic acid-grafted chitosan scavenges extracellular reactive oxygen species via catechol redox reactions. These components synergistically suppress excessive local inflammation, prevent T-cell exhaustion, and elicit robust immune memory that prevents postsurgical recurrence and metastasis in breast cancer.