Localized chemo-immunotherapy for HNSCC via CpG-synergized doxorubicin release from injectable TPGS/Na₂CO₃ hydrogel remodeling tumor immunity

Background Patients with locally advanced head and neck squamous cell carcinoma (HNSCC) exhibit poor survival due to tumor microenvironment (TME) barriers and systemic toxicity of chemo-immunotherapy associated with chemo-immunotherapy. Methods An injectable thermoresponsive hydrogel was engineered by crosslinking D-α-tocopheryl polyethylene glycol succinate (TPGS) with Na₂CO₃ (15 % w/v TPGS: 9 % w/v Na₂CO₃). This platform co-encapsulated doxorubicin-loaded nanoparticles (DOX NP) synthesized via PEI-cis-aconitic acid conjugation and CpG-loaded adjuvant nanoparticles (CpG NP) prepared through genipin-mediated PEI crosslinking. The hydrogel exhibited rapid temperature-triggered gelation, shear-thinning injectability, and a macroporous architecture that enabled dual drug retention and immune cell infiltration. Results In vitro , the hydrogel provided the sustained release of DOX NP with pH-responsive acceleration in acidic TME. In vivo , localized delivery of Gel-DOX NP-CpG NP significantly suppressed tumor growth ( p  < 0.05) and enhanced cytotoxic CD8 + T-cell infiltration in TME (3.1-fold) and spleens (2.4-fold). RNA sequencing revealed 88 immune-related differentially expressed genes, including downregulated immunosuppressors and enriched cytokine pathways. Conclusion This TPGS/Na₂CO₃ hydrogel platform coordinates chemotherapy-induced immunogenic cell death (DOX NP) with CpG-driven innate immunity, overcoming TME barriers to enhance localized and systemic anti-tumor responses in HNSCC.