A Mn ²⁺ -crosslinked dual-adjuvant hydrogel for spatiotemporal immune activation in lung cancer therapy

Lung cancer remains one of the most lethal malignancies worldwide. Despite recent advances, current immunotherapies are often limited by the immunosuppressive tumor microenvironment and insufficient local immune activation. Herein, we report the development of an injectable dual-adjuvant hydrogel (CpG@Mn-Gel) formed by coordinating phosphate-functionalized hyaluronic acid with Mn²⁺ ions. This hydrogel enables <i>in situ</i> gelation and sustained release of both CpG oligodeoxynucleotides, Toll-like receptor 9 (TLR9) agonists, and Mn²⁺, a stimulator of the STING pathway, thereby providing spatiotemporally controlled immune activation. In a metastatic lung cancer model, CpG@Mn-Gel significantly inhibited tumor progression, reduced pulmonary metastases, and prolonged overall survival. Mechanistic studies revealed that CpG@Mn-Gel enhanced dendritic cell maturation in draining lymph nodes, promoted CD8⁺ T cell infiltration into tumor tissues, and upregulated local expression of effector cytokines including IFN-γ and TNF-α. Moreover, systemic immune memory was established, as evidenced by an increased proportion of CD44⁺CD62L^- effector memory T cells in the spleen. These results demonstrate that combining CpG and Mn²⁺ within a localized hydrogel matrix can synergistically activate antitumor immunity, offering a promising platform for lung cancer immunotherapy.