A Transient Immunostimulatory Niche Synergizes Adoptive and Endogenous Immunity for Enhanced Tumor Control.

Adoptive Cell Therapy (ACT) has achieved curative responses in hematological malignancies, yet its translation to solid tumors remains limited by manufacturing bottlenecks, systemic toxicities, and poor T-cell infiltration and persistence within the immunosuppressive tumor microenvironment (TME). Here, we report the development and mechanism of ACTIVATE (Adoptive Cell Therapy and Immunostimulatory Vehicle for Anti-Tumor Efficacy), which leverages an injectable hydrogel depot technology that forms a transient inflammatory niche for localized co-delivery of adoptive T cells and native cytokines. By tuning cytokine identity, ACTIVATE enables precise modulation of T-cell expansion, effector function, and interaction with endogenous immune networks. We found that enhancing T-cell proliferation alone is insufficient to drive robust tumor control; instead, coordinated engagement of both adoptive and endogenous immune responses is critical for durable anti-tumor efficacy. In vivo , this orchestration via ACTIVATE led to enhanced infiltration and cytotoxicity of both adoptive and host-derived immune effectors, while driving robust recruitment and activation of T cells, B cells, dendritic cells, and macrophages in the tumor-draining lymph nodes. This local immune activation can further reshape the TME, promoting antigen presentation and suppressing immunoregulatory populations, thus enhancing anti-tumor efficacy in a murine melanoma model. These findings establish ACTIVATE as a modular platform for orchestrating coordinated immune responses to improve ACT outcomes in solid tumors.