High-Density Wild-Type IL-2 Nanoparticles Preferentially Enhance CD8⁺ T-Cell Expansion and Reprogram the Tumor Microenvironment

Low response rates to immune checkpoint inhibitors (ICIs) in solid tumors are often driven by insufficient tumor-infiltrating CD8⁺ T cells and immunosuppressive tumor microenvironment (TME). Although interleukin-2 (IL-2) potently expands and activates CD8⁺ T cells, its clinical use is limited by rapid clearance, dose-limiting toxicity, and regulatory T cell (T _reg ) stimulation. Engineered IL-2 variants have not yet achieved meaningful clinical efficacy. Here, polymer-modified mesoporous silica nanoparticles displaying dense, unmodified wild-type IL-2 on their surface (IL2-NP) are developed, conferring proteolytic stability and tumor retention. IL2-NP enables avidity-mediated CD8⁺ T cell binding and enhances proliferation and effector function without increased T _reg binding or proliferation.

Intratumoral IL2-NP expands CD8⁺ T cells, increases CD8⁺/T _reg ratios, and reprograms TME through dendritic cell activation and M1-like macrophage polarization. IL2-NP induces regression of both treated and untreated distant colorectal tumors in a CD8⁺ T cell-dependent manner. IL2-NP synergizes with ICIs and leads to complete tumor regression and immunological memory that protect against rechallenge. Treatment is well tolerated, with strong efficacy also observed in triple-negative breast and metastatic ovarian cancer models.

Overall, intratumoral IL2-NP elicits robust systemic antitumor immunity, offering a promising strategy to enhance ICIs, cancer vaccines, and adoptive T-cell therapies.