Ultrasound-Activated Nanobubbles Induce Durable Systemic Antitumor Immunity

Clinical outcomes in aggressive breast cancer vary widely, in part because the tumor microenvironment is structured to exclude immune infiltration. Low antigen load, dysfunctional antigen-presenting cells, T cell exclusion and exhaustion, and a stiff extracellular matrix that physically restricts immune cell trafficking work together to form a suppressive barrier that current immunotherapies struggle to overcome. We addressed this barrier using ultrasound (US)-activated nanobubbles (NBs), a drug-free intervention based on perfluoropropane-filled nanoparticles. The size and deformable phospholipid shell enable NBs to achieve deep tumor penetration and a uniform distribution throughout the entire tumor. Upon ultrasound activation, NBs generate localized mechanical forces that restore extracellular matrix elasticity, disrupt tumor transport barriers, and drive HMGB1 release, re-engaging endogenous antitumor immunity without pharmacological agents. In a syngeneic triple-negative breast cancer model, US-NB treatment depleted immunosuppressive myeloid cells 3-fold within 3 hours, followed by a greater than 5-fold increase in the ratio of antigen-experienced to suppressive T cells at 48 hours. US-NB drives rapid infiltration of CD4 ⁺ and CD8 ⁺ T cells within 48 hours. US-NB treatment achieved an 85% cure rate in the D2A1 model; cured animals maintained durable systemic immune memory, rejecting both local and systemic tumor rechallenge. Consistent therapeutic benefit was observed in a luminal B-like mammary tumor model (E0771), supporting activity across breast cancer subtypes. These results establish US-NB mechanical immunomodulation as a drug-free therapeutic strategy capable of generating robust and durable antitumor immunity, acting through biophysical tissue properties rather than tumor-specific molecular targets.