Focused Ultrasound Thermal Ablation and CD40 Agonism Reprograms Breast Tumor Immunity to Drive Regression and Memory

Focused ultrasound thermal ablation (T-FUS) is a clinically accessible, non-invasive modality capable of inducing rapid tumor cytoreduction while mobilizing early immunologic danger signals. However, its capacity to synergize with potent co-stimulatory immunotherapies in breast cancer (BC) remains undefined. Here, we demonstrate that subtotal T-FUS cooperates with CD40 agonism to elicit durable, T cell-dependent tumor control across four immunologically and hormonally distinct murine BC models. Partial thermal ablation triggered canonical immunogenic cell-death signatures and acute remodeling of intratumoral myeloid populations, while expanding circulating CD4^⁺ and CD8^⁺ T cells. When layered onto this immunogenic milieu, αCD40 markedly constrained tumor outgrowth, yielding significant reductions in tumor burden across all models and complete tumor eradication in 33% of E0771 tumors, with additional complete responses in BRPKP110 and EMT6. Efficacy required both CD4^⁺ and CD8^⁺ T cells, and complete responders mounted robust systemic immunity, rejecting contralateral tumor rechallenge with 100% protection and displaying persistent effector-memory T cell activation. Together, these findings establish T-FUS as an immune-potentiating partner for CD40 agonism, capable of driving durable, robust BC regression and immunological memory. This work positions T-FUS+CD40 agonism as a clinically scalable, in situ vaccination-like strategy with potential to benefit breast cancers, including luminal subtypes, that remain largely refractory to immune checkpoint blockade.