Vaccination may cure cancer patients by inducing tumor-specific immune responses. Radiotherapy is an appealing strategy to generate cancer vaccines in situ
thus far, however, only modest and short-lived immune responses are achieved. We here show that radiation combined with co-activating STING-TLR9 can generate powerful in situ cancer vaccines. Notably, radiation at a dose of 12Gy is found to be optimal for boosting tumor cell immunogenicity, and STING-TLR9 co-stimulation by a dual immune activation nano-agonist overrides key immunosuppressive effects associated with radiotherapy. Local radiotherapy combined with the dual immune activation nano-agonists elicits strong systemic anti-tumor immune responses, resulting in complete regression of tumors and metastases in multiple syngeneic murine tumor models. This work introduces a novel and highly potent cancer immunotherapeutic strategy that holds promise for the personalized treatment of intractable cancers.