This technology includes a straightforward and versatile nanotechnology-based approach for in situ therapeutic vaccination that exploits a primary tumor as a vaccine depot to initiate robust personalized anti-tumor immune responses. In the method, diselenide-bridged hollow mesoporous organosilica nanocapsules (HMSeN) are prepared for immobilization of Annexin A5, which can block phosphatidylserine (PS) exposure on dying tumor cells and thereby converts immunosuppressive apoptosis into immunostimulatory secondary necrosis, which simultaneously renders the primary tumor immunogenic and inflames the tumor microenvironment.