We report that antibodies can be spontaneously loaded in functionalized mesoporous silica (FMS) with superhigh density (0.4-0.8 mg of antibody/mg of FMS) due to their comprehensive noncovalent interaction. The superhigh loading density and noncovalent interaction between FMS and antibodies allow long-lasting local release of the immunoregulatory molecules from FMS under physiological conditions. Preliminary data indicate that FMS-anti-CTLA4 antibody injected directly into a mouse melanoma induces much greater and extended inhibition of tumor growth than the antibody given systemically. Our findings open up a novel approach for local delivery of therapeutically active proteins to tumors and, potentially, other diseases.