A method for potentiating the antitumor immunity in an animal by administering REIC/Dkk-3, or a therapeutic agent for malignant mesothelioma containing REIC/Dkk-3, or a vector containing the DNA as an active ingredient； wherein the DNA consists of the nucleotide sequence shown in SEQ ID NO: 1； or (b) a DNA hybridizing under stringent conditions to the DNA consisting of a nucleotide sequence complementary to the nucleotide sequence shown in SEQ ID NO: 1 and encoding a protein having apoptosis-inducing activity and interleukin (IL-7) production-accelerating activity in cells.
