In order to provide a gene expression enhancer for enhancing expression of FoxP3 gene in a cell； a cell differentiation inducer for inducing differentiation of a cell into a regulatory T cell； an immunosuppressor for suppressing immunity and an agent for treating hyperimmune diseases based on the abovementioned actions； an inhibitor of enhancement of gene expression for inhibiting enhancement of expression of FoxP3 gene in a cell； an inhibitor of induction of cell differentiation for inhibiting induction of differentiation of a cell into a regulatory T cell； a reducer of immunosuppression for reducing immunosuppression, a stimulator of tumor immunity and an antitumor agent based on the abovementioned actions； and the like, for example, an agent containing at least one of a cell expressing Snail protein, MCP1 protein, FSTL1 protein, membrane IL-13Ra2 protein or secretory IL-13Ra2 protein, or MCP1 protein, FSTL1 protein or secretory IL-13Ra2 protein, is used as a gene expression enhancer for FoxP3, an inducer of regulatory T cell differentiation, an immunosuppressor or an agent for treating hyperimmune diseases； and an agent containing an anti-MCP1 antibody, an anti-FSTL1 antibody or an anti-IL-13Ra2 antibody is used as an inhibitor of enhancement of FoxP3 gene expression, a reducer of immunosuppression, a stimulator of tumor immunity, an antitumor agent, or the like.
