The present invention relates to new medical use of (tetrahydropyran-4-yl)-[2-phenyl-5-(1, 1-dioxo-thiomorpholine-4-yl)methyl-1H-indol-7-yl]amine, and more particularly, to a pharmaceutical composition containing the compound as an active ingredient, which is used for inhibiting an immune response, and/or for inducing differentiation into regulator T cells from undifferentiated T cells and/or promoting proliferation of regulator T cells.