To provide an immunomodulation composition which has a regulatory T-cell differentiation-inhibiting action and is useful as an immune derepression or immunostimulation composition.SOLUTION: A regulatory T-cell differentiation inhibitor and an immunomodulation composition comprise, as an active ingredient, the compound represented by the formula (I) in the figure, a salt thereof, or a solvate of them.SELECTED DRAWING: None【課題】制御性Ｔ細胞分化抑制作用を有し、免疫抑制解除または免疫賦活化用組成物として有用な免疫調節用組成物を提供する。【解決手段】下式（Ｉ）で示される化合物、その塩またはそれらの溶媒和物を有効成分とする制御性Ｔ細胞分化抑制剤、及び免疫調節用組成物：【化１】【選択図】なし
