Xanthene derivatives represented by the general formula:
wherein R 1 is a carboxyl group which may be esterified or amidated; R 2 is a hydrogen atom, a hydroxyl group, or a hydrocarbon group which may be substituted; R 3 and R 4 are the same or different and are a hydroxyl group which may be substituted; R 5 and R 6 are a hydrogen atom or a halogen atom; R 7 is a hydrogen atom, a nitro group, a halogen atom, a hydrocarbon group which may be substituted, a heterocyclic group which may be substituted, or an acyl group which may be substituted; n is an integer of 0 to 2; and Y is an oxygen atom or two hydrogen atoms; and when n is 0, R 2 may be a group represented by the formula:
wherein the symbols have the same meanings as defined above, or a salt thereof inhibit a binding of B7-1 to CD28, prevent the B7-1-dependent activation of T cells and inhibit IL-2 production from T cells, thus being used as an immunomodulator such as a graft rejection inhibitor or a pharmaceutical composition for therapeutic treatment of allergy, rheumatoid arthritis, autoimmune disease, nephritis, diabetes mellitus and so on.