Compounds of formula (I) are inhibitors of CD80 and useful in immunomodulation therapy: wherein R1 and R3 independently represent H; F; CI; Br; -NO2; -CN; C1-C6 alkyl optionally substituted by F or Cl; or C1-C6 alkoxy optionally substituted by F; R4 represents a carboxylic acid group (-COOH) or an ester thereof, or -C(=O)NR6R7, -NR7C(=O)R6, -NR7C(=O)OR6, -NHC(=O)NR7R6 or -NHC(=S)NR7R6 wherein R6 represents H, or a radical of formula - (Alk)m-Q wherein m is 0 or 1, Alk is an optionally substituted divalent straight or branched C1-C12 alkylene, or C2-C12 alkenylene, or C2-C12 alkynylene radical or a divalent C3-C12 carbocyclic radical, any of which radicals may contain one or more -O-, -S- or -N(R8)- links wherein R8 represents H or C1-C4 alkyl, C3-­C4 alkenyl, C3-C4 alkynyl, or C3-C6 cycloalkyl, and Q represents H; -NR9R10 wherein R9 and R10 independently represents H; C1-C4 alkyl; C3-C4 alkenyl; C3-C4 alkynyl; C3-C6 cycloalkyl; an ester group; an optionally substituted carbocyclic or heterocyclic group; or R9 and R10 form a ring when taken together with the nitrogen to which they are attached, which ring is optionally substituted; and R7 represents H or C1-C6 alkyl; or when taken together with the atom or atoms to which they are attached R6 and R7 form an optionally substituted monocyclic heterocyclic ring having 5, 6 or 7 ring atoms; and X represents a bond or a divalent radical of formula - (Z)n-(Alk)- or - (Alk)-(Z)n- ­wherein Z represents -O-, -S- or -NH-, Alk is as defined in relation to R6 and n is 0 or 1.