The present invention is directed to methods of suppressing an immune response in a subject in need thereof comprising administering a therapeutically effective amount of a compound having the following formula: 3-phenyl-4,5-dihydro-5-isoxazoleacetic acid to the subject in need thereof, wherein R1-5 represents from one to five substituents independently selected from hydrogen, nitro, cyano, C1-C3-alkyl, halogen, carboxy, amino, trifluoromethyl, hydroxy, C1-C3-alkoxy groups, X is hydrogen, halo, N3, SH, =O, =CH2, an aromatic, preferably phenyl, ring optionally substituted by R1-5 groups as defined above, amino, mono- or disubstituted amino groups wherein the substituents are selected from C1-C4 alkyl, phenyl or benzyl groups optionally substituted by R1-5 groups as defined above Y is hydrogen, allyl C1-C4, amino, or a group of formula --(CH2)0-1A wherein A is an aromatic, preferably phenyl, ring optionally substituted by R1-5 groups as defined above with the proviso that when X and Y are hydrogen, R1-5 cannot represent a 4-hydroxy or 4-alkoxy groups.