The present invention relates to an immunosuppressive agent which comprises at least one compound selected from the compounds of formula ##STR1## wherein R represents a hydrogen atom or an acyl, Y represents carbonyl or hydroxymethylene and represents a single bond or a double bond and their lactones, in an effective amount and a pharmaceutically acceptable carrier; a method of prophylaxis and therapy for suppressing rejection or autoimmune diseases which comprises administering the above-mentioned compound or its lactone in an effective amount; and a novel compound of formula ##STR2## or its lactone.