The present invention provides a method for the prophylaxis or treatment of systemic lupus erythematosus and/or lupus nephritis in a patient in need thereof, which comprises administering an effective amount of [(IR) -1- ({[(2,5-dichloroben - zoyl) amino] acetyl} amino) -3-methylbutyl] boronic acid or a citric acid ester thereof, or a pharmaceutically acceptable salt thereof S to the patient.