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 [ (1R) -1- ( { [ (2, 5- dichlorobenzoyl) amino] acetyl}amino) -3-methylbutyl] boronic acid or a citric acid ester thereof, or a pharmaceutically acceptable salt thereof to the patient.