The present invention relates in particular to a cathepsin S inhibitor for use in a method for reducing or preventing the formation of anti-drug antibodies (ADA) against a therapeutic agent in a subject who is receiving a treatment with said therapeutic agent.本發明特別關於一種組織蛋白酶(cathepsin)S抑制劑,其用於為正接受治療劑治療之個體減少或防止形成對抗該治療劑之抗藥抗體(ADA)之方法。