This invention relates to the use of a pharmaceutically acceptable agent being able to acidify the cell cytoplasm, for the manufacture of a pharmaceutical composition useful for causing immunosuppression in a person or an animal, wherein an effective amount of said agent is administered in an essentially non-dissociated form to the person or animal, and wherein the agent is admixed with a carrier adjusting the pH of the composition to the pH range 6.1 to 7.0. The invention also concerns a pharmaceutical composition.