Graft rejection is a serious problem associated with tissue or organ transplantation (e.g., allotransplantation or xenotransplantation), performed to treat various organ failures (e.g., liver, heart, lung, kidney, or pancreas). Described are pharmaceutical compositions for suppressing, treating, or preventing graft rejection comprising a substance having an activity to modulate signal transduction mediated by AILIM, and a pharmaceutically acceptable carrier.