PROBLEM TO BE SOLVED: To provide an antibody or a fragment thereof which binds to CD3ε constituting a complex of CD3 with a novel human T cell antigen receptor.SOLUTION: The invention provides an antibody or a fragment thereof which binds to CD3ε constituting the complex of CD3 with a human T cell antigen receptor, and which induces the decreased expression of a TCR-CD3 complex, and additionally induces neither a T cell proliferation response nor activation (production of IL-2). The antibody or a fragment thereof may be advantageously used as an immunosuppressive agent at the time of an organ transplantation or as a therapeutic agent of autoimmune disease, because it has a character to induce unresponsiveness also to a naive T cell and a primed T cell with or without an antigenic sensitization.SELECTED DRAWING: Figure 9【課題】新規なヒトＴ細胞の抗原受容体とＣＤ３の複合体を構成するＣＤ３εに結合する抗体又はそのフラグメントを提供する。【解決手段】ＴＣＲ－ＣＤ３複合体の発現低下を誘導し、しかも、Ｔ細胞の増殖反応も活性化（ＩＬ－２の産生）も誘導しない、ヒトＴ細胞の抗原受容体とＣＤ３の複合体を構成するＣＤ３εに結合する抗体又はそのフラグメント。さらに、抗原の感作の有無にかかわらず、すなわちナイーブＴ細胞に対しても、感作Ｔ細胞に対しても不応答性を誘導する性質を有し、臓器移植時の免疫抑制剤として或いは自己免疫疾患の治療剤として有利に使用し得る、前記抗体又はそのフラグメント。【選択図】図９
