PROBLEM TO BE SOLVED: To provide a bispecific antibody that specifically binds a T-cell activating antigen and a tumor antigen, a method for producing the antibody, a pharmaceutical composition comprising the antibody, and a method of use thereof.SOLUTION: According to the present invention, there is provided a bispecific antibody that specifically binds a T-cell activating antigen and a tumor antigen (TA), comprising a first Fab fragment and a second Fab fragment, wherein either the variable regions or the constant regions of the second Fab heavy and light chain are exchanged, and the bispecific antibody does not comprise a Fc domain. In the bispecific antibody, preferably, the first Fab fragment comprises one or more antigen binding sites specific for a tumor antigen, and the second Fab fragment comprises one or more antigen binding sites specific for a T-cell activating antigen. In the bispecific antibody, preferably, the T-cell activating antigen is a CD3 T-cell co-receptor (CD3) antigen, and the N-terminus of the second Fab fragment is connected to the C-terminus of the first Fab fragment.SELECTED DRAWING: None【課題】Ｔ細胞活性化抗原および腫瘍抗原に特異的に結合する二重特異性抗体、抗体の生産方法、抗体を含む薬学的組成物、及びその使用方法の提供。【解決手段】第一のＦａｂ断片及び第二のＦａｂ断片を含む、Ｔ細胞活性化抗原及び腫瘍抗原（ＴＡ）に特異的に結合する二重特異性抗体であって、第二のＦａｂの重鎖及び軽鎖の可変領域又は定常領域のどちらかが交換され、二重特異性抗体がＦｃドメインを含まない二重特異性抗体。第一のＦａｂ断片が、腫瘍抗原に特異的な一つ以上の抗原結合部位を含み、第二のＦａｂ断片が、Ｔ細胞活性化抗原に特異的な一つ以上の抗原結合部位を含むことが、好ましい、二重特異性抗体。Ｔ細胞活性化抗原がＣＤ３Ｔ細胞共受容体（ＣＤ３）抗原であり、第二のＦａｂ断片のＮ末端が第一のＦａｂ断片のＣ末端に連結されていることが望ましい、二重特異性抗体。【選択図】なし
