PROBLEM TO BE SOLVED: To provide antibodies useful as therapeutic agents for treating and/or preventing diseases associated with cells expressing claudin (CLD) 18, including tumor-related diseases such as gastric cancer, esophageal cancer, pancreatic cancer, lung cancer, ovarian cancer, colon cancer, hepatic cancer, head-neck cancer, and gallbladder cancer.SOLUTION: An antibody is obtained by the method comprising immunizing an animal with a protein or peptide having a specific amino acid sequence, or an immunogenic fragment thereof, or a nucleic acid or host cell expressing the protein or peptide, or immunogenic fragment thereof. An antibody has the binding ability to CLD18 and mediates the death of cells expressing CLD18. An antibody binds to CLD18A1 and CLD18A2 or binds to CLD18A or binds to CLD18A and does not bind to CLD18B.SELECTED DRAWING: None【課題】胃癌、食道癌、膵癌、肺癌、卵巣癌、結腸癌、肝癌、頭頸部癌、および胆嚢の癌などの腫瘍関連疾患を含む、クローディン（ＣＬＤ）１８を発現する細胞に関連する疾患を治療する及び／又は予防するための治療薬として有用な抗体の提供。【解決手段】特定のアミノ酸配列を有するタンパク質又はペプチド、又はその免疫原性フラグメント、又はタンパク質、ペプチド、免疫原性フラグメントを発現する核酸又は宿主細胞で動物を免疫する工程を含む方法によって得られ得る抗体。ＣＬＤ１８に結合する能力を有し、ＣＬＤ１８を発現する細胞の死を媒介する抗体。ＣＬＤ１８Ａ１及びＣＬＤ１８Ａ２に結合する又はＣＬＤ１８Ａに結合するか又はＣＬＤ１８Ａに結合し、ＣＬＤ１８Ｂには結合しない、抗体。【選択図】なし
