PROBLEM TO BE SOLVED: To provide antibodies useful as therapeutics for treating and/or preventing diseases associated with cells expressing claudin 18 (CLD18), including tumor-related diseases such as gastric cancer, esophageal cancer, pancreatic cancer, lung cancer, ovarian cancer, colon cancer, hepatic cancer, head-neck cancer, and cancer of the gallbladder.SOLUTION: The present invention provides an antibody having the ability of binding to CLD18 and mediating killing of and/or growth inhibition of cancer cells expressing CLD18. The present invention also provides antibodies that bind to CLD18A1 and CLD18A2 or bind to CLD18A2 but not to CLD18A1.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、胆嚢癌、及びそれらの転移などの腫瘍関連疾患を含む、クローディン18(CLD18)を発現する細胞に関連する疾患を治療及び/又は予防のための治療薬として有用な抗体の提供。【解決手段】CLD18に結合する能力を有し、CLD18を発現する癌細胞の死滅及び/又は増殖の阻害を媒介する抗体。CLD18A1及びCLD18A2に結合するか、又は、CLD18A2に結合するが、CLD18A1には結合しない抗体。【選択図】なし