PROBLEM TO BE SOLVED: To provide a method for producing a mammalian organ having a complicated cell structure composed of plural kinds of cells such as kidney, pancreas, hair and thymus in a living body of an animal, particularly a non-human animal. SOLUTION: The target organ derived from a different host mammal different from the human host mammal is produced in the living body of the non-human host mammal having an abnormality in which the development of the target organ does not occur at the developmental stage. A method comprising: a) preparing cells derived from the heterologous host mammal； b) transplanting the cells into blastocyst stage fertilized eggs of the non-human host mammal； c) the fertilization. A method for producing a target organ, comprising the steps of: developing an egg in the mother's womb of the non-human host mammal to obtain a litter； and d) obtaining the target organ from the litter. [Selection diagram] None【課題】腎臓、すい臓、毛および胸腺などの複数種の細胞からなる複雑な細胞構成を有する哺乳動物の臓器を、動物、特に非ヒト動物の生体中で作製する方法の提供。【解決手段】発生段階において目的臓器の発生が生じない異常を有する非ヒト宿主哺乳動物の生体内において、該ヒト宿主哺乳動物とは異なる個体の異個体宿主哺乳動物由来の該目的臓器を製造する方法であって、ａ）該異個体宿主哺乳動物由来の細胞を調製する工程；ｂ）該非ヒト宿主哺乳動物の胚盤胞期の受精卵中に、該細胞を移植する工程；ｃ）該受精卵を該非ヒト宿主哺乳動物の母胎中で発生させて、産仔を得る工程；およびｄ）該産仔個体から、該目的臓器を取得する工程を含む、目的臓器を製造する方法。【選択図】なし
