The present invention relates to a method for screening at least one CD3 gene selected from the group consisting of endogenous CD3, CD3 and CD3 functionally in the genome and comprising at least one member selected from the group consisting of human CD3, CD3 and CD3 Human genetically modified non-human animal functionally expressing the human CD3 gene. The genetically modified non-human animal of the present invention differentiates and produces mature T cells, and immunocompetent cells including T cells can exert their functions. The genetically modified nonhuman animal of the present invention enables efficient evaluation and screening in the development of therapeutic methods and therapeutic drugs using a targeted drug via human CD3.本発明は、内因性のCD3ε、CD3δ及びCD3γからなる群より選ばれる少なくとも1種以上のCD3遺伝子がゲノム上で機能的に欠損し、ヒトCD3ε、CD3δ及びCD3γからなる群より選ばれる少なくとも1種以上のヒトCD3遺伝子を機能的に発現する遺伝子改変非ヒト動物を提供する。本発明の遺伝子改変非ヒト動物は成熟T細胞を分化・生成し、T細胞を含む免疫担当細胞が機能を発揮できる。本発明の遺伝子改変非ヒト動物は、ヒトCD3を介した標的医薬を用いる治療法や治療薬の開発において効率的な評価やスクリーニングを可能とする。
