RAG2 and severe combined immunodeficiency: Still, benefits from the development of transcription activator-like effector nuclease (TALENs) and CRISPR/Cas9 technology, there is some progress in immunodeficiency big mammals, which could be candidates in future preclinical studies [42], such as RAG 1- and 2-deficient rabbits [43], X-linked severe combined immunodeficiency (X-SCID) rabbits [44], RAG2 biallelic KO pig [45], and IL2Rγ KO pigs [46].