NKG mice are a kind of severe immunodeficient mice generated by Cyagen by deleting the Il2rg gene from NOD-Scid genetic background mice. NKG mice exhibit deficiency of mature T cells, B cells, and functional NK cells, reduced complement activity, and weak phagocytosis of human-derived cells by macrophages, which are well suited for transplantation of human hematopoietic stem cells (HSC), peripheral blood mononuclear cells (PBMC), adult stem cells and tissues, and patient-derived xenograft (PDX).