The NCG-hIL15 mouse is an enhanced version of the NCG strain with a humanized IL-15 gene knock-in. IL-15 is a pleiotropic cytokine produced by various cells such as activated monocytes/macrophages, epidermal cells, and fibroblasts, exhibiting biological activity similar to IL-2. It plays a critical role in activating and supporting the proliferation and survival of T cells, B cells, and NK cells. The expression of human IL-15 in NCG-hIL15 mice improve the the function and persistence of human NK cells, making this strain especially valuable for immuno-oncology research and reconstitution of the human immune system. Additionally, NCG-hIL15 can be combined with other humanized cytokine strains to create advanced humanized models.