NKG mice are a type of severe immunodeficient mouse developed by Cyagen by deleting the Il2rg gene from the NOD-Scid strain. This strain lacks mature T, B, and NK cells, exhibits reduced complement activity, and weak macrophage phagocytosis of human cells. As a result, NKG mice can efficiently engraft human hematopoietic stem cells (HSC), peripheral blood mononuclear cells (PBMC), patient-derived xenografts (PDX), or adult stem cells and tissues.

In immunology research, direct studies on mice may not fully represent the human immune system due to physiological and immune system differences. However, by transplanting human peripheral blood mononuclear cells (PBMCs) or hematopoietic stem cells (HSCs) into immunodeficient mice, we can partially or completely replace the mouse immune system with a human counterpart. This approach enables in vivo simulation of human immune system function, providing an effective model for studying human immunity. However, in actual human-mouse xenotransplantation, due to the lack of specific human cytokines and supportive stromal cells in mice, transplantation using conventional immunodeficient mice is likely to result in variations in immune reconstitution efficiency. Modifying immunodeficient mice via gene editing technology to establish a humanized immune microenvironment in mice and promote the functional maturation of human-derived cells is a universal strategy for improving the efficiency of immune reconstitution in xenotransplantation.

The THPO gene (Thrombopoietin) provides instructions for creating the protein thrombopoietin, a crucial humoral growth factor for hematopoiesis (the formation of blood cellular components). The gene's expression is most pronounced in the liver and kidneys, though it also occurs in other tissues, including the bone marrow, spleen, and striated muscle ^[1]. Thrombopoietin is a lineage-specific cytokine that functions as the primary physiological regulator of platelet production. It binds to the c-MPL receptor on the surface of megakaryocytes and hematopoietic stem cells, promoting the proliferation and maturation of megakaryocytes—the bone marrow cells that produce platelets. Mutations in the THPO gene are associated with various conditions, including hereditary thrombocythemia (a high platelet count) and congenital amegakaryocytic thrombocytopenia (a severe reduction in platelets at birth) ^[2]. These conditions arise from either overproduction of thrombopoietin or, in some cases, a loss of function that impairs its ability to regulate platelet levels. Humanizing the mouse's thrombopoietin (THPO) gene effectively solves the species compatibility issues between human hematopoietic stem cells and mouse growth factors. This modification enables the long-term maintenance and self-renewal of human hematopoietic stem cells in mice, allowing for the successful reconstruction of the human immune system even in non-irradiated mice, and promotes the multi-lineage differentiation of hematopoietic cells ^[3-4].

NKG-huTHPO mouse is a model constructed via gene editing technology, in which the mouse Thpo endogenous extracellular domain is replaced with the human THPO extracellular domain . The murine signal peptide is kept. Compared to NKG mice, NKG-huTHPO mice express human thrombopoietin in HSC transplantation studies, effectively promoting the long-term maintenance and self-renewal of HSCs in vivo, and directly supporting the differentiation of HSCs into various human blood cell types. NKG-huTHPO mice without irradiation treatment can also well reconstitute the human immune system and support HSC multi-lineage differentiation and human megakaryocyte development ^[3-4]. This model provides an excellent experimental platform for studying hematopoietic diseases with limited HSC function (such as aplastic anemia) and testing new THPO-targeted drugs in more clinically relevant models.