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 B2M gene encodes beta-2 microglobulin, a serum protein on the surface of nearly all nucleated cells along with the major histocompatibility complex (MHC) class I heavy chain. It is an essential component for transporting MHC class I proteins to the cell surface. Human leukocyte antigen (HLA), or the major histocompatibility complex (MHC), is a group of protein molecules on the surface of antigen-presenting cells responsible for antigen presentation. HLA mainly includes HLA class I, HLA class II, and HLA class III. HLA class I molecules (such as HLA-A, HLA-B, and HLA-C) primarily present antigens to CD8+ T cells and play a central role in the immune system. Through antigen presentation by HLA class I, the body can effectively recognize abnormal peptides, triggering targeted immune responses for immune clearance. Studies have shown that peptide vaccines composed of covalently linked minimal cytotoxic T lymphocyte (CTL) and T helper cell (TH) epitopes have significant effects in inducing cellular immune responses ^[1]. Due to species differences between mice and humans, and the varying ability of different HLA molecule subtypes to present different antigens, mouse-derived HLA cannot effectively simulate the immune response of human HLA subtypes. Therefore, constructing mice carrying human HLA genes helps to advance the study of HLA-restricted cytotoxic responses, such as identifying immunodominant HLA-restricted CTL epitopes and optimizing DNA vaccine constructs for human use ^[2-3].

NKG-H11-hB2M&HLA-A2.1 mouse is a model constructed via gene editing technology, in which the H2-K1 chimeric HLA-A2.1 gene is knocked into the H11 locus of mice on the NKG strain background. Compared with NKG mice, NKG-H11-hB2M&HLA-A2.1 mice generate functional human T cell subsets with HLA-restricted immune responses after hematopoietic stem cell (HSC) transplantation. Human cytotoxic T lymphocytes (CTLs) developed in immunologically reconstituted mice recognize pathogens in an HLA-restricted manner and exert HLA-restricted cytotoxicity against infected human B cells ^[4]. This model provides an ideal platform for investigating human immune responses to pathogens, HLA-restricted cytotoxic responses, and related research areas.