Development of a humanized mouse model to analyze antibodies specific for human leukocyte antigen (HLA)

In organ transplantation, human leukocyte antigen (HLA)-mismatch grafts not only induce the activation of cellular mediated immune response but also the development of chronic antibody-mediated rejection due to the donor-specific anti-HLA antibody (DSA) produced by B cells and plasma cells interacting with the graft endothelium. Significant improvement in long-term survival after transplantation can be expected if antibody-mediated rejection due to the DSA can be overcome. However, the mechanism of producing or controlling the DSA remains to be elucidated. In recent decades, "humanized mouse model" have been widely used for the basic research of human immune systems, but a humanized mouse model to analyze the mechanism of DSA production has not been established yet. Thus, we aimed to create a humanized mouse using a severe immunodeficiency mouse (NSG mouse) administered with human peripheral blood mononuclear cells (PBMCs). Initially, we detected very low level of human total-IgG and no anti-HLA antibodies (Abs) in these mice. The responder PBMCs with antibody-producing B cell activating factors added or regulatory T cells depleted were subsequently co-cultured with the irradiated stimulator PBMCs in vitro, and these whole cells were administered into naive NSG mice. The humanized model with sufficient human total-IgG and anti-HLA antibody production was consequently established. Interestingly, in all these mouse models, allo-specific anti-HLA Abs production was prominently suppressed, whereas non-allo-specific anti-HLA Abs were sufficiently detectable. Therefore, this novel humanized mouse model might be useful for analyzing the mechanism of anti-allogeneic human B cell tolerance induction.