Generation of a Severe Hemophilia A Humanized Mouse Model Capable of Inducing an Anti-FVIII Immune Response

Factor VIII (FVIII) replacement therapy induces anti-FVIII neutralizing antibodies in approximately 30% of patients with severe hemophilia A (HA). Owing to the lack of experimental systems that allow for the study of human anti-FVIII immune responses, the mechanisms underlying replacement therapy-induced anti-FVIII antibodies in HA patients remain largely unknown. Therefore, experimental systems that enable the study of human anti-FVIII immune responses are needed.We generated severe immunodeficient NOD-scid IL-2Rnull; FVIIInull mice (NOG HA) that can serve as hosts for human cord blood (hCB) transplantation and established a HA mouse with a humanized immune system to induce the anti-FVIII responses in human immune cells <i>in vivo</i>.The proportions of immune cell subsets (CD8+ T cells, CD4+ T cells, CD19+ B cells, CD33+ macrophages, and CD56+ natural killer (NK) cells) in the bone marrow, spleen, and peripheral blood were similar between NOG HA and NOG mice 4 months after hCB transplantation. The hCB-engrafted NOG HA mice retained HA severity. To activate the anti-FVIII immune response in hCB-engrafted NOG HA mice, we administered recombinant (r)FVIII plus lipopolysaccharide (LPS) once a week for 3 months. We detected both anti-FVIII IgM and IgG in the plasma of hCB-engrafted NOG HA mice after treatment with 12 doses of rFVIII and LPS. Taken together, our humanized mice with HA maintained a severe phenotype and generated human anti-FVIII IgG antibodies <i>in vivo</i>, thus representing a valuable model for studying human anti-FVIII immune responses.