Humanized severe combined immunodeficient mice as a potential model for the study of tolerance to factor VIII

A Severe Combined Immunodeficient (SCID) mouse model has been established to evaluate experimental conditions leading to the production of factor VIII (FVIII) autoantibodies. To this end, we humanized 10 groups of 7 mice with peripheral blood mononuclear cells of 10 unrelated healthy blood donors (15 x 10(6) cells/mouse). Mice were injected with saline or immunized i.p. with 50 IU of a plasma derived human FVIII 24 h after reconstitution. Further immunization was made with 25 IU of FVIII every fortnight during 6 weeks and animals were sacrificed after 8 weeks. All reconstituted mice showed a spontaneous production of anti-FVIII antibodies in the absence of immunization with the corresponding antigen. However, no differences were observed regarding the quantity or the quality of these antibodies produced in the immunized or the saline group, indicating that tolerance to FVIII had been transferred with cell reconstitution. Affinity purified FVIII specific antibodies were capable of inhibiting FVIII activity and preventing the binding of FVIII to phospholipids in a dose-dependent manner. Immunoprecipitation experiments showed that the antibodies recognized only the C1 and C2 light chain domains. Since antibodies of interest can be found in the SCID mouse model and, moreover, since they are qualitatively comparable with the source donor's antibodies, this model provides a tool to study the regulation of tolerance against self antigens in normal subjects and in acquired haemophilia patients.