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 t o 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 (1 5 x 10(6) cells/mouse). Mice were injected with saline or immunized i.p. wi th 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 a nd animals were sacrificed after 8 weeks. All reconstituted mice showed a s pontaneous production of anti-FVIII antibodies in the absence of immunizati on with the corresponding antigen. However, no differences were observed re garding the quantity or the quality of these antibodies produced in the imm unized or the saline group, indicating that tolerance to FVIII had been tra nsferred with cell reconstitution. Affinity purified FVIII specific antibod ies were capable of inhibiting FVIII activity and preventing the binding of FVIII to phospholipids in a dose-dependent manner. Immunoprecipitation exp eriments showed that the antibodies recognized only the C1 and C2 light cha in domains. Since antibodies of interest can be found in the SCID mouse mod el and, moreover, since they are qualitatively comparable with the source d onor's antibodies, this model provides a tool to study the regulation of to lerance against self antigens in normal subjects and in acquired haemophili a patients.