Effect of B-Cell Depletion On Inhibitor Antibody Formation and Immune Tolerance Induction to Human Factor VIII in Hemophilia A Mice.

Abstract 2137

Poster Board II-114

B-cell depletion using anti-human CD20 monoclonal antibodies has been reported to be effective in autoimmunity and in temporarily eliminating inhibitory antibodies in hemophilia A patients. In the current study, we examined the effect of anti-murine CD20 (αCD20) depletion on the immune response to factor VIII (FVIII) and its influence on an immune tolerance induction (ITI) protocol. Previous studies have shown that IgG subclasses of anti-murine CD20 monoclonal antibody (αCD20) have differential effects on B-cell depletion in the mouse. Thus, IgG1 αCD20 selectively depletes follicular B cells, while sparing marginal zone (MZ) B cells. Combined with evidence that MZ B cells may be tolerogenic antigen-presenting cells, we tested the hypothesis that follicular B-cell depletion using αCD20 IgG1 might favor tolerance induction to human FVIII. Hemophilic (FVIII knockout) mice were primed with physiological doses of recombinant human FVIII by weekly IV injection, followed by αCD20 IgG1 or control IgG1 treatment. Ten days after the αCD20 treatment, the mice were treated with daily high dose (2μg) FVIII IV injections to model ITI in hemophilia A patients. After 4 weekly injections, 70% of the mice developed titers of anti-FVIII IgG as high as 1:12,800. Unlike whole B-cell depletion, subsequent follicular B-cell depletion did not significantly decrease the anti-FVIII IgG titer, compared with mice receiving control IgG1. Repeated high dose FVIII injections to mimic ITI significantly increased the anti-FVIII IgG titer in both groups. However, in the mice that received αCD20 IgG1 treatment, the increase of anti-FVIII IgG levels were significantly lower than that in control IgG1 treated mice. In conclusion, we found that follicular B-cell depletion by αCD20 IgG1 antibody in hemophilia A mice did not switch the immune response to tolerance, but it diminished the immunogenicity of human FVIII in vivo in hemophilic mice. (Supported by NIH R01 HL061883)