A novel human CD32 mAb blocks experimental immune haemolytic anaemia in FcgammaRIIA transgenic mice

A fully human IgG1 kappa antibody (MDE-8) was generated, which recognised Fc-gamma receptor IIa (FcgammaRIIa) molecules on CD32 transfectants, peripheral blood monocytes, polymorphonuclear cells and platelets. This antibody blocked FcgammaRIIa ligand-binding via its F(ab')(2) fragment. Overnight incubation of monocytes with F(ab')(2) fragments of MDE-8 leads to a c. 60% decrease in cell surface expression of FcgammaRIIa. MDE-8 whole antibody induced a concomitant c. 30% decrease of FcgammaRI on THP-1 cells and monocytes. In humans FcgammaRIIa plays an important role in the clearance of antibody-coated red blood cells in vivo. As an equivalent of FcgammaRIIa does not exist in mice, the in vivo effect of MDE-8 was studied in an FcgammaRIIa transgenic mouse model. In these mice, antibody-induced anaemia could readily be blocked by MDE-8. These data document a new human antibody that effectively blocks FcgammaRIIa, induces modulation of both FcgammaRIIa and FcgammaRI from phagocytic cells, and ameliorates antibody-induced anaemia in vivo.