A novel monoclonal antibody with improved FcγR blocking ability demonstrated non-inferior efficacy compared to IVIG in cynomolgus monkey ITP model at considerably lower dose.

Intravenous immunoglobulin (IVIG) is a well-established treatment for various autoimmune and inflammatory diseases. However, the standard dose prescribed for autoimmune diseases, including immune thrombocytopenic purpura (ITP), is 2 g/kg, which is markedly high and leads to a high treatment burden. In this study, we generated fragment crystallizable (Fc)-modified anti-haptoglobin (Hp) monoclonal antibodies with non-inferior efficacy compared to IVIG at considerably lower doses than IVIG, as shown by in vitro experiments. We evaluated binding activity of anti-Hp antibodies to Fc gamma receptors (FcγRs) with ELISA and inhibitory activity against the ADCC reaction. Furthermore, we successfully established a novel cynomolgus monkey ITP model and demonstrated that the anti-Hp antibody exerted its effect in this model with only a single dose. This Fc-modified anti-Hp monoclonal antibody could be a valuable therapeutic replacement for IVIG for the treatment of ITP.