A bispecific soluble receptor fusion protein that targets TNF‐α and IL‐21 for synergistic therapy in inflammatory arthritis

This study was aimed at investigating the therapeutic effects of BITRAP, a bispecific fusion protein targeting TNF-alpha and IL-21, on the development of autoimmune arthritis in humans and mice. To verify the effects of BITRAP in human, peripheral blood mononuclear cells were cultured with BITRAP under IL-17-producing T (Th17) cell-polarizing conditions or osteoclast differentiation conditions. BITRAP treatment inhibited the production of IL-17 and vascular endothelial growth factor but increased the production of IL-10 in CD4(+) T cells, as well as directly suppressed osteoclastogenesis. Collagen-induced arthritis (CIA) and IL-1R antagonist (IL-1Ra) knockout mice were treated with BITRAP. Following injection in CIA mice, BITRAP rapidly migrated into the inflamed joints and remained there for 72 hours. Application of BITRAP attenuated the severity of autoimmune arthritis in CIA and IL-1Ra knockout mice by reducing the numbers of inflammatory cytokine-expressing cells and Th17 cells and antibody secretion. Finally, BITRAP suppressed STAT3 phosphorylation, as well as production of IL-17 and TNF-alpha, in murine splenic CD4(+) T cells. These findings suggest that BITRAP, a bispecific fusion protein targeting TNF-alpha and IL-21, may be an effective treatment to overcome the limitations of anti-TNF therapy for patients with rheumatoid arthritis.