Objective: This study aimed to investigate the therapeutic effects of BITRAP, a bispecific fusion protein targeting TNF-α and IL-21, on the development of autoimmune arthritis in humans and mice.
Methods: Human peripheral blood mononuclear cells were cultured with BITRAP under IL-17-producing T (Th17) cell-polarizing conditions or osteoclast differentiation conditions and examined the effects of BITRAP. Collagen-induced arthritis (CIA) and IL-1R antagonist (IL-1Ra) knockout mice were treated with BITRAP, and disease severity was assessed. In vivo real-time tracking of BITRAP was performed in CIA mice intravenously injected with quantum-dot-conjugated BITRAP using an in vivo fluorescence imaging system. Finally, splenic CD4+ T cells were treated with BITRAP under IL-21 stimulation or Th17-polarizing conditions and monitored for STAT3 activity, as well as IL-17 and TNF-α expression.
Results: BITRAP treatment inhibited the production of IL-17 and VEGF but increased the production of IL-10 in CD4+ T cells, as well as directly suppressed osteoclastogenesis in humans. Following injection in CIA mice, BITRAP rapidly migrated into the inflamed joints and remained there for 72 h. 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-α, in murine splenic CD4+ T cells.
Conclusions: These findings suggest that BITRAP, a bispecific fusion protein targeting TNF-α and IL-21, may be an effective treatment to overcome the limitations of anti-TNF therapy for patients with rheumatoid arthritis.