Dual Immune Checkpoint and Cytokine Receptor Modulation by an Engineered Human CTLA-4/IL-10 Bispecific Fusion Protein

Bispecific fusion proteins represent a unique strategy for developing precision therapeutics. By linking functional domains from distinct proteins, these biomolecules can engage multiple targets, enhancing both therapeutic efficacy and safety. Unlike bispecific antibodies, low-molecular-weight fusion proteins offer distinct advantages, including reduced immunogenicity and superior tissue penetration due to their relatively compact size and structure. Such a profile is particularly valuable in managing complex inflammatory diseases, where modulating multiple pathways is required to impart an effective anti-inflammatory effect. Among the various regulators of immune signaling, the cytotoxic T-lymphocyte-associated protein 4 (CTLA-4) and interleukin-10 (IL-10) play imperative roles in immune suppression through their interactions with CD80/86 and IL-10R, respectively. While Fc-fused CTLA-4 is a clinically approved drug (e.g., Abatacept), the clinical development of IL-10 has been hampered by unpredictable immunostimulatory side effects. Here, we engineered a bispecific fusion protein linking the extracellular domain of CTLA-4 to IL-10. We successfully expressed the protein in E. coli as an N-terminal GST-tagged variant and refolded it from the inclusion bodies. Additionally, we achieved soluble expression of an Fc-tagged variant in mammalian CHO cells. Both origins demonstrated binding to their cognate receptors, CD80 and IL-10R. Finally, the fusion protein demonstrated a T cell-inhibitory effect by reducing Interferon-γ (IFNγ) secretion levels in an in vitro human Virus-Specific T cells (VSTs) model. This innovative protein engineering offers a promising strategy for addressing unmet clinical needs in autoimmune and inflammatory diseases.