Dual-function fab-scFv fusion antibody ameliorates ulcerative colitis by targeting hFcRn-mediated colonic enrichment and TNF-α neutralization.

Ulcerative colitis (UC), a chronic inflammatory bowel disease (IBD), is characterized by disruption of intestinal barrier function and complex inflammatory manifestations locally and systemically. Although anti-tumor necrosis factor-α (TNF-α) agents such as Infliximab (IFX) are effective in treating IBD, their intestinal tissue concentration has been regarded as determinant of therapeutic efficacy while was restrained by the large molecular weight. Considering the enhanced expression of human neonatal Fc receptor (hFcRn) in UC tissues, we attempted to deliver the therapeutic entity of IFX into UC tissues by developing a novel dual-acting IFX Fab-F8 (IFX-F8) fusion protein for UC treatment. The IFX Fab was fused to the hFcRn-binding scFv F8, generating a bispecific Fab-scFv protein with half the molecular weight of full-length IgG. IFX-F8 maintained independent high-affinity binding to both TNF-α and hFcRn, conferring prolonged serum half-life and enhanced intestinal epithelial retention through hFcRn-mediated recycling. In DSS-induced UC hFcRn mice, intraperitoneal IFX-F8 administration significantly attenuated the weight loss and improved survival and ZO-1 of the experimental animals compared to IFX. The fusion protein exhibited preferential accumulation in inflamed colonic tissues and superior therapeutic efficacy over IFX or IFX Fab monotherapy. Mechanistically, IFX-F8 more effectively suppressed pathogenic Th17 cells and IL-17 signaling than IFX, leading to sustained disease remission. Collectively, our findings suggest that the IFX-F8 fusion protein is a potential UC therapeutic agent and deserves further study.