Abstract Background Tumor necrosis factor-like ligand 1A (TL1A) is a member of the TNF superfamily implicated in the pathogenesis of inflammatory bowel disease (IBD) as a key amplifier of effector immune cell function. TL1A is expressed by multiple immune cell types, including macrophages, dendritic cells, and exists as either a membrane-bound or cleaved soluble form. TL1A signals through death receptor 3 (DR3), activating the NF-κB pathway in effector T cells and innate lymphoid cells (ILCs). TL1A can exist in trimeric or monomeric form. Afimkibart is a fully human monoclonal antibody that has demonstrated clinical benefit in Phase 2 studies and selectively neutralizes trimeric, functionally active TL1A. In contrast, monomeric TL1A has been described, but its physiological role needs to be further investigated. Methods Recombinant monomeric and trimeric TL1A proteins were evaluated for binding to afimkibart using surface plasmon resonance (SPR) and for functional activity in primary immune cells and cell lines by measuring NF-κB signaling and interferon-gamma (IFNγ) production. Results Trimeric recombinant human TL1A (rhTL1A) robustly induced NF-κB activation in peripheral T lymphocytes and, in the presence of IL12 and IL18 co-stimulation, significantly enhanced IFN-γ production in human PBMCs. Both readouts were potently inhibited by afimkibart. Monomeric rhTL1A, even at high concentrations (100 ng/mL), elicited only minimal NF-κB activation and a marginal IFN-γ response. Importantly, afimkibart does not bind monomeric TL1A, confirming it selectively recognizes the active, trimeric species. This selectivity prevents afimkibart from being sequestered by any non-signaling TL1A monomers, thereby avoiding the target “sink” effects that impact in vitro potency for antibodies binding both monomeric and trimeric TL1A. Afimkibart also effectively blocked both soluble and membrane-bound forms of endogenous active TL1A. Conclusion Afimkibart is a potent and selective antagonist of the functionally active, trimeric TL1A, efficiently blocking TL1A-induced NF-κB signaling and IFN-γ production. The inability of afimkibart to bind monomeric TL1A may represent a distinct pharmacologic advantage by ensuring selective targeting of the signaling-competent TL1A form for optimal pharmacokinetic and pharmacodynamic properties. This functional specificity underpins the therapeutic potential of afimkibart in TL1A-driven diseases such as IBD. Conflict of interest: Fuh, Franklin: Employment and stock/stock options at Genentech Inc. Varfolomeev, Eugene: I am an employee and shareholder of Genentech-Roche. Nguyen, Allen: I am employed by Genentech, Inc., a subsidiary of Roche, Inc. I own Roche shares/stock. Oh, Angela: I am an employee of Genentech, Inc. and have Roche stock. Merana, Geil: I am an employee and shareholder of Genentech-Roche. Tao, Xiao: I am a full-time employee of Genentech, Inc. (a Roche subsidiary) where the data is sourced/generated. And I am a Roche stock owner. Lasch, Karen: Employed by Roche/Genentech with stock or other ownership interests in Roche/Genentech. Dr. Neighbors, Maggie: I am a full-time employee of Genentech, Inc., a wholly owned subsidiary of Roche, and receive Roche stock/options. Mohanan, Vishnu: Full time employee of Genentech/Roche and holds Roche shares. Vucic, Domagoj: I am an employee and shareholder of Genentech-Roche.
Fuh et al. (Thu,) studied this question.