Bispecific targeting of CHI3L1 and PD-1 as a therapeutic strategy for pulmonary fibrosis.

CHI3L1, a chitinase-like protein, is implicated in pulmonary fibrosis, yet its mechanisms are incompletely understood. We demonstrated that CHI3L1 coordinates profibrotic macrophage activation and invasive myofibroblast differentiation, and their crosstalk. In vitro, CHI3L1 drove M2-like macrophage polarization with increased CD163, CD206, and PD-L1, and amplified TGF-β1-induced fibroblast responses, including myofibroblast transformation, migration, and invasion. Mechanistically, CHI3L1 enhanced TGF-β1 signaling through SMAD, AKT, and ERK pathways, and PD-L1 was required for CHI3L1/TGF-β1-driven myofibroblast transformation. Coculture studies further demonstrated the ability of CHI3L1 to induce profibrotic macrophage activation that enhanced myofibroblast transformation mediated via a CD44/PD-L1 axis. In vivo, following bleomycin challenge, CHI3L1-transgenic mice exhibited increased PD-L1+ M2 macrophages, PD-L1+PDGFRα+ fibroblasts, and PD-1+ immune cells compared with WT controls. Therapeutically, combined anti-CHI3L1 and anti-PD-1 antibodies, or a bispecific anti-CHI3L1-anti-PD-1 antibody, produced greater antifibrotic efficacy than monotherapy. These findings demonstrate crosstalk between CHI3L1 and the PD-1/PD-L1 pathway that promotes profibrotic macrophage activation and invasive fibroblast differentiation and support dual targeting of CHI3L1 and PD-1/PD-L1 as a promising therapeutic strategy for pulmonary fibrosis.