CAR-macrophage immunotherapy targeting fibroblast-like synoviocytes ameliorates inflammatory and degenerative arthritis

Rheumatoid arthritis (RA) is an inflammatory arthritis, whereas osteoarthritis (OA) is a degenerative joint disease. Despite their distinct etiologies, both are characterized by the pathogenic activation of fibroblast-like synoviocytes (FLS), which contribute to synovial hyperplasia, persistent inflammation, and cartilage destruction. Accordingly, pathogenic FLS represent an attractive therapeutic target for both RA and OA. Macrophages exhibit remarkable phenotypic plasticity, and interleukin-4 (IL-4) promotes an anti-inflammatory, tissue-reparative M2-like phenotype. Fibroblast activation protein α (FAP) and nucleolin (NCL) are highly expressed on the surface of pathological FLS while exhibiting limited accessibility in normal tissues. Here, we developed two IL-4-armored, FLS-targeted chimeric antigen receptor macrophage (CAR-M) platforms directed against FAP or NCL, termed CAR-M2-FAP and CAR-M2-NCL, respectively. In vitro, both platforms enhanced FLS phagocytosis and promoted an M2-like transcriptional profile. Transcriptomic analysis further revealed enrichment of phagocytic, anti-inflammatory, and tissue-reparative programs. In a mouse model of RA, both CAR-M2 platforms attenuated arthritis severity, synovial hyperplasia, cartilage loss, and bone erosion. Similarly, in a mouse model of OA, they reduced synovitis, cartilage degeneration, and osteophyte formation. No overt acute toxicity was observed in either RA or OA mice following treatment with CAR-M2-FAP or CAR-M2-NCL. Collectively, the concordant therapeutic effects of CAR-M2-FAP and CAR-M2-NCL across RA and OA models provide preclinical proof of concept for FLS-targeted CAR-M2 as a potential therapeutic strategy for inflammatory and degenerative arthritis.