Immunofluorescence staining of synovial organoids exposed to synovial fluid confirmed the loss of the TREM2high phenotype and the expansion of SPP1-producing macrophages within the hyperplastic lining layer niche (Fig.6H–I and fig.S8B–C), closely recapitulating active RA tissue (Fig.1F). The gene discussed is SPP1; the disease is rheumatoid arthritis.