CCL4 and rheumatoid arthritis: Here, we demonstrate that this niche provides in turn unique signals for the development of perivascular LYVE1pos STMs, particularly clusters with pro-inflammatory phenotypes, such as CCL3/CCL4-expressing ERG1pos and CXCL9 and CCL18-expressing SELENOPpos, which are features of active RA synovium compared with healthy tissue.