CXCR5 and synovial sarcoma: We first analysed circulating IL-21 level and the frequency of IL-21 production in conventional Tfh (CXCR5+PD1+ICOS+) and the recently described Tph (CXCR5-PD1hi ICOS+) in patients with SS and their correlation with clinical, immunological and histopathological activity.