ICOS and peeling skin syndrome: A trend for the highest ICOS expression within the PD-1hi subset was seen for CXCR5/CCR9 co-expressing cells (CCR9+ Tfh) in pSS patients (p = 0.08 and p = 0.06 compared to CXCR5+CCR9- and CXCR5-CCR9+ cells, respectively) (Figure 2C).