A significant enrichment of activated (ICOS+) cTfh (CD4+CXCR5+PD-1+) cells has been assigned to Tfh subsets, namely, Tfh1 and Tfh17 cells, and these subsets were identified as the major source for IL-21 in generalized MG patients (22, 23). Here, ICOS is linked to myasthenia gravis.