cTFH are activated and proliferate in patients with active cGVHD. (A) Frequency of ICOS^hiPD-1^hi in cTFH (CXCR5⁺CD45RA⁻CD4⁺ T cells) was determined in different patient groups. (B) Ki67 expression within cTFH (CXCR5⁺CD45RA⁻CD4⁺ T cells) was determined in different patient groups. (C) Positive correlation between proliferation and frequency of highly activated ICOS^hiPD-1^hi cTFH in the active cGVHD group. Black bar represents median value for each group. The Wilcoxon rank-sum test was used in panels A and B. The Spearman test was used in panel C. *P < .05; **P < 10⁻⁴. The gating strategy for identifying ICOS^hiPD-1^hi in cTFH is shown in supplemental Figure 1.