Expansion of Tph cells is associated with cGVHD severity. Frozen peripheral blood mononuclear cells from patients detailed in supplemental Tables 1 and 2 were thawed and stained with multiple monoclonal antibodies. (A) PD1 versus CXCR5 expression among CD3⁺ CD45RO⁺/ CD45RA^- CD4⁺ memory T cells from HDs (N = 11) and patients with no GVHD (N = 7), mild cGVHD(N = 7), moderate cGVHD (N = 8), or severe cGVHD (N = 8) was examined by flow cytometry. (B) Percentage and yield of PD1^-CXCR5⁺ pre-Tfh cells, PD1⁺CXCR5⁺ Tfh cells, and PD1^hiCXCR5^- Tph cells were calculated. (C) Correlation between percentage of Tph cells and percentage of Tfh cells, between percentage of Tph cells and percentage of pre-Tfh cells, and between yield of Tph cells and yield of pre-Tfh cells in patients with cGVHD (N = 23). Data represent mean ± standard error of the mean (SEM). P values were calculated by 1-way analysis of variance (ANOVA) with Holm-Sidak test (B) and nonparametric Spearman correlation (C). ∗P < .05; ∗∗P < .01; ∗∗∗P < .001; ∗∗∗∗P < .0001.