B cells from patients with cGVHD have increased BCR-driven proliferation. (A) B cells isolated from healthy donors and patients with and without cGVHD, stained with CFSE and stimulated with α-IgM (50 μg/mL) for 6 days. Unstimulated controls are shown as dashed lines. (Left) Representative histograms of B-cell proliferation from patients without cGVHD (gray area, thin line) and with cGVHD (white area, bold line). (Center) Frequency of B-cell proliferation quantified in healthy donors (HD, filled triangles), patients without cGVHD (−cGVHD, open circles), and patients with cGVHD (+cGVHD, filled squares). (Right) Proliferation index quantified in healthy donors (HD, filled triangles), patients without cGVHD (−cGVHD, open circles), and patients with cGVHD (+cGVHD, filled squares). Data are median ± range pooled from 4 independent experiments. *P < .05. (B) B cells isolated from patients with and without cGVHD, stained with CFSE, and stimulated with α-CD40 (100 ng/mL) + IL-4 (5 ng/mL) for 6 days. Unstimulated controls are shown as dashed lines. (Left) Representative histograms of B-cell proliferation from patients without cGVHD (gray area, thin line) and with cGVHD (white area, bold line). (Center) Frequency of B-cell proliferation quantified in patients without cGVHD (−cGVHD, open circles) and with cGVHD (+cGVHD, filled squares). (Right) Proliferation index quantified in patients without cGVHD (−cGVHD, open circles) and with cGVHD (+cGVHD, filled squares). Data are median ± range pooled from 3 independent experiments. *P < .05. Proliferation index = total number of divisions divided by the number of cells that went into division calculated using FlowJo Version 8.8.7.