CCL9 blockade reverses cGVHD clinical manifestations and immunological hallmark. Transplanted mice were treated with anti CCL9 (100 mg) from day 28 after bone marrow transplant. Experiments were terminated at days 42 through 56. (A) Pulmonary function tests suggest CCL9 blockade reverses cGVHD lung disease. (B) Collagen deposition, (C) macrophage infiltration, and (D) immunoglobulin deposition were significantly reduced by CCL9 blockade. (E-H) Splenic GC reactions analysis. Frequency of (E) GC B cells, (F) Tfh, (G) Tfr, and (H) Tfh/Tfr ratio were normalized by CCL9 blockade. Data shown are representative of 2 to 3 independent experiments with 5 to 8 mice per group. An unpaired Student t test was used when comparing 2 groups. Significance: *P < .05; **P < .01; ***P < .001; ****P < .0001. Ig, immunoglobulin.