EZH2 expression in both donor T cells and B cells is necessary for cGVHD/BO. (A-D) Mice were transplanted as in Figure 1. Groups shown are defined by the contents of the graft given on day 0. BM (EZH2 KO) refers to T-cell-depleted BM from B6 EZH2 fl/fl CD19-Cre mice. T (EZH2 KO) refers to purified T cells from B6 EZH2 fl/fl CD4 Cre mice. Results shown are pooled from 2 transplant replicates. (A-B) Results of pulmonary function tests on mice 49 days posttransplant show significant improvement in pulmonary function if (A) BM or (B) T cells are obtained from EZH2 KO donors (n = 7/BM-only, n = 9/cGVHD, n = 7/BM [EZH2 KO] only, n = 9/BM [EZH2 KO] + T [WT], n = 6/BM [WT] + T [EZH2 KO]). (C,E) Representative images of cryopreserved lung sections from mice 49 days posttransplant (n = 4/BM-only, n = 6/cGVHD, n = 4/BM [EZH2 KO] only, n = 8/BM [EZH2 KO] + T [WT], n = 5/BM [WT] + T [EZH2 KO]). Sections were stained with Masson trichrome and analyzed for collagen deposition, which is significantly reduced in recipients of T cells or BM from EZH2 KO donors. (D,F) Representative images of cryopreserved lung sections from mice 49 days posttransplant (n = 5/BM-only, n = 8/cGVHD, n = 4/BM [EZH2 KO] only, n = 6/BM [EZH2 KO] + T [WT], n = BM [WT] + T [EZH2 KO]). Sections were stained with anti-IgG FITC and DAPI and show reduction of IgG⁺ tissue in both the EZH2 KO T cell and EZH2 KO BM transplanted samples. Quantification of FITC⁺ area is shown in panel C. All images are at ×200 magnification. Quantification of trichrome-positive area is shown in the left panel of D. Statistics shown are results of an unpaired t test with Bonferroni corrected P values when appropriate. *P < .05, **P < .01, ***P < .001, ****P < .0001. KO, knockout.