MSCs ameliorate cGVHD. Mice with severe GVHD were treated with MSCs (MSC-GVHD) or normal saline (non–MSC-GVHD) on day 7 after HCT (aGVHD symptoms peak). Non-GVHD mice served as control. Mice were monitored for aGVHD clinical symptoms, cutaneous cGVHD, survival, and histopathology of cGVHD target tissues. Thymus size and structure were assessed on day 20 and day 40 after HCT with H&E and immunofluorescent staining. (A-C) aGVHD symptom scores, cutaneous cGVHD symptom score, and survival curve. Each group contained between 12 and 16 recipients combined from 3 replicate experiments. (D) Representative photomicrographs of the salivary gland, skin, lung, and liver. Histopathology scores are shown as mean ± SE (n = 4-6); scale bar, 50 μm. Arrows indicate the following: infiltration and loss of ductal structure in the salivary gland; hyperplasia in the epidermis, expansion of the dermis, and loss of subcutaneous fat; perivascular and peribronchiolar infiltration; infiltration in the liver, involved tracts, and liver cell necrosis. (E) Representative photographs of the thymus, and thymus cellularity in each group, results are shown as mean ± SE (n = 6). (F) Representative photomicrographs of H&E-stained thymus tissue section (scale bar, 50 μm) and thymus pathology score, results are shown as mean ± SE (n = 6). (G) Medulla area in the thymus was measured by immunofluorescent staining for CK8 and CK5, results are shown as mean ± SE (n = 4-6); scale bar, 50 μm. ∗∗P ＜ .01; ∗∗∗P ＜ .001. ns, not significant.