Absence of T-bet in donor T cells reduces expansion of Tph and Trh cells and ameliorates cGVHD. (A) Irradiated BALB/c recipients were engrafted with T cells from WT or T-bet^-/- C57BL/6 donors together with TCD-BM from WT C57BL/6 donors. The recipients were monitored for body weight changes and survival for up to 60 days after HCT. Curves of percent body weight, percent survival, and cutaneous cGVHD score are shown. (B) GVHD pathology score. (C) One representative pattern of IgG deposition in the liver, lung, and skin is shown for 4 replicate experiments. Original magnification ×200. (D) Percentages of Tph cells among CD4⁺ T cells from the blood and Trh cells among CD4⁺ T cells from the liver and lung of recipients given WT or T-bet^-/- donor T cells were examined by flow cytometry. (E) Representative confocal images show CD4⁺ and B220⁺ cells inside the lung iBALT of WT and T-bet^-/- cGVHD mice. Original magnification ×200. Counts of CD4⁺ and B220⁺ cells per iBALT are also shown. (F) Percentages of Fas⁺GL7⁺ B among total B cells, memory B cells among IgD^- B cells, and plasma cells were measured. (G) Concentration of serum total IgG and anti-dsDNA IgG was measured with ELISA. Mean ± SEM is combined from 2 replicate experiments, N = 10. P values were calculated by nonlinear regression with comparison of fits and log-rank test (A), 2-way ANOVA with Holm-Sadik test (B, D, F), and unpaired Student t test (E, G). ∗P < .05; ∗∗P < .01; ∗∗∗P < .001; ∗∗∗∗P < .0001.