GVHD acceleration induced by PD-1/PD-L1 blockade resulted in increased metabolic stress in donor T-cells. Lethally irradiated wt B6, PD-L1^−/−, or Thy1.2⁺ BALB/c recipients were given 10⁷ Thy1.2⁺ BALB/c BM cells with 30 × 10⁶ CFSE-labeled Thy1.1⁺ BALB/c splenocytes. (A-H) Mice were killed on day 5 after BMT, and experiments were performed as described. Thy1.1⁺ donor T-cells were purified, and lactate (A) and pyruvate (B) production and oxygen consumption (C) by donor T-cells were measured. Naive Thy1.1⁺ BALB/c mice (n = 4) were included as control. Mice splenocytes were analyzed by flow cytometry for GLUT1 (D), TMRM (E), dihydroethidium (F), and annexin V (H) expression in undivided (CFSE^hi) and divided (CFSE^lo) donor T-cells. MFI; mean fluorescence intensity. (G) Splenocytes were also analyzed by flow cytometry for CFSE dilution. Cells were gated on Thy1.1⁺ and analyzed for CD4⁺ or CD8⁺ events. (A-H) Data are representative of 5–9 mice/group from 2-3 independent experiments. *P < .05; **P < .01; ***P < .001.