Blockade of PD-1/PD-1 ligand interactions induced preferential tissue damage by donor T-cells. (A) Lethally irradiated B10.BR recipients were given 107 B6 BM cells with 2 × 106 B6 T-cells and treated with isotype-matched control antibody or anti-PD-L1 and anti-PD-L2 mAbs. Immunohistochemistry staining for CD4 (clone RM4-5) and CD8 (clone 53-6.7) T-cells on day 7 and day 10 after BMT. Cell numbers in spleen, liver, colon, and ileum are shown. Cells were quantified by counting the number of antibody-binding-positive cells in a 100 mm2 field of view under the microscope and obtaining an average of counts from 4 representative fields (n = 4 mice/group). (B) Lethally irradiated B10.BR recipients were given 107 B6 BM cells alone or with 10 × 106 B6 splenocytes and treated with isotype-matched control antibody or anti-PD-L1 mAb. Plasma FITC-dextran concentration was measured on day 7 after BMT (n = 5 mice/group). (C) Lethally irradiated BALB/c recipients were given 107 B6 BM cells alone or with 1.5 × 106 B6 luciferase transgenic T-cells and treated with isotype-matched control antibody or anti-PD-L1 mAb. On day 4 and day 6 after BMT, mice were injected intraperitoneally with luciferin, and after 5 minutes, mice were imaged using a Xenogen IVIS imaging system for 2 minutes (n = 7–9 mice/group). On day 6 after BMT, mice were killed, and isolated organs were imaged for 1 minute in the presence of luciferin (n = 7 mice/group). (A−C) Data are representative of 2 independent experiments. *P < .05; **P < .01; ***P < .001.
