Host PD-1 ligand expression affect proliferation and survival of allogeneic donor T-cells. Lethally irradiated B10.BR recipients were given 10⁷ B6 BM cells with 50 × 10⁶ CFSE-labeled B6 splenocytes and treated with isotype-matched control antibody or anti-PD-L1 and anti-PD-L2 mAbs. (A) Mice were killed on day 5 after BMT (n = 5 mice/group), and splenocytes and MLNs were analyzed by flow cytometry for CFSE dilution. Cells were gated on H-2Kb⁺ and analyzed for CD4⁺ or CD8⁺ events. (B) Spleen and MLNs were harvested (n = 5 mice/group) on day 5 and analyzed by flow cytometry for annexin V-positive donor CD4 and CD8 T-cells. (A-B) Data are representative of 2 independent experiments. *P < .05; **P < .01; ***P < .001.