NFAT1 is not required for PD-1 up-regulation in vivo. Syngeneic chimeras with a mixture of WT CD45.1 and WT or NFAT1 KO CD45.2 BM were generated as depicted in panel A. On day 7 after allogeneic BMT, splenocytes were analyzed directly ex vivo for PD-1 expression on CD8 T cells. (B-D) The dotted line depicts basal levels of PD-1 expression in conditioned control animals receiving TBI but no BM. PD-1 expression on WT versus NFAT1 KO cells within the same animals was compared with (C) and without (D) administration of anti-CD154.