PDCD1 and cyclic hematopoiesis: Thus, anti-PD-1 mAb activated WHV-specific CTLs more often when PBMC originated from CH established after neonatal infection (i.e., 2/4 animals with ≥ 50% and 1/4 with < 50% cells activated) than from animals experimentally infected with WHV as adults (i.e., 1/4 with ≥ 50% cells activated; see Figure 5A).