CD4 and cyclic hematopoiesis: In one of the previous studies examining the in vivo effect of woodchuck-specific anti-PD-L1, it was noticed that WHV-specific CTLs, defined as CD3+/CD4-T cells, resisted ex vivo activation by WHV peptides when PBMC from animals with CH acquired after experimental WHV infection in the early neonatal period were investigated (Balsitis et al., 2018).