PDCD1 and infection: At late time points, 8 months after the initial infection, the number of PD-1+ activated CD8+ further decreased in PbNK65 hrfΔ-infected mice, returning to the basal levels found in uninfected mice, whereas a residual number of PD-1+ activated CD4+ T cells persisted but at a significantly lower level as compared to early time points (day 6 p.i) (Fig. 5B, hatched bars).