As for the PD-1/PD-L1 axis, Yang et al. showed that the activation of the PD-1/PD-L1 pathway suppresses cell-mediated immunity (CMI), by inhibiting pro-inflammatory cytokines and upregulating anti-inflammatory cytokines, thus leading to localized immunosuppression and high-risk HPV-induced CIN progression (44) (Figure 1). Here, PDCD1 is linked to cervical squamous intraepithelial neoplasia.