Studies suggest that E6/E7 activates the PD-1/PD-L1 axis causing an increase in Th2-type cytokine and IL-10 expression and a decrease in Th1 cytokine IFN-c and IL-12 expression leading to immunosuppression and further progression of CIN (101, 102) (Figure 1). Here, PDCD1 is linked to cervical squamous intraepithelial neoplasia.