Loss of ICOSL expression in the progression to cervical carcinoma

Human papillomavirus (HPV)-related lesions contain types with benign outcomes and those with a risk of progression to cancer. We addressed the role of immune surveillance in 76 cervical biopsies (normal = 23, HPV+ benign = 16, HPV+ precancer = 37) by studying the infiltration of cytotoxic T cells and the expression of the immune modulators PDL1, ICOSL, and <i>miR-155</i> and compared the data to 101 cervical squamous cell carcinomas. In the normal cervix, ICOSL expression was restricted to the endocervical epithelia whereas neither <i>miR-155</i> nor PDL1 were detected. <i>MiR-155</i> was up-regulated in both the benign (88%) and precancerous (92%) HPV squamous intraepithelial lesions (SIL) and colocalized to cells in the upper part of the lesion that is the area with productive viral infection. Both PDL1 (95%) and ICOSL (89%) were only evident in the precancerous SIL and each localized to squamous cells in the basal aspect that lacked replicating virus. In both microinvasive and invasive cervical squamous cell cancer <i>miR-155</i> expression remained high (83%) as did PDL1 expression (80%) but ICOSL detection was reduced to 17%. Infiltration by CD8+ T cells was intense in the invasive lesions and these cells were mostly inactive as determined by the lack of granzyme B colocalization. It is concluded that <i>miR-155</i> expression is a marker of HPV infection in both benign and precancerous lesions, whereas the approximately 10% of the latter lesions that progress to cancer gain PDL1 and lose ICOSL expression, which are important factors in avoiding immune surveillance.