Increased expression of programmed death (PD)-1 and its ligand PD-L1 correlates with impaired cell-mediated immunity in high-risk human papillomavirus-related cervical intraepithelial neoplasia

Abstract

Impaired local cellular immunity contributes to the pathogenesis of persistent high-risk human papillomavirus (HR-HPV) infection and related cervical intraepithelial neoplasia (CIN), but the underlying molecular mechanisms remain unclear. Recently, the programmed death 1/programmed death 1 ligand (PD-1/PD-L1; CD279/CD274) pathway was demonstrated to play a critical role in attenuating T-cell responses and promoting T-cell tolerance during chronic viral infections. In this study, we examined the expression of PD-1 and PD-L1 on cervical T cells and dendritic cells (DCs), respectively, from 40 women who were HR-HPV-negative (-) or HR-HPV-positive (+) with CIN grades 0, I and II-III. We also measured interferon-γ, interleukin-12 (IL-12) and IL-10 in cervical exudates. The most common HPV type was HPV 16, followed by HPV 18, 33, 51 and 58. PD-1 and PD-L1 expression on cervical T cells and DCs, respectively, was associated with HR-HPV positivity and increased in parallel with increasing CIN grade. The opposite pattern was observed for CD80 and CD86 expression on DCs, which decreased in HR-HPV+ patients in parallel with increasing CIN grade. Similarly, reduced levels of the T helper type 1 cytokines interferon-γ and IL-12 and increased levels of the T helper type 2 cytokine IL-10 in cervical exudates correlated with HR-HPV positivity and CIN grade. Our results suggest that up-regulation of the inhibitory PD-1/PD-L1 pathway may negatively regulate cervical cell-mediated immunity to HPV and contribute to the progression of HR-HPV-related CIN. These results may aid in the development of PD-1/PD-L1 pathway-based strategies for immunotherapy of HR-HPV-related CIN.

Keywords: cervical intraepithelial neoplasia; cytokines; human papillomavirus; programmed death-1; programmed death-1 ligand.

Figure 1

Cytological and histological changes in the cervix. No cytological or histological alterations were observed in samples from the cervical intraepithelial neoplasia (CIN) 0 groups (a1 and a2). Slides from the CIN I group showed slight dysplasia limited to the basal third of the epithelial layer, and the nuclei of the dysplastic cells were enlarged, irregular and hyperchromatic (b1 and b2). Slides from the CIN II–III group showed markedly increased nuclear-to-cytoplasmic ratios in the dysplastic cells, and these atypical cells occupied at least two-thirds of the epithelial layer (CIN II: c1 and c2; CIN III: d1 and d2). a1–d1, Papanicolaou staining of cervical smears, original magnification × 800. a2–d2, haematoxylin & eosin staining of tissue sections, original magnification × 400.

Figure 2

Increased programmed death 1 (PD-1) expression on T cells in high-risk human papillomavirus (HR-HPV) -related cervical intraepithelial neoplasia (CIN). Cervical cells were labelled with a mixture of monoclonal antibodies against CD3 and PD-1 and the percentage of positive cells was determined by flow cytometry. Representative dot plots showing CD3⁺ PD-1⁻ (dashed lines) and CD3⁺ PD-1⁺ (solid lines) T-cell subsets (a), percentage of PD-1⁺ T cells (b) and ratio of PD-1⁺ to PD-1^– cells (c). Error bars indicate SD. *P < 0·05; **P < 0·01.

Figure 3

CD80, CD86 and programmed death 1 ligand (PD-L1) expression on dendritic cells (DCs) in high-risk human papillomavirus (HR-HPV) -related cervical intraepithelial neoplasia (CIN). Cervical cells were labelled with monoclonal antibodies against CD11c plus CD80, CD86 or PD-L1 and the percentage of positive cells was determined by flow cytometry. Representative dot plots (a). Percentage of DC subsets expressing CD11c⁺ CD80⁺ (b), CD11c⁺ CD86⁺ (c) and CD11c⁺ PD-L1⁺ (d). Error bars indicate SD. *P < 0·05; **P < 0·01.

Figure 4

Cytokine levels in cervical exudates. Levels of interferon-γ (IFN-γ) (a), interleukin-12 (IL-12) (b) and IL-10 (c). Compared with the high-risk human papillomavirus-positive [HR-HPV(+)] cervical intraepithelial neoplasia (CIN) 0 group, samples from the CIN I and CIN II–III groups contained reduced levels of the T helper type 1 cytokines IFN-γ and IL-12 and increased levels of the T helper type 2 cytokine IL-10. Error bars indicate SD. *P < 0·05; **P < 0·01.