Activating NK cell receptor ligands are differentially expressed during progression to cervical cancer

Low NKp30, NKp46 and NKG2D expression and reduced cytotoxic activity on NK cells in cervical cancer and precursor lesions

Background

Persistent high risk HPV infection can lead to cervical cancer, the second most common malignant tumor in women worldwide. NK cells play a crucial role against tumors and virus-infected cells through a fine balance between activating and inhibitory receptors. Expression of triggering receptors NKp30, NKp44, NKp46 and NKG2D on NK cells correlates with cytolytic activity against tumor cells, but these receptors have not been studied in cervical cancer and precursor lesions. The aim of the present work was to study NKp30, NKp46, NKG2D, NKp80 and 2B4 expression in NK cells from patients with cervical cancer and precursor lesions, in the context of HPV infection.

Methods

NKp30, NKp46, NKG2D, NKp80 and 2B4 expression was analyzed by flow cytometry on NK cells from 59 patients with cervical cancer and squamous intraepithelial lesions. NK cell cytotoxicity was evaluated in a 4 hour CFSE/7-AAD flow cytometry assay. HPV types were identified by PCR assays.

Results

We report here for the first time that NK cell-activating receptors NKp30 and NKp46 are significantly down-regulated in cervical cancer and high grade squamous intraepithelial lesion (HGSIL) patients. NCRs down-regulation correlated with low cytolytic activity, HPV-16 infection and clinical stage. NKG2D was also down-regulated in cervical cancer patients.

Conclusion

Our results suggest that NKp30, NKp46 and NKG2D down-regulation represent an evasion mechanism associated to low NK cell activity, HPV-16 infection and cervical cancer progression.

Host immune responses to cervical cancer

PURPOSE OF REVIEW

The purpose of this review is to understand the role of the host immune system in clearing the human papillomavirus (HPV) infection, strategies adopted by HPV to subvert the host immune responses and analyze the challenges to the future immunotherapeutic treatment modalities.

RECENT FINDINGS

Cervical epithelium provides a protective niche to the virus to subvert the immune responses. The absence of an inflammatory milieu in the cervix makes the resident dendritic and langerhan cells tolerogenic to HPV antigens. CD4 cells predominated in regressing cervical intraepithelial neoplasia lesions, whereas CD8 cells were dominant in invasive carcinoma. A reduced expression of T cell signaling molecule T-cell receptor zeta chain was observed in CD8 lymphocytes. Decreased numbers of NKG2D expressing natural killer and T cells were present in patients with cervical cancer and cervical intraepithelial neoplasia. Increased frequencies of CD4 CD25+ FoxP3+ T regulatory cells were observed in patients with cervical cancer. The Nrp-1+Treg showed greater suppressive activity. A network of Treg and indoleamine 2, 3-dioxygenase expressed in tumor cells facilitates immune escape of tumor cells.

SUMMARY

The HPV uses different strategies to evade immune recognition. Understanding the immune evasion mechanisms used by HPV will help in designing newer therapeutic strategies for cervical cancer.

Interaction of human papillomaviruses with the host immune system: a well evolved relationship

Human papillomavirus (HPV) infections are generally long lasting, and a host immune response to infection is hard to detect. Nevertheless immunocompromised subjects control HPV infection less well than those with intact immunity. Immune responses are best documented for the papillomavirus groups that cause evident human disease, particularly those responsible for anogenital cancers and genital warts. Humoral immunity to the viral capsid has been shown sufficient for protection against infection, while innate and adaptive cell mediated immunity appears important for eventual elimination of HPV infection. However, molecular and cellular mechanisms responsible for protection from and clearance of HPV infection are not completely established.