Human papillomavirus entry into NK cells requires CD16 expression and triggers cytotoxic activity and cytokine secretion

Abstract

Human papillomavirus (HPV) infections account for more than 50% of infection-linked cancers in women worldwide. The immune system controls, at least partially, viral infection and around 90% of HPV-infected women clear the virus within two years. However, it remains unclear which immune cells are implicated in this process and no study has evaluated the direct interaction between HPVs and NK cells, a key player in host resistance to viruses and tumors. We demonstrated an NK-cell infiltration in HPVassociated preneoplastic cervical lesions. Since HPVs cannot grow in vitro, virus-like particles (VLPs) were used as a model for studying the NK-cell response against the virus. Interestingly, NK cells displayed higher cytotoxic activity and cytokine production (TNF-a and IFN-c) in the presence of HPV-VLPs. Using flow cytometry and microscopy, we observed that NK-cell stimulation was linked to rapid VLP entry into these cells by macropinocytosis. Using CD16 1 and CD16 À NK-cell lines and a CD16-blocking antibody, we demonstrated that CD16 is necessary for HPV-VLP internalization, as well as for degranulation and cytokine production. Thus, we show for the first time that NK cells interact with HPVs and can participate in the immune response against HPV-induced lesions. IntroductionHigh-risk human papillomaviruses (HPVs) are the causative agents of uterine cervical cancer and are also etiologically associated with other anogenital tumors and with head and neck carcinomas [1].Among the 100 HPV genotypes already characterized, 15 are oncogenic and more than 50% of uterine cervical cancers are associated with HPV16 [2]. Because of their keratinocyte differentiation-dependent life cycle, virus production in vitro has required complex cell culture systems and only low virus titers can be obtained [3]. Consequently, most studies aiming to investigate interactions between virus and host cells have used virus-like particles (VLPs), which result from HPV L1 major capsid protein self-assembly and which are morphologically and immunologically [5,6]. Yet, these vaccines have no therapeutic efficacy and it has been estimated that there will be no measurable decline of HPVassociated tumors before 2040 [7].HPV infection can be controlled by the host immune response and the vast majority of HPV-infected women clear the virus within two years [8]. Moreover, the prevalence of HPV-induced tumors is higher in immunodeficient patients [9]. However, it remains unclear which immune cells are implicated in this process and no study has been performed evaluating the direct interaction between HPVs and NK cells, although these cells play a key role in host resistance to viruses [10] (Fig. 1A and B), but not in squamous cell carcinoma (SCC) (Fig. 1D) despite the presence of more numerous NK cells in the surrounding stroma (Supporting Information Fig. 1). Interestingly, virus particles have been detected mainly in SILs and not in SCC [19] where the virus is usually integrated into the host genome [20]. Our results thus suggest that NK cells could...

Human Papillomavirus Immunization Is Associated with Increased Expression of Different Innate Immune Regulatory Receptors

“…Interestingly, we have observed that the enhanced synthesis of IFN-␥ observed in vitro upon quadrivalent HPV (type 6/11/16/18) vaccine immunization is not affected by ILT2 engagement, indicating that the regulatory effect of this receptor is not exerted on all immune parameters that are relevant in the response to HPV. In this regard, it has been recently reported that NK cells exposed to HPV VLPs show increased cytotoxic activity and cytokine production (including IFN-␥) (19). Therefore, it is possible that the enhanced production of IFN-␥ observed by us upon HPV immunization could be related to the increased expression of activating receptors by NK cells and to a lack of a regulatory effect mediated by ILT2 on this immune parameter.…”

NK Cells and Virus-Related Cancers

“…In most individuals, HPV is cleared within 2 years after infection, but in ~10% of infected people, the virus persists long term, and can cause low-grade intraepithelial squamous lesions that may progress to dysplasia, in situ carcinoma, and finally invasive carcinoma. 69 HPV has developed multiple immune evasion strategies to escape CTL- and NK-cell–mediated control.…”

High Level of Tregs Is a Positive Prognostic Marker in Patients with HPV-Positive Oral and Oropharyngeal Squamous Cell Carcinomas

“…The authors suggest that NK cells might be activated by HPV viral particles. It has been shown that NK cells are abundantly present in the tissue of preneoplastic cervical lesions but much less cells have been detected in cervical squamous cell carcinomas [15, 16]. In patients with HNSCC, decreased numbers of NK cells in the peripheral blood have been detected independently of the etiology of the tumor [17, 18].…”