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...

Historically, the name of natural killer (NK) cells came from their natural ability to kill tumor cells in vitro. From the 1970s to date, accumulating data highlighted the importance of NK cells in host immune response against cancer and in therapy-induced antitumor response. The recognition and the lysis of tumor cells by NK cells are regulated by a complex balance of inhibitory and activating signals. This review summarizes NK cell mechanisms to kill cancer cells, their role in host immune responses against tumor growth or metastasis, and their implications in antitumor immunotherapies via cytokines, antibodies, or in combination with other therapies. The regulatory role of NK cells in autoimmunity is also discussed.

Virus-like particles (VLPs) of human papillomavirus (HPV) are used as a vaccine against HPV-induced cancer, and recently we have shown that these VLPs are able to activate natural killer (NK) cells. Since NK cells collaborate with dendritic cells (DCs Keywords: Cell crosstalk · DC HPV vaccines · NK cells · Vaccination · Viral infectionAdditional supporting information may be found in the online version of this article at the publisher's web-site IntroductionVirus-like particles (VLPs) are an active area of vaccine research [1], but until now the mechanism required by these vaccines to induce a protective immune response is not fully understood. InCorrespondence: Dr. Nathalie Jacobs e-mail: n.jacobs@ulg.ac.be the context of human papillomavirus (HPV) infections, two prophylactic VLP vaccines based on self-assembly of L1 major capsid protein are licensed: a bivalent HPV-16/18 product (Cervarix R )[2] and a quadrivalent HPV-16/18/6/11 product (Gardasil R ) [3].Fifteen oncogenic types of HPVs are identified in uterine cervical cancers, the third most frequent malignancy among women in the world [4], and HPV-16 is alone the etiologic agent of more than 50% of these cancers [5]. HPV-6 and HPV-11 are not oncogenic Eur. J. Immunol. 2014. 44: 3585-3595 and are linked to genital warts [6]. Oncogenic HPV, especially HPV-16, can also be associated with other anogenital tumors and head and neck carcinomas [7]. HPV-VLP based vaccines are highly efficient to protect against HPV infections by inducing neutralizing antibodies and cellular immunity against HPV, but how these adaptive immune responses are initiated is still partially unknown. Moreover, it would be interesting to amplify the cellular part of the immune response to be able to protect against established infections, which is not the case with the current vaccines [8] [14]. They are able to take up pathogens or tumor cell apoptotic bodies of tumor cells and need to receive maturation signals to migrate to the draining lymph nodes where they specifically activate T cells [15,16]. It was shown that VLPs were able to, at least partially, induce DC maturation [17][18][19]. Despite the fact that the collaboration between DCs and NK cells plays an important role in host resistance against viral infections (such as HIV) and tumors [20,21], no study was performed evaluating their crosstalk in the context of VLP vaccination. Here, we evaluated the immune response of myeloid DCs and NK cells derived from the same donor in the presence of HPV-16 VLPs produced by baculovirus in insect cells [22]. We demonstrated that VLP amplified the collaboration between DCs and NK cells via IL-12p70 secretion and CD40 interaction. Results NK cells potentiate DC activation in the presence of VLPsRecently, we have shown that NK cells are activated by VLPs via CD16 [11]. Here, we investigated the impact of this activation on DC maturation. First, we confirmed that VLPs (10 μg/mL) induce DC maturation [19,23] as shown by the upregulation of costimulatory molecules such as CD86, CD80, CD83, and ...

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The cover shows a modified electron microscopic image of HPV16‐virus‐like particle (HPV16‐VLP)‐internalization by NK cells. The colour added to the cover image is purely for aesthetic purposes and has no biological significance. The original, unmodified image is from Renoux et al. (pp. 3240–3252) in which the authors demonstrate that HPV16‐VLPs are taken up by NK cells by macropinocytosis. CD16 is shown to play a central role in the NK cell response to HPV16, being shown to be required for viral uptake, and for granzyme and cytokine release.