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Cancers attributable to human papillomavirus (HPV) place a huge burden on the health of both men and women. The current commercial vaccines are genotype specific and provide little therapeutic benefit to patients with existing HPV infections. Identifying the conformational epitopes on the virus capsid supports the development of improved recombinant vaccines to maximize long-term protection against multiple types of HPV. Fragments of antibody (Fab) digested from the neutralizing monoclonal antibodies H16.V5 (V5) and H16.U4 (U4) were bound to HPV16 capsids and the structures of the two virus-Fab complexes were solved to near atomic resolution using cryo-electron microscopy. The structures reveal virus conformational changes, the Fab-binding mode to the capsid, the residues comprising the epitope and indicate a potential interaction of U4 with the minor structural protein, L2. Competition enzyme-linked immunosorbent assay (ELISA) showed V5 outcompetes U4 when added sequentially, demonstrating a steric interference even though the footprints do not overlap. Combined with our previously reported immunological and structural results, we propose that the virus may initiate host entry through an interaction between the icosahedral five-fold vertex of the capsid and receptors on the host cell. The highly detailed epitopes identified for the two antibodies provide a framework for continuing biochemical, genetic and biophysical studies. [ABSTRACT FROM AUTHOR]

A substantial percentage of the population remains at risk for cervical cancer due to pre-existing human papillomavirus (HPV) infections, despite prophylactic vaccines. Early diagnosis and treatment are crucial for better disease outcomes. The development of new treatments heavily relies on suitable preclinical model systems. Recently, we established a mouse papillomavirus (MmuPV1) model that is relevant to HPV genital pathogenesis. In the current study, we validated the use of Papanicolaou (Pap) smears, a valuable early diagnostic tool for detecting HPV cervical cancer, to monitor disease progression in the MmuPV1 mouse model. Biweekly cervicovaginal swabs were collected from the MmuPV1-infected mice for viral DNA quantitation and cytology assessment. The Pap smear slides were evaluated for signs of epithelial cell abnormalities using the 2014 Bethesda system criteria. Tissues from the infected mice were harvested at various times post-viral infection for additional histological and virological assays. Over time, increased viral replication was consistent with higher levels of viral DNA, and it coincided with an uptick in epithelial cell abnormalities with higher severity scores noted as early as 10 weeks after viral infection. The cytological results also correlated with the histological evaluation of tissues harvested simultaneously. Both immunocompromised and immunocompetent mice with squamous cell carcinoma (SCC) cytology also developed vaginal SCCs. Notably, samples from the MmuPV1-infected mice exhibited similar cellular abnormalities compared to the corresponding human samples at similar disease stages. Hence, Pap smear screening proves to be an effective tool for the longitudinal monitoring of disease progression in the MmuPV1 mouse model., Importance: Papanicolaou (Pap) smear has saved millions of women's lives as a valuable early screening tool for detecting human papillomavirus (HPV) cervical precancers and cancer. However, more than 200,000 women in the United States alone remain at risk for cervical cancer due to pre-existing HPV infection-induced precancers, as there are currently no effective treatments for HPV-associated precancers and cancers other than invasive procedures including a loop electrosurgical excision procedure (LEEP) to remove abnormal tissues. In the current study, we validated the use of Pap smears to monitor disease progression in our recently established mouse papillomavirus model. To the best of our knowledge, this is the first study that provides compelling evidence of applying Pap smears from cervicovaginal swabs to monitor disease progression in mice. This HPV-relevant cytology assay will enable us to develop and test novel antiviral and anti-tumor therapies using this model to eliminate HPV-associated diseases and cancers., Competing Interests: The authors declare no conflict of interest.

Human papillomaviruses (HPVs) have been shown to bind to Laminin-332 (Ln-332) on the extracellular matrix (ECM) secreted by human keratinocytes. The assay described here is an important tool to study HPV receptor binding to the ECM. The assay can also be modified to study the receptors required for HPV infection and for binding to tissues. We previously showed that Ln-332 is essential for the binding of HPV11 to human keratinocytes and that infectious entry of HPV11 requires α6β4 integrin for the transfer of HPV11 from ECM to host cells (Culp et al., J Virol 80:8940-8950, 2006). We also demonstrated that several of the high-risk HPV types (16, 18, 31 and 45) bind to Ln-332 and/or other components of the ECM in vitro (Broutian et al., J Gen Virol 91:531-540, 2010). The exact binding and internalization mechanism(s) for HPV are still under investigation. A better understanding of these mechanisms will aid in the design of therapeutics against HPVs and ultimately help prevent many cancers. In this chapter, we describe the HPV binding assay to Ln-332/integrin α6β4 on human keratinocytes (ECM). We also present data and suggestions for modifying the assay for testing the specificity of HPV for receptors (by blocking receptors) and binding to human tissues (basement membrane, BM) in order to study binding mechanisms.

Human papillomavirus (HPV) 58 is a high-risk HPV type associated with progression to invasive genital carcinomas. We developed six monoclonal antibodies (mAbs) against HPV58 L1 virus-like particles that bind conformational epitopes on HPV58. The hybridoma cell lines were adapted to serum- and animal component-free conditions and the mAb supernatants were affinity-purified. The six mAbs neutralized HPV58 pseudoviruses (PsVs) and 'quasivirions' with different capacities. The mAbs differed in their ability to prevent PsV58 attachment to HaCaT cells, to the extracellular matrix (ECM) deposited by HaCaT cells, to heparin and to purified human laminin 5, a protein in the ECM. These mAbs provide a unique set of tools to study the binding properties of a previously untested, high-risk HPV type and the opportunity to compare these characteristics with the binding of other HPV types.

The focus of this research was to compare the binding profiles of human papillomavirus (HPV) 11, 16, 18 and 45 virus-like particles (VLPs) to HaCaT cells and to the extracellular matrix (ECM) secreted by these cells. All four HPV types tested bind to a component(s) of the ECM. HPV11 VLP binding is blocked when the ECM is pretreated with an anti-laminin 5 (LN5) polyclonal antibody. A series of treatments utilizing heparins and heparinase revealed that HPV18 VLPs are dependent on heparan sulfates (HS) for binding to cells and ECM. HPV16 and HPV45 VLPs are dependent on HS for binding to HaCaT cells and dependent on both HS and LN5 for binding to ECM. These studies emphasize the need to study the binding characteristics of different HPV types before applying universal binding principles to all papillomaviruses.