Neutralization of HPV16, 18, 31, and 58 pseudovirions with antisera induced by immunizing rabbits with synthetic peptides representing segments of the HPV16 minor capsid protein L2 surface region

Neutralizing antibodies against human papillomavirus types 16, 18, 31, 52, and 58 in serum samples from women in Japan with low-grade cervical intraepithelial neoplasia

We have very limited information on serum neutralizing antibody in women naturally infected with the human papillomaviruses (HPVs) that are causally associated with cervical cancer. In this study, serum samples collected from 217 Japanese women with low-grade cervical intraepithelial neoplasia were examined for their neutralizing activities against HPV16, -18, -31, -52, and -58 pseudovirions. Eighty-four patients (39%), 35 patients (16%), 17 patients (8%), and 1 patient were positive for neutralizing antibodies against one, two, three, and four of these types, respectively. Presence of neutralizing antibody did not always correlate with detection of HPV DNA in cervical swabs collected at the time of blood collection. The neutralizing titers of the majority of sera, ranging between 40 and 640, were found to be conserved in the second sera, collected 24 months later, independently of emergence of HPV DNA in the second cervical swabs. The data strongly suggest that HPV infection induces anti-HPV neutralizing antibody at low levels, which are maintained for a long period of time.

Clinical and epidemiological correlates of antibody response to human papillomaviruses (HPVs) as measured by a novel ELISA based on denatured recombinant HPV16 late (L) and early (E) antigens

BACKGROUND

At present, seroreactivity is not a valuable parameter for diagnosis of Human Papillomavirus (HPV) infection but, it is potentially valuable as marker of viral exposure in elucidating the natural history of this infection. More data are needed to asses the clinical relevance of serological response to HPV.

OBJECTIVES

The objective was to assess the clinical and epidemiological correlates of HPV-seroreactivity in a cohort of HIV-negative and HIV-positive women.

METHODS

Seroreactivity of 96 women, evaluated in an ELISA test based on denatured HPV16 late (L) and early (E) antigens, was correlated with their clinical and epidemiological data previously collected for a multi-centre Italian study, HPV-PathogenISS study.

RESULTS

No significant correlation was found between HPV DNA detection and seroreactivity. Women, current smokers showed significantly less seroreactivity to L antigens as compared with the non-smokers. HIV-positive women showed significantly less (66.7%) antibody response as compared with HIV-negative women (89.3%), with particularly impaired response to L antigens. Women, HIV-positive and current smokers, showed by far the lowest seroprevalence (33.3%) as compared to 75.9% among all other women (OR = 0.158; 95%CI 0.036-0.695, p = 0.014; Fisher's exact test). Importantly, this association did not loose its significance when controlled for confounding from age (continuous variable) in multivariate analysis or using Mantel-Haenszel test for age-groups.

CONCLUSION

It is tempting to speculate that HIV-positive current smokers comprise a special high-risk group, with highly impaired immunological response that could prevent eradication of persistent HPV infections and thus contribute to development of CIN3/CC.

Modification of human papillomavirus-like particle vaccine by insertion of the cross-reactive L2-epitopes

Infection with human papillomavirus 16 (HPV16), which is one of the 15 types of HPV causally associated with cervical cancer and accounts for 50% of the cases, can be prevented in a type-specific manner by an HPV16 virus-like particle (VLP) vaccine comprised of particles of the L1 protein alone. We attempted to modify the VLP vaccine by inserting the HPV16 L2-peptides including cross-neutralization epitopes into the L1 polypeptide. The chimeric L1 had, between L1 amino acids (aa) 430 and 433, the L2 sequence of aa 18-38, 56-75, or 96-115 (with the replacements of S at aa 101 and T at aa 112 with L and S, respectively). The three chimeric L1s were each expressed from the recombinant baculovirus in insect Sf9 cells, and the resultant VLPs were characterized. The chimeric VLPs were shown to present the L2-peptides on their surface. By immunizing rabbits with the VLPs, it was shown that they retained capability to induce the antibody neutralizing HPV16 and acquired capability to elicit antibodies cross-neutralizing the infectious HPV18, 31, 52, and 58 pseudovirions. Although the cross-neutralizing titers were lower than the type-specific neutralizing titer, the results suggest that the chimeric VLPs have potential to serve as a vaccine candidate for a broad spectrum of high-risk HPVs.

Arrangement of L2 within the papillomavirus capsid

Papillomaviruses are a family of nonenveloped DNA tumor viruses. Some sexually transmitted human papillomavirus (HPV) types, including HPV type 16 (HPV16), cause cancer of the uterine cervix. Papillomaviruses encode two capsid proteins, L1 and L2. The major capsid protein, L1, can assemble spontaneously into a 72-pentamer icosahedral structure that closely resembles native virions. Although the minor capsid protein, L2, is not required for capsid formation, it is thought to participate in encapsidation of the viral genome and plays a number of essential roles in the viral infectious entry pathway. The abundance of L2 and its arrangement within the virion remain unclear. To address these questions, we developed methods for serial propagation of infectious HPV16 capsids (pseudoviruses) in cultured human cell lines. Biochemical analysis of capsid preparations produced using various methods showed that up to 72 molecules of L2 can be incorporated per capsid. Cryoelectron microscopy and image reconstruction analysis of purified capsids revealed an icosahedrally ordered L2-specific density beneath the axial lumen of each L1 capsomer. The relatively close proximity of these L2 density buttons to one another raised the possibility of homotypic L2 interactions within assembled virions. The concept that the N and C termini of neighboring L2 molecules can be closely apposed within the capsid was supported using bimolecular fluorescence complementation or "split GFP" technology. This structural information should facilitate investigation of L2 function during the assembly and entry phases of the papillomavirus life cycle.

Detection of human papillomavirus type 31-neutralizing antibodies from naturally infected patients by an assay based on intracellular assembly of luciferase-expressing pseudovirions

The aim of this study was to develop a highly sensitive human papillomavirus type 31 (HPV31) neutralization assay based on the production of pseudovirions carrying luciferase. Neutralizing antibodies against HPV31 were investigated in a set of HPV31 monoclonal antibodies and in women with evidence of HPV31 infection. Neutralizing antibodies were detected in 78% of subjects with a positive enzyme-linked immunosorbent assay.

Thiol-reactive reagents inhibits intracellular trafficking of human papillomavirus type 16 pseudovirions by binding to cysteine residues of major capsid protein L1

Background

A human papillomavirus (HPV) virion is composed of capsid proteins L1 and L2. Several cysteine residues are located on L1 of various HPVs at markedly similar relative positions, suggesting their important functions. Although the authentic virions cannot be studied with cultured cells, surrogate pseudovirions consisting of capsid and reporter plasmid are available for studies dealing with infectivity.

Results

HPV type16-pseudovirions (16PVs) were found to lose their infectivity after incubation with thiol-reactive reagents [biotin polyethyleneoxide iodoacetamide (BPEOIA), 5,5'-dithiobis(2-nitrobenzoic acid) (DTNB), N-ethylmaleimide (NEM), 4-(N-maleimido)benzyl-trimethylammonium iodide (MBTA), and [2-(trimethylammonium)ethyl] methanethiosulfonate bromide (MTSET)]. A labelled streptavidin was detected to bind to the complex of BPEOIA and L1 of the 16PVs incubated with BPEOIA. The analysis of molecular mass of trypsin-fragments derived from the complex of the BPEOIA and L1 indicated that BPEOIA bound to at least C146, C225, and C229. No appreciable change of the 16PVs carrying DTNB or NEM was detected by sedimentation analysis or electron microscopy. The 16PVs carrying DTNB or NEM were able to bind to and enter HeLa cells but degraded before they reached the perinuclear region.

Conclusion

HPV16 L1 C146, C225, and C229 have free thiol, which are accessible to BPEOIA, DTNB, NEM, MBTA, and MTSET. Binding of DTNB or NEM to the thiols may cause conformational changes that result in the inhibition of the entry and trafficking of the 16PVs.

A protective and broadly cross-neutralizing epitope of human papillomavirus L2

We generated a monoclonal antibody, RG-1, that binds to highly conserved L2 residues 17 to 36 and neutralizes human papillomavirus 16 (HPV16) and HPV18. Passive immunotherapy with RG-1 was protective in mice. Antiserum to the HPV16 L2 peptide comprising residues 17 to 36 (peptide 17-36) neutralized pseudoviruses HPV5, HPV6, HPV16, HPV 18, HPV31, HPV 45, HPV 52, HPV 58, bovine papillomavirus 1, and HPV11 native virions. Depletion of HPV16 L2 peptide 17-36-reactive antibodies from cross-neutralizing rabbit and human L2-specific sera abolished cross-neutralization and drastically reduced neutralization of the cognate type. This cross-neutralization of diverse HPVs associated with cervical cancer, genital warts, and epidermodysplasia verruciformis suggests the possibility of a broadly protective, peptide-based vaccine.

Bovine papillomavirus type 1 infection is mediated by SNARE syntaxin 18

Events that lead to viral infections include the binding of the virus to the target cells, internalization of the virus into the cells, and the ability of the viral genome to be expressed. These steps are mediated by cellular and viral proteins and are temporally regulated. The papillomavirus capsid consists of two virally encoded capsid proteins, L1 and L2. Much is known about the role of the major capsid protein L1 compared to what is known of the role of the L2 protein. We identified the interaction of the L2 protein with SNARE protein syntaxin 18, which mediates the trafficking of vesicles and their cargo between the endoplasmic reticulum, the cis-Golgi compartment, and possibly the plasma membrane. Mutations of L2 residues 41 to 44 prevented the interaction of L2 protein with syntaxin 18 in cotransfection experiments and resulted in noninfectious pseudovirions. In this paper, we describe that syntaxin 18 colocalizes with infectious bovine papillomavirus type 1 (BPV1) pseudovirions during infection but does not colocalize with the noninfectious BPV1 pseudovirions made with an L2 mutant at residues 41 to 44. We show that an antibody against BPV1 L2 residues 36 to 49 (alpha L2 36-49) binds to in vitro-generated BPV1 pseudoviral capsids and does not coimmunoprecipitate syntaxin 18- and BPV1 L2-transfected proteins. alpha L2 36-49 was able to partially or completely neutralize infection of BPV1 pseudovirions and genuine virions. These results support the dependence of syntaxin 18 during BPV1 infection and the ability to interfere with infection by targeting the L2-syntaxin 18 interaction and further define the infectious route of BPV1 mediated by the L2 protein.

[Human papillomavirus and cervical cancer]

Human papillomavirus (HPV) is a small non-enveloped icosahedral virus with a circular double-stranded DNA genome of 8 kilo base pairs. HPV particles reach and infect the basal cells of the stratified epithelia through small epithelial lesions. In the basal cells the viral DNA is maintained as episomes, which start to replicate when the host cells initiate terminal differentiation. In these differentiating cells the degradation of p53 by the E6 protein and the abrogation of the pRb functions by the E7 protein lead to the reactivation of the DNA synthesis machinery. After virus propagation the host cells usually die. On the other hand, in some of the infected cells, the E6 and E7 genes are integrated on rare occasion into cell DNA. The cell continuously expressing the E6 and E7 proteins from the integrated genes is immortalized and sometimes acquires malignant phenotype induced by the accumulated damages to DNA. Of more than 100 HPV genotypes recorded to date, 13 including types 16 and 18 are associated with cervical cancer. Expression of HPV major capsid protein L1 in some cultured cells results in production of virus-like particles (VLPs). The VLPs of types 6, 11, 16, and 18 were used as a prophylactic vaccine in recent clinical trials and shown to successfully induce type-specific neutralizing antibodies in the recipients.