Antibody-mediated neutralization of human papillomavirus type 11 (HPV-11) infection in the nude mouse: detection of HPV-11 mRNAs

Impact of the human papilloma vaccine on cervical cancer

During the last decade, research progress on cervical cancer has elucidated the role of human papilloma virus (HPV) in the pathogenesis of cervical cancer. Clinical trials on the viral-like particle HPV vaccines have good safety profiles and promising efficacy in preventing genital warts, cervical neoplasia, and cervical cancer. The implementation of the HPV vaccine is a tremendous milestone in our effort toward preventing cervical cancers. However, screening programs will continue to serve as a critical component in prevention due to the limitations of the current vaccines. The greatest impact in cervical cancer incidence worldwide requires improved health care access to underserved areas. Advances are needed to develop single-dose, heat-stable, needle-free, and affordable formulations of the HPV vaccine to overcome the socioeconomic barriers associated with this disease.

Human papillomavirus therapeutic vaccines in head and neck tumors

Head and neck cancer represents one of the most challenging diseases as the mortality remains high despite advances in early diagnosis and treatment. Human papillomavirus has been implicated in a third of head and neck squamous cell carcinomas and human papillomavirus type 16 is strongly associated with carcinomas arising from the oropharynx, the tonsil being the preferred infected site. Novel therapeutic approaches including immunotherapy are currently under investigation. Immune vaccines developed against human papillomavirus in the genital area are already available and could simultaneously protect other anatomical localizations; however, prophylactic vaccines are expected to be effective in reducing the incidence of tumors after many years and, therefore, there is an urgent need to improve therapeutic interventions, such as immunotherapy. To date, human papillomavirus therapeutic vaccines are either at the preclinical level or at early phase human trials for genital pathologies. Nevertheless, accumulating evidence from animal and clinical studies suggests that the enhancement of specific and innate immune responses is effective in clearance of the human papillomavirus infection, promoting a cautious optimism regarding the achievement of an efficacious immunotherapy. This article reviews what has been achieved and what remains to be done in the field for the development of future viral vaccines in head and neck tumors.

How will HPV vaccines affect cervical cancer?

Cancer of the uterine cervix is the second largest cause of cancer deaths in women, and its toll is greatest in populations that lack screening programmes to detect precursor lesions. Persistent infection with 'high risk' genotypes of human papillomavirus (HPV) is necessary, although not sufficient, to cause cervical carcinoma. Therefore, HPV vaccination provides an opportunity to profoundly affect cervical cancer incidence worldwide. A recently licensed HPV subunit vaccine protects women from a high proportion of precursor lesions of cervical carcinoma and most genital warts. Here we examine the ramifications and remaining questions that surround preventive HPV vaccines.

Correlation of Histology, Human Papillomavirus, and Viral Load in Laryngeal Papillomas of Childhood

The purpose of this study was to analyze 47 laryngeal papillomas in children for human papillomavirus (HPV) DNA by in situ hybridization and RT in situ PCR and to correlate these results with the histologic findings. HPV DNA was detected by in situ hybridization in 29 of 47 (62%) of the cases; all positive cases contained HPVs 6 or 11. HPV DNA detection was associated with a statistically significant increase in the presence of keratohyaline granules, nonuniform perinuclear halos, and marked papillomatosis (P<0.02). The viral load was low, defined by less than 20 HPV-positive cells per tissue with a correspondingly weak signal, in 19 of 29 (65%) of the positive cases. In comparison, a high viral load was evident in 19 of 21 (90%) of vulvar condylomas. The laryngeal lesions negative for HPV by in situ hybridization were tested for HPV by RT in situ PCR using primers specific for HPVs 6 and 11. The detection rate of HPV increased to 38 of 47 (81%) after PCR amplification. It is concluded that laryngeal papillomas in childhood are characterized, in general, by a relatively low HPV viral load and that the cases with productive viral infection, as demonstrated by in situ hybridization, are associated with nonuniform keratohyaline granules, nonuniform perinuclear halos, and marked papillomatosis.

Dose-ranging studies of the safety and immunogenicity of human papillomavirus Type 11 and Type 16 virus-like particle candidate vaccines in young healthy women

Two candidate vaccines to prevent infection with human papillomavirus (HPV) Types 11 and 16 were studied in similar double-blind, placebo-controlled, dose-escalation trials. L1 virus-like particle (VLP) vaccines were made from recombinant L1 capsid protein of HPV11 or HPV16. Participants received 10, 20, 50, or 100 microg of HPV11 L1 VLPs, 10, 40, or 80 microg of HPV16 L1 VLPs, or placebo at Months 0, 2, and 6. Serum geometric mean antibody levels at Month 7 were 258, 644, 647, and 1112 milli-Merck units (mMU)/ml for the 10, 20, 50, and 100 microg doses of the HPV11 L1 VLP vaccine, respectively, and 479, 808, and 732 mMU/ml for the 10, 40, and 80 microg doses of the HPV16 L1 VLP vaccine, respectively. Antibody to HPV11 and 16 was still present at Month 36 in 96.8 and 93.5% of vaccinees, respectively. Both vaccines were well tolerated and were associated with only mild to moderate injection-site reactions.

Oral immunogenicity of human papillomavirus-like particles expressed in potato

Human papillomavirus-like particles (HPV VLPs) have shown considerable promise as a parenteral vaccine for the prevention of cervical cancer and its precursor lesions. Parenteral vaccines are expensive to produce and deliver, however, and therefore are not optimal for use in resource-poor settings, where most cervical HPV disease occurs. Transgenic plants expressing recombinant vaccine immunogens offer an attractive and potentially inexpensive alternative to vaccination by injection. For example, edible plants can be grown locally and can be distributed easily without special training or equipment. To assess the feasibility of an HPV VLP-based edible vaccine, in this study we synthesized a plant codon-optimized version of the HPV type 11 (HPV11) L1 major capsid protein coding sequence and introduced it into tobacco and potato. We show that full-length L1 protein is expressed and localized in plant cell nuclei and that expression of L1 in plants is enhanced by removal of the carboxy-terminal nuclear localization signal sequence. We also show that plant-expressed L1 self-assembles into VLPs with immunological properties comparable to those of native HPV virions. Importantly, ingestion of transgenic L1 potato was associated with activation of an anti-VLP immune response in mice that was qualitatively similar to that induced by VLP parenteral administration, and this response was enhanced significantly by subsequent oral boosting with purified insect cell-derived VLPs. Thus, papillomavirus L1 protein can be expressed in transgenic plants to form immunologically functional VLPs, and ingestion of such material can activate potentially protective humoral immune responses.

Hybrid papillomavirus L1 molecules assemble into virus-like particles that reconstitute conformational epitopes and induce neutralizing antibodies to distinct HPV types

Human papillomavirus (HPV) hybrid virus-like particles (VLPs) were prepared using complementary regions of the major capsid L1 proteins of HPV-11 and -16. These hybrid L1 proteins were tested for assembly into VLPs, for presentation and mapping of conformational neutralizing epitopes, and as immunogens in rabbits and mice. Two small noncontiguous hypervariable regions of HPV-16 L1, when replaced into the HPV-11 L1 backbone, produced an assembly-positive hybrid L1 which was recognized by the type-specific, conformationally dependent HPV-16 neutralizing monoclonal antibody (N-MAb) H16.V5. Several new N-MAbs that were generated following immunization of mice with wild-type HPV-16 L1 VLPs also recognized this reconstructed VLP, demonstrating that these two hypervariable regions collectively constituted an immunodominant epitope. When a set of hybrid VLPs was tested as immunogens in rabbits, antibodies to both HPV-11 and -16 wild-type L1 VLPs were obtained. One of the hybrid VLPs containing hypervariable FG and HI loops of HPV-16 L1 replaced into an HPV-11 L1 background provoked neutralizing activity against both HPV-11 and HPV-16. In addition, conformationally dependent and type-specific MAbs to both HPV-11 and HPV-16 L1 VLP were obtained from mice immunized with hybrid L1 VLPs. These data indicated that hybrid L1 proteins can be constructed that retain VLP-assembly properties, retain type-specific conformational neutralizing epitopes, can map noncontiguous regions of L1 which constitute type-specific conformational neutralizing epitopes recognized by N-MAbs, and trigger polyclonal antibodies which can neutralize antigenically unrelated HPV types.

Human papillomavirus type 11 recombinant L1 capsomeres induce virus-neutralizing antibodies

The human papillomavirus type 11 (HPV-11) L1 major capsid protein can be trypsinized to generate recombinant capsomeres that retain HPV genotype-restricted capsid antigenicity (M. Li, T. P. Cripe, P. A. Estes, M. K. Lyon, R. C. Rose, and R. L. Garcea, J. Virol. 71:2988-2995, 1997). In the present study, HPV-11 virion-neutralizing monoclonal antibodies H11.F1 and H11.H3, previously characterized as recognizing two distinct HPV-11 capsid-neutralizing antigenic domains (S. W. Ludmerer, D. Benincasa, and G. E. Mark III, J. Virol. 70:4791-4794, 1996), were each found to be highly immunoreactive with trypsin-generated capsomeres in an enzyme-linked immunosorbent assay (ELISA). Capsomeres were used to generate high-titer polyclonal immune sera that demonstrated HPV genotype-restricted reactivity by ELISA. The capsomere antisera were then tested in an in vitro infectivity assay and found to neutralize HPV-11 virions. In this assay, HPV-11 capsomere polyclonal antisera exhibited neutralization titers (10(-5) to 10(-6)) comparable to those obtained with a virion-neutralizing antiserum raised previously against intact HPV-11 VLPs (R. C. Rose, R. C. Reichman, and W. Bonnez, J. Gen. Virol. 75:2075-2079, 1994). These results indicate that highly immunogenic, genotype-restricted HPV capsid-neutralizing antigenic domains are contained entirely within capsomeres. Thus, capsomeres may be viable vaccine candidates for the prevention of HPV disease.

Isolation and propagation of human papillomavirus type 16 in human xenografts implanted in the severe combined immunodeficiency mouse

We report the isolation and propagation of human papillomavirus type 16, the main agent of cervical cancer, using human foreskin fragments implanted in severe combined immunodeficiency mice. The infection produced viral particles, and with each passage of the virus it caused lesions identical to intraepithelial neoplasia, the precursor to carcinoma.

In vitro infection and type-restricted antibody-mediated neutralization of authentic human papillomavirus type 16

Human papillomavirus type 16 (HPV-16) is strongly associated with the development of cervical cancer. Studies of model systems with animal papillomaviruses have demonstrated the importance of neutralizing antibodies in preventing papillomavirus-associated disease. The assessment of neutralizing antibody responses against HPV-16, previously hampered by the lack of a viral source, was enabled by the recent propagation of an HPV-16 stock in xenografted severe combined immunodeficiency (SCID) mice. HPV-16 infection of an immortalized human keratinocyte cell line was demonstrated by detection of an HPV-16-specific spliced mRNA amplified by reverse transcriptase PCR. Infection was blocked by preincubation of the virus with antiserum generated against HPV-16 virus-like particles (VLPs) composed of the major capsid protein, L1. To examine potential cross-neutralizing activity among the different genital HPV types, rabbit antisera to L1 VLPs corresponding to HPV-6, -11, -18, -31, -33, -35, -39, and -45 were assayed for the ability to block the HPV-16 infection of cultured cells. Antiserum raised against HPV-33 L1 VLPs was the only heterologous antiserum which inhibited HPV-16 infection. Thus, a neutralization assay for HPV-16 may help to characterize the components required to compose a broadly efficacious genital HPV vaccine.

Human papillomavirus type 11 neutralization in the athymic mouse xenograft system: correlation with virus-like particle IgG concentration

Neutralization of virus is likely to be necessary for development of an effective prophylactic vaccine against genital human papillomavirus (HPV) infection. Two New Zealand white rabbits were immunized with purified HPV type 11 (HPV 11) virions in Freund's adjuvant. An enzyme linked immunoassay (ELISA) was used to determine the quantity of IgG which recognized the HPV 11 major capsid protein (L1 protein) virus-like particles (VLPs) in the two anti-HPV 11 sera (serum A and serum B). The concentration of HPV 11 L1 VLP-specific IgG in the A and B sera were determined to be 37 and 90 micrograms per ml, respectively. The A and B sera were used in neutralization experiments in the athymic mouse xenograft system with known quantities of purified HPV 11 virions. The concentration of HPV 11 L1 VLP-specific IgG required to neutralize HPV 11 was determined for each antiserum. This concentration of IgG was approximately 700 to 900 ng per ml. This study demonstrates a positive correlation between the level of HPV 11 L1 VLP-specific IgG in animals immunized with HPV 11 virions and neutralization of HPV 11 in the athymic mouse model. Further studies are needed 1) to determine if sera or genital secretions from other species are neutralizing in the athymic mouse xenograft system, and 2) to determine if the VLP ELISA can be used as a reliable substitute for more cumbersome neutralization assays.

Cell mediated immunity induced in mice by HPV 16 L1 virus-like particles

Recombinant human papillomavirus (HPV) type 16 L1 virus-like particles (VLPs) expressed in the baculovirus system were used to investigate the cellular immune response to human papillomavirus type 16. The cell-mediated immune response was evaluated through immunization of mice with HPV 16 L1 virus-like particles using a lymphoproliferation assay and cytokine production and cytometric analysis of lymphocyte subsets. A significant proliferative response was observed which was associated with secretion of both interferon-gamma and interleukin-2. FACS analysis of splenic lymphocytes revealed that CD8+ T-cells were increased in the immunized mice. These results demonstrate that HPV 16 L1 VLPs induce a T-cell response characterized by a Th1 profile and confirm that the HPV 16 VLP is a reasonable candidate for vaccine development.

Expression of the human papillomavirus type 11 L1 capsid protein in Escherichia coli: characterization of protein domains involved in DNA binding and capsid assembly

The L1 major capsid protein of human papillomavirus type 11 (HPV-11) was expressed in Escherichia coli, and the soluble recombinant protein was purified to near homogeneity. The recombinant L1 protein bound DNA as determined by the Southwestern assay method, and recombinant mutant L1 proteins localized the DNA-binding domain to the carboxy-terminal 11 amino acids of L1. Trypsin digestion of the full-length L1 protein yielded a discrete 42-kDa product (trpL1), determined by sodium dodecyl sulfate-polyacrylamide gel electrophoresis, resulting from cleavage at R415, 86 amino acids from the L1 carboxy terminus. Sucrose gradient sedimentation analysis demonstrated that trpL1 sedimented at 11S, while L1 proteins with amino-terminal deletions of 29 and 61 residues sedimented at 4S. Electron microscopy showed that the full-length L1 protein appeared as pentameric capsomeres which self-assembled into capsid-like particles. The trpL1 protein also had a pentameric morphology but was unable to assemble further. In an enzyme-linked immunosorbent assay, the trpL1 and L1 capsids reacted indistinguishably from virus-like particles purified after expression of HPV-11 L1 in insect cells. The carboxy terminus of L1 therefore constitutes the interpentamer linker arm responsible for HPV-11 capsid formation, much like the carboxy-terminal domain of the polyomavirus VP1 protein. The trypsin susceptibility of HPV-11 L1 capsids suggests a possible mechanism for virion disassembly.

Titration of HPV-11 infectivity and antibody neutralization can be measured in vitro

Human papillomavirus type 11 (HPV-11), produced from the athymic mouse xenograft system, was shown to infect cultured neonatal human foreskin keratinocytes and the HaCaT keratinocyte cell line in vitro. Infection was documented by the appearance of HPV-11-specific spliced mRNA, detected by reverse transcriptase-polymerase chain reaction. Purified HPV-11 virions at concentrations of approximately 10(7) particles/ml could successfully evoke infection in this system. Infection was completely abrogated by preincubation of the HPV-11 inoculum with mouse anti-HPV-11 monoclonal antibodies, experimentally immunized animal sera, or sera of human patients with HPV infection. Concurrent detection of cellular mRNA for the beta-actin gene, also by reverse transcriptase-polymerase chain reaction, provided an internal control confirming RNA recovery and successful reverse transcriptase-polymerase chain reaction. Using this approach, it was possible to determine semiquantitative titers for test solutions of HPV-11-neutralizing antibodies. The in vitro system for HPV-11 infectivity and neutralization may be useful in the study of the immune response to HPV-11 infection or immunization in patients.

Two E2 binding sites (E2BS) alone or one E2BS plus an A/T-rich region are minimal requirements for the replication of the human papillomavirus type 11 origin

Human papillomaviruses (HPVs) cannot be propagated in vitro, but the DNA can be replicated transiently in an assay in the presence of two trans-acting viral proteins, E1 and E2. Using this assay, we have defined the minimal cis-acting elements of the origin of replication of HPV type 11. Most HPV genomes are conserved at the origin of replication, and the core contains three E2 binding sites (E2BS) surrounding an A/T-rich spacer region. The present results show that the minimal requirement for replication is either two E2BS alone or the A/T-rich region plus one E2BS; in the latter case the relative position of the E2BS is important. In all the studies, the presence of both E1 and E2 proteins was essential for replication, yet only the E2BS was required at the origin. We have shown that E1, E2, and the origin of replication containing an E2BS from a complex in vitro, and our data are consistent with a model in which E2 acts to target E1 to the HPV type 11 replication origin.

In vitro HPV-11 infection of human foreskin

Study of the infectious process of human papillomavirus type 11 (HPV-11) has been facilitated by the discovery that HPV-11-infected neonatal human foreskin epithelium can proliferate as xenografts into condyloma-like growths within athymic nude mice. Here we describe detection of HPV-11 infection of neonatal human foreskin-derived keratinocytes, infected and cultured entirely in vitro, by use of the polymerase chain reaction and primers straddling the splice donor/acceptor site of the most prevalent early gene HPV-11 transcript (E1 increase E4). Expression of the E1 increase E4 HPV-11 mRNA is abrogated by 60 degrees C heat inactivation of the inoculum. HPV-11-infected foreskin explants continue to produce the E1 increase E4 mRNA for up to 5 weeks in culture, and second-passage keratinocytes derived from infected explant outgrowths continue to produce the E1 increase E4 mRNA. The in vitro system described here provides a new way to study HPV-11 infection and may be useful in evaluating early events of infection.

Monoclonal antibody neutralization of BPV-1

Mouse monoclonal antibodies were generated against intact infectious BPV-1 virions by methods previously described (Christensen et al., 1990). ELISA was used to screen for reactivities to intact and/or disrupted BPV-1, CRPV and HPV-11 virions. Several hybridomas were initially selected that showed antibody reactivity by ELISA to both intact and disrupted BPV-1, to disrupted BPV-1 only, or to intact BPV-1 virions. One monoclonal antibody, designated B1.A1, which reacted only to intact BPV-1 was selected for virus neutralization analyses. ELISA demonstrated that this monoclonal antibody bound to intact BPV-1 virions, but not to intact CRPV, HPV-11 or to disrupted papillomavirus (PV) antigens. Strong neutralization of BPV-1-induced focus formation of mouse C127 cells by monoclonal B1.A1 was observed. The neutralization titer was equivalent to the neutralization titer obtained with a polyclonal rabbit anti-BPV-1 virion antisera, and directly correlated with antibody concentration as determined by ELISA. These results extend our previous analyses on the epitopes of infectious papillomaviruses as defined by monoclonal antibodies that identify neutralizing epitopes. The nature of these epitopes is such that maintenance of the quaternary structure of the infectious virions is necessary for preservation of the antigenicity of the neutralizing epitope.

Expression of human papillomavirus type 11 L1 protein in insect cells: in vivo and in vitro assembly of viruslike particles

The L1 coat protein of human papillomavirus type 11 (HPV-11) was expressed in Sf-9 insect cells with the recombinant baculovirus vector Ac11L1. Viruslike particles (VLPs) were identified by electron microscopy in the nucleus and cytoplasm of Sf-9 cells infected with Ac11L1. The L1 protein was purified from Ac11L1-infected insect cells. The purified protein spontaneously assembled in vitro into various aggregates, including particles appearing similar to empty virions. Reaction of VLP-containing insect cell extracts with antisera directed against either denatured or nondenatured capsid epitopes in Western blot (immunoblot) and immuno-dot blot assays suggested that conformational epitopes present in native HPV-11 infectious virions were also present on the baculovirus-produced HPV-11 VLPs. Immuno-dot blot assays using human sera obtained from individuals with biopsy-proven condyloma acuminatum correlated closely with results previously obtained in HPV-11 whole virus particle-based enzyme-linked immunosorbent assays. These morphologic and immunologic similarities to native HPV-11 virions suggest that recombinant VLPs produced in the baculovirus system may be useful in seroepidemiology and pathogenesis studies of genital HPV infection and that they may also be potential candidates for vaccine development.

Antibody response to human papillomavirus (HPV) type 11 in children with juvenile-onset recurrent respiratory papillomatosis (RRP)

We previously established, using an ELISA, the presence of specific antibodies directed at human papillomavirus (HPV) type 11 virions in the sera of patients with condylomata acuminata, mostly a disease of young adults that, like recurrent respiratory papillomatosis (RRP), is caused by two closely related HPVs, types 6 and 11. The present study was done to investigate if children with RRP can make viral-specific antibodies to an infection that is acquired at birth. Using the same ELISA, we studied the sera of 32 children with biopsy-documented juvenile-onset RRP and compared them to the sera of 31 control children. The median (and interquartile range) of the OD values in the controls and the cases was 0.078 (0.003, 0.101) and 0.230 (0.063, 0.725), respectively, a statistically significant difference (P = 0.001). Among the cases, there was no difference in seroreactivity between children with HPV-11-induced RRP and those with HPV-6-induced RRP (P = 0.31). Since HPV-11 viral particles do bind to the ELISA plate and remain intact and accessible to antibodies, we conclude that children with RRP, like adults with condylomata acuminata, develop antibodies directed at HPV-11 virions.