Human papillomavirus (HPV) type distribution and serological response to HPV type 6 virus-like particles in patients with genital warts

Chapter 13: Current findings from prophylactic HPV vaccine trials

Early data from randomized controlled trials consistently show that prophylactic human papillomavirus virus-like particle (HPV VLP) vaccines are effective in preventing infection and lesions caused by the targeted HPV type(s). Two vaccines, a bivalent HPV-16/18 VLP vaccine and a quadrivalent HPV-6/11/16/18 VLP vaccine, are currently undergoing evaluation in phase III trials with anticipation of receiving regulatory approval for use in immunization programs worldwide. Both vaccines have the potential to substantially reduce HPV-related morbidity and mortality. This review focuses on published data from clinical trials of these two vaccines.

Genital human papillomavirus infection

Over the past few decades, epidemiology and natural history studies have led to improved understanding of human papillomavirus (HPV) infection and to promising prevention strategies. HPV infection is the cause of anogenital warts and cervical cancer, as well as a proportion of other anogenital and head and neck cancers. Data from clinical trials have resulted in recommendations that support the use of an HPV test in the context of cervical cancer screening and management. Prophylactic HPV vaccine trials have demonstrated high efficacy, and an HPV vaccine that prevents cervical cancer precursors, cervical cancer, and anogenital warts caused by HPV types 6, 11, 16, and 18 was licensed for use in girls and women aged 9-26 years by the US Food and Drug Administration (FDA) in June 2006. In this article, we review genital HPV for the clinician, with a primary focus on the prevalence of HPV infection in the United States.

Condom use and the risk of genital human papillomavirus infection in young women

BACKGROUND

To evaluate whether the use of male condoms reduces the risk of male-to-female transmission of human papillomavirus (HPV) infection, longitudinal studies explicitly designed to evaluate the temporal relationship between condom use and HPV infection are needed.

METHODS

We followed 82 female university students who reported their first intercourse with a male partner either during the study period or within two weeks before enrollment. Cervical and vulvovaginal samples for HPV DNA testing and Papanicolaou testing were collected at gynecologic examinations every four months. Every two weeks, women used electronic diaries to record information about their daily sexual behavior. Cox proportional-hazards models were used to evaluate risk factors for HPV infection.

RESULTS

The incidence of genital HPV infection was 37.8 per 100 patient-years at risk among women whose partners used condoms for all instances of intercourse during the eight months before testing, as compared with 89.3 per 100 patient-years at risk in women whose partners used condoms less than 5 percent of the time (adjusted hazard ratio, 0.3; 95 percent confidence interval, 0.1 to 0.6, adjusted for the number of new partners and the number of previous partners of the male partner). Similar associations were observed when the analysis was restricted to high-risk and low-risk types of HPV and HPV types 6, 11, 16, and 18. In women reporting 100 percent condom use by their partners, no cervical squamous intraepithelial lesions were detected in 32 patient-years at risk, whereas 14 incident lesions were detected during 97 patient-years at risk among women whose partners did not use condoms or used them less consistently.

CONCLUSIONS

Among newly sexually active women, consistent condom use by their partners appears to reduce the risk of cervical and vulvovaginal HPV infection.

Prophylactic human papillomavirus vaccines

Human papillomavirus (HPV) infection causes virtually all cases of cervical cancer, the second most common cause of death from cancer among women worldwide. This Review examines prophylactic HPV subunit vaccines based on the ability of the viral L1 capsid protein to form virus-like particles (VLPs) that induce high levels of neutralizing antibodies. Following preclinical research by laboratories in the nonprofit sector, Merck and GlaxoSmithKline are developing commercial versions of the vaccine. Both vaccines target HPV16 and HPV18, which account for approximately 70% of cervical cancer. The Merck vaccine also targets HPV6 and HPV11, which account for approximately 90% of external genital warts. The vaccines have an excellent safety profile, are highly immunogenic, and have conferred complete type-specific protection against persistent infection and associated lesions in fully vaccinated women. Unresolved issues include the most critical groups to vaccinate and when the vaccine's cost may be low enough for widespread implementation in the developing world, where 80% of cervical cancer occurs.

Genital human papillomavirus infection in men

Genital human papillomavirus (HPV) infection, globally one of the most common sexually transmitted infections, is associated with cancers, genital warts, and other epithelial lesions. Although a consistent and coherent picture of the epidemiology and pathogenesis of genital HPV infections in women has developed over the past two decades, less is known about these infections in men. Available data suggest that, as with women, most genital HPV infections in men are symptomless and unapparent, and that HPV16 is probably the most frequently detected type. In populations of similar age, the prevalence of specific HPV types is usually lower in men than in women. Whether this observation relates to lower incidence or shorter duration of infection in men than in women has not yet been determined. Seroprevalence of specific anti-HPV antibodies also seems to be lower in men than in women of similar age, a difference that might be due to lower viral load, lower incidence or duration of infection or lower antibody responses, or both, in men compared with women. Differences in sexual behaviour may also be important predictors of genital HPV infection. With the anticipated availability of prophylactic HPV vaccines in the near future, it becomes increasingly important to understand the incidence and duration of HPV infections in men to develop cost-effective approaches to prevention through a combination of immunisation and promotion of risk-reduction strategies.

Therapy for genital human papillomavirus-related disease

Genital human papillomavirus (HPV) infection is very common, and often sub-clinical and usually resolves without any treatment. Genital warts are caused by HPV 6/11 infection and are one of the commonest clinically recognised disease manifestations of genital HPV. Subjects with genital warts usually perceive them as cosmetically disfiguring, often leading to adverse psychological symptoms, and most subjects with genital warts will present requesting treatment. A wide variety of treatments are available including both provider- and patient-applied therapies. Various individual subject and disease factors mediate appropriate therapy choice. Some of the treatments that are used for genital warts can also be used for some cases of intraepithelial neoplasia caused by high-oncogenic risk HPVs occurring at vulval, anal or penile sites. Specific treatment considerations apply to genital warts in pregnancy and laryngeal papillomatosis and these are also discussed.

Strategies for the prevention of cervical cancer by human papillomavirus vaccination

As cervical cancer is causally associated with 14 high-risk types of human papillomavirus (HPV), a successful HPV vaccine will have a major impact on this disease. Although some persistent HPV infections progress to cervical cancer, host immunity is generally able to clear most HPV infections. Both cell-mediated and antibody responses have been implicated in influencing the susceptibility, persistence or clearance of genital HPV infection. There have been two clinical trials that show that vaccines based on virus-like particles (VLPs) made from the major capsid protein, L1, are able to type specifically protect against cervical intra-epithelial neoplasia and infection. However, there is no evidence that even a mixed VLP vaccine will protect against types not included in the vaccine, and a major challenge that remains is how to engineer protection across a broader spectrum of viruses. Strategies for production of HPV vaccines using different vaccine vectors and different production systems are also reviewed.

Kinetics and isotype profile of antibody responses in rhesus macaques induced following vaccination with HPV 6, 11, 16 and 18 L1-virus-like particles formulated with or without Merck aluminum adjuvant

BACKGROUND: Human papillomaviruses (HPV) are the most common sexually transmitted viruses. Infection of the cervical epithelium by HPVs can lead to the development of cervical cancer. Recent advances in vaccine research have shown that immunization with papillomavirus-like particles (VLPs) containing the major structural viral protein, L1 from HPV 16 can provide protection from the establishment of a chronic HPV 16 infection and related cervical intraepithelial neoplasia (CIN) in baseline HPV 16 naive women. METHODS: To better understand the quantitative and qualitative effects of aluminum adjuvant on the immunogenic properties of an HPV 6, 11, 16 and 18L1 VLP vaccine, we used an HPV-specific, antibody isotyping assay and a competitive immunoassay that measures antibodies to neutralizing epitopes to profile sera from rhesus macaques immunized with the HPV L1 VLP vaccine formulated with or without aluminum adjuvant. RESULTS: Immunization with VLPs formulated with the aluminum adjuvant elicited a significantly stronger immune response with higher peak antibody titers both at four weeks post vaccination (12.7 to 41.9-fold higher) as well as in the persistent phase at week 52 (4.3 to 26.7-fold higher) than that of VLPs alone. Furthermore, the aluminum adjuvant formulated HPV VLP vaccine elicited a predominantly T helper type 2 response, with high levels of IgG1 and IgG4 and low levels of IgG2. The vaccine also elicited high levels of serum IgA, which may be important in providing mucosal immunity to impart protection in the anogenital tract. CONCLUSION: These results show that the HPV 6, 11, 16 and 18 L1-VLP vaccine formulated with Merck aluminum adjuvant elicits a robust and durable immune response and holds promise as a vaccine for preventing cervical cancer.

The epidemiology of human papillomavirus infections

Infection with oncogenic human papillomavirus (HPV) types is a necessary cause of cervical cancer, the second most frequently occurring cancer in women worldwide. Rates of acquisition of HPV are high, particularly among sexually active young adults. Reported estimates of incident HPV infection among initially negative women have reached as high as 60% over a 5-year follow-up period. In this article, we review the epidemiology of HPV infection. In addition to estimates of disease frequency, we highlight risk factors for HPV infection, including the number of lifetime sex partners, which is the most salient risk factor. We discuss significant issues surrounding the natural history of HPV infection, including viral persistence versus clearance, immune response, development of lesions and development of cancer. Finally, we discuss strategies for preventing HPV infection.

Role of human papillomavirus in penile cancer, penile intraepithelial squamous cell neoplasias and in genital warts

Using PCR, the overall prevalence of human papillomavirus (HPV) DNA in penile carcinoma is about 40-45%, which is similar to the detection rate of HPV-DNA in vulvar carcinoma (50%). In analogy to vulvar cancer two different pathways of penile carcinogenesis seem to exist. In contrast to basaloid and warty penile cancers which are regularly HPV-associated (about 80-100%), only a part of keratinizing and verrucous penile carcinomas appear to be related with HPV (33-35%). Penile intraepithelial neoplasias comprising Bowen's disease, erythroplasia of Queyrat and bowenoid papulosis are precursor lesions of basaloid and warty carcinomas of the penis. Precursors of keratinizing carcinomas and verrucous carcinomas are not established. Whether lichen sclerosus and squamous-cell hyperplasia precede penile keratinizing carcinoma is a matter of discussion. Giant condylomata acuminata may precede the development of verrucous carcinomas in some cases. Since high risk HPVs are more frequently found in verrucous carcinomas than in giant condylomas, HPV typing may be a helpful diagnostic step to differentiate giant condyloma from verrucous carcinoma.

Papillomavirus-like particle vaccines

Papillomavirus-like particle (VLP)-based subunit vaccines have undergone rapid development over the past 8 years. Three types are being investigated. The most basic type is composed of only the L1 major capsid protein and is designed to prevent genital human papillomavirus (HPV) infection by inducing virus-neutralizing antibodies. On the basis of positive results in animal models, clinical trials of this type of vaccine for HPV16, and other types, are currently under way. Preliminary results have been encouraging in that systemic immunization with the L1 VLPs induced high serum titers of neutralizing antibodies without substantial adverse effects. The second type of vaccine incorporates other papillomavirus polypeptides into the VLPs as L1 or L2 fusion proteins. These chimeric VLPs are designed to increase the therapeutic potential of an HPV vaccine by inducing cell-mediated responses to nonstructural viral proteins, such as E7. Studies in mice indicate that these vaccines generate potent antitumor cytotoxic lymphocyte (CTL) responses while retaining the ability to induce high-titer neutralizing antibodies. It is likely that prophylactic and therapeutic clinical trials of chimeric VLPs will be initiated in the near future. The third type of VLP-based vaccine is designed to induce autoantibodies against central self-antigens by incorporating self-peptides into the outer surface of VLPs, a process that could have therapeutic potential in various disease settings unrelated to HPV infection. In a recent proof of concept study, a peptide from an external loop of mouse CCR5 protein was inserted into a neutralizing epitope of L1. In mice, the particles generated by this chimeric L1 were able to induce high titers of CCR5 antibodies that specifically recognized the surface of CCR5-transfected cells and blocked in vitro infection of an M-tropic human immunodeficiency virus strain.

Priming of human papillomavirus type 11-specific humoral and cellular immune responses in college-aged women with a virus-like particle vaccine

In this study, we evaluated the potency of a human papillomavirus (HPV) virus-like particle (VLP)-based vaccine at generating HPV type 11 (HPV-11)-specific cellular and humoral immune responses in seronegative women. The vaccine was administered by intramuscular immunizations at months 0, 2, and 6. A fourth immunization was administered to approximately half of the women at month 12. All vaccine recipients had positive HPV-11 VLP-specific lymphoproliferative responses at month 3 following the second immunization (geometric mean lymphoproliferative stimulation index [SI] = 28.4; 95% confidence interval [CI] = 16.9 to 48.0) and HPV-11 VLP-specific antibody titers following the first immunization at month 1 (geometric mean antibody titer = 53.9 milli-Merck units/ml, 95% CI, 34.8 to 83.7). In contrast, lymphoproliferative and antibody titer responses were never detected in the participants who received placebo. Relatively homogeneous lymphoproliferative responses were observed in all vaccinated women. The mean lymphoproliferative SI of the vaccinated group over the first 12 months of the study was 7.6-fold greater than that of the placebo group following the initial immunization. The cellular immune responses generated by VLP immunization were both Th1 and Th2, since peripheral blood mononuclear cells from vaccinees, but not placebo recipients, secreted interleukin 2 (IL-2), IL-5, and gamma interferon (IFN-gamma) in response to in vitro stimulation with HPV-11 VLP. The proliferation-based SI was moderately correlated with IFN-gamma production and significantly correlated with IL-2 production after the third immunization (P = 0.078 and 0.002, respectively). The robust lymphoproliferative responses were specific for HPV-11, since SIs generated against bovine papillomavirus and HPV-16 VLPs were not generally observed and when detected were similar pre- and postimmunization.

The impact of HIV infection and immunodeficiency on human papillomavirus type 6 or 11 infection and on genital warts

BACKGROUND

HIV infection and associated immunodeficiency are known to alter the course of human papillomavirus (HPV) infections and of associated diseases.

GOAL

This study investigated the association between HIV and HPV and genital warts.

STUDY DESIGN

HPV testing and physical examinations were performed in two large prospective studies: the Women's Interagency HIV Study (WIHS) and the HIV Epidemiology Research Study (HERS). Statistical methods incorporating dependencies of longitudinal data were used to examine the relationship between HIV and HPV and genital warts.

RESULTS

A total of 1008 HIV-seronegative and 2930 HIV-seropositive women were enrolled in the two studies. The prevalence of HPV 6 or 11 was 5.6 times higher in HIV-seropositive women in the WIHS and 3.6 times higher in the HERS. Genital wart prevalence increased by a factor of 3.2 in the WIHS and 2.7 in the HERS in HIV-seropositive women. In the WIHS, infection with HPV type 6 or 11, in comparison with no HPV infection, was associated with odds of genital wart prevalence of 5.1 (95% CI: 2.9-8.8), 8.8 (95% CI: 6.1-12.8), and 12.8 (95% CI: 8.8-18.8) in HIV-seronegative women, HIV-seropositive women with > or =201 CD4 cells/microl, and HIV-seropositive women with < or =200 CD4 cells/microl, respectively. In the HERS, infection with HPV type 6 or 11 was associated with odds of 2.7 (95% CI: 1.6-4.6), 4.9 (95% CI: 3.2-7.7), and 5.3 (95% CI: 3.3-8.5) in these same groups. Other HPV types showed a similar dose-response relation, but of substantially lower magnitude and statistical significance.

CONCLUSIONS

HIV infection and immunodeficiency synergistically modified the relation between HPV 6 or 11 infection and genital wart prevalence.

Developing HPV virus-like particle vaccines to prevent cervical cancer: a progress report

BACKGROUND

the knowledge that sexually transmitted infection with one of a limited number of human papillomaviruses (HPVs) is a central cause of almost all cervical cancers affords the opportunity to prevent this common cancer through anti-viral vaccination.

OBJECTIVE

the spectacular success of vaccines in preventing several other viral diseases offers hope that immunoprophylaxis against the relevant HPVs could lead to a major reduction in cervical cancer incidence.

RESULTS AND CONCLUSION

the results of preclinical studies and early phase clinical trials of virus-like particle (VLP) based subunit vaccines have been very encouraging. However, unique aspects of papillomavirus biology and genital tract infections, and the lack of sexual a transmission model for papillomavirus, make it far from certain that effective prophylactic vaccination against genital HPV infection will be easily achieved. Future clinical efficacy trials will likely test the hypothesis that parenteral injection of VLPs can induce antibody mediated and type specific protection against genital tract HPV infection and subsequent development of premalignant neoplastic disease.

Capture ElISA and in vitro cell binding assay for the detection of antibodies to human papillomavirus type 6b virus-like particles in patients with anogenital warts

To investigate human papillomavirus (HPV) virus-like particle (VLP)-specific antibody responses among anogenital warts patients, a VLP-based capture ELISA was established. Twenty-six percent (35/134) of control subjects and 50.0% (39/78) of patients with current anogenital warts showed IgG seropositivity to HPV 6b VLPs. HPV 6b VLP-specific antibody responses recognised native VLPs only, and had no cross-reaction with HPV type 16 VLPs. No differences in reactivity were observed between L1 and L1 + L2 VLPs, suggesting that L2 contributes little to the total immunogenicity of the papillomavirus virion. A VLP-cell binding assay was also established. Some sera from patients with anogenital warts specifically inhibited VLP binding to the surface of epithelial cells, suggesting that these antibodies might be functionally neutralising. These data show that serological responses to HPV 6b VLPs were induced among some but not all patients with anogenital warts, and give a proportional estimate of infection in the community.

Papillomavirus-like particle vaccines for cervical cancer

Most cervical cancers are now known to be caused by human papillomavirus (HPV) infections. This provides an opportunity to prevent a major cause of cancer deaths in women through vaccination. Subunit vaccines based upon non-infectious papillomavirus-like particles (VLPs) are attractive candidates to prevent infection by oncogenic HPVs, and clinical trials are now underway. In addition, the strongly immunogenic characteristics of VLPs raise the possibility that they could also serve as vehicles for inducing therapeutic responses against HPV-induced neoplasia and other diseases.

Papillomaviruses: prophylactic vaccine prospects

Identification of a subset of HPV types as etiologic agents of cervical cancer and other malignancies implies that development of an effective vaccine against HPV infection could have a major impact on tumors attributable to these viruses. The ability of the L1 major capsid protein of papillomaviruses to self-assemble into VLPs that can, when inoculated systemically, induce high levels of neutralizing antibodies and protect animals against experimental viral challenge makes L1 VLPs an excellent candidate subunit vaccine. VLPs have the limitation of inducing type-specific immunity. Studies in humans are required to determine whether systemic vaccination with L1 VLPs will prevent sexually transmitted HPV infection. Since prospective efficacy trials will take several years to complete, considering alternative approaches is also worthwhile.

Phase I safety and antigenicity of TA-GW: a recombinant HPV6 L2E7 vaccine for the treatment of genital warts

A phase I double-blind, randomized, placebo-controlled study was carried out in healthy subjects to assess the safety and immunogenicity of TA-GW, a recombinant HPV6 L2E7 fusion protein vaccine for the treatment of genital warts. Forty-two healthy male volunteers were randomised to receive three intramuscular injections of either 0, 3, 30 or 300 microg of recombinant L2E7 adsorbed onto Alhydrogel. Two vaccination schedules were compared: weeks 0, 1 and 4 (accelerated schedule) and weeks 0, 4 and 8 (classical schedule). Subjects were monitored for adverse events throughout. Immunogenicity was assessed by measuring L2E7 specific in vitro T cell proliferative responses, production of IFNgamma and IL-5 and serum antibodies. Dose-dependent and long-lived T and B cell immune responses were elicited by TA-GW with both vaccination schedules. In conclusion, TA-GW is both safe, well-tolerated and immunogenic. The results allow the selection of the 300-microg vaccine formulation and accelerated vaccination schedule for phase II trials in patients with genital warts.

Immunoglobulin A, G, and M responses to L1 and L2 capsids of human papillomavirus types 6, 11, 16, 18, and 33 L1 after newly acquired infection

OBJECTIVES

We performed a study to establish the pattern of serological reactivity for immunoglobulins (Ig), to capsids of human papilloma virus (HPV) after new HPV infection in two groups of subjects.

METHODS

The pattern of serological reactivity after acquisition of infection with HPV was investigated by measuring IgA, IgM, and IgG antibodies to capsids containing L1 and L2 proteins of HPV types 6, 11, 16, 18, and 33 in longitudinal studies of groups with different patterns of sexual activity. Individuals who tested negative for HPV DNA by the polymerase chain reaction at enrolment, but who became HPV DNA positive during follow up, were examined for antibodies to HPV capsids by enzyme linked immunosorbent assay. One group consisted of 15 young girls (with eight controls who remained HPV DNA negative) who were becoming sexually active and the other comprised 12 male (with five controls) and 35 female (with seven controls) heterosexual attenders of a sexually transmitted disease clinic who had had multiple sexual partners.

RESULTS

The sexually inexperienced girls showed IgA and IgG responses, but seldom an IgM response to infection with HPV types 6/11, 16, and 18. No consistent pattern of serological reactivity was apparent for the heterosexuals with multiple partners. The lack of association between current HPV DNA positivity and detectable antibodies in these individuals was possibly related to the duration of infection or to prior exposure to HPV. For the latter group serological reactivity to HPV capsids was significantly greater in women than in men (p = 0.001, p = 0.003, and p = 0.024, for IgG to HPV 6, 11, and 16, respectively).

CONCLUSION

The sex difference in antibody response detected in previous studies with assays based on peptide antigens was thus corroborated in the present study with capsid based serological assays. This sex difference might reflect a difference in sexual activity and prior exposure to HPV between men and women in this particular group.

Isolation and characterization of human papillomavirus type 6-specific T cells infiltrating genital warts

The potential role of T cells in the control of human papillomavirus type 6 (HPV-6) infections is an appealing premise, but their actual role has been sparsely investigated. Since HPV-6 infections are confined to the epithelium, such an investigation should focus on the T cells present at the site of infection (i.e., the warts). Therefore, we isolated wart-infiltrating lymphocytes (WIL) from patients with clinically diagnosed anogenital warts. These WIL were characterized by their phenotype and their specificity for E7 and L1 proteins of HPV-6. The phenotype of WIL varied drastically from patient to patient, as determined by their expression of CD4, CD8, T-cell receptor alpha/beta chain (TCR alpha beta), and TCR gamma delta. Despite this heterogeneity in phenotype, HPV-6 E7 and/or L1-specific WIL, as determined by lymphoproliferation, could be isolated from more than 75% of the patients studied. Among all L1 peptides recognized by WIL, peptides 311-330 and 411-430 were the most consistently detected, with seven of nine patients for whom L1 peptide reactivity was observed responding to at least one of them. Moreover, the HPV-6 epitopic peptides recognized by WIL differed to some extent from those recognized by peripheral T cells.

Immunology of papillomavirus infection

Studies of the immunology of papillomavirus infection have come of age. Synthetic virus-like particles have been validated as vaccines for several animal papillomaviruses, and have been used to map the sero-epidemiology of human papillomavirus infection and to define papillomavirus neutralizing antibodies. Induction of cell-mediated immunity to papillomavirus early proteins is poised to become a therapeutic approach to papillomavirus infection. Studies on the immune response to papillomavirus proteins in keratinocytes are shedding light on the immunological consequences of antigen presentation by epithelial cells.