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.     

A phase I study to evaluate a human papillomavirus (HPV) type 18 L1 VLP vaccine

Human papillomavirus (HPV) infection can cause genital warts and cervical cancer. HPV types 6 and 11 cause >90% of genital wart cases; HPV16 and 18 cause 70% of cervical cancers. A prophylactic HPV (types 6, 11, 16, 18) L1 virus-like particle (VLP) vaccine may substantially reduce the incidence of these lesions. This report describes the results of a phase I study of the HPV18 component of such a vaccine. Forty women were randomized to receive either HPV18 L1 VLP vaccine or placebo. Anti-HPV18 responses were measured using a competitive radioimmunoassay (cRIA). Tolerability was evaluated using vaccination report cards (VRC). The study showed that the HPV18 L1 VLP vaccine was generally well-tolerated and highly immunogenic. Peak anti-HPV18 geometric mean titers (GMT) in vaccines were 60-fold greater than those observed in women following natural HPV18 infection. Further studies of a multivalent HPV L1 VLP vaccines are warranted.     

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.     

Safety and immunogenicity of co-administered quadrivalent human papillomavirus (HPV)-6/11/16/18 L1 virus-like particle (VLP) and hepatitis B (HBV) vaccines

Adolescents and young adults are at high risk for human papillomavirus (HPV) and hepatitis B virus (HBV) infections, which are preventable by currently available, safe and effective, prophylactic vaccines. However, development of a combined immunization strategy may lead to better compliance for these vaccines, thereby contributing to the overall goal of protection against these diseases. This study assessed the safety and immunogenicity of co-administered quadrivalent HPV-6/11/16/18 L1 VLP and HBV vaccines in women (n=1877) aged 16-23 years. Co-administration of HPV and HBV vaccines induced robust anti-HPV-6, HPV-11, HPV-16, HPV-18 geometric mean titers (GMTs) and > or =99% seroconversion rates (Month 7) that were both non-inferior (p<0.001) to those induced by HPV vaccine alone. High Month 7 anti-HBs GMTs were also observed following concomitant vaccination. These GMTs were lower compared to those induced by the HBV vaccine itself; however, >96% of subjects achieved an anti-HBs seroprotection level of > or =10 mIU/mL that was non-inferior (p<0.001) to that of HBV vaccine alone. Overall, co-administered and individual vaccines were generally well-tolerated and did not interfere with the immune response of either vaccine (ClinicalTrials.gov number, NCT00092521).     

Prophylactic HPV vaccines: reducing the burden of HPV-related diseases

HPV-associated diseases, such as cervical and other anogenital cancers, cervical and anal intraepithelial neoplasia, genital warts, and recurrent respiratory papillomatosis confer considerable morbidity and mortality, and are significant health care concerns. Successful vaccination strategies that protect against HPV infection are expected to substantially reduce HPV-related disease burden. Prophylactic HPV vaccines in late stages of clinical testing are composed of HPV L1 capsid protein that self-assemble into virus-like particles (VLPs) when expressed in recombinant systems. Proof-of-principle trials have suggested that intramuscular injections of VLPs results in strong adaptive immune responses, both B- and T-cell mediated, that are capable of neutralizing subsequent natural infections. Furthermore, phase 2 trials of a bivalent vaccine designed to protect against high-risk HPV types 16 and 18 and a quadrivalent vaccine designed to protect against HPV 16 and 18, and low-risk, genital wart-causing HPV 6 and 11 have demonstrated that VLP vaccines reduce the incidence of HPV-associated disease in vaccinated individuals. To derive the greatest public health benefit, HPV vaccines offering protection from cervical cancer and genital warts will, ideally, be administered prior to the initiation of sexual activity; therefore, educational initiatives will be essential to communicate the risks and adverse consequences of HPV infection and to foster widespread vaccine acceptance.     

Chapter 12: Prophylactic HPV vaccines: underlying mechanisms

Human papillomavirus virus-like particles (HPV VLP) can be generated by the synthesis and self-assembly in vitro of the major virus capsid protein L1. HPV L1 VLPs are morphologically and antigenically almost identical to native virions, and this technology has been exploited to produce HPV L1 VLP subunit vaccines. The vaccines elicit high titres of anti-L1 VLP antibodies that persist at levels 10 times that of natural infections for at least 48 months. At present the assumption is that the protection achieved by these vaccines against incident HPV infection and HPV-associated ano-genital pathology is mediated via serum neutralising Immunoglobulin G (IgG). However, since there have been very few vaccine failures thus far, immune correlates of protection have not been established. The available evidence is that the immunodominant neutralising antibodies generated by L1 VLPs are type-specific and are not cross-neutralising, although highly homologous HPV pairs share minor cross-neutralisation epitopes. Important issues remaining to be addressed include the duration of protection and genotype replacement.     

Introducing human papillomavirus vaccines into the health system in South Africa

South Africa has a high incidence of cervical cancer, with an age-standardised rate of approximately 27 per 100,000. In 2000, South Africa launched a national screening programme for cervical cancer prevention, offering three Papanicolaou smears per lifetime starting after the age of 30 with 10-year intervals. However, in the public sector, this national screening programme has not been implemented widely. Vaccination would offer the best primary prevention. Currently there are two HPV vaccines registered in South Africa: the bivalent vaccine Cervarix?, containing VLP antigens for oncogenic HPV types 16 and 18; and the quadrivalent vaccine Gardasil?, containing VLP antigens for HPV types 16 and 18, as well as non-oncogenic HPV types 6 and 11, which are the most common types causing genital warts. The vaccines are recommended for prophylactic use, and should ideally be given before exposure to HPV, which is before sexual debut, to girls aged 11-12 years. Possible routes for delivering the HPV vaccine could be either the routine EPI programme at the age of 12 years when dT is being administered, or through the school system, e.g. to girls attending grade 5 or 6.     

Antibody response to human papillomavirus vaccine in subjects with inherited bone marrow failure syndromes

Patients with Fanconi anemia (FA) and other inherited bone marrow failure syndromes (IBMFS) have extremely high risks of squamous cell head and neck, and gynecologic carcinomas. In the general population, these sites are often associated with infection with human papillomaviruses (HPV), particularly HPV16 and HPV18. Our objectives were to measure the levels of HPV antibodies in unvaccinated patients, and to determine whether these patients developed and maintained similar levels of antibodies as those observed in healthy women, following vaccination with the currently licensed HPV L1 virus-like particles (VLP) vaccines. We measured anti-HPV IgG antibody levels in sera from patients using an HPV16 or HPV18 L1 VLP enzyme-linked immunoabsorbent assay. Most unvaccinated patients did not have detectable antibody levels, except for a few women above age 25. Both FA and other IBMFS patients developed antibody levels following vaccination that were similar to those previously described in healthy women, and those levels appeared to be sustained out to 5 years after immunization. Thus, antibody responses to the HPV L1 VLP vaccine in patients with FA and other IBMFS appeared to be similar to the responses reported in the general population, implying potential efficacy against future infections with the HPV types contained in the vaccine.     

Enhanced humoral and memory B cellular immunity using HPV16/18 L1 VLP vaccine formulated with the MPL/aluminium salt combination (AS04) compared to aluminium salt only

An effective virus-like particle (VLP) based prophylactic vaccine designed to protect against persistent infection with human papillomavirus (HPV) types 16 and 18 and subsequent lesion development will need to induce a strong humoral and cellular immune response capable of providing long-term protection. Our objective was to evaluate the ability of an HPV16/18 L1 VLP vaccine formulated with the AS04 adjuvant system (3-O-desacyl-4'-monophosphoryl lipid A (MPL) and aluminium salt) to induce an immune response of higher magnitude and persistence compared to a vaccine formulated with aluminium salt only. We demonstrated that MPL adsorbed onto aluminium salt retains its capacity to activate an innate immune response as assessed by the production of TNFalpha by human monocytes (U937). In addition, vaccination of mice, monkeys or human subjects with AS04 formulations induced higher total anti-L1 VLP16 and L1 VLP18 antibody responses (1.6-8.5-fold) than the aluminium salt only formulations. The enhanced antibody response induced by the AS04 vaccine formulation (1.6-4.1-fold) in monkeys and humans was shown to be targeted to functional neutralising L1 VLP16 and L1 VLP18 epitopes as assessed by V5/J4 specific ELISAs or HPV16 and HPV18 pseudo-neutralization assays. The enhanced immune profile observed with the AS04 formulation in terms of both total, V5/J4 specific and neutralizing antibodies was shown to persist for at least 3.5-year post-vaccination in human subjects. Finally, using the newly developed B cell ELISPOT assay we also demonstrated that the AS04 formulation elicited an increased frequency (2.2-5.2-fold) of HPV L1 VLP specific memory B cells when compared with the aluminium salt only formulations. These data strongly support the role of the AS04 adjuvant, which includes the immunostimulant MPL, in triggering a persistent vaccine-induced immune response of high quality.     

Antibody, cytokine and cytotoxic T lymphocyte responses in chimpanzees immunized with human papillomavirus virus-like particles

We evaluated antibody, cytokine (IFN-gamma, IL-5, TNF-alpha), and cytotoxic T lymphocyte (CTL) responses in chimpanzees immunized with monovalent or quadrivalent (HPV-6, -11, -16, -18) L1 virus-like particle (VLP) vaccines administered i.m. on aluminum hydroxyphosphate (alum) at weeks 0, 8 and 24. Maximum serum antibody titers to type-specific, neutralizing, conformational epitopes on HPV-11 or -16 L1 VLPs were detected by radioimmunoassay (RIA) four weeks after the second and third immunizations. HPV-11 and -16 neutralizing antibodies were also detected at similar time points with an Human papillomaviruses (HPV) neutralization assay using pseudovirions. Depending on the VLP type used for immunization, HPV type-specific cytokine responses were most frequently seen four weeks after the second or third immunizations and between weeks 44-52. Transient HPV-16 L1-specific CTL activity was observed only between weeks 16-24 in 3 of 22 (13.6%) chimpanzees immunized with HPV-16 L1 VLPs. These findings provide evidence that immunization with multivalent L1 VLPs on alum can evoke both neutralizing antibodies and Th1 and Th2 cytokine responses to several HPV types; however, induction of CTLs is infrequent.     

Characterization of the HPV-specific memory B cell and systemic antibody responses in women receiving an unadjuvanted HPV16 L1 VLP vaccine

Human papillomavirus (HPV)-specific antibodies are proposed to be the correlate of protection afforded by HPV L1 virus-like particle (VLP) vaccines. Previous studies have characterized the systemic antibody response to immunization in terms of both the quantity and the ability to neutralize HPV. Here, we have adapted a generalized memory B cell ELISPOT to the HPV16 system and expanded the analysis of the systemic antibody response to include an avidity measurement of HPV L1 VLP-specific antibodies. We show the results of the memory B cell ELISPOT significantly correlated with IgG and neutralizing antibody titers, but not with the avidity measurement. This is the first comprehensive study to correlate a variety of humoral aspects potentially associated with protective immunity following vaccination with a HPV16 L1 VLP vaccine.     

Immune responses induced by lower airway mucosal immunisation with a human papillomavirus type 16 virus-like particle vaccine

Cervical cancer results from cervical infection by human papillomaviruses (HPV), especially HPV16. Previous studies have shown that intramuscular vaccination of women with an HPV16 virus-like particle (VLP) vaccine induced a strong IgG response and protected against genital HPV16 infection. However, an alternative route of administration that avoids parenteral injection while inducing mucosal immunity might facilitate vaccine implementation in some settings, and partially overcome the substantial variation in HPV16 antibodies at the cervix seen in ovulating women. In this study, women were vaccinated with escalating doses of HPV16L1 VLPs via nasal nebulisation, bronchial aerosolisation, or a combination of intramuscular and aerosol vaccination. The alternative routes of vaccination were well tolerated and many of the volunteers who received aerosol vaccinations exhibited serum antibody titers that were comparable to those induced by intramuscular vaccination. A mucosal immune response was induced by aerosol vaccination as demonstrated by the induction of anti-HPV16 VLP IgA secreting cells in PBMC and SIgA in secretions. Our data suggest that aerosol administration of HPV VLPs may represent a potential alternative to parenteral injection.     

Immunologic responses following administration of a vaccine targeting human papillomavirus Types 6, 11, 16, and 18

Human papillomavirus (HPV) infection causes cervical cancer and genital warts. Young women (1106) were randomized to receive one of three formulations of a quadrivalent HPV (Types 6/11/16/18) L1 virus-like particle (VLP) vaccine or one of two placebo formulations. The goal was to assess vaccine safety and immunogenicity in baseline HPV 6/11/16 or 18-naïve and previously infected subjects. All three formulations were highly immunogenic. At Month 2 (postdose 1), among women with vaccine-type antibodies at baseline, vaccine-induced anti-HPV responses were ∼12- to 26-fold higher than those observed in baseline-naïve women, suggesting an anamnestic response. Following an initial, similar sized decline, anti-HPV responses plateaued and remained stable through end-of-study (3.0 years). No vaccine-related serious adverse experiences were reported.     

A papillomavirus-like particle (VLP) vaccine displaying HPV16 L2 epitopes induces cross-neutralizing antibodies to HPV11

Peptides of the papillomavirus L2 minor capsid protein can induce antibodies (Ab) that neutralize a broad range of human papillomavirus (HPV) genotypes. Unfortunately, L2 is antigenically subdominant to L1 in the virus capsid. To induce a strong anti-L2 Ab response with cross-neutralizing activity to other mucosal types, chimeric virus-like particles (VLP) were generated in which HPV16 L2 neutralization epitopes (comprising L2 residues 69-81 or 108-120) are inserted within an immunodominant surface loop (between residues 133 and 134) of the L1 major capsid protein of bovine papillomavirus type 1 (BPV1). These chimeras self-assembled into pentameric capsomers, or complete VLP similar to wild type (wt) L1 protein. Immunization of rabbits with assembled particle preparations induced L2-specific serum Ab with titers 10-fold higher than those induced by cognate synthetic L2 peptides coupled to KLH. Antisera to both chimeric proteins partially neutralized HPV16 pseudovirions, confirming that both HPV16 L2 peptides define neutralization epitopes. When analyzed for the ability to cross-neutralize infection by authentic HPV11 virions, using detection of early viral RNA by RT-PCR-assays as the readout, immune serum to chimeric protein comprising L2 residues 69-81, but not 108-120, was partially neutralizing. In addition, mouse-antiserum induced by vaccinations with synthetic L2 peptide 108-120, but not 69-81, was partially neutralizing in this assay. Induction of cross-neutralization Ab by L2 epitopes displayed on chimeric VLP represents a possible strategy for the generation of broad-spectrum vaccines to protect against relevant mucosal HPV and associated neoplasia.     

Human papillomavirus and HPV vaccines: a review

Cervical cancer, the most common cancer affecting women in developing countries, is caused by persistent infection with "high-risk" genotypes of human papillomaviruses (HPV). The most common oncogenic HPV genotypes are 16 and 18, causing approximately 70% of all cervical cancers. Types 6 and 11 do not contribute to the incidence of high-grade dysplasias (precancerous lesions) or cervical cancer, but do cause laryngeal papillomas and most genital warts. HPV is highly transmissible, with peak incidence soon after the onset of sexual activity. A quadrivalent (types 6, 11, 16 and 18) HPV vaccine has recently been licensed in several countries following the determination that it has an acceptable benefit/risk profile. In large phase III trials, the vaccine prevented 100% of moderate and severe precancerous cervical lesions associated with types 16 or 18 among women with no previous infection with these types. A bivalent (types 16 and 18) vaccine has also undergone extensive evaluation and been licensed in at least one country. Both vaccines are prepared from non-infectious, DNA-free virus-like particles produced by recombinant technology and combined with an adjuvant. With three doses administered, they induce high levels of serum antibodies in virtually all vaccinated individuals. In women who have no evidence of past or current infection with the HPV genotypes in the vaccine, both vaccines show > 90% protection against persistent HPV infection for up to 5 years after vaccination, which is the longest reported follow-up so far. Vaccinating at an age before females are exposed to HPV would have the greatest impact. Since HPV vaccines do not eliminate the risk of cervical cancer, cervical screening will still be required to minimize cancer incidence. Tiered pricing for HPV vaccines, innovative financing mechanisms and multidisciplinary partnerships will be essential in order for the vaccines to reach populations in greatest need.     

Comparison of the immune responses to the CIA06-adjuvanted human papillomavirus L1 VLP vaccine with those against the licensed HPV vaccine Cervarix™ in mice

CIA05 is a toll-like receptor (TLR) 4 agonist derived from an Escherichia coli lipopolysaccharide (LPS) mutant and has been shown to have potential as a vaccine adjuvant. In this study, we investigated the immunopotentiating activity of the adjuvant system CIA06, which is comprised of CIA05 and aluminum hydroxide (alum), when used with the human papillomavirus (HPV) L1 virus-like particles (VLPs) vaccine. BALB/c mice were immunized intramuscularly three times at 2-week intervals with HPV16 L1 VLPs alone or in the presence of various combinations of CIA05 and alum, and the immune responses were assessed. We found that the combination of CIA05 and alum at a ratio of 1:50 (designated CIA06B) yielded the highest immune response in terms of serum anti-HPV L1 VLP IgG antibody titers, splenocyte interferon (IFN)-γ secretion, and antigen-specific memory B cell responses. The immunogenicity of the CIA06B-adjuvanted HPV16/18 L1 VLP vaccine was compared with that of the currently licensed HPV vaccine Cervarix™. The CIA06B-adjuvanted vaccine was similar to Cervarix™ with regard to eliciting serum antigen-specific IgG antibodies and virus-neutralizing antibodies but more effective at inducing splenic cytokine production and memory B cells. We also observed that the antigen-specific IgG antibody titers, splenic IFN-γ secretion and memory B cells induced by the CIA06B-adjuvanted HPV vaccine remained high up to 24 weeks post-immunization. Based on these data, we concluded that CIA06B may have potential as an adjuvant in a potent prophylactic vaccine against HPV infection.     

Rectal and vaginal immunization of mice with human papillomavirus L1 virus-like particles

Human papillomavirus (HPV) vaccines based on L1 virus-like particle (VLP) can prevent genital HPV infection and associated lesions after three intramuscular injections. Needle-free administration might facilitate vaccine implementation, especially in developing countries. Here we have investigated rectal and vaginal administration of HPV16 L1 VLPs in mice and their ability to induce anti-VLP and HPV16-neutralizing antibodies in serum and in genital, rectal and oral secretions. Rectal and vaginal immunizations were not effective in the absence of adjuvant. Cholera toxin was able to enhance systemic and mucosal anti-VLPs responses after rectal immunization, but not after vaginal immunization. Rectal immunization with Resiquimod and to a lesser extent Imiquimod, but not monophosphoryl lipid A, induced anti-HPV16 VLP antibodies in serum and secretions. Vaginal immunization was immunogenic only if administered in mice treated with nonoxynol-9, a disrupter of the cervico-vaginal epithelium. Our findings show that rectal and vaginal administration of VLPs can induce significant HPV16-neutralizing antibody levels in secretions, despite the fact that low titers are induced in serum. Imidazoquinolines, largely used to treat genital and anal warts, and nonoxonol-9, used as genital microbicide/spermicide were identified as adjuvants that could be safely used by the rectal or vaginal route, respectively.     

Chapter 17: Second generation HPV vaccines to prevent cervical cancer

Prophylactic human papillomavirus (HPV) vaccines based on intramuscular injection of non-infectious L1 virus-like particles (VLPs) are undergoing intense clinical evaluation. As documented in preceding chapters of this monograph, clinical trials of these vaccines have demonstrated their safety and high efficacy at preventing type-specific persistent cervical HPV infection and the development of type-specific cervical intraepithelial neoplasia (CIN) cervical neoplasia. There is widespread optimism that VLP vaccines will become commercially available within the next few years. The prospects for development of alternative HPV vaccines must be considered in light of the likelihood that a safe and effective prophylactic HPV vaccine will soon be available. Three questions need to be addressed: (1) Is there sufficient need for a second generation vaccine? (2) Are there sufficiently attractive candidates for clinical trials? (3) Is there a realistic development/commercialization path?     

HPV vaccines to prevent cervical cancer and genital warts: an update

Cervical cancer is an important public health problem worldwide, and especially in developing countries. The link between cervical cancer and oncogenic human papillomavirus (HPV) infection has been clearly established. Furthermore, non-oncogenic HPV are responsible for the majority of genital warts. Two prophylactic HPV vaccines are available, which have the potential of considerably reducing HPV-related morbidity and mortality. Both vaccines are based on virus-like particles of the L1 capsid protein, and are highly efficacious and immunogenic if given before exposure to HPV, i.e. to adolescent girls between 9 and 13 years of age in a three-dose schedule. This review describes the immunology of natural HPV infections and the immune response evoked through vaccination. The current duration of protection is 8.4 years with the bivalent vaccine (HPV16/18) and 5 years with the quadrivalent vaccine (HPV6/11/16/18). Research is on-going to evaluate the efficacy of the current vaccines in a two-dose schedule, as compared to the recommended three-dose schedule. To increase the protection, the development and testing of a nine-valent prophylactic HPV vaccine (HPV6/11/16/18/31/33/45/52/58) is being undertaken. Research is also directed towards therapeutic vaccines and the development of a prophylactic L2 vaccine.     

Vaccination with multimeric L2 fusion protein and L1 VLP or capsomeres to broaden protection against HPV infection

Immunization with L1 as pentavalent capsomeres or virus-like particles (VLPs) generates high and long-lived titers of neutralizing antibodies and protection primarily against the human papillomavirus (HPV) type from which the vaccine was derived. Conversely, vaccination with L2 minor capsid protein derived from multiple HPV types induces lower titer, but more broadly neutralizing and protective antibody responses. We combined the advantages of each protective antigen by immunization with titrated doses of multi-type L2 with either L1 capsomeres or VLP. We observed no significant interference between the L1 and L2 antibody response upon co-administration of L1 vaccines with multi-type L2 vaccines.