Kinetic and HPV infection effects on cross-type neutralizing antibody and avidity responses induced by Cervarix(®)

Distribution of high- and low-risk human papillomavirus genotypes and their prophylactic vaccination coverage among West African women: systematic review

INTRODUCTION

The second most deadly gynecological cancer worldwide, cervical cancer is steadily on the rise in sub-Saharan Africa, while vaccination programs are struggling to get off the ground. This systematic review's aim was to assess the prevalence and distribution of high- and low-risk HPV genotypes in West African women.

METHODS

Original studies were retrieved from PubMed/Medline, Embase, Scopus, Google Scholar, and Science Direct. In these studies, Human papillomavirus (HPV) DNA was assessed in cervical samples by polymerase chain reaction (PCR), Hybrid capture, and sequencing. The quality of the articles was assessed and the results were extracted and reviewed.

RESULTS

Thirty-nine studies from 10 West African countries were included for the systematic review including 30 for the pooled analysis. From an overall of 17358 participants, 5126 of whom were infected with at least one HPV genotype, the systematic review showed a prevalence varying from 8.9% to 81.8% in the general population. In contrast, the pooled prevalence of infection was 28.6% (n = 3890; 95% CI 27.85-29.38), and HPV-52 (13.3%), HPV-56 (9.3%), and HPV-35 (8.2) were the most frequent. Quadrivalent and nonavalent vaccines covered 18.2% and 55.8% of identified genotypes respectively.

CONCLUSION

Faced with this growing public health challenge in West Africa, it would be necessary for all its countries to have reliable data on HPV infection and to introduce the nonavalent vaccine. A study of the genotypic distribution of HPV in high-grade precancerous lesions and cervical cancer would be very useful in West Africa.

Optimization of a protocol for the evaluation of antibody responses to human papillomavirus (HPV) vaccination in low-resource settings

Introduction

Available human papillomavirus (HPV) vaccines could have an important primary role in cervical cancer prevention once their long-term immunogenicity and safety are evaluated at the population level. The aim of this study was to optimize an assay to be used in evaluating the long-term durability of HPV vaccine response following a pilot vaccination of adolescent girls in Ghana.

Methods

A rapid, high-throughput, indirect enzyme-linked immunosorbent assay (ELISA) was optimized for the detection and quantitation of anti-HPV L1 (late expression protein: types 6, 11, 16 and 18) immunoglobulin G (IgG) in human serum (n = 89). The utility of the assay was demonstrated using serum collected from a cohort of pre-adolescent girls (n = 49) previously vaccinated with a quadrivalent vaccine and non-immune serum obtained from age-matched controls (n = 40).

Results

The assay showed good discrimination of antibody levels between cases and control sera: seroprevalence of anti-HPV IgG antibodies was significantly higher among vaccinated than unvaccinated girls for both HPV-16 (63.3% vs. 12.5%; p < 0.001) and HPV-18 (34.7% vs. 20.0%; p = 0.042), respectively. Thirty-six months after receiving the third dose of vaccine, significantly higher mean anti-HPV-16 (0.618 vs. 0.145), anti-HPV-18 (0.323 vs. 0.309), and anti-HPV-6 (1.371 vs. 0.981) antibody levels were measured, compared to unvaccinated girls (all p < 0.05). A correlation between optical density and antibody activity indicated assay sensitivity to increasing levels of antibody activity.

Conclusion

We have successfully optimized and implemented a robust and sensitive assay for the evaluation of antibody responses among immunized adolescent girls for monitoring future large-scale HPV vaccination studies in low-income settings. Our results demonstrated greater immunoglobulin G antibody activity within serum drawn from adolescent girls immunized 36 months prior.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12905-022-01821-y.

Immunity after HPV Vaccination in Patients after Sexual Initiation

Vaccinations against human papillomavirus (HPV) are included in the primary prevention of precancerous intraepithelial lesions and HPV-related cancers. Despite the undeniable effectiveness of vaccination in the juvenile population, there is still little research on the effect in patients after sexual initiation. Our study aims to assess anti-HPV (L1 HPV) antibodies in healthy patients and diagnosed cervical pathology after 9-valent vaccination. We provide a prospective, ongoing 12-month, non-randomised pilot study in which 89 subjects were enrolled. We used an enzyme-linked immunosorbent assay to determine IgG class antibodies to HPV. We noted significantly higher levels of antibodies in vaccinated individuals than in the unvaccinated control group. The above work shows that vaccination against HPV might be beneficial in patients after sexual initiation as well as in those already diagnosed with HPV or SIL infection.

HPV16 infection decreases vaccine-induced HPV16 antibody avidity: the CVT trial

The HPV vaccine has shown sustained efficacy and consistent stabilization of antibody levels, even after a single dose. We defined the HPV16-VLP antibody avidity patterns over 11 years among women who received one- or three doses of the bivalent HPV vaccine in the Costa Rica HPV Vaccine Trial. Absolute HPV16 avidity was lower in women who received one compared to three doses, although the patterns were similar (increased in years 2 and 3 and remained stable over the remaining 8 years). HPV16 avidity among women who were HPV16-seropositive women at HPV vaccination, a marker of natural immune response to HPV16 infection, was significantly lower than those of HPV16-seronegative women, a difference that was more pronounced among one-dose recipients. No differences in HPV16 avidity were observed by HPV18 serostatus at vaccination, confirming the specificity of the findings. Importantly, point estimates for vaccine efficacy against incident, six-month persistent HPV16 infections was similar between women who were HPV16 seronegative and seropositive at the time of initial HPV vaccination for both one-dose and three-dose participants. It is therefore likely that this lower avidity level is still sufficient to enable antibody-mediated protection. It is encouraging for long-term HPV-vaccine protection that HPV16 antibody avidity was maintained for over a decade, even after a single dose.

Prevalence of vaccine and non-vaccine human papillomavirus types among women in Accra and Kumasi, Ghana: a cross-sectional study

BACKGROUND

Human Papillomavirus (HPV) infection is the main etiological factor for pre-invasive and invasive cervical cancer. HPV type-specific vaccination is being widely recommended to control the burden of disease, but the genotype-specific distribution of HPV may vary in different countries. The aim of the study was to determine the prevalence and distribution of HPV genotypes among women attending reproductive health services in Ghana, their associated risk factors, and to assess the potential coverage of identified HPV genotypes by three licensed vaccines among these women.

METHOD

Women presenting for reproductive health services in two regional hospitals in Accra and Kumasi from October 2014 to March 2015 were conveniently recruited into the study (n = 317). HPV-DNA detection and genotype identification were carried out by a nested multiplex PCR assay that combines degenerate E6/E7 consensus primers and type-specific primers for the detection and typing of eighteen HPV genotypes. Cytology was performed to screen women for cervical cancer lesions. Risk factors for HPV infection were analyzed by logistic regression. Statistical significance was accepted for p < 0.05.

RESULTS

The age of study participants ranged from 21 to 76 years. Among women positive for HPV, 35.0% were infected with high-risk HPV, 14.5% with probable high-risk HPV, and 17.0% with low-risk HPV. The prevalence of HPV 16/18 was 8.2%, HPV 6/11/16/18 was 9.1% and HPV 6/11/16/18/31/33/45/52/58 was 28.4%. The most prevalent among HR-HPV were types 52 (18.3%) and 58 (8.8%). HPV positivity may be associated with educational background (p < 0.001), age at first pregnancy (p = 0.028), and age at coitarche (p = 0.016).

CONCLUSIONS

Our study revealed a high prevalence of HR-HPV infection among women. The high prevalence of HR HPV indicates that multivalent vaccines will be useful for controlling HPV burden in general population contexts. The distribution of HPVs in this population suggests that of the three currently available vaccines the nonavalent vaccine, which protects against seven HPV types in addition to HPV 16 and 18, has the highest coverage of HPV infections among Ghanaian women. Healthcare officials planning to reduce the transmission of HPV and cervical cancer must consider the coverage of the nonavalent vaccine as an advantage.

Review of long-term immunogenicity following HPV vaccination: Gaps in current knowledge

The licensed HPV vaccines are highly efficacious and induce high levels of neutralizing antibody levels, the assumed mediators of protection. However, a correlate of protection against HPV is lacking, and the evidence is still limited as to long-term persistence of antibodies, especially following reduced dosing schedules. The World Health Organization (WHO) urges immunization of young girls as part of the strategy to eliminate cervical cancer, thus long-lasting protection is required. The current review describes long-term follow-up regarding vaccine-induced seropositivity and antibody level development following the different vaccines and dosing schedules. Implications and opportunities of long-term vaccine-induced immune responses are discussed, such as the gaps in monitoring of long-term immunogenicity, the possibilities of reduced dosing schedules, and the importance of evidence for durable immunity.

Antibody avidity, persistence, and response to antigen recall: comparison of vaccine adjuvants

Differences in innate immune ‘imprinting’ between vaccine adjuvants may mediate dissimilar effects on the quantity/quality of persisting adaptive responses. We compared antibody avidity maturation, antibody/memory B cell/CD4⁺ T cell response durability, and recall responses to non-adjuvanted fractional-dose antigen administered 1-year post-immunization (Day [D]360), between hepatitis B vaccines containing Adjuvant System (AS)01_B, AS01_E, AS03, AS04, or Alum (NCT00805389). Both the antibody and B cell levels ranked similarly (AS01_B/E/AS03 > AS04 > Alum) at peak response, at D360, and following their increases post-antigen recall (D390). Proportions of high-avidity antibodies increased post-dose 2 across all groups and persisted at D360, but avidity maturation appeared to be more strongly promoted by AS vs. Alum. Post-antigen recall, frequencies of subjects with high-avidity antibodies increased only markedly in the AS groups. Among the AS, total antibody responses were lowest for AS04. However, proportions of high-avidity antibodies were similar between groups, suggesting that MPL in AS04 contributes to avidity maturation. Specific combinations of immunoenhancers in the AS, regardless of their individual nature, increase antibody persistence and avidity maturation.

Systematic literature review of neutralizing antibody immune responses to non-vaccine targeted high-risk HPV types induced by the bivalent and the quadrivalent vaccines

INTRODUCTION

Studies on the cross-protective effect of HPV bivalent and quadrivalent vaccines demonstrated inconsistent findings against additional HPV types covered by the nonavalent vaccine. The objective of this study was to conduct a systematic literature review to assess the consistency and durability of the cross-protective neutralizing antibody immune responses of the currently licensed bivalent and quadrivalent vaccines to non-vaccine HPV types targeted by the nonavalent vaccine (HPV 6, 11, 31, 33, 45, 52, and 58).

METHODS

PubMed and EMBASE databases were searched from 2008 to 2019 to identify studies reporting antibody/immune response after vaccination with either the bivalent, quadrivalent, or nonavalent vaccine. Key outcomes were seroconversion, seropositivity or geometric mean titers against HPV types 6, 11, 31, 33, 45, 52, and 58.

RESULTS

Eighteen publications met inclusion criteria, reporting on 14 interventional and five observational studies. Across all studies, immune responses to non-vaccine high-risk HPV types after bivalent vaccination were higher than baseline or quadrivalent vaccine. Nonavalent vaccine elicited near total seroconversion to HPV types 31, 33, 45, 52, and 58, with seropositivity remaining near 100% up to 24 months post-dose 1. In contrast, bivalent and quadrivalent vaccination resulted in lower seroconversion levels for non-vaccine types, which waned over time.

CONCLUSIONS

The cross-protection antibody/immune response among participants having received all three doses of bivalent or quadrivalent vaccine is not comparable to the specific response elicited by HPV vaccine types. Even in cases where a statistically significant cross-reactive immunological response is reported, long-term data on the duration of the response beyond two years are very limited. Further, the lack of a standard for assays limits comparability of results between studies.

Design Concepts of Virus-Like Particle-Based HIV-1 Vaccines

Prophylactic vaccines remain the best approach for controlling the human immunodeficiency virus-1 (HIV-1) transmission. Despite the limited efficacy of the RV144 trial in Thailand, there is still no vaccine candidate that has been proven successful. Consequently, great efforts have been made to improve HIV-1 antigens design and discover delivery platforms for optimal immune elicitation. Owing to immunogenic, structural, and functional diversity, virus-like particles (VLPs) could act as efficient vaccine carriers to display HIV-1 immunogens and provide a variety of HIV-1 vaccine development strategies as well as prime-boost regimes. Here, we describe VLP-based HIV-1 vaccine candidates that have been enrolled in HIV-1 clinical trials and summarize current advances and challenges according to preclinical results obtained from five distinct strategies. This mini-review provides multiple perspectives to help in developing new generations of VLP-based HIV-1 vaccine candidates with better capacity to elicit specific anti-HIV immune responses.

Role of Multivalency and Antigenic Threshold in Generating Protective Antibody Responses

Vaccines play a vital role in protecting our communities against infectious disease. Unfortunately, some vaccines provide only partial protection or in some cases vaccine-mediated immunity may wane rapidly, resulting in either increased susceptibility to that disease or a requirement for more booster vaccinations in order to maintain immunity above a protective level. The durability of antibody responses after infection or vaccination appears to be intrinsically determined by the structural biology of the antigen, with multivalent protein antigens often providing more long-lived immunity than monovalent antigens. This forms the basis for the Imprinted Lifespan model describing the differential survival of long-lived plasma cell populations. There are, however, exceptions to this rule with examples of highly attenuated live virus vaccines that are rapidly cleared and elicit only short-lived immunity despite the expression of multivalent surface epitopes. These exceptions have led to the concept that multivalency alone may not reliably determine the duration of protective humoral immune responses unless a minimum number of long-lived plasma cells are generated by reaching an appropriate antigenic threshold of B cell stimulation. Examples of long-term and in some cases, potentially lifelong antibody responses following immunization against human papilloma virus (HPV), Japanese encephalitis virus (JEV), Hepatitis B virus (HBV), and Hepatitis A virus (HAV) provide several lessons in understanding durable serological memory in human subjects. Moreover, studies involving influenza vaccination provide the unique opportunity to compare the durability of hemagglutinin (HA)-specific antibody titers mounted in response to antigenically repetitive whole virus (i.e., multivalent HA), or detergent-disrupted “split” virus, in comparison to the long-term immune responses induced by natural influenza infection. Here, we discuss the underlying mechanisms that may be associated with the induction of protective immunity by long-lived plasma cells and their importance in future vaccine design.

Recombinant baculovirus vaccine expressing hemagglutinin of H7N9 avian influenza virus confers full protection against lethal highly pathogenic H7N9 virus infection in chickens

The emergent highly pathogenic avian influenza A (H7N9) (HPAI) virus is a major public concern in China. Therefore, it is crucially important to develop an effective vaccine against this virus. In this study, we constructed a baculovirus vaccine expressing the hemagglutinin (HA) of H7N9 strain A/Chicken/Jiaxing/148/2014 (JX148). The recombinant baculovirus (rBac-JX148HA) generated in this study showed good growth in insect cells and good safety, and it stably expressed the HA protein. We compared the immunogenicity and efficacy of the inactivated whole-virus vaccine JX148 and rBac-JX148HA. One chicken in the JX148-treated group died on day 4 post-challenge, and three chickens had typical clinical symptoms (survival rate, 90%; morbidity, 40%). However, no chickens immunized with rBac-JX148HA showed clinical signs during the 14-day observation period. An analysis of viral shedding and viral replication demonstrated that rBac-JX148HA more efficiently inhibited viral shedding and viral replication than the inactivated whole-virus vaccine. Taken together, these results indicate that the inactivated recombinant baculovirus vaccine induces a high hemagglutination inhibition antibody titer, provides complete protection against challenge with the highly pathogenic H7N9 virus, and effectively inhibits viral shedding. Therefore, the candidate vaccine has potential utility in the prevention and control of H7N9 avian influenza and is also appropriate for veterinary vaccines using cell suspension culture technology.

Immunogenicity of HPV prophylactic vaccines: Serology assays and their use in HPV vaccine evaluation and development

When administered as standard three-dose schedules, the licensed HPV prophylactic vaccines have demonstrated extraordinary immunogenicity and efficacy. We summarize the immunogenicity of these licensed vaccines and the most commonly used serology assays, with a focus on key considerations for one-dose vaccine schedules. Although immune correlates of protection against infection are not entirely clear, both preclinical and clinical evidence point to neutralizing antibodies as the principal mechanism of protection. Thus, immunogenicity assessments in vaccine trials have focused on measurements of antibody responses to the vaccine. Non-inferiority of antibody responses after two doses of HPV vaccines separated by 6 months has been demonstrated and this evidence supported the recent WHO recommendations for two-dose vaccination schedules in both boys and girls 9-14 years of age. There is also some evidence suggesting that one dose of HPV vaccines may provide protection similar to the currently recommended two-dose regimens but robust data on efficacy and immunogenicity of one-dose vaccine schedules are lacking. In addition, immunogenicity has been assessed and reported using different methods, precluding direct comparison of results between different studies and vaccines. New head-to-head vaccine trials evaluating one-dose immunogenicity and efficacy have been initiated and an increase in the number of trials relying on immunobridging is anticipated. Therefore, standardized measurement and reporting of immunogenicity for the up to nine HPV types targeted by the current vaccines is now critical. Building on previous HPV serology assay standardization and harmonization efforts initiated by the WHO HPV LabNet in 2006, new secondary standards, critical reference reagents and testing guidelines will be generated as part of a new partnership to facilitate harmonization of the immunogenicity testing in new HPV vaccine trials.

Comparative Cost-Effectiveness Analysis of Two Different Two-Dose Human Papillomavirus Vaccines in Malaysia

Purpose:

To comparatively evaluate the results of a 2-dose human papillomavirus (HPV) vaccination programme with the AS04-adjuvanted HPV16/18 vaccine (AS04-HPV-16/18v) or HPV-6/11/16/18 vaccine (4vHPVv), in addition to cervical cancer (CC) screening, in Malaysia.

Methods:

A lifetime Markov model replicating the natural history of HPV in 13-year-old girls was adapted to Malaysia to assess the impact of vaccination on pre-cancerous lesions, genital warts and CC cases, CC deaths, quality-adjusted life years (QALYs), and costs from the perspective of the Malaysian Ministry of Health. Vaccine effectiveness was based on efficacy and HPV type distribution. Both vaccines were assumed to have equal efficacy against vaccine-type HPV but differed for protection against non-vaccine types. Vaccine price parity was used and health and cost outcomes were discounted at 3%/annum. Sensitivity analyses tested the robustness of the results.

Results:

The model predicted that AS04-HPV-16/18v would result in 361 fewer CC cases and 115 fewer CC deaths than 4vHPVv, whereas 4vHPVv averted 4,241 cases of genital warts over the cohort’s lifetime. Discounted total costs showed savings of 18.50 million Malaysian Ringgits and 246 QALYs in favour of AS04-HPV-16/18v. In one-way sensitivity analyses, the discount rate was the most influential variable for costs and QALYs, but AS04-HPV-16/18v remained dominant throughout. A two-way sensitivity analysis to assess the longevity of cross-protection for both vaccines confirmed the base-case.

Conclusions:

In Malaysia, the use of AS04-HPV-16/18v, in addition to screening, was modelled to be dominant over 4vHPVv, with greater estimated CC benefits and lower costs.

Opportunities and challenges for human papillomavirus vaccination in cancer

The discovery of genotype 16 as the prototype oncogenic human papillomavirus (HPV) initiated a quarter century of laboratory and epidemiological studies that demonstrated their necessary, but not sufficient, aetiological role in cervical and several other anogenital and oropharyngeal cancers. Early virus-induced immune deviation can lead to persistent subclinical infection that brings the risk of progression to cancer. Effective secondary prevention of cervical cancer through cytological and/or HPV screening depends on regular and widespread use in the general population, but coverage is inadequate in low-resource settings. The discovery that the major capsid antigen L1 could self-assemble into empty virus-like particles (VLPs) that are both highly immunogenic and protective led to the licensure of several prophylactic VLP-based HPV vaccines for the prevention of cervical cancer. The implementation of vaccination programmes in adolescent females is underway in many countries, but their impact critically depends on the population coverage and is improved by herd immunity. This Review considers how our expanding knowledge of the virology and immunology of HPV infection can be exploited to improve vaccine technologies and delivery of such preventive strategies to maximize reductions in HPV-associated disease, including incorporation of an HPV vaccine covering oncogenic types within a standard multitarget paediatric vaccine.

Explanations for the high potency of HPV prophylactic vaccines

HPV L1 virus-like particle (VLP) vaccines administered in a prime/boost series of three injections over six months have demonstrated remarkable prophylactic efficacy in clinical trials and effectiveness in national immunization programs with high rates of coverage. There is mounting evidence that the vaccines have similar efficacy and effectiveness even when administered in a single dose. The unexpected potency of one dose of these VLP vaccines may largely be attributed to structural features of the particles, which lead to the efficient generation of long-lived antigen-specific antibody-producing cells and unique features of the virus life cycle that make the HPV virions highly susceptible to antibody-mediated inhibition of infection.

Cross-reactivity of antigens and antibodies belonging to different pathogenic types of human papillomaviruses

The analysis of the properties of a quadrivalent peroral vaccine against the cervical cancer, which was created in a plant expression system on the base of transgenic tomato fruits, by immunoassay and Western blot hybridization showed that the antibodies against human papilloma virus 16 L1 (HPV16 L1) actively interacted not only with the antigenic proteins HPV18 L1, HPV31 L1, and HPV45 L1, but also with the antigenic protein HPV6 L1, which belongs to another HPV family. Thus, new data on the possibility of crossreactivity between antibodies and antigens belonging to remote HPV families were obtained.

Description of a novel multiplex avidity assay for evaluating HPV antibodies

Limited data exists regarding antibody avidity for human papillomavirus (HPV). We describe development of a multiplex electrochemiluminescent avidity ELISA for four HPV types (HPV 6, 11, 16, 18) by adding a dissociating step to our established multiplex HPV VLP ELISA. Initial experiments exploring ammonium thiocyanate, sodium thiocyanate and guanidine hydrochloride (GuHCl) as dissociating agents identified GuHCl as most promising. Dissociation conditions with GuHCl were varied (concentration, incubation time, temperature) to select conditions with minimal impact on VLP integrity as measured with monoclonal antibodies to conformational epitopes. Avidity index (AI) was calculated based on a standard curve as ratio of bound IgG in GuHCl treated versus untreated sample. To evaluate our assay we determined AI in sera with known HPV titers. We selected 32 residual anonymized sera from individuals with a wide range of titers for HPV6, 11, 16, and 18. AIs were similar across multiple dilutions of serum within the assay's dynamic range and were reproducible with two plate lots. This assay will aid in understanding HPV antibody avidity and maturation in response to natural infection and varying vaccine schedules. This is the first report of a VLP-based multiplexed avidity ELISA that evaluates assay parameters for all nine HPV vaccine types.

Human papillomavirus (HPV)-16/18 AS04-adjuvanted vaccine for the prevention of cervical cancer and HPV-related diseases

Vaccines are available against human papillomavirus (HPV), the causal agent of cervical and other cancers. Efficacy data from the HPV-16/18 AS04-adjuvanted vaccine clinical trial program were reviewed. Six randomized, controlled phase II/III trials evaluating cervical endpoints enrolled women from diverse populations and geographical locations. The program analyzed extensively the cohorts most relevant from a public health perspective: the total vaccinated cohort (TVC), approximating a general population including those with existing or previous HPV infection, and TVC-naïve, approximating a population of young women before sexual debut. Results show that the vaccine reduces HPV-16/18 infection and associated cervical endpoints in women regardless of age, location, or sexual experience. It provides cross-protection against some non-vaccine oncogenic HPV types and types causing genital warts, and may be effective against vulvar, oral, and anal HPV infection. Early epidemiology data following its introduction suggest a decline in the prevalence of vaccine and some non-vaccine HPV types.

HPV vaccines: how many doses are needed for protection?

HPV virus-like particle vaccines are highly immunogenic, well tolerated and are in the national immunization programs in more than 62 countries. Genital HPV is a sexually transmitted infection with first infection occurring just after the onset of sexual activity. The routine cohort for immunization in almost all countries are adolescent girls 9–15 years of age with or without catch-up for older adolescents and young women. In countries with vaccine coverage exceeding 50%, reductions in vaccine type HPV geno-prevalence and disease are being shown. The mechanism of protection is assumed to be via neutralizing antibody. Antibody concentration in adolescents less than 14 years of age after two doses of vaccine at 0 and 6 months are noninferior to women after three doses and in whom efficacy was demonstrated in randomized control trials. The original three-dose schedules have already been reduced in many countries, for those 14 years of age and under, to two doses at least 6 months apart for the licensed vaccines Cervarix® and GARDASIL®. There is preliminary evidence that one dose of vaccine is as effective as two or three doses at preventing persistent HPV infection in the cervix in young women and a one-dose schedule may be possible if supported by evidence from randomized controlled trials.

Efficacy of commercial genotype 1 porcine reproductive and respiratory syndrome virus (PRRSV) vaccine against field isolate of genotype 2 PRRSV

Although several recent studies have found that type 1 porcine reproductive and respiratory syndrome virus (PRRSV) modified live virus (MLV) vaccine showed appreciable levels of cross-protection against type 2 PRRSV infection, the possibility of cross-protection between two genotype of PRRSV is still controversial. To determine potential protective efficacy against hetero-genotype field strain of PRRSV and to improve understandings of the mechanisms underlying performance improvement after infection in vaccinated animals, piglets were vaccinated with type 1 PRRSV MLV vaccine and challenged with type 2 field strain of PRRSV. As a result, vaccinated animals gained on average 8.45 kg in comparison to 4.77 kg measured in non-vaccinated animals during a 3-week period after viral challenge, which shows using a certain PRRSV vaccine could be clinically effective against heterologous genotypic virus challenge. In vaccinated animals, viremia was reduced and cleared rapidly, whilst viral load was much higher and reduced more slowly, indicating rebound viremia in non-vaccinated animals. The titers of neutralizing antibody against the type 2 PRRSV did not exceed the protective level in any animal from both vaccinated and control groups. Instead, antibody avidity of vaccinated animals was much higher than in the control group clearly. Furthermore, a strong negative correlation between antibody avidity and viremia was noted in 80% of vaccinated animals. Through those results from tests evaluating degree of antibody maturation and its relevance with clearing viremia, it could be suggested that non-neutralizing antibodies induced by vaccination prior to challenge might play a key role in protection against PRRSV infection, especially in early time course.

Cross-protection of the Bivalent Human Papillomavirus (HPV) Vaccine Against Variants of Genetically Related High-Risk HPV Infections

BACKGROUND

Results from the Costa Rica Vaccine Trial (CVT) demonstrated partial cross-protection by the bivalent human papillomavirus (HPV) vaccine, which targets HPV-16 and HPV-18, against HPV-31, -33, and -45 infection and an increased incidence of HPV-51 infection.

METHODS

A study nested within the CVT intention-to-treat cohort was designed to assess high-risk HPV variant lineage-specific vaccine efficacy (VE). The 2 main end points were (1) long-term incident infections persisting for ≥2 years and/or progression to high-grade squamous intraepithelial lesions (ie, cervical intraepithelial neoplasia grade 2/3 [CIN 2/3]) and (2) incident transient infections lasting for <2 years. For efficiency, incident infections due to HPV-16, -18, -31, -33, -35, -45, and -51 resulting in persistent infection and/or CIN 2/3 were matched (ratio, 1:2) to the more-frequent transient viral infections, by HPV type. Variant lineages were determined by sequencing the upstream regulatory region and/or E6 region.

RESULTS

VEs against persistent or transient infections with HPV-16, -18, -33, -35, -45, and -51 did not differ significantly by variant lineage. As the possible exception, VEs against persistent infection and/or CIN 2/3 due to HPV-31 A/B and HPV-31C variants were -7.1% (95% confidence interval [CI], -33.9% to 0%) and 86.4% (95% CI, 65.1%-97.1%), respectively (P = .02 for test of equal VE). No difference in VE was observed by variant among transient HPV-31 infections (P = .68).

CONCLUSIONS

Overall, sequence variation at the variant level does not appear to explain partial cross-protection by the bivalent HPV vaccine.

Prophylactic HPV vaccination: past, present, and future

Human papillomavirus (HPV) is the necessary cause of cervical cancer, the fourth most common cancer and cause of cancer-related death in females worldwide. HPV also causes anal, vaginal, vulvar, penile, and oropharyngeal cancer. Prophylactic HPV vaccines based on recombinantly expressed virus-like particles have been developed. Two first-generation, U.S. Food and Drug Administration (FDA)-approved vaccines prevent infections and disease caused by HPV16 and HPV18, the two HPV genotypes that cause approximately 70% of cervical cancer, and one of these vaccines also prevents HPV6 and HPV11, the two HPV genotypes that cause 90% of genital warts. A next-generation vaccine, recently approved by the U.S. FDA, targets HPV16, HPV18, and five additional HPV genotypes that together causes approximately 90% of cervical cancer as well as HPV6 and HPV11. In clinical trials, these vaccines have shown high levels of efficacy against disease and infections caused by the targeted HPV genotypes in adolescent females and males and older females. Data indicate population effectiveness, and therefore cost effectiveness, is highest in HPV-naive young females prior to becoming sexually active. Countries that implemented HPV vaccination before 2010 have already experienced decreases in population prevalence of targeted HPV genotypes and related anogenital diseases in women and via herd protection in heterosexual men. Importantly, after more than 100 million doses given worldwide, HPV vaccination has demonstrated an excellent safety profile. With demonstrated efficacy, cost-effectiveness, and safety, universal HPV vaccination of all young, adolescent women, and with available resources at least high-risk groups of men, should be a global health priority. Failure to do so will result in millions of women dying from avertable cervical cancers, especially in low- and middle-income countries, and many thousands of women and men dying from other HPV-related cancers.

JC polyomavirus mutants escape antibody-mediated neutralization

JC polyomavirus (JCV) persistently infects the urinary tract of most adults. Under conditions of immune impairment, JCV causes an opportunistic brain disease, progressive multifocal leukoencephalopathy (PML). JCV strains found in the cerebrospinal fluid of PML patients contain distinctive mutations in surface loops of the major capsid protein, VP1. We hypothesized that VP1 mutations might allow the virus to evade antibody-mediated neutralization. Consistent with this hypothesis, neutralization serology revealed that plasma samples from PML patients neutralized wild-type JCV strains but failed to neutralize patient-cognate PML-mutant JCV strains. This contrasted with serological results for healthy individuals, most of whom robustly cross-neutralized all tested JCV variants. Mice administered a JCV virus-like particle (VLP) vaccine initially showed neutralizing "blind spots" (akin to those observed in PML patients) that closed after booster immunization. A PML patient administered an experimental JCV VLP vaccine likewise showed markedly increased neutralizing titer against her cognate PML-mutant JCV. The results indicate that deficient humoral immunity is a common aspect of PML pathogenesis and that vaccination may overcome this humoral deficiency. Thus, vaccination with JCV VLPs might prevent the development of PML.

Cancer prevention in HIV-infected populations

People living with human immunodeficiency virus (HIV) are living longer since the advent of effective combined antiretroviral therapy (cART). While cART substantially decreases the risk of developing some cancers, HIV-infected individuals remain at high risk for Kaposi sarcoma, lymphoma, and several solid tumors. Currently HIV-infected patients represent an aging group, and malignancies have become a leading cause of morbidity and mortality. Tailored cancer-prevention strategies are needed for this population. In this review we describe the etiologic agents and pathogenesis of common malignancies in the setting of HIV, as well as current evidence for cancer prevention strategies and screening programs.

A comparative study of two different assay kits for the detection of secreted alkaline phosphatase in HPV antibody neutralization assays

To assess immunogenicity and development of antibodies in the context of vaccination, it is critical to quantify titers of neutralizing antibodies. We have been employing the 293TT cell-based neutralization assay system to quantify anti-HPV neutralizing antibodies. In this system, human papillomavirus (HPV) pseudovirion (PsV) particles encapsidating secreted alkaline phosphatase (SEAP) gene are used to measure infection of 293TT cells in 72-hr cell-culture supernatants. SEAP has traditionally been measured by Great EscAPe™ SEAP Chemiluminescence Kit 2.0 (GE). To reduce the cost, and to potentially increase efficiency, we sought a cheaper kit with better detection capability. Performance characteristics of the newer chemiluminescence kit, ZiVa® Ultra SEAP Plus Assay (Ziva) and GE were compared using the 293TT system. Dose titration of HPV PsV 16 or 18 showed that signal-to-noise ratios at 48 and 72 hr post-infection were higher for ZiVa at nearly all doses. ZiVa was superior to GE as it was able to detect SEAP at 48 hr, as well as when lower numbers of 293TT cells were used. The ability of ZiVa to quantitate HPV-16 and -18 neutralizing antibody titers was tested using sera from Cervarix® immunized individuals. Spearman rank correlational analyses showed excellent correlations between the titers obtained with ZiVa and GE for anti-HPV16 (r = 0.9822, p < 0.0001) and anti-HPV18 (r = 0.9832, p < 0.0001) antibodies. We concluded that ZiVa is superior to GE in detecting SEAP, and the antibody titers in sera of vaccinated individuals were similar to those obtained with GE. Thus, Ziva is a suitable alternative to GE.

Human papillomavirus vaccines: key factors in planning cost-effective vaccination programs

Prophylactic HPV vaccines hold tremendous potential for reducing cervical and non-cervical HPV-related disease burden worldwide. To maximize on this potential, policy officials will need to carefully consider available evidence, existing uncertainties and the cost-effectiveness of mass HPV vaccination programs in the context of their respective nations and/or regions. Proper harmonization of primary prevention strategies with secondary prevention efforts will also be important. Decisions following such considerations may ultimately depend on programmatic objectives, infrastructure and available resources. Continued research and surveillance surrounding HPV vaccination will be essential for filling current knowledge gaps, and forcing ongoing reconsiderations of selected immunization strategies.

Pre-clinical immunogenicity of human papillomavirus alpha-7 and alpha-9 major capsid proteins

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Comprehensive pre-clinical immunogenicity evaluation of HPV L1 major capsid protein.

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Majority neutralizing antibody response was genotype-specific.

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Reciprocal cross-neutralization between some Alpha-7 and Alpha-9 genotypes.

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Tetravalent formulation (HPV16/18/39/58) induced broadly neutralizing antibodies.

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These data improve our understanding of the antigenic diversity of the L1 protein.

Human papillomavirus (HPV) vaccines confer protection against the oncogenic genotypes HPV16 and HPV18 through the generation of type-specific neutralizing antibodies raised against the constituent virus-like particles (VLP) based upon the major capsid proteins (L1) of these genotypes. The vaccines also confer a degree of cross-protection against some genetically related types from the Alpha-9 (HPV16-like: HPV31, HPV33, HPV35, HPV52, HPV58) and Alpha-7 (HPV18-like: HPV39, HPV45, HPV59, HPV68) species groups. The mechanism of cross-protection is unclear but may involve antibodies capable of recognizing shared inter-genotype epitopes. The relationship(s) between the genetic and antigenic diversity of the L1 protein, particularly for non-vaccine genotypes, is poorly understood.

We carried out a comprehensive evaluation of the immunogenicity of L1 VLP derived from genotypes within the Alpha-7 and Alpha-9 species groups in New Zealand White rabbits and used L1L2 pseudoviruses as the target antigens in neutralization assays.

The majority antibody response against L1 VLP was type-specific, as expected, but several instances of robust cross-neutralization were nevertheless observed including between HPV33 and HPV58 within the Alpha-9 species and between HPV39, HPV59 and HPV68 in the Alpha-7 species. Immunization with an experimental tetravalent preparation comprising VLP based upon HPV16, HPV18, HPV39 and HPV58 was capable of generating neutralizing antibodies against all the Alpha-7 and Alpha-9 genotypes. Competition of HPV31 and HPV33 cross-neutralizing antibodies in the tetravalent sera confirmed that these antibodies originated from HPV16 and HPV58 VLP, respectively, and suggested that they represent minority specificities within the antibody repertoire generated by the immunizing antigen. These data improve our understanding of the antigenic diversity of the L1 protein per se and may inform the rational design of a next generation vaccine formulation based upon empirical data.

Immunogenicity and safety of the bivalent HPV vaccine in female patients with juvenile idiopathic arthritis: a prospective controlled observational cohort study

OBJECTIVES

To compare the immunogenicity and safety of the bivalent human papillomavirus (HPV)16/18 vaccine between female patients with juvenile idiopathic arthritis (JIA) and healthy female adolescents.

METHODS

68 patients and 55 healthy girls aged 12-18 years were included in a prospective controlled observational cohort and were vaccinated at 0, 1 and 6 months. Primary outcomes were immunogenicity expressed as seropositivity rate after three vaccine doses at 7 and 12 months and HPV-specific geometric mean antibody concentrations. Secondary outcomes were HPV16/18-specific memory B cell responses in a subset of participants and safety, defined as adverse events and the effect of vaccination on JIA disease activity.

RESULTS

All participants were seropositive for HPV16 and HPV18 at 7 months. One patient turned seronegative at 12 months for HPV16/18. No significant differences were found between patients and controls in HPV-specific antibody concentrations; however, antibody concentrations were consistently lower in patients. No effect of methotrexate on HPV16 antibodies (p=0.79) or HPV18 antibodies (p=0.37) was detected. All patients on anti-TNFα treatment were seropositive after vaccination. The kinetics of HPV16/18 memory B cell responses was comparable between patients and controls, but the magnitude of B cell responses at 7 and 12 months appeared lower in patients. No relevant differences in adverse events were found. HPV vaccination did not aggravate JIA disease.

CONCLUSIONS

The bivalent HPV16/18 vaccine is immunogenic and well tolerated in JIA patients. However, HPV-specific antibodies and B cell responses tended to be lower in patients compared with healthy controls.

CLINICAL TRIAL LISTING

NCT00815282.

Impact of smoking on the quantity and quality of antibodies induced by human papillomavirus type 16 and 18 AS04-adjuvanted virus-like-particle vaccine - a pilot study

Background

The AS04-adjuvanted bivalent L1 virus-like-particle (VLP) vaccine (Cervarix™) against infection with human papillomavirus (HPV) types 16/18 holds great promise to prevent HPV16/18 infections and associated neoplasias, but it is important to rule out significant co-factors of the neoplasias like smoking.

Methods

We conducted a pilot study to compare the quantity and quality of HPV16/18 antibody response at baseline and 7 months post vaccination in 104 non-smoking and 112 smoking female participants vaccinated at 0, 1 and 6 months with Cervarix™ (55 and 48 study participants) or with Hepatitis A vaccine (HAVRIX™) (48 and 64 participants, respectively). These 216 women were a sub-sample of 4808 baseline 16- to 17-year old Finnish women initially enrolled in the double-blind, randomized controlled phase III PATRICIA trial. Following end-of-study unblinding in 2009 they were randomly chosen out of all the participants of the three major Finnish PATRICIA study sites in the Helsinki metropolitan area (University of Helsinki, N = 535, and Family Federation Finland, N = 432) and Tampere (University of Tampere, N = 428). Following enrolment, serum samples were collected at month 0 and month 7 post 1st vaccination shot, and were analysed for levels and avidity of IgG antibodies to HPV16 and HPV18 using standard and modified (4 M urea elution) VLP ELISAs.

Results

We found that at month 7 post vaccination women who smoked (cotinine level > 20 ng/ml) had levels of anti-HPV16/18 antibodies comparable to those of non-smoking women. Low-avidity HPV16/18 IgG antibodies were observed in 16% of the vaccinated women, and active smoking conferred a three-fold increased risk (95% CI 1.0-9.3) of having the low-avidity antibodies.

Conclusion

Our data suggest that while smoking does not interfere with the quantity of vaccine-induced peak IgG levels, it may affect the avidity of IgG induced by HPV16/18 vaccination.

Efficacy of the HPV-16/18 vaccine: final according to protocol results from the blinded phase of the randomized Costa Rica HPV-16/18 vaccine trial

BACKGROUND

A community-based randomized trial was conducted in Costa Rica to evaluate the HPV-16/18 AS04-adjuvanted vaccine (NCT00128661). The primary objective was to evaluate efficacy of the vaccine to prevent cervical intraepithelial neoplasia 2 or more severe disease (CIN2+) associated with incident HPV-16/18 cervical infections. Secondary objectives were to evaluate efficacy against CIN2+ associated with incident cervical infection by any oncogenic HPVs and to evaluate duration of protection against incident cervical infection with HPV-16/18. Vaccine safety and immunogenicity over the 4-year follow-up were also evaluated.

METHODS

We randomized (3727 HPV arm; 3739 control arm), vaccinated (HPV-16/18 or Hepatitis A) and followed (median 53.8 months) 7466 healthy women aged 18-25 years. 5312 women (2635 HPV arm; 2677 control arm) were included in the according to protocol analysis for efficacy. The full cohort was evaluated for safety. Immunogenicity was considered on a subset of 354 (HPV-16) and 379 (HPV-18) women. HPV type was assessed by PCR on cervical specimens. Immunogenicity was assessed using ELISA and inhibition enzyme immunoassays. Disease outcomes were histologically confirmed. Vaccine efficacy and 95% confidence intervals (95%CI) were computed.

RESULTS

Vaccine efficacy was 89.8% (95% CI: 39.5-99.5; N=11 events total) against HPV-16/18 associated CIN2+, 59.9% (95% CI: 20.7-80.8; N=39 events total) against CIN2+ associated with non-HPV-16/18 oncogenic HPVs and 61.4% (95% CI: 29.5-79.8; N=51 events total) against CIN2+ irrespective of HPV type. The vaccine had an acceptable safety profile and induced robust and long-lasting antibody responses.

CONCLUSIONS

Our findings confirm the high efficacy and immunogenicity of the HPV-16/18 vaccine against incident HPV infections and cervical disease associated with HPV-16/18 and other oncogenic HPV types. These results will serve as a benchmark to which we can compare future findings from the ongoing extended follow-up of participants in the Costa Rica trial.

TRIAL REGISTRATION

Registered with clinicaltrials.gov: NCT00128661.

HPV vaccine stimulates cytotoxic activity of killer dendritic cells and natural killer cells against HPV-positive tumour cells

Cervarix™ is approved as a preventive vaccine against infection with the human papillomavirus (HPV) strains 16 and 18, which are causally related to the development of cervical cancer. We are the first to investigate in vitro the effects of this HPV vaccine on interleukin (IL)-15 dendritic cells (DC) as proxy of a naturally occurring subset of blood DC, and natural killer (NK) cells, two innate immune cell types that play an important role in antitumour immunity. Our results show that exposure of IL-15 DC to the HPV vaccine results in increased expression of phenotypic maturation markers, pro-inflammatory cytokine production and cytotoxic activity against HPV-positive tumour cells. These effects are mediated by the vaccine adjuvant, partly through Toll-like receptor 4 activation. Next, we demonstrate that vaccine-exposed IL-15 DC in turn induce phenotypic activation of NK cells, resulting in a synergistic cytotoxic action against HPV-infected tumour cells. Our study thus identifies a novel mode of action of the HPV vaccine in boosting innate immunity, including killing of HPV-infected cells by DC and NK cells.

Durable antibody responses following one dose of the bivalent human papillomavirus L1 virus-like particle vaccine in the Costa Rica Vaccine Trial

The Costa Rica HPV16/18 Vaccine Trial (CVT) showed that four-year vaccine efficacy against 12-month HPV16/18 persistent infection was similarly high among women who received one, two, or the recommended three doses of the bivalent HPV16/18 L1 virus-like particle (VLP) vaccine. Live-attenuated viral vaccines, but not simple-subunit vaccines, usually induce durable lifelong antibody responses after a single dose. It is unclear whether noninfectious VLP vaccines behave more like live-virus or simple-subunit vaccines in this regard. To explore the likelihood that efficacy will persist longer term, we investigated the magnitude and durability of antibodies to this vaccine by measuring HPV16- and HPV18-specific antibodies by VLP-ELISA using serum from enrollment, vaccination, and annual visits through four years in four vaccinated groups; one-dose (n = 78), two-doses separated by one month (n = 140), two doses separated by six months (n = 52), and three scheduled doses (n = 120, randomly selected). We also tested enrollment sera from n = 113 HPV16- or HPV18 L1-seropositive women prevaccination, presumably from natural infection. At four years, 100% of women in all groups remained HPV16/18 seropositive; both HPV16/18 geometric mean titers (GMT) among the extended two-dose group were non-inferior to the three-dose group, and ELISA titers were highly correlated with neutralization titers in all groups. Compared with the natural infection group, HPV16/18 GMTs were, respectively, at least 24 and 14 times higher among the two-dose and 9 and 5 times higher among one-dose vaccinees. Antibody levels following one-dose remained stable from month 6 through month 48. Results raise the possibility that even a single dose of HPV VLPs will induce long-term protection.

Development of neutralizing monoclonal antibodies for oncogenic human papillomavirus types 31, 33, 45, 52, and 58

Human papillomavirus (HPV) is the etiological agent for all cervical cancers, a significant number of other anogenital cancers, and a growing number of head and neck cancers. Two licensed vaccines offer protection against the most prevalent oncogenic types, 16 and 18, responsible for approximately 70% of cervical cancer cases worldwide and one of these also offers protection against types 6 and 11, responsible for 90% of genital warts. The vaccines are comprised of recombinantly expressed major capsid proteins that self-assemble into virus-like particles (VLPs) and prevent infection by eliciting neutralizing antibodies. Adding the other frequently identified oncogenic types 31, 33, 45, 52, and 58 to a vaccine would increase the coverage against HPV-induced cancers to approximately 90%. We describe the generation and characterization of panels of monoclonal antibodies to these five additional oncogenic HPV types, and the selection of antibody pairs that were high affinity and type specific and recognized conformation-dependent neutralizing epitopes. Such characteristics make these antibodies useful tools for monitoring the production and potency of a prototype vaccine as well as monitoring vaccine-induced immune responses in the clinic.

Cross-neutralizing antibodies elicited by the Cervarix® human papillomavirus vaccine display a range of Alpha-9 inter-type specificities

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We explored Cervarix^® HPV vaccine cross-reactive antibody specificity.

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L1 VLP binding was a poor surrogate for L1L2 pseudovirus neutralization specificity.

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Cross-neutralizing antibodies comprise a small proportion of total antibody.

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Multiple, overlapping cross-neutralizing antibody specificities exist.

The highly efficacious human papillomavirus (HPV) vaccines contain virus-like particles (VLP) representing genotypes HPV16 and HPV18, which together account for approximately 70% of cervical cancer cases. Vaccine-type protection is thought to be mediated by high titer, type-specific neutralizing antibodies. The vaccines also confer a degree of cross-protection against some genetically-related types from the Alpha-9 (HPV16-like: HPV31, HPV33, HPV35, HPV52, HPV58) and Alpha-7 (HPV18-like: HPV39, HPV45, HPV59, HPV68) species groups. Cross-protection is coincident with the detection of low titer serum responses against non-vaccine types by vaccinees. Such antibodies may be the effectors of cross-protection or their detection may be useful as a correlate or surrogate.

This study evaluated whether cross-neutralization of HPV types from the Alpha-9 species group is mediated by antibodies with a predominantly type-restricted specificity for HPV16 that nevertheless exhibit low affinity interactions with non-vaccine types, or by antibody specificities that demonstrate similar recognition of vaccine and non-vaccine types but are present at very low levels.

Antibodies generated following Cervarix^® vaccination of 13–14 year old girls were evaluated by pseudovirus neutralization, VLP ELISA and by enrichment of target antigen specificity using VLP-immobilized beads. Two-dimensional hierarchical clustering of serology data demonstrated that the antibody specificity profile generated by VLP ELISA was both quantitatively and qualitatively different from the neutralizing antibody specificity profile. Target-specific antibody enrichment demonstrated that cross-neutralization of non-vaccine types was due to a minority of antibodies rather than by the weak interactions of a predominantly type-restricted HPV16 antibody specificity. Furthermore, cross-neutralization of non-vaccine types appeared to be mediated by multiple antibody specificities, recognizing single and multiple non-vaccine types, and whose specificities were not predictable from examination of the serum neutralizing antibody profile. These data contribute to our understanding of the antibody specificities elicited following HPV vaccination and have potential implications for vaccine-induced cross-protection.

Comparison of antibody responses to human papillomavirus vaccination as measured by three assays

BACKGROUND

Different assays, including the competitive Luminex immunoassay (cLIA), secreted alkaline phosphatase neutralization assay (SEAP-NA), and virus-like particle-based ELISA, are commonly used to measure antibody responses after human papillomavirus (HPV) vaccination. Direct assay comparisons aid interpretation of immunogenicity data evaluated by different assays.

METHODS

We compared cLIA to SEAP-NA and ELISA among 51 HPV16/18-vaccinated women enrolled in the Costa Rica Vaccine Trial. We tested replicate serum samples collected at months 0, 1, and 12 by HPV16/18 cLIA, SEAP-NA, and ELISA. For a subset (N = 10), we further tested month 6, 24 and 36 samples. We calculated seroprevalence estimates and Spearman rank correlation coefficients comparing cLIA to SEAP-NA and ELISA.

RESULTS

After one vaccine dose, seroprevalence by SEAP-NA and ELISA was 100% (both HPV16 and HPV18), and by cLIA was 96% (95% CI 87-100%) for HPV16 and 71% (95% CI 56-83%) for HPV18. Seroprevalence was 100% by all assays after three doses. Correlation between assays was high after one vaccine dose [cLIA/SEAP-NA ρ = 0.91 (HPV16) and ρ = 0.86 (HPV18); cLIA/ELISA ρ = 0.84 (HPV16) and ρ = 0.74 (HPV18); all p < 0.001] and remained high through month 36. Ratios of mean antibody levels to seropositivity cutoffs at month 36 were lower for cLIA than for SEAP-NA or ELISA, particularly for HPV18 (HPV18 ratio for cLIA 1.9, SEAP-NA 3.5, ELISA 3.4).

CONCLUSION

Though correlation between cLIA and SEAP-NA/ELISA is high and stable after vaccination, the assays differ in scale and sensitivity, with notable differences after one vaccine dose and for HPV18. Our results demonstrate that comparisons of antibody responses to HPV vaccination measured by different assays are approximate, and must consider biological and technical differences between assays.

Immunogenicity assessment of HPV16/18 vaccine using the glutathione S-transferase L1 multiplex serology assay

The glutathione S-transferase (GST)-L1 multiplex serology assay has favorable properties for use in clinical trials and epidemiologic studies, including low cost, high throughput capacity, and low serum volume requirement. Therefore, we evaluated the GST-L1 assay as a measure of HPV16/18 vaccine immunogenicity. Our study population included 65 women selected from the Costa Rica Vaccine Trial who received the bivalent HPV16/18 virus-like particle (VLP) vaccine at the recommended 0/1/6-month schedule. We tested replicate serum samples from months 0/1/12 (i.e., after 0/1/3 doses) by GST-L1 and 3 other commonly used serology assays, VLP-ELISA, SEAP-NA, and cLIA. We calculated the percentage of women seropositive by GST-L1 by time point and HPV type (14 HPV types), and compared GST-L1 to other assays using Spearman rank correlation coefficients. After 1 vaccine dose, seropositivity by GST-L1 was 40% each for HPV16 and HPV18, increasing to 100% and 98%, respectively, after 3 doses. Seropositivity after 3 doses ranged from 32% to 69% for HPV types 31/33/45, for which partial vaccine efficacy is reported, though increases also occurred for types with no evidence for cross-protection (e.g., HPV77). GST-L1 correlated best after 3 doses with VLP-ELISA (HPV16 and HPV18 each ρ = 0.72) and SEAP-NA (HPV16 ρ = 0.65, HPV18 ρ = 0.71) (all P < 0.001); correlation was lower with cLIA. The GST-L1 is suitable for evaluating HPV16/18 vaccine immunogenicity after 3 vaccine doses, although in contrast to other assays it may classify some samples as HPV16/18 seronegative. The assay's utility is limited for lower antibody levels such as after receipt of 1 dose.

Estimation of the potential overall impact of human papillomavirus vaccination on cervical cancer cases and deaths

BACKGROUND

Human papillomavirus (HPV) vaccination offers potential for primary prevention of HPV-related pre-cancers and cancers as demonstrated in clinical trials. Mathematical models have estimated the potential real-life impact of vaccination on the burden of cervical cancer (CC). However, these are restricted to evaluations in a limited number of countries.

METHODS

Potential decline in CC cases and deaths with the AS04-adjuvanted HPV-16/18 vaccine of young girls naïve to HPV, was estimated at steady-state (vaccine coverage: 0-100%) based on clinical trial and country-specific incidence data. Data on vaccine efficacy were taken from the end of study PATRICIA trial of the AS04-adjuvanted HPV-16/18 vaccine. The numbers of cases and deaths due to HPV-16/18 were estimated and compared with those due to any HPV type to estimate the additional cases prevented. This difference estimates CC cases and deaths avoided due to protection against non-vaccine HPV types. Cost-offsets due to reductions in CC treatment were estimated for five countries (Brazil, Canada, Italy, Malaysia and South African Republic) using country-specific unit cost data. Additionally, cervical intraepithelial neoplasia grade 2 or 3 (CIN2/3)-related burden (cases and treatment costs) prevented by vaccination were estimated for two countries (Italy and Malaysia).

RESULTS

HPV vaccination could prevent a substantial number of CC cases and deaths in countries worldwide, with associated cost-offsets due to reduced CC treatment. Cross-protection increased the estimated potential number of CC cases and deaths prevented by 34 and 18% in Africa and Oceania, respectively. Moreover, vaccination could result in a substantial reduction in the number of CIN2/3 lesions and associated costs.

CONCLUSION

HPV vaccination could reduce the burden of CC and precancerous lesions in countries worldwide, part of disease burden reduction being related to protection against non HPV-16/18 related types.

Virus-like particle-based human vaccines: quality assessment based on structural and functional properties

Human vaccines against three viruses use recombinant virus-like particles (VLPs) as the antigen: hepatitis B virus, human papillomavirus, and hepatitis E virus. VLPs are excellent prophylactic vaccine antigens because they are self-assembling bionanoparticles (20 to 60 nm in diameter) that expose multiple epitopes on their surface and faithfully mimic the native virions. Here we summarize the long journey of these vaccines from bench to patients. The physical properties and structural features of each recombinant VLP vaccine are described. With the recent licensure of Hecolin against hepatitis E virus adding a third disease indication to prophylactic VLP-based vaccines, we review how the crucial quality attributes of VLP-based human vaccines against all three disease indications were assessed, controlled, and improved during bioprocessing through an array of structural and functional analyses.

Characteristics of HPV-specific antibody responses induced by infection and vaccination: cross-reactivity, neutralizing activity, avidity and IgG subclasses

OBJECTIVES

In order to assess HPV-specific IgG characteristics, we evaluated multiple aspects of the humoral antibody response that will provide insight in the HPV humoral immune response induced by HPV infection and vaccination.

METHODS

Cross-reactivity of HPV-specific antibodies induced by infection or vaccination was assessed with VLP16 or 18 inhibition using a VLP-based multiplex immunoassay (MIA) for HPV16, 18, 31, 33, 45, 52 and 58. HPV16/18 specific IgG1-4 subclasses and avidity were determined with the VLP-MIA in sera after HPV infection and after vaccination. Neutralizing antibodies were determined in a small subset of single-seropositive and multi-seropositive naturally derived antibodies.

RESULTS

Naturally derived antibodies from single-positive sera were highly genotype-specific as homologue VLP-inhibition percentages varied between 78-94%. In multi-positive sera, cross-reactive antibodies were observed both within and between α7 and α9 species. After vaccination, cross-reactive antibodies were mainly species-specific. Avidity of vaccine-derived HPV-specific antibodies was 3 times higher than that of antibodies induced by HPV infection (p<0.0001). IgG1 and IgG3 were found to be the predominant subclasses observed after HPV infection and vaccination. In the small subset tested, the number of single-positive sera with neutralizing capacity was higher than of multi-positive sera.

CONCLUSION

Naturally derived HPV-specific antibodies from single-positive samples showed different characteristics in terms of cross-reactivity and neutralizing capacity compared with antibodies from multi-positive sera. Post-vaccination, HPV antibody avidity was approximately 3 times higher than antibody avidity induced by HPV infection. Therefore, antibody avidity might be a potential surrogate of protection.

The papillomavirus major capsid protein L1

The elegant icosahedral surface of the papillomavirus virion is formed by a single protein called L1. Recombinant L1 proteins can spontaneously self-assemble into a highly immunogenic structure that closely mimics the natural surface of native papillomavirus virions. This has served as the basis for two highly successful vaccines against cancer-causing human papillomaviruses (HPVs). During the viral life cycle, the capsid must undergo a variety of conformational changes, allowing key functions including the encapsidation of the ~8 kb viral genomic DNA, maturation into a more stable state to survive transit between hosts, mediating attachment to new host cells, and finally releasing the viral DNA into the newly infected host cell. This brief review focuses on conserved sequence and structural features that underlie the functions of this remarkable protein.

Use of baculovirus expression system for generation of virus-like particles: successes and challenges

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A brief overview of principles and applications of BES.

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Generation of VLPs using BES.

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Major properties of BES: promoting generation of VLPs.

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Bioprocess considerations for generation of VLPs.

The baculovirus expression system (BES) has been one of the versatile platforms for the production of recombinant proteins requiring multiple post-translational modifications, such as folding, oligomerization, phosphorylation, glycosylation, acylation, disulfide bond formation and proteolytic cleavage. Advances in recombinant DNA technology have facilitated application of the BES, and made it possible to express multiple proteins simultaneously in a single infection and to produce multimeric proteins sharing functional similarity with their natural analogs. Therefore, the BES has been used for the production of recombinant proteins and the construction of virus-like particles (VLPs), as well as for the development of subunit vaccines, including VLP-based vaccines. The VLP, which consists of one or more structural proteins but no viral genome, resembles the authentic virion but cannot replicate in cells. The high-quality recombinant protein expression and post-translational modifications obtained with the BES, along with its capacity to produce multiple proteins, imply that it is ideally suited to VLP production. In this article, we critically review the pros and cons of using the BES as a platform to produce both enveloped and non-enveloped VLPs.