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

Persisting Antibody Response 9 Years After Bivalent Human Papillomavirus (HPV) Vaccination in a Cohort of Dutch Women: Immune Response and the Relation to Genital HPV Infections

The bivalent human papillomavirus (HPV) vaccine is highly effective and induces robust serological responses. Using a Dutch prospective cohort initiated in 2009, including 744 vaccinated and 294 unvaccinated girls (1993–1994) who provide a vaginal self-swab sample, serum sample, and questionnaire yearly, we report a high, persisting antibody response up to 9 years after vaccination for vaccine types HPV-16 or HPV-18. Antibodies against nonvaccine HPV types 31, 33, 45, 52, and 58 were lower but still significantly higher than in unvaccinated individuals. This was also reflected in the seroprevalence. We compared participant characteristics and antibody levels between vaccinated women with and those without HPV infections 1 year before infection (204 incident and 64 persistent infections), but we observed no consistent difference in type-specific antibody levels. Having a high-risk HPV infection was associated with sexual risk behavior and smoking 1 year before infection. Although high antibody levels are necessary for protection, our study suggests that on the individual level other factors such as HPV exposure or antibody avidity could be important.

Updates on immunologic correlates of vaccine-induced protection

Correlates of protection (CoPs) are increasingly important in the development and licensure of vaccines. Although the study of CoPs was initially directed at identifying a single immune function that could explain vaccine efficacy, it has become increasingly clear that there are often multiple functions responsible for efficacy. This review is meant to supplement prior articles on the subject, illustrating both simple and complex CoPs.

Infection and vaccine-induced HPV-specific antibodies in cervicovaginal secretions. A review of the literature

Background

Human papillomavirus (HPV) infects and propagates in the cervical mucosal epithelium. Hence, in addition to assessing systemic immunity, the accurate measurement of cervical immunity is important to evaluate local immune responses to HPV infection and vaccination. This review discusses studies that investigated the presence of infection and vaccine-induced HPV-specific antibodies in cervicovaginal secretions (CVS).

Methods

We searched the two main health sciences databases, PubMed and the ISI Web of Science, from the earliest dates available to March 2019. From the eligible publications, information was extracted regarding: (i) study design, (ii) the reported HPV-specific antibody concentrations in CVS (and the associated serum levels, when provided), (iii) the CVS collection method, and (iv) the immunoassays used.

Results

The systematic search and selection process yielded 44 articles. The evidence of HPV-specific antibodies in CVS after natural infection (26/44) and HPV vaccination (18/44) is discussed. Many studies indicate that HPV-specific antibody detection in CVS is variable but feasible with a variety of collection methods and immunoassays. Most CVS samples were collected by cervicovaginal washing or wicks, and antibody presence was mostly determined by VLP-based ELISAs. The moderate to strong correlation between vaccine-induced antibody levels in serum and in CVS indicates that HPV vaccines generate antibodies that transudate through the cervical mucosal epithelium.

Conclusion

Although HPV-specific antibodies have lower titres in CVS than in serum samples, studies have shown that their detection in CVS is feasible. Nevertheless, the high variability of published observations and the lack of a strictly uniform, well-validated method for the collection, isolation and quantification of antibodies indicates a need for specific methods to improve and standardize the detection of HPV-specific antibodies in CVS.

Altered antigenicity and immunogenicity of human papillomavirus virus-like particles in the presence of thimerosal

Thimerosal has been widely used as a preservative in human vaccines for decades. Thimerosal, a thiol capping agent with ethyl mercury being the active degradant, could have impacts on the vaccine potency due to potential thiol modification. The effects on the antigenicity and immunogenicity of human papillomavirus (HPV) virus-like particles (VLPs) in the presence of thimerosal was studied. In general, reduced binding activity was observed between HPV antigens and monoclonal antibodies (mAbs) upon thimerosal treatment, accompanied by reduced protein conformational stability. The immunogenicity of a pentavalent vaccine formulation (HPV6, HPV11, HPV16, HPV18 and hepatitis E virus) with or without thimerosal was studied in mice. The functional antibody titres, as well as the binding titres, were determined, showing a substantial decrease for vaccine formulations containing thimerosal for HPV16/18. Similarly, epitope-specific competition assays using specific and functional mAbs as tracers also showed a significant reduction in immunogenicity for HPV16/18 in the presence of thimerosal. Structural alterations in the capsid protein for HPV18 were observed with cryo-electron microscopy and 3-dimensional reconstruction in the comparative structural analysis. The results should alert scientists in formulation development field on the choice for vaccine preservatives, in particular for thiol-containing antigens.

Exploring the Papillomaviral Proteome to Identify Potential Candidates for a Chimeric Vaccine against Cervix Papilloma Using Immunomics and Computational Structural Vaccinology

The human papillomavirus (HPV) 58 is considered to be the second most predominant genotype in cervical cancer incidents in China. HPV type-restriction, non-targeted delivery, and the highcost of existing vaccines necessitate continuing research on the HPV vaccine. We aimed to explore the papillomaviral proteome in order to identify potential candidates for a chimeric vaccine against cervix papilloma using computational immunology and structural vaccinology approaches. Two overlapped epitope segments (23⁻36) and (29⁻42) from the N-terminal region of the HPV58 minor capsid protein L2 are selected as capable of inducing both cellular and humoral immunity. In total, 318 amino acid lengths of the vaccine construct SGD58 contain adjuvants (Flagellin and RS09), two Th epitopes, and linkers. SGD58 is a stable protein that is soluble, antigenic, and non-allergenic. Homology modeling and the structural refinement of the best models of SGD58 and TLR5 found 96.8% and 93.9% favored regions in Rampage, respectively. The docking results demonstrated a HADDOCK score of -62.5 ± 7.6, the binding energy (-30 kcal/mol) and 44 interacting amino acid residues between SGD58-TLR5 complex. The docked complex are stable in 100 ns of simulation. The coding sequences of SGD58 also show elevated gene expression in Escherichia coli with 1.0 codon adaptation index and 59.92% glycine-cysteine content. We conclude that SGD58 may prompt the creation a vaccine against cervix papilloma.

Persistence of immune response following bivalent HPV vaccination: A follow-up study among girls routinely vaccinated with a two-dose schedule

BACKGROUND

In this cohort study, we examined antibody levels and avidity after a two-dose schedule (0, 6 months) of the bivalent HPV-vaccine in girls routinely vaccinated in the Dutch HPV-vaccination program, up to 2 years following vaccination.

METHODS

A blood sample at 7, 12 and 24 months after the first dose and questionnaire data were collected (n = 56). HPV type-specific antibody concentrations (lU/ml) against seven types (HPV16/18/31/33/45/52/58) were assessed using a validated virus-like particles (VLP) multiplex immunoassay. Avidity was tested using a modification of this assay.

RESULTS

Seropositivity for vaccine types HPV 16 and 18 was 100% up to month 24, but declined for HPV-types 31/33/45/52/58, although not statistically significant for HPV45. All Geometric Mean Concentrations (GMCs) declined by months 12 and 24, but remained high for HPV16/18. Between month 7 and 12, GMCs declined more for other types. High avidity antibodies were induced up to 24 months for vaccine types (75%, 76-78% and 81-82% at months 7, 12 and 24, respectively), but for other types antibody avidity was 16-29% at month 7, 20-32% at month 12 and 19-32% at month 24.

CONCLUSIONS

GMCs declined over time for HPV-types 16/18/31/33/45/52/58, but remained high for vaccine-types HPV16/18 up to 24 months of follow-up. Antibody avidity was >75% for vaccine types but <35% for other HPV-types. Further follow-up of this cohort will provide insight into antibody and avidity kinetics over time.

Epitope clustering analysis for vaccine-induced human antibodies in relationship to a panel of murine monoclonal antibodies against HPV16 viral capsid

Human papillomavirus (HPV) type 16 is the most common type implicated as the etiological agent that causes cervical cancer. The marketed prophylactic vaccines against HPV infection are composed of virus-like particles (VLPs) assembled from the recombinant major capsid protein L1. Elicitation of functional and neutralizing antibodies by vaccination is the mode of action by which the vaccines prevent the viral infection. In this study, a panel of murine mAbs against HPV16 L1 were generated and comprehensively characterized with respect to their mapping to the epitope spectrum on the viral capsid. These mAbs were categorized into five epitope bins by two different methods based on the pairwise cross-inhibition and competition with human polyclonal antibodies. In addition, a preliminary demonstration of the spatial relationship of the epitopes recognized by these mAbs was performed using a cross-blocking assay with a well-characterized human mAb, 26D1. Interestingly, two mAbs recognizing different epitopes were found to act synergistically in the pseudovirion-based neutralization assay (PBNA). To facilitate cross-lab and cross-study comparison, the international standard (IS) serum 05/134 was used to calibrate the mAbs as well as the human serum samples from the HPV16/18 vaccine recipients. The neutralizing mAbs, particularly those that recognizing immunodominant epitopes, would be useful in developing epitope-specific assays for monitoring the vaccine production process and for serological assessment.