Prevalence of Human Papillomavirus 16 and 18 Neutralizing Antibodies in Prenatal Women in British Columbia

Abstract

Human papillomavirus (HPV) type 16 and 18 neutralizing antibody (NAb) titers were measured in 1,020 prenatal women in British Columbia aged 15 to 39. HPV 16 and 18 NAbs were detected in 183/1,020 (17.9%) and 97/1,020 (9.5%), respectively, and 39 (3.8%) had NAbs to both types. Titers were similar across age strata.Measurement of type-specific antibody responses to human papillomavirus (HPV) is important for seroprevalence estimates and assessment of vaccine efficacy. Vaccine manufacturers have developed enzyme immunoassays (EIAs) targeting neutralizing epitopes (3, 10), but neutralizing antibody (NAb) tests could be a suitable alternative because they confirm blocking of infection of susceptible cells and they potentially measure antibodies to more epitopes than existing manufacturers' assays (13). Pseudovirus (PsV)-based NAb assays utilizing in vitro-generated HPV capsids containing a reporter plasmid have been described (1, 11). NAbs inhibit PsVs from infecting cells and from expressing the reporter plasmid product. For this study, we developed and validated a PsV NAb assay for HPV 16 and 18 and determined the seroprevalence among prenatal women in British Columbia (BC).HPV 16 and 18 PsVs were prepared as previously described (1), except that the reporter plasmid encoded red fluorescent protein (RFP) (11). Electron microscopic examination of the PsV preparations showed typical papillomavirus morphology. Bands at 55 kDa (capsid protein L1) and 70 kDa (capsid protein L2) were observed on Western blot analysis with rabbit antisera. Cesium chloride density gradient ultracentrifugation showed that over half of the PsV fraction had a buoyant density of approximately 1.34 g/ml, consistent with capsids containing DNA. PsVs were titrated in 293TT cells by monitoring the cultures for red fluorescent cells, with each fluorescent cell representing one infectious unit.NAb tests were performed as follows: sera were heated at 56°C for 30 min, and duplicate serial dilutions were prepared. Each serum dilution was mixed with 100 infectious units of the respective PsV and incubated for 1 h at 37°C, followed by transfer to 293TT cells on microtiter plates. Plates were incubated at 37°C and read after 4 to 6 days. The endpoint (100% neutralizing titer [NT 100 ]) was the highest dilution of serum which completely blocked cells displaying red fluorescence. Back-titrations of the PsV and serially diluted positive and negative serum controls were included in each run.For initial NAb test validation, five anti-HPV positive control sera (two against HPV 16, one against HPV 18, one against HPV 6, 11, 16, and 18, and one against HPV 6 and 11) and one anti-HPV negative control obtained from the National Institute for Biological Standards and Control (NIBSC), United Kingdom, were titrated. NAb titers corresponded with known antibody status (Table 1), although some were near the assay cutoff (1:40). Control sera for routine use were obtained from a volunteer 1 month after receiving a full course of Gardasil vaccine and from an HPV 16-and 18-s...

Reduction in cervical intraepithelial neoplasia in young women inBritishColumbia after introduction of theHPVvaccine: An ecological analysis

“…Rates of cervical intraepithelial neoplasia (CIN) 21 for each age stratum (15)(16)(17)(18)(19)(20)(21)(22) in the calendar years 2004-2012 for the province of British Columbia were obtained from the BC Cancer Agency's population-based cervical cancer program. Incidence rate ratios (IRR) of CIN21 were described and compared before and after HPV vaccine program introduction in cohorts born in vaccine eligible years, and in non-vaccine eligible years using piece-wise Poisson regression analysis, and adjusted for age.…”

“…16 The program has also reported on HPV prevalence in British Columbia prior to the HPV vaccine implementation in women and men, 17,18 and assessed rates of HPV seropositivity in women receiving prenatal care. 19 To evaluate the impact of the HPV vaccine in the province, we used data from British Columbia's centralized cervical cancer screening program (CCSP) to report on the ecological trends in cervical intraepithelial neoplasia (CIN) 2 and CIN21 in young women aged 15-22 years before and after the implementation of the provincial HPV vaccine program.…”

Human Papillomavirus 16 (HPV 16) and HPV 18 Antibody Responses Measured by Pseudovirus Neutralization and Competitive Luminex Assays in a Two- versus Three-Dose HPV Vaccine Trial

“…Conventional NAb assays for HPV are not feasible because of the inability of HPV to replicate in conventional cell cultures. This has been overcome by the use of HPV pseudoviruses (PsV) containing a reporter plasmid which is expressed when the PsV infect susceptible cells (1,10). NAb prevent PsV from infecting cells and expressing the reporter gene product.…”

“…In this study, we compare HPV 16 and HPV 18 antibody responses at 7 months in cohorts of females enrolled in an ongoing 2-versus 3-dose Q-HPV vaccine trial (4), using both the Merck cLIA and an in-house PsV NAb assay (10).…”

Update on Human Papillomavirus (HPV) Vaccines

“…In a seroprevalence study based on a sample of 1020 agestratified anonymous sera from women 15 to 39 years of age in BC undergoing prenatal testing, (5) HPV type 16 and 18 antibodies were detected in 17.9% and 9.5% of subjects respectively, and 3.9% had antibodies to both types. Based on age-stratified data, the authors concluded that exposure to HPV types 16 and 18 occurred at a young age.…”