Nonavalent HPV vaccination induces robust systemic and mucosal HPV16-neutralizing antibody responses in previously infected women

<title>Abstract</title> <p> Background Neutralizing antibody responses to human papillomavirus (HPV) vaccines are typically assessed in serum, while mucosal immunity at sites of infection remains less well characterized, particularly in HPV-positive individuals. We evaluated systemic and mucosal HPV16-neutralizing antibody responses following nonavalent HPV vaccination in women with a recent HPV16/18-positive cervical test. Methods In this longitudinal RIFT-HPV study, 39 previously unvaccinated adult women with an HPV16/18-positive cervical test done in the previous 12 months received a three-dose schedule of the nonavalent HPV vaccine (Gardasil-9). Paired serum, cervical, and oral samples were collected before and during vaccination. Neutralizing activity against HPV16 pseudovirions was measured using an enhanced green fluorescent protein pseudovirion-based neutralization assay (EGFP-PBNA). Results Vaccination significantly increased HPV16-neutralizing antibody responses in serum, cervical, and oral samples, irrespective of baseline HPV16 positivity. Serum EC ₅₀ detection increased from 33% at baseline to 100% after three doses, while cervical and oral detection increased from 8% and 10% after one dose, to 100% and 80% after three doses, respectively. With assay conditions exceeding physiological viral exposure levels, cervical HPV16 pseudovirion neutralization progressively increased from 36% before vaccination to 61%, 68% and 78% after one, two and three vaccine doses, respectively. Systemic and mucosal neutralizing responses were positively correlated. The EGFP-PBNA demonstrated high reproducibility (ICC = 0.98) and good concordance with the reference method. Conclusions Nonavalent HPV vaccination induced strong systemic and mucosal HPV16-neutralizing antibody responses, regardless of current HPV16 positivity. These findings demonstrate enhanced mucosal HPV16-neutralizing immunity following nonavalent vaccination in previously infected women and support further investigation of its potential role in reducing viral infectivity and transmission. Trial registration: ClinicalTrials.gov, NCT05334706. Registered on 19 April 2022. </p>