Naturally Acquired Antibodies Against Human Papillomavirus are Protective Against Subsequent Homotypic Infection: A Large-Scale Prospective Cohort Study

Background: Currently, knowledge of the protective effects of natural acquired immunity against human papillomavirus (HPV) is mostly based on studies using binding antibodies (IgG) as biomarkers due to the labor-consuming characteristics of neutralizing antibodies assays, and the conclusions from different studies are inconsistent. Methods: In a phase III clinical trial of the Escherichia coli-produced HPV-16/18 bivalent vaccine, participants were tested for neutralizing antibodies and IgG antibodies with pseudovirion-based neutralization assay and L1 virus-like particle-based ELISA, respectively. HPV-16 and HPV-18 infections were identified using cervical specimens periodically collected during the over 5·5 years of follow-up. Data of the 3,634 women aged 18-45 years in the control arm were used to evaluate the protective effects of the type-specific neutralizing antibodies as well as the IgG antibodies. Findings: For the persistent infection (PI) endpoints of HPV-16/18 lasting for over 6/12 months, the prevalence of type-specific neutralizing antibodies was highly protective (6 m PI: RR = 0·16, 95% CI: 0·04, 0·63; 12 m PI: RR = 0·23, 95% CI: 0·06, 0·95), while the prevalence of IgG antibodies was associated with minor and nonsignificant protection (6 m PI: RR = 0·71, 95% CI: 0·44, 1·16; 12 m PI: RR = 0·76, 95% CI: 0·43, 1·36). Women with neutralizing antibodies had a lower risk of subsequent homotypic infection, irrespective of their IgG status. In contrast, women with positive IgG while negative neutralizing antibodies showed a similar risk of subsequent infection as those with neither neutralizing nor IgG antibodies. Interpretation: The findings indicate that naturally acquired neutralizing antibodies are associated with a substantially reduced risk of subsequent homotypic infection. Funding: National Natural Science Foundation of China ; The Fujian Province Health Education Joint Research Project; Xiamen Science and Technology Major Project; Chinese Academy of Medical Sciences Innovation Fund for Medical Sciences; and Xiamen Innovax. Declaration of Interest: We declare no competing interests. Ethical Approval: Written informed consent was obtained from all participants, and the trial was conducted in accordance with Good Clinical Practice and was approved by independent ethics committees.