Abstract
Immunogenicity evaluations in human papillomavirus (HPV) vaccine trials have relied on serological samples, yet cervical antibodies are likely to be most relevant for protection against infection. In order to assess functional antibody levels at the cervix, the secreted-alkaline-phosphatase neutralization assay (SEAPNA) was used to measure HPV-neutralizing activity. We assessed the variability of the SEAPNA with serum samples after vaccination with an HPV type 16 (HPV16) L1 virus-like particle vaccine and whether the SEAPNA can be used to monitor neutralizing activity at the cervix. The SEAPNA has an overall coefficient of variation of 29.3%. Recovery from ophthalmic sponges was assessed by spiking V5 (mouse anti-HPV16) antibody onto and extracting it from sterile Merocel and Ultracell sponges and sponges used to collect specimens from participants. V5 recovery from sterile Merocel sponges was complete, yet that from Ultracell sponges was null. The mean V5 recoveries from participant Ultracell and Merocel sponges were 61.2% and 93.5%, respectively, suggesting that Merocel sponges are more appropriate for specimen collection. The SEAPNA can be applied to determine the surrogates of protection and to examine the durability of protection at the cervix.