HPV11 mutant virus-like particles elicit immune responses that neutralize virus and delineate a novel neutralizing domain

Characterization of the regions of human papillomaviruses (HPVs) that elici t neutralizing immune responses supports studies on viral infectivity and p rovides insight for the development and evaluation of prophylactic vaccines . HPV11 is a major etiologic agent of genital warts and a likely vaccine ca ndidate. A conformationally dependent epitope for the binding of three neut ralizing monoclonal antibodies (mAbs) has been mapped to residues G(131)T(1 32) of the L1 major capsid protein. The mAbs bind L1 only when it is assemb led into virions or into virus-like particles (VLPs) that mimic the capsid structure. We were interested in identifying other domains of L1 that elici t neutralizing responses. To this end, we have generated a panel of mAbs ag ainst VLPs derived from HPV11 L1 harboring a G131S substitution. The new mA bs are unlike the neutralizing mAbs previously mapped to residues G(131)T(1 32) in that they bind both prototype and HPV11:G131S mutant VLPs. Some of t he new mAbs neutralized virus in vitro. We have mapped epitopes for three o f these new mAbs, as well as a neutralizing mAb generated against HPV11 vir ions, by measuring binding to HPV6 VLPs substituted with HPV11-like amino a cids. Two regions are critical: one defined by HPV11 L1 residues 263-290 an d the other by residues 346-349. mAbs H11.H3 and H11.G131S.G3 bind HPV6 VLP s with substitutions derived from the 346-349 region; in addition, H11.G131 S.G3 binds HPV6 VLPs with substitutions derived only from the 263-290 regio n. Although H11.H3 does not bind HPV6 VLPs with substitutions derived from the 263-290 region, binding to HPV6 VLPs is enhanced when both sets of subs titutions are present. mAbs H11.G131S.11 and H11.G131S.K5 bind HPV6 VLPs wi th the 263-290 substitutions, but show little binding to HPV6 VLPs with the 346-349 substitutions. However, binding to HPV6 VLPs is enhanced when subs titutions at both regions are present. The 346-349 region has not previousl y been described as eliciting a neutralizing response for any HPV type. In addition, the work demonstrates a complex binding site contributed by two d istinct regions of L1. (C) 2000 Academic Press.