A Chimeric 18L1-45RG1 Virus-Like Particle Vaccine Cross-Protects against Oncogenic Alpha-7 Human Papillomavirus Types

Abstract

Persistent infection with oncogenic human papillomaviruses (HPV) types causes all cervical and a subset of other anogenital and oropharyngeal carcinomas. Four high-risk (hr) mucosal types HPV16, 18, 45, or 59 cause almost all cervical adenocarcinomas (AC), a subset of cervical cancer (CxC). Although the incidence of cervical squamous cell carcinoma (SCC) has dramatically decreased following introduction of Papanicolaou (PAP) screening, the proportion of AC has relatively increased. Cervical SCC arise mainly from the ectocervix, whereas AC originate primarily from the endocervical canal, which is less accessible to obtain viable PAP smears. Licensed (bivalent and quadrivalent) HPV vaccines comprise virus-like particles (VLP) of the most important hr HPV16 and 18, self-assembled from the major capsid protein L1. Due to mainly type-restricted efficacy, both vaccines do not target 13 additional hr mucosal types causing 30% of CxC. The papillomavirus genus alpha species 7 (α7) includes a group of hr types of which HPV18, 45, 59 are proportionally overrepresented in cervical AC and only partially (HPV18) targeted by current vaccines. To target these types, we generated a chimeric vaccine antigen that consists of a cross-neutralizing epitope (homologue of HPV16 RG1) of the L2 minor capsid protein of HPV45 genetically inserted into a surface loop of HPV18 L1 VLP (18L1-45RG1). Vaccination of NZW rabbits with 18L1-45RG1 VLP plus alum-MPL adjuvant induced high-titer neutralizing antibodies against homologous HPV18, that cross-neutralized non-cognate hr α7 types HPV39, 45, 68, but not HPV59, and low risk HPV70 in vitro, and induced a robust L1-specific cellular immune response. Passive immunization protected mice against experimental vaginal challenge with pseudovirions of HPV18, 39, 45 and 68, but not HPV59 or the distantly related α9 type HPV16. 18L1-45RG1 VLP might be combined with our previously described 16L1-16RG1 VLP to develop a second generation bivalent vaccine with extended spectrum against hr HPV.

Broad Cross-Protection Is Induced in Preclinical Models by a Human Papillomavirus Vaccine Composed of L1/L2 Chimeric Virus-Like Particles

“…Both experiments used PsVs representing HPV-11, -16, -35, or -58. The four viruses were chosen based on a range of anticipated outcomes (PsV-16, for harboring homology with HPV-16 L1, PsV-11 for harboring homology with L2 DE (17)(18)(19)(20)(21)(22)(23)(24)(25)(26)(27)(28)(29)(30)(31)(32)(33)(34)(35)(36) , PsV-58 for harboring homology with L2 CT(56 -75) , and PsV-35 for harboring partial [90%] homology with either of the two L2 peptides). The first experiment also used PsVs representing HPV-45 and -59 [two viruses which have relatively low, i.e., Յ75%, similarity with the L2 peptide].…”

“…This strategy is supported by evidence that vaccines based on L2 peptides can confer broad protection in mouse or rabbit HPV challenge models and elicit neutralizing antibodies against a wide range of HPVs (27,(29)(30)(31)(32)(33). However, during natural infection, the immunogenicity of L2 epitopes appears subdominant relative to L1 epitopes, probably because the density of L2 exposed on the capsid surface with respect to L1 is low and/or because L2 is buried within the HPV capsid and may be only transiently exposed after receptor engagement on the cell surface (34).…”

“…An alternative strategy to broaden the protection of HPV vaccines that is also being considered is to use conserved epitopes from the L2 minor capsid protein incorporated into HPV L1 VLPs (22)(23)(24)(25)(26)(27)(28)(29). This strategy is supported by evidence that vaccines based on L2 peptides can confer broad protection in mouse or rabbit HPV challenge models and elicit neutralizing antibodies against a wide range of HPVs (27,(29)(30)(31)(32)(33).…”

“…One L2 epitope (consisting of amino acid residues 17 to 36; L2 [17][18][19][20][21][22][23][24][25][26][27][28][29][30][31][32][33][34][35][36] ), recognized as a linear neutralizing epitope (RG1 epitope) (30)(31)(32), has been incorporated into the capsid surface DE loop of HPV-16 L1 or HPV-18 L1 to create chimeric L1/L2 VLP vaccines (24,25,27). Both L1/L2 vaccines (based on either HPV-16 or HPV-18 L1) provided protection in a mouse challenge model against a broad range of high-risk HPVs (25,27) and generated L2-specific neutralizing antibodies together with L1-specific neutralizing antibodies (24,25,27). However, the insertion of epitopes into the DE loop can also disrupt the epitope recognized by the V5 and J4 monoclonal neutralizing antibodies, thus disrupting epitopes important for HPV-16/18 neutralization (22).…”

“…The antigens were constructed by inserting the well-conserved L2 [17][18][19][20][21][22][23][24][25][26][27][28][29][30][31][32][33][34][35][36] and L2 56 -75 neutralizing epitopes within the DE loop and/or C-terminal arm of HPV-16 or HPV-18 L1 proteins. The immunogenicity and/or efficacy of the different formulations was compared using mouse and rabbit models.…”