title: Analysis of modified human papillomavirus type 16 L1 capsomeres: the ability to assemble into larger particles correlates with higher immunogenicity.
abstract: L1 capsomeres purified from Escherichia coli represent an economic alternative to the recently launched virus-like particle (VLP)-based prophylactic vaccines against infection with human papillomavirus types 16 and 18 (HPV-16 and HPV-18), which are causative agents of cervical cancer. It was recently reported that capsomeres are much less immunogenic than VLPs. Numerous modifications of the L1 protein leading to the formation of capsomeres but preventing capsid assembly have been described, such as the replacement of the cysteine residues that form capsid-stabilizing disulfide bonds or the deletion of helix 4. So far, the influence of these modifications on immunogenicity has not been thoroughly investigated. Here, we describe the purification of eight different HPV-16 L1 proteins as capsomeres from Escherichia coli. We compared them for yield, structure, and immunogenicity in mice. All L1 proteins formed almost identical pentameric structures yet differed strongly in their immunogenicity, especially regarding the humoral immune responses. Immunization of TLR4(-/-) mice and DNA immunization by the same constructs confirmed that immunogenicity was independent of different degrees of contamination with copurifying immune-stimulatory molecules from E. coli. We hypothesize that immunogenicity correlates with the intrinsic ability of the capsomeres to assemble into larger particles, as only assembly-competent L1 proteins induced high antibody responses. One of the proteins (L1DeltaN10) proved to be the most immunogenic, inducing antibody titers equivalent to those generated in response to VLPs. However, preassembly prior to injection did not increase immunogenicity. Our data suggest that certain L1 constructs can be used to produce highly immunogenic capsomeres in bacteria as economic alternatives to VLP-based formulations.
authors.affiliation: German Cancer Research Center, Division of Genome Modifications and Carcinogenesis, F020, Im Neuenheimer Feld 242, 69120 Heidelberg, Germany. l.schaedlich@dkfz.de
authors.forename: Lysann
authors.initials: L
authors.lastname: Schädlich
authors.forename: Tilo
authors.initials: T
authors.lastname: Senger
authors.forename: Britta
authors.initials: B
authors.lastname: Gerlach
authors.forename: Norbert
authors.initials: N
authors.lastname: Mücke
authors.forename: Corinna
authors.initials: C
authors.lastname: Klein
authors.forename: Ignacio G
authors.initials: IG
authors.lastname: Bravo
authors.forename: Martin
authors.initials: M
authors.lastname: Müller
authors.forename: Lutz
authors.initials: L
authors.lastname: Gissmann
mesh_terms: D020816:Amino Acid Motifs; D000818:Animals; D000914:Antibodies, Viral / Q000097:blood; D002213:Capsid / Q000737:chemistry / Q000276:immunology; D036022:Capsid Proteins / Q000737:chemistry / Q000235:genetics / Q000276:immunology*; D052162:Human papillomavirus 16 / Q000737:chemistry / Q000235:genetics / Q000276:immunology / Q000502:physiology*; D006801:Humans; D007114:Immunization; D051379:Mice; D008809:Mice, Inbred C3H; D008810:Mice, Inbred C57BL; D030361:Papillomavirus Infections / Q000276:immunology* / Q000821:virology; D014771:Virion / Q000737:chemistry / Q000235:genetics / Q000276:immunology / Q000502:physiology*; D019065:Virus Assembly
chemical_list: D000914:Antibodies, Viral; D036022:Capsid Proteins