title: The adjuvant effect of TLR7 agonist conjugated to a meningococcal serogroup C glycoconjugate vaccine.
abstract: Conjugation of a small molecule immunopotentiator to antigens has been proposed to deliver the ligand to the receptor, localize its action and minimize systemic inflammation. However, the effect of conjugation of Toll like receptor 7 agonists (TLR7a) on the immunogenicity of carbohydrate-based vaccines is unknown. In this study we synthesized an anti-Neisseria meningitidis serogroup C (MenC) glycoconjugate vaccine composed of MenC oligosaccharide antigens covalently linked to the carrier protein CRM197, to which a TLR7a was in turn conjugated. This vaccine was able to activate in vitro the TLR7 comparably to the unconjugated ligand. The magnitude and the quality of the immune response against MenC capsular polysaccharide were evaluated in mice, comparing the MenC-CRM-TLR7a construct to a MenC-CRM197 vaccine, prepared through the same conjugation chemistry and co-administered with the unconjugated TLR7a. A commercially licensed anti-MenC glycoconjugate was used as further control to determine the influence of the coupling approach and the level of carbohydrate incorporation on the anti-MenC immune response. The possible additive effect of co-administration with Alum hydroxide (AlumOH) was also examined. The bactericidal titers against N. meningitidis were in agreement with the elicited anti-carbohydrate IgGs, and unequivocally showed that TLR7a conjugation to CRM197 enhanced the anti-MenC immune response. TLR7a conjugation induced a shift to a Th1 type response, as assessed by the increased IgG2a subclass production, both in the absence and in the presence of AlumOH. The increased immune response was clearly present only in the absence of AlumOH and was less pronounced than the co-administration of a licensed glycoconjugate with a standard dose of TLR7a-phosphonate adsorbed on the inorganic salt. The amount of MenC saccharide that was covalently linked to CRM197 after previous CRM197-TLR7a conjugation resulted in lower responses than achieved with conventional MenC-CRM197 glycoconjugation in the absence of TLR7a. As result, the benefit of the adjuvant conjugation in terms of anti-MenC immune response was jeopardized by the lower saccharide/protein ratio obtained in the MenC-CRM-TLR7a conjugate. While adsorption on AlumOH offers more flexibility in the administered dose of TLR7a, conjugation of the small molecule immunopotentiator could be particularly suited for vaccination routes such as skin delivery, where insoluble aluminum salts cannot be used because of their reactogenicity in this site.
authors.affiliation: GSK Vaccines, Via Fiorentina 1, 53100 Siena, Italy.
authors.forename: Agnese
authors.initials: A
authors.lastname: Donadei
authors.affiliation: GSK Vaccines, Via Fiorentina 1, 53100 Siena, Italy.
authors.forename: Cristiana
authors.initials: C
authors.lastname: Balocchi
authors.affiliation: GSK Vaccines, Via Fiorentina 1, 53100 Siena, Italy.
authors.forename: Francesca
authors.initials: F
authors.lastname: Mancini
authors.affiliation: GSK Vaccines, Via Fiorentina 1, 53100 Siena, Italy.
authors.forename: Daniela
authors.initials: D
authors.lastname: Proietti
authors.affiliation: GSK Vaccines, Via Fiorentina 1, 53100 Siena, Italy.
authors.forename: Simona
authors.initials: S
authors.lastname: Gallorini
authors.affiliation: GSK Vaccines, Via Fiorentina 1, 53100 Siena, Italy.
authors.forename: Derek T
authors.initials: DT
authors.lastname: O'Hagan
authors.affiliation: GSK Vaccines, Via Fiorentina 1, 53100 Siena, Italy.
authors.forename: Ugo
authors.initials: U
authors.lastname: D'Oro
authors.affiliation: GSK Vaccines, Via Fiorentina 1, 53100 Siena, Italy.
authors.forename: Francesco
authors.initials: F
authors.lastname: Berti
authors.affiliation: GSK Vaccines, Via Fiorentina 1, 53100 Siena, Italy.
authors.forename: Barbara C
authors.initials: BC
authors.lastname: Baudner
authors.affiliation: GSK Vaccines, Via Fiorentina 1, 53100 Siena, Italy. Electronic address: roberto.x.adamo@gsk.com.
authors.forename: Roberto
authors.initials: R
authors.lastname: Adamo
mesh_terms: D000276:Adjuvants, Immunologic / Q000737:chemistry / Q000494:pharmacology*; D000818:Animals; D001426:Bacterial Proteins / Q000737:chemistry / Q000494:pharmacology*; D002240:Carbohydrate Sequence; D004591:Electrophoresis, Polyacrylamide Gel; D005260:Female; D006001:Glycoconjugates / Q000737:chemistry*; D022401:Meningococcal Vaccines / Q000737:chemistry*; D051379:Mice; D038542:Neisseria meningitidis, Serogroup C / Q000276:immunology*; D051199:Toll-Like Receptor 7 / Q000819:agonists*; D018074:Vaccines, Conjugate / Q000737:chemistry*
chemical_list: D000276:Adjuvants, Immunologic; D001426:Bacterial Proteins; D006001:Glycoconjugates; D022401:Meningococcal Vaccines; C495348:TLR7 protein, human; D051199:Toll-Like Receptor 7; D018074:Vaccines, Conjugate; C028581:CRM197 (non-toxic variant of diphtheria toxin)
keywords: Adjuvants; Carbohydrate-based vaccines; Glycoconjugates; Meningitidis; TLR7 agonist