Glycoconjugate vaccine using a genetically modified O antigen induces protective antibodies toFrancisella tularensis

Abstract

Francisella tularensisis the causative agent of tularemia, a category A bioterrorism agent. The lipopolysaccharide (LPS) O antigen (OAg) ofF. tularensishas been considered for use in a glycoconjugate vaccine, but conjugate vaccines tested so far have failed to confer protection necessary against aerosolized pulmonary bacterial challenge. WhenF. tularensisOAg was purified under standard conditions, the antigen had a small molecular size [25 kDa, low molecular weight (LMW)]. Using milder extraction conditions, we found the native OAg had a larger molecular size [80 kDa, high molecular weight (HMW)], and in a mouse model of tularemia, a glycoconjugate vaccine made with the HMW polysaccharide coupled to tetanus toxoid (HMW-TT) conferred better protection against intranasal challenge than a conjugate made with the LMW polysaccharide (LMW-TT). To further investigate the role of OAg size in protection, we created anF. tularensislive vaccine strain (LVS) mutant with a significantly increased OAg size [220 kDa, very high molecular weight (VHMW)] by expressingin F. tularensisa heterologous chain-length regulator gene (wzz) from the related speciesFrancisella novicida. Immunization with VHMW-TT provided markedly increased protection over that obtained with TT glycoconjugates made using smaller OAgs. We found that protective antibodies recognize a length-dependent epitope better expressed on HMW and VHMW antigens, which bind with higher affinity to the organism.

Enhancing the antigenicity and immunogenicity of monomeric forms of hepatitis C virus E2 for use as a preventive vaccine

“…This is well recognized for large-sized antigen platforms such as VLP or liposomes or the coupling of small antigens to larger carrier molecules, but has been less well studied for singlecomponent multimeric complexes. Larger multimeric forms of the lipopolysaccharide O antigen of Francisella tularensis and the meningococcal capsular polysaccharide of Neisseria meningitidis have been shown to mediate enhanced immunogenicity compared to smaller forms of the same antigen (33,34).…”

Synthesis and delivery ofStreptococcus pneumoniaecapsular polysaccharides by recombinant attenuatedSalmonellavaccines

“…The results support a previous finding that the HMW polysaccharide provides more efficient protection against bacterial infection. One of the reasons for this was attributed to potent high-affinity antibodies induced by the HMW polysaccharide antigens ( 70 ). Wzz is a regulator, which can regulate length of polysaccharide during synthesizing polysaccharide with a Wzx/Wzy mixture ( 71 ).…”

On-demand, cell-free biomanufacturing of conjugate vaccines at the point-of-care

“…FtO-PS to protein in bioconjugates yields enhanced protection against F. tularensis Schu S4 in a rat inhalation model of tularemia (Marshall et al, 2018). In addition, a recent study showed that a conjugate vaccine made with a high molecular weight (80 kDa) FtO-PS coupled to TT conferred better protection against intranasal challenge with F. tularensis live vaccine strain compared to a conjugate made with a low molecular weight (25 kDa) polysaccharide (Stefanetti et al, 2019).…”

“…tularensis (Stefanetti et al, 2019). Notably, our attempts to synthesize the same panel of bioconjugates using the established PGCT approach in living E. coli yielded less promising results.…”