Engineering a Next-Generation Glycoconjugate-Like Streptococcus pneumoniae Vaccine

Abstract

We detail the development of a next-generation Streptococcus pneumoniae liposomal encapsulation of polysaccharides (LEPS) vaccine, with design characteristics geared toward best-in-class efficacy. The first generation LEPS vaccine, which contained 20 encapsulated pneumococcal capsular polysaccharides (CPSs) and two surface-displayed virulence-associated proteins (GlpO and PncO), enabling prophylactic potency against 70+ serotypes of Streptococcus pneumoniae (the causative agent of pneumococcal disease), was rationally redesigned for advanced clinical readiness and best-in-class coverage. In doing so, the virulent-specific GlpO protein antigen was removed from the final formulation due to off-target immunogenicity toward bacterial species within the human microbiome, while directed protection was maintained by increasing the dose of PncO from 17 to 68 μg. LEPS formulation parameters also readily facilitated an increase in CPS valency (to a total of 24) and systematic variation in protein-liposome attachment mechanisms in anticipation of clinical translation. An additional safety assessment study demonstrated that LEPS does not exhibit appreciable toxicological effects even when administered at ten times the effective dose. In summary, this new design offers the broadest, safest, and most-complete protection while maintaining desirable glycoconjugate-like features, positioning the LEPS vaccine platform for clinical success and a global health impact.

Extended Polysaccharide Analysis within the Liposomal Encapsulation of Polysaccharides System

“…The LEPS platform offers the noncovalent attachment of protein to the surface of the liposomal carrier to mimic the glycoconjugate vaccines that have been used effectively as pneumococcal disease prophylactics [ 12 ]. For the LEPS system, protein attachment is completed through metal coordination chemistry in which nickel-doped liposomal content chelates 6× histidine-tagged recombinant protein products (initially, green fluorescent protein (GFP)) [ 8 , 20 ]. The data presented in Figure 2 support efficient polysaccharide encapsulation within the liposomal formulation prior to surface protein attachment.…”

“…Pneumococcal capsular polysaccharides (serotypes 19F, 4, and 3) were obtained from American Type Culture Collection (ATCC), and certain molecular details of the polysaccharides have been reported previously [ 17 , 18 ]. Green fluorescent protein (GFP) and a virulent-specific pneumococcal disease protein antigen (PncO) were produced recombinantly as previously reported [ 8 , 12 , 15 , 19 ]; briefly, the GFP and PncO proteins were generated through gene expression within Escherichia coli , with the protein products containing 6× histidine tags to facilitate affinity chromatography purification using a Ni-NTA packed bed column matrix.…”

“…In addition to traditional therapy using antibiotics, vaccines have been developed based upon the polysaccharide capsule associated with the S. pneumoniae bacteria [ 5 , 6 , 7 ]. Complicating success, however, is the variation in capsule polysaccharide content resulting in so-called bacterial serotypes with slight variation in polysaccharide structure [ 8 , 9 ].…”

“…In response, our research has focused on an alternative vaccine platform termed Liposomal Encapsulation of Polysaccharides (LEPS), in which a liposomal carrier simultaneously encapsulates polysaccharide content while allowing for the surface attachment of protein content ( Figure 1 ) [ 8 , 12 , 15 , 16 ]. The end result is a glycoconjugate mimic that offers a simpler, noncovalent form of polysaccharide–protein co-localization and a more tractable and scalable route to full serotype vaccine coverage.…”

Impact of Influenza on Pneumococcal Vaccine Effectiveness during Streptococcus pneumoniae Infection in Aged Murine Lung

“…As recent work has illustrated differential efficacy of Prevnar vaccination in modulating the immune responses of adult mice to a post-influenza infection with a serotype 3 strain of Streptococcus pneumoniae, we chose to examine the impact of Pneumovax on these responses [30,40]. Given these findings, it would be plausible that other vaccines, designed with specific bacterial components, such as pneumococcal surface protein A (PspA) and pneumolysin (Ply) or liposomal encapsulation of polysaccharides (LEPS), may improve efficacy to post-influenza S. pneumoniae infection [31,[43][44][45]. Future work will need to evaluate if additional vaccine types can prove efficacious and further reduce inflammatory cytokine production while improving bacterial clearance post-influenza infection.…”