Impact of Protein Nanoparticle Shape on the Immunogenicity of Antimicrobial Glycoconjugate Vaccines.

Protein self-assembling nanoparticles (NPs) can be used as carriers for antigen delivery to increase vaccine immunogenicity. NPs mimic the majority of invading pathogens, inducing a robust adaptive immune response and long-lasting protective immunity. In this context, we investigated the potential of NPs of different sizes and shapes-ring-, rod-like, and spherical particles-as carriers for bacterial oligosaccharides by evaluating in murine models the role of these parameters on the immune response. Oligosaccharides from Neisseria meningitidis type W capsular polysaccharide were conjugated to ring-shape or nanotubes of engineered Pseudomonas aeruginosa Hemolysin-corregulated protein 1 (Hcp1cc) and to spherical Helicobacter pylori ferritin. Glycoconjugated NPs were characterized using advanced technologies such as High-Performance Liquid Chromatography (HPLC), Asymmetric Flow-Field Flow fractionation (AF4), and Transmission electron microscopy (TEM) to verify their correct assembly, dimensions, and glycosylation degrees. Our results showed that spherical ferritin was able to induce the highest immune response in mice against the saccharide antigen compared to the other glycoconjugate NPs, with increased bactericidal activity compared to benchmark MenW-CRM197. We conclude that shape is a key attribute over size to be considered for glycoconjugate vaccine development.

Synergic complement-mediated bactericidal activity of monoclonal antibodies with distinct specificity.

The classical complement pathway is triggered when antigen-bound immunoglobulins bind to C1q through their Fc region. While C1q binds to a single Fc with low affinity, a higher avidity stable binding of two or more of C1q globular heads initiates the downstream reactions of the complement cascade ultimately resulting in bacteriolysis. Synergistic bactericidal activity has been demonstrated when monoclonal antibodies recognize nonoverlapping epitopes of the same antigen. The aim of the present work was to investigate the synergistic effect between antibodies directed toward different antigens. To this purpose, we investigated the bactericidal activity induced by combinations of monoclonal antibodies (mAbs) raised against factor H-binding protein (fHbp) and Neisserial Heparin-Binding Antigen (NHBA), two major antigens included in Bexsero, the vaccine against Meningococcus B, for prevention from this devastating disease in infants and adolescents. Collectively, our results show that mAbs recognizing different antigens can synergistically activate complement even when each single Mab is not bactericidal, reinforcing the evidence that cooperative immunity induced by antigen combinations can represent a remarkable added value of multicomponent vaccines. Our study also shows that the synergistic effect of antibodies is modulated by the nature of the respective epitopes, as well as by the antigen density on the bacterial cell surface.

Meningococcal factor H binding protein as immune evasion factor and vaccine antigen.

Factor H binding protein (fHbp) is a key virulence factor of Neisseria meningitidis and a main component of the two licensed vaccines against serogroup B meningococcus (Bexsero and Trumenba). fHbp is a surface-exposed lipoprotein that enables the bacterium to survive in human blood by binding the human complement regulator factor H (fH). When used as vaccine, the protein induces antibodies with potent bactericidal activity. While the fHbp gene is present in the majority of N. meningitidis serogroup B isolates, the expression level varies up to 15 times between different strains and more than 700 different sequence variants have been described. Antigenically, the protein has been divided into three variants or two subfamilies. The 3D structure of fHbp alone, in combination with fH or in complex with bactericidal antibodies, has been key to understanding the molecular details of the protein. In this article, we will review the biochemical and immunological properties of fHbp, and its key role in meningococcal pathogenesis, complement regulation, and immune evasion.

Synergistic Activity of Colistin in Combination With Resveratrol Against Colistin-Resistant Gram-Negative Pathogens.

Objectives: In this study, we investigated the antimicrobial activity of resveratrol in combination with colistin, a last-resort agent for the treatment of severe infections caused by multidrug resistant Gram-negative pathogens. Methods: The synergistic activity and the bactericidal activity of colistin in combination with resveratrol was investigated by checkerboard assays and time-kill assays, respectively. A total of 21 strains were investigated, including 16 strains of different species (Klebsiella pneumoniae, n = 6, Escherichia coli, n = 6; Citrobacter braakii, n = 1; Stenotrophomonas malthophilia, n = 1; Enterobacter cloaceae, n = 1; Acinetobacter baumannii, n = 1) with acquired colistin resistance, three colistin-susceptible K. pneumoniae precursors, and two strains of intrinsically colistin-resistant species (Serratia marcescens, n = 1; Proteus mirabilis, n = 1). Mechanisms of acquired colistin resistance included chromosomal mutations (i.e., mgrB, pmrAB) and plasmid genes (mcr-1, mcr-1.2). Results: Resveratrol did not show any significant intrinsic antimicrobial activity. Overall, a relevant synergistic antimicrobial activity of resveratrol in combination with colistin was observed with all tested strains, except for the three colistin-susceptible K. pneumoniae strains, and for two mcr-1-positive E. coli strains. In time-kill assays, performed with 15 selected strains, the combination of colistin 2 mg/L plus resveratrol 128 mg/L was bactericidal with 11 strains, and bacteriostatic for the remaining ones. Conclusions: Resveratrol was found to potentiate colistin activity against a wide panel of colistin-resistant strains, regardless of species and resistance mechanisms, which would deserve further investigation for potential clinical applications.