Evaluation of Protective Efficacy of Selected Immunodominant B-Cell Epitopes within Virulent Surface Proteins of Streptococcus pneumoniae

Abstract

Four previously identified immunodominant B-cell epitopes, located within known virulent pneumococcal proteins CbpD, PhtD, PhtE, and ZmpB, had shown promising immunological characteristics, indicating their potential to be used as vaccine antigens. In this study, we further evaluated the opsonophagocytic activity of antibodies against these epitopes and their capacity to protect mice from pneumococcal sepsis. An opsonophagocytic killing assay (OPKA) revealed that OPKA titers of human anti-peptide antibodies against pneumococcal serotypes 1, 3, and 19A were significantly higher ( < 0.001) than those of the control sera, suggesting their functional potential against virulent clinical isolates. Data obtained from mice actively immunized with any of the selected epitope analogues or with a mixture of these (G_Mix group) showed, compared to controls, enhanced survival against the highly virulent pneumococcal serotype 3 ( < 0.001). Moreover, passive transfer of hyperimmune serum from G_Mix to naive mice also conferred protection to a lethal challenge with serotype 3, which demonstrates that the observed protection was antibody mediated. All immunized murine groups elicited gradually higher antibody titers and avidity, suggesting a maturation of immune response over time. Among the tested peptides, PhD_pep19 and PhtE_pep40 peptides, which reside within the zinc-binding domains of PhtD and PhtE proteins, exhibited superior immunological characteristics. Recently it has been shown that zinc uptake is of high importance for the virulence of ; thus, our findings suggest that these epitopes deserve further evaluation as novel immunoreactive components for the development of a polysaccharide-independent pneumococcal vaccine.

Competence remodels the pneumococcal cell wall exposing key surface virulence factors that mediate increased host adherence

“…The impact of CbpD and CBPs in general on virulence is quite compelling, as it has been shown that the deletion of CbpD inhibits biofilm formation [ 74 ], while immunization with purified antibodies against a CbpD peptide fragment significantly increased survival of mice challenged intraperitoneally with lethal levels of a virulent serotype 3 pneumococcal strain [ 75 ]. Moreover, the addition of a mutated CSP1 peptide that inhibits the development of competence through outcompeting native CSP1, reduced CbpD and LytA expression levels and significantly decreased murine mortality after pneumococcal intranasal infection [ 76 ].…”

Differences in Pneumococcal and Haemophilus influenzae Natural Antibody Development in Papua New Guinean Children in the First Year of Life

“…Chimeras of NTHi DNABII proteins were also immunogenic against NTHi biofilm in vitro ( 50 ). Likewise, a PD peptide was shown to elicit a superior immunogenic response compared to the whole PD protein ( 51 ). These mapping studies should also be performed for pneumococcal antigens to further understand vaccine potential and design.…”

Synthesis of biologically active proteins as L6KD‐SUMO fusions forming inclusion bodies in Escherichia coli

“…A unique BamHI site separates the sequences encoding SUMO and His 6 in these plasmids. Plasmid pET28s-L 6 KD-SUMO-PhtD19 was used for the synthesis of the L 6 KD-SUMO-PhtD19 protein; this protein contains the PhtD19 peptide from pneumococcal histidine triad protein D (a.a. 200-219) (Papastamatiou et al, 2018) that is of interest as a vaccine component (Gorbunov et al, 2022).…”