Unit:
Faculty of MedicineLibrary of the School of Health Sciences
Author:
Papastamatiou Theodora
Dissertation committee:
Τσακρής Αθανάσιος, Καθηγητής, Ιατρική Σχολή, ΕΚΠΑ
Τσολιά Μαρίζα, Καθηγήτρια, Ιατρική Σχολή, ΕΚΠΑ
Κανακά Gantenbein Χριστίνα, Καθηγήτρια, Ιατρική Σχολή, ΕΚΠΑ
Σπούλου Βασιλική, Αναπληρώτρια Καθηγήτρια, Ιατρική Σχολή, ΕΚΠΑ
Σπυρίδης Νικόλαος, Αναπληρωτής Καθηγητής, Ιατρική Σχολή, ΕΚΠΑ
Ρούτσιας Γιάννης, Επίκουρος Καθηγητής, Ιατρική Σχολή, ΕΚΠΑ
Ντότσικα Ελένη, Ερευνήτρια A’ βαθμίδος, Eλληνικό Iνστιτούτο Πάστερ
Original Title:
Μελέτη της προστατευτικής ικανότητας ειδικών αντιπεπτιδικών αντισωμάτων έναντι του πνευμονιόκοκκου
Translated title:
Evaluation of protective efficacy of selected immunodominant b-cell epitopes within virulent surface proteins of streptococcus pneumoniae
Summary:
Pneumococcal conjugated vaccines (PCV) in countries with high vaccine uptake resulted in a sharp reduction of invasive pneumococcal disease (IPD) and induced significant herd protection. However, vaccine-induced immunological pressure and natural genetic transformations of S. pneumoniae have led to the global phenomenon of serotype replacement, resulting in a rapid increase of IPD caused by serotypes not included in currently used pneumococcal vaccines.
Pneumococcal surface proteins (VPPs), which are conserved between different serotypes, are known to elicit protective immunity in animals and could be used for the development of serotype-independent pneumococcal vaccines. However, obstacles related to the fact that their synthesis is not fully and chemically controlled as well as their cost and their frequent denaturation place hurdles in the clinical development of pneumococcal protein vaccines.
Aiming to overcome these barriers, efforts have been directed toward the identification of major immunogenic epitopes within VPPs. Thus, four immunodominant B-cell epitopes located within known virulent pneumococcal proteins CbpD, PhtD, PhtE, and ZmpB, identified by sera obtained from pediatric patients convalescing from invasive pneumococcal disease. They showed promising in vitro immunological characteristics indicating their potential to be used as vaccine antigens. So, in this study we further evaluated the opsonophagocytic activity of antibodies against these epitopes and their capacity to protect immunized mice from pneumococcal sepsis.
The opsonophagocytic killing assay (OPKA) revealed the functional potential of human anti-peptide antibodies against virulent pneumococcal serotypes 1, 3, and 19A. 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. 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.
Further evaluation of immunological response from the by repeated immunizations showed that all immunized murine groups elicited gradually higher antibody titers and avidity, suggesting the establishment of memory immune response and the maturation of produced anti-peptide antibodies (Affinity Maturation). 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. Of note, it has been shown that zinc uptake is of high importance for the virulence of Streptococcus pneumoniae. Moreover, cross-recognition was observed in the case of these peptides which share the His-triad motif sequence (HxxHxH). Finally, we found that PhtD peptide, compaire to the others, contains at least one T-cell epitope.
To date, only a few peptide/protein fragments from pneumococcal surface proteins could exhibit such promising in vitro and in vivo immunological characteristics. Thus, we anticipated that this study would be a further step toward the use of these peptides for the development of an effective serotype independent epitope-based pneumococcal vaccine.
Main subject category:
Health Sciences
Keywords:
S. pneumoniae, Protein based vaccines, Mice
Number of references:
192
File:
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PhD..pdf
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