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A new candidate epitope-based vaccine against PspA PhtD of Streptococcus pneumoniae: a computational experimental
Mona Shafaghi1,2, Zohreh Bahadori1,2, Seyed Mahmoud Barzi2
1Department of Medical Biotechnology, faculty of Medicine, Semnan University of Medical Sciences, Semnan, Iran.
Insights
A novel fusion protein combining PspA and PhtD antigens offers a promising, serotype-independent vaccine candidate against pneumococcus. This peptide-based vaccine demonstrated superior immunogenicity and protective efficacy in mice compared to individual components.
Area of Science:
- Immunology
- Vaccinology
- Computational Biology
Background:
- * *Streptococcus pneumoniae* (pneumococcus) is a major cause of childhood and elderly mortality.
- * Current polysaccharide vaccines have limitations.
- * Protein-based vaccines targeting pneumococcal virulence factors are a promising alternative.
Purpose of the Study:
- * To develop and evaluate a novel fusion protein vaccine (PAD) combining PspA and PhtD antigens.
- * To assess the immunogenicity and protective efficacy of PAD against pneumococcal infection.
- * To compare PAD's efficacy with individual PspA (PA) and PhtD (PD) components and their combination.
Main Methods:
- * Immunoinformatics approaches were used to design the PAD fusion construct.
- * Computational predictions assessed physicochemical properties, antigenicity, allergenicity, toxicity, and 3D structure.
- * Mice were immunized with PAD, PA, PD, or a combination, followed by challenge with *S. pneumoniae*.
- * Antibody and cytokine levels, antibody functionality, survival rates, and bacterial load were evaluated.
Main Results:
- * Computational analyses predicted PAD to be antigenic, non-allergenic, non-toxic, and soluble.
- * Immunization induced high levels of antibodies and cytokines in mice.
- * Antibodies exhibited complement-mediated bactericidal activity.
- * Mice immunized with PAD showed improved survival rates after pneumococcal challenge.
- * Experimental results validated the immunoinformatics predictions.
Conclusions:
- * A novel peptide-based vaccine candidate (PAD) combining PspA and PhtD was successfully developed.
- * The PAD fusion protein demonstrated superior immunogenicity and protective efficacy compared to individual components or their combination.
- * PAD holds potential as a serotype-independent pneumococcal vaccine or a component in conjugate vaccines.
Introduction:
Pneumococcus is an important respiratory pathogen that is associated with high rates of death in newborn children and the elderly. Given the disadvantages of current polysaccharide-based vaccines, the most promising alternative for developing improved vaccines may be to use protein antigens with different roles in pneumococcus virulence. PspA and PhtD, highly immunogenic surface proteins expressed by almost all pneumococcal strains, are capable of eliciting protective immunity against lethal infections.
Methods:
In this study using immunoinformatics approaches, we constructed one fusion construct (called PAD) by fusing the immunodominant regions of PspA from families 1 & 2 (PA) to the immunodominant regions of PhtD (PD). The objective of this project was to test the immunogenicity of the fusion protein PAD and to compare its protective activity against S. pneumoniae infection with PA or PD alone and a combination of PA and PD. The prediction of physicochemical properties, antigenicity, allergenicity, toxicity, and 3D-structure of the constructs, as well as molecular docking with HLA receptor and immune simulation were performed using computational tools. Finally, mice were immunized and the serum levels of antibodies/cytokines and functionality of antibodies in vitro were evaluated after immunization. The mice survival rates and decrease of bacterial loads in the blood/spleen were examined following the challenge.
Results:
The computational analyses indicated the proposed constructs could be antigenic, non-allergenic, non-toxic, soluble and able to elicit robust immune responses. The results of actual animal experiments revealed the candidate vaccines could induce the mice to produce high levels of antibodies and cytokines. The complement-mediated bactericidal activity of antibodies was confirmed and the antibodies provided favorable survival in immunized mice after bacterial challenge. In general, the experimental results verified the immunoinformatics studies.
Conclusion:
For the first time this report presents novel peptide-based vaccine candidates consisting of immunodominant regions of PspA and PhtD antigens. The obtained findings confirmed that the fusion formulation could be relatively more efficient than the individual and combination formulations. The results propose that the fusion protein alone could be used as a serotype-independent pneumococcal vaccine or as an effective partner protein for a conjugate polysaccharide vaccine.
