In-silico design and evaluation of an epitope-based serotype-independent promising vaccine candidate for highly cross-reactive regions of pneumococcal surface protein A

Abstract

Background The pathogenicity of pneumococcus with high morbidity, mortality, and multi-drug resistance patterns has been increasing. The limited coverage of the licensed polysaccharide-based vaccines and the replacement of the non-vaccine serotypes are the main reasons for producing a successful serotype-independent vaccine. Pneumococcal surface protein A (PspA) is an extremely important virulence factor and an interesting candidate for conserved protein-based pneumococcal vaccine classified into two prominent families containing five clades. PspA family-elicited immunity is clade-dependent, and the level of the PspA cross-reactivity is restricted to the same family. Methods To cover and overcome the clade-dependent immunity of the PspAs in this study, we designed and tested a PspA1-5c+p vaccine candidate composed of the highest immunodominant coverage of B- and T-cell epitope truncated domain of each clade focusing on two cross-reactive B and C regions of the PspAs. The antigenicity, toxicity, physicochemical properties, 3D structure prediction, stability and flexibility of the designed protein using molecular dynamic (MD) simulation, molecular docking of the construct withHLADRB1*(01:01) and human lactoferrin N-lop, and immune simulation were assessed using immunoinformatics tools. In the experimental section, after intraperitoneal immunization of the mice with Alum adjuvanted recombinant PspA1-5c+p, we evaluated the immune response, cross-reactivity, and functionality of the Anti-PspA1-5c+p antibody using ELISA, Opsonophagocytic killing activity, and serum bactericidal assay. Results For the first time, this work suggested a novel PspA-based vaccine candidate using immunoinformatics tools. The designed PspA1-5c+p protein is predicted to be highly antigenic, non-toxic, soluble, stable with low flexibility in MD simulation, and able to stimulate both humoral and cellular immune responses. The designed protein also could interact strongly with HLADRB1*(01:01) and human lactoferrin N-lop in the docking study. Our immunoinformatics predictions were validated using experimental data. Results showed that the anti-PspA1-5c+p IgG not only had a high titer with strong and same cross-reactivity coverage against all pneumococcal serotypes used but also had high and effective bioactivity for pneumococcal clearance using complement system and phagocytic cells. Conclusion Our findings elucidated the potential application of the PspA1-5c+p vaccine candidate as a serotype-independent pneumococcal vaccine with a strong cross-reactivity feature. Further in-vitro and in-vivo investigations against other PspA clades should be performed to confirm the full protection of the PspA1-5c+p vaccine candidate.

A new candidate epitope-based vaccine against PspA PhtD of Streptococcus pneumoniae: a computational experimental approach

“…However, this polarization might be associated with the nature of antigens or the immunological pathway. This result is consistent with recent literature which reported that the PspA or PhtD antigens could stimulate dominant Th2 responses ( Kothari et al., 2015 ; Malekan et al., 2019 ; Afshari et al., 2023b ).…”

Recent progress in pneumococcal protein vaccines

“…PspA plays pivotal roles in inhibiting complement component C3 deposition on the pneumococcal surface ( 25 ), reducing phagocytosis of pneumococci ( 58 , 59 ), and providing substantial protection against bactericidal peptides of lactoferrin ( 26 ). Given its functional significance, PspA has been explored for over three decades as an immunogen and a potential vaccine candidate ( 22 , 60 , 61 ).…”

“…Initially, there were concerns that a vaccine targeting PspA might not provide adequate coverage due to its high variability ( 68 ). However, recent research has brought attention to the proline-rich domain of PspA, which has been found to be considerably more conserved ( 60 ). This discovery suggests that the proline-rich domain could be utilized to target uncommon strains beyond those belonging to family 1 or family 2, potentially enhancing the vaccine’s efficacy and widening its scope of protection ( 22 , 68 ).…”

Combined Immunoinformatics to Design and Evaluate a Multi-Epitope Vaccine Candidate against Streptococcus suis Infection

“…Further, the minimal immunogenic region-antigenic epitope for candidate subunit proteins can be predicted [ 27 ]. Multiple candidate antigenic epitopes joined by linkers to target diverse conserved surface proteins has resulted in cross-protection and has been demonstrated to be a well-established and safety-stable strategy in several bacteria such as Staphylococcus aureus [ 28 ], Escherichia coli [ 29 ] and Streptococcus pneumoniae [ 30 ]. Recently, a universal multi-epitope candidate vaccine was constructed against S. suis infection in swine using an immunoinformatics approach [ 31 ].…”