Use of the enterobacterial outer membrane protein PhoE in the development of new vaccines and DNA probes

Combing Immunoinformatics with Pangenome Analysis To Design a Multiepitope Subunit Vaccine against Klebsiella pneumoniae K1, K2, K47, and K64

Klebsiella pneumoniae is an opportunistic Gram-negative bacterium that has become a leading causative agent of nosocomial infections, mainly infecting patients with immunosuppressive diseases. Capsular (K) serotypes K1, K2, K47, and K64 are commonly associated with higher virulence (hypervirulent Klebsiella pneumoniae), and more threateningly, isolates belonging to the last two K serotypes are also frequently associated with resistance to carbapenem (hypervirulent carbapenem-resistant Klebsiella pneumoniae). The prevalence of these isolates has posed significant threats to human health, and there are no appropriate therapies available against them. Therefore, in this study, a method combining immunoinformatics and pangenome analysis was applied for contriving a multiepitope subunit vaccine against these four threatening serotypes. To obtain cross-protection, 12 predicted conserved antigens were screened from the core genome of 274 complete Klebsiella pneumoniae genomes (KL1, KL2, KL47, and KL64), from which the epitopes of T and B cells were extracted for vaccine construction. In addition, the immunological properties, the interaction with Toll-like receptors, and the stability in a simulative humoral environment were evaluated by immunoinformatics methods, molecular docking, and molecular dynamics simulation. All of these evaluations indicated the potency of this constructed vaccine to be an effective therapeutic agent. Lastly, the cDNA of the designed vaccine was optimized and ligated to pET-28a(+) for expression vector construction. Overall, our research provides a newly cross-protective control strategy against these troublesome pathogens and paves the way for the development of a safe and effective vaccine.

IMPORTANCEKlebsiella pneumoniae is an opportunistic Gram-negative bacterium that has become a leading causative agent of nosocomial infections. Among the numerous capsular serotypes, K1, K2, K47, and K64 are commonly associated with higher virulence (hypervirulent K. pneumoniae). More threateningly, the last two serotypes are frequently associated with resistance to carbapenem (hypervirulent carbapenem-resistant K. pneumoniae). However, there is currently no therapeutic agent or vaccine specifically against these isolates. Therefore, development of a vaccine against these pathogens is very essential. In this study, for the first time, a method combining pangenome analysis, reverse vaccinology, and immunoinformatics was applied for contriving a multiepitope subunit vaccine against K. pneumoniae isolates of K1, K2, K47, and K64. Also, the immunological properties of the constructed vaccine were evaluated and its high potency was revealed. Overall, our research will pave the way for the vaccine development against these four threatening capsular serotypes of K. pneumoniae.

Combining pangenome analysis to identify potential cross-protective antigens against avian pathogenic Escherichia coli

AbstractAvian pathogenic Escherichia coli (APEC) is the bacterial pathogen of poultry colibacillosis, which causes significant economic losses to the poultry industry. The lack of an effective vaccine against multiple serotypes and the emergence of multi-resistant isolates have made the control of avian colibacillosis troublesome. To identify conserved potential vaccine candidates, 58 genomes of APEC were obtained (54 sequenced by our laboratory and 4 downloaded from NCBI). A reverse vaccinology (RV) method based on the pangenome - called Pan-RV analysis - was performed in APEC-protective protein mining for the first time. Finally, four proteins were selected, and their immunoreactivity with anti-O1, O2, and O78 serum was verified by western blotting. Our in silico method of analysis will pave the way for rapid screening of vaccine candidates and will lay the foundation for the development of a highly effective subunit vaccine controlling APEC infection.

Autodisplay: efficacious surface exposure of antigenic UreA fragments from Helicobacter pylori in Salmonella vaccine strains

Live attenuated Salmonella strains expressing antigens of pathogens are promising oral vaccine candidates. There is growing evidence that the topology of expression of the foreign antigens can have a dramatic impact on the immunogenicity. We examined the potential of the AIDA-I (Escherichia coli adhesin involved in diffuse adherence) autotransporter domain to display antigenic fragments of the urease A subunit of Helicobacter pylori for the induction of a protective immune response. In the murine H. pylori model, protection is mainly mediated by CD4(+) T cells, and we therefore used the AIDA-I expression system to successfully express both nearly full-length UreA and defined T-helper-cell epitopes on the surface of an attenuated Salmonella enterica serovar Typhimurium vaccine strain. Surface exposure of the large UreA fragment or of one UreA T-cell epitope mediated a significant reduction in the level of H. pylori in immunized mice after challenge infection, whereas conventional cytoplasmic expression of UreA in Salmonella had no effect. These results support the concept that surface display increases the immunogenicity of recombinant antigens expressed on oral live vaccine carriers and further demonstrate the feasibility of immunizing against H. pylori with Salmonella vaccine strains expressing CD4(+) T-cell epitopes.

Autodisplay: development of an efficacious system for surface display of antigenic determinants in Salmonella vaccine strains

To optimize antigen delivery by Salmonella vaccine strains, a system for surface display of antigenic determinants was established by using the autotransporter secretion pathway of gram-negative bacteria. A modular system for surface display allowed effective targeting of heterologous antigens or fragments thereof to the bacterial surface by the autotransporter domain of AIDA-I, the Escherichia coli adhesin involved in diffuse adherence. A major histocompatibility complex class II-restricted epitope, comprising amino acids 74 to 86 of the Yersinia enterocolitica heat shock protein Hsp60 (Hsp60(74-86)), was fused to the AIDA-I autotransporter domain, and the resulting fusion protein was expressed at high levels on the cell surface of E. coli and Salmonella enterica serovar Typhimurium. Colonization studies in mice vaccinated with Salmonella strains expressing AIDA-I fusion proteins demonstrated high genetic stability of the generated vaccine strain in vivo. Furthermore, a pronounced T-cell response against Yersinia Hsp60(74-86) was induced in mice vaccinated with a Salmonella vaccine strain expressing the Hsp60(74-86)-AIDA-I fusion protein. This was shown by monitoring Yersinia Hsp60-stimulated IFN-gamma secretion and proliferation of splenic T cells isolated from vaccinated mice. These results demonstrate that the surface display of antigenic determinants by the autotransporter pathway deserves special attention regarding the application in live attenuated Salmonella vaccine strains.

Biotechnological applications of phage and cell display

In recent years, the use of surface-display vectors for displaying polypeptides on the surface of bacteriophage and bacteria, combined with in vitro selection technologies, has transformed the way in which we generate and manipulate ligands, such as enzymes, antibodies and peptides. Phage display is based on expressing recombinant proteins or peptides fused to a phage coat protein. Bacterial display is based on expressing recombinant proteins fused to sorting signals that direct their incorporation on the cell surface. In both systems, the genetic information encoding for the displayed molecule is physically linked to its product via the displaying particle. Using these two complementary technologies, we are now able to design repertoires of ligands from scratch and use the power of affinity selection to select those ligands having the desired (biological) properties from a large excess of irrelevant ones. With phage display, tailor-made proteins (fused peptides, antibodies, enzymes, DNA-binding proteins) may be synthesized and selected to acquire the desired catalytic properties or affinity of binding and specificity for in vitro and in vivo diagnosis, for immunotherapy of human disease or for biocatalysis. Bacterial surface display has found a range of applications in the expression of various antigenic determinants, heterologous enzymes, single-chain antibodies, and combinatorial peptide libraries. This review explains the basis of phage and bacterial surface display and discusses the contributions made by these two leading technologies to biotechnological applications. This review focuses mainly on three areas where phage and cell display have had the greatest impact, namely, antibody engineering, enzyme technology and vaccine development.

Antigenic determinants of the OmpC porin from Salmonella typhimurium

The antigenic determinants of Salmonella typhimurium OmpC were investigated by the analysis of cyanogen bromide (CNBr)-generated porin peptides with antiporin monoclonal antibodies (MAbs). We identified six bands (f1 to f6) with estimated molecular masses of 35.5, 31.0, 25.0, 22.5, 13.8, and 10.0 kDa, respectively. In addition, two small fragments (f7 and f8; 3.0 to 6.0 kDa) were detected only infrequently. The OmpC monomer or its CNBr-generated peptides were electrophoretically transferred to a polyvinylidene difluoride membrane and then subjected to amino acid composition analysis and N-terminal sequencing. A comparison of the amino acid composition data with known compositions of Escherichia coli and Salmonella typhi OmpC showed some differences; however, the amino acid sequences of 71 residues identified in S. typhimurium showed 88 and 98% identity with OmpC from E. coli and S. typhi, respectively. The screening of CNBr peptides with the 12 anti-(S. typhimurium) OmpC MAbs by Western blot (immunoblot), in conjunction with the prediction of the OmpC folding pattern based on the known three-dimensional structure of E. coli OmpF, showed that four MAbs reacted with surface-exposed epitopes on loops L2, L8, and L4 to L7, four MAbs reacted with a region in the eyelet structure on loop L3, and four MAbs reacted with the buried epitopes on transmembrane beta strands. The MAbs reacting with surface-exposed loops showed no cross-reaction with E. coli OmpC, whose sequence has diverged extensively from that of S. typhi and (probably) S. typhimurium OmpC only in regions of the externally exposed loops. In contrast, MAbs reacting with transmembrane beta strands, whose sequence is strongly conserved, showed strong cross-reaction with E. coli OmpC. These results show that comparison with the E. coli OmpF structure predicts the folding pattern of S. typhimurium OmpC rather accurately and that evolutionary divergence in sequences is confined to the external loops. The possible roles of these surface-exposed and buried epitopes as potentially useful antigenic regions for diagnostic assays and vaccine development are discussed.