Oligomerization of IC43 resulted in improved immunogenicity and protective efficacy against Pseudomonas aeruginosa lung infection

A rational designed multi-epitope vaccine elicited robust protective efficacy against Klebsiella pneumoniae lung infection

BACKGROUND

The emergence of drug-resistant strains of Klebsiella pneumoniae (K. pneumoniae) has become a significant challenge in the field of infectious diseases, posing an urgent need for the development of highly protective vaccines against this pathogen.

METHODS AND RESULTS

In this study, we identified three immunogenic extracellular loops based on the structure of five candidate antigens using sera from K. pneumoniae infected mice. The sequences of these loops were linked to the C-terminal of an alpha-hemolysin mutant (mHla) from Staphylococcus aureus to generate a heptamer, termed mHla-EpiVac. In vivo studies confirmed that fusion with mHla significantly augmented the immunogenicity of EpiVac, and it elicited both humoral and cellular immune responses in mice, which could be further enhanced by formulation with aluminum adjuvant. Furthermore, immunization with mHla-EpiVac demonstrated enhanced protective efficacy against K. pneumoniae channeling compared to EpiVac alone, resulting in reduced bacterial burden, secretion of inflammatory factors, histopathology and lung injury. Moreover, mHla fusion facilitated antigen uptake by mouse bone marrow-derived cells (BMDCs) and provided sustained activation of these cells.

CONCLUSIONS

These findings suggest that mHla-EpiVac is a promising vaccine candidate against K. pneumoniae, and further validate the potential of mHla as a versatile carrier protein and adjuvant for antigen design.

Oligomerization and Adjuvant Activity of Peptides Derived from the VirB4-like ATPase of Clostridioides difficile

In a previous study, we demonstrated that the Clostridioides difficile VirB4-like ATPase forms oligomers in vitro. In the current investigation, to study the observed phenomenon in more detail, we prepared a library of VirB4-derived peptides (delVirB4s) fused to a carrier maltose-binding protein (MBP). Using gel chromatography and polyacrylamide gel electrophoresis, we found a set of overlapping fragments that contribute most significantly to protein aggregation, which were represented as water-soluble oligomers with molecular masses ranging from ~300 kD to several megadaltons. Membrane filtration experiments, sucrose gradient ultracentrifugation, and dynamic light scattering measurements indicated the size of the soluble complex to be 15-100 nm. It was sufficiently stable to withstand treatment with 1 M urea; however, it dissociated in a 6 M urea solution. As shown by the changes in GFP fluorescence and the circular dichroism spectra, the attachment of the delVirB4 peptide significantly altered the structure of the partner MBP. The immunization of mice with the hybrid consisting of the selected VirB4-derived peptide and MBP, GST, or GFP resulted in increased production of specific antibodies compared to the peptide-free carrier proteins, suggesting significant adjuvant activity of the VirB4 fragment. This feature could be useful for the development of new vaccines, especially in the case of "weak" antigens that are unable to elicit a strong immune response by themselves.

Pseudomonas aeruginosa: Recent Advances in Vaccine Development

Pseudomonas aeruginosa is an important opportunistic human pathogen. Using its arsenal of virulence factors and its intrinsic ability to adapt to new environments, P. aeruginosa causes a range of complicated acute and chronic infections in immunocompromised individuals. Of particular importance are burn wound infections, ventilator-associated pneumonia, and chronic infections in people with cystic fibrosis. Antibiotic resistance has rendered many of these infections challenging to treat and novel therapeutic strategies are limited. Multiple clinical studies using well-characterised virulence factors as vaccine antigens over the last 50 years have fallen short, resulting in no effective vaccination being available for clinical use. Nonetheless, progress has been made in preclinical research, namely, in the realms of antigen discovery, adjuvant use, and novel delivery systems. Herein, we briefly review the scope of P. aeruginosa clinical infections and its major important virulence factors.

α-Hemolysin-Aided Oligomerization of the Spike Protein RBD Resulted in Improved Immunogenicity and Neutralization Against SARS-CoV-2 Variants

The increase in confirmed COVID-19 cases and SARS-CoV-2 variants calls for the development of safe and broad cross-protective vaccines. The RBD of the spike protein was considered to be a safe and effective candidate antigen. However, the low immunogenicity limited its application in vaccine development. Herein, we designed and obtained an RBD heptamer (mHla-RBD) based on a carrier protein-aided assembly strategy. The molecular weight of mHla-RBD is up to 450 kDa, approximately 10 times higher than that of the RBD monomer. When formulated with alum adjuvant, mHla-RBD immunization significantly increased the immunogenicity of RBD, as indicated by increased titers of RBD-specific antibodies, neutralizing antibodies, Th2 cellular immune response, and pseudovirus neutralization activity, when compared to RBD monomer. Furthermore, we confirmed that RBD-specific antibodies predominantly target conformational epitopes, which was approximately 200 times that targeting linear epitopes. Finally, a pseudovirus neutralization assay revealed that neutralizing antibodies induced by mHla-RBD against different SARS-CoV-2 variants were comparable to those against the wild-type virus and showed broad-spectrum neutralizing activity toward different SARS-CoV-2 variants. Our results demonstrated that mHla-RBD is a promising candidate antigen for development of SARS-CoV-2 vaccines and the mHla could serve as a universal carrier protein for antigen design.

Fusion of Streptococcus iniae α-enolase to IMX313 enhanced antibody titer and survival rate in olive flounder (Paralichthys olivaceus)

The polymerization of monomeric antigens can be a strategy to overcome the low immunogenicity of subunit vaccines. IMX313 is a hybrid oligomerization domain of chicken C4bp, and has been demonstrated to have potent activity as adjuvants for the fused antigens in mammals. In the present study, we investigated whether the oligomerization of α-enolase of Streptococcus iniae by fusion with IMX313 affected on antibody induction and on protection against S. iniae infection in olive flounder (Paralichthys olivaceus). The oligomerization of S. iniae enolase by fusion with IMX313 (enolase-IMX313) was verified by non-reducing PAGE, and the antibody titer against enolase in olive flounder immunized with enolase-IMX313 was significantly higher than that in fish immunized with enolase alone. Furthermore, although the survival of olive flounder immunized with enolase alone was low, fish immunized with enolase-IMX313 showed much higher survival (RPS 50%) in accordance with higher serum antibody titer, suggesting that fusion of antigens with IMX313 can be an effective way to enhance protective efficacy of subunit vaccines in olive flounder.

Metallacarborane Derivatives Effective against Pseudomonas aeruginosa and Yersinia enterocolitica

Pseudomonas aeruginosa is an opportunistic human pathogen that has become a nosocomial health problem worldwide. The pathogen has multiple drug removal and virulence secretion systems, is resistant to many antibiotics, and there is no commercial vaccine against it. Yersinia pestis is a zoonotic pathogen that is on the Select Agents list. The bacterium is the deadliest pathogen known to humans and antibiotic-resistant strains are appearing naturally. There is no commercial vaccine against the pathogen, either. In the current work, novel compounds based on metallacarborane cage were studied on strains of Pseudomonas aeruginosa and a Yersinia pestis substitute, Yersinia enterocolitica. The representative compounds had IC₅₀ values below 10 µM against Y. enterocolitica and values of 20–50 μM against P. aeruginosa. Artificial generation of compound-resistant Y. enterocolitica suggested a common mechanism for drug resistance, the first reported in the literature, and suggested N-linked metallacarboranes as impervious to cellular mechanisms of resistance generation. SEM analysis of the compound-resistant strains showed that the compounds had a predominantly bacteriostatic effect and blocked bacterial cell division in Y. enterocolitica. The compounds could be a starting point towards novel anti-Yersinia drugs and the strategy presented here proposes a mechanism to bypass any future drug resistance in bacteria.

Secretory System Components as Potential Prophylactic Targets for Bacterial Pathogens

Bacterial secretory systems are essential for virulence in human pathogens. The systems have become a target of alternative antibacterial strategies based on small molecules and antibodies. Strategies to use components of the systems to design prophylactics have been less publicized despite vaccines being the preferred solution to dealing with bacterial infections. In the current review, strategies to design vaccines against selected pathogens are presented and connected to the biology of the system. The examples are given for Y. pestis, S. enterica, B. anthracis, S. flexneri, and other human pathogens, and discussed in terms of effectiveness and long-term protection.

Understanding Pseudomonas aeruginosa-Host Interactions: The Ongoing Quest for an Efficacious Vaccine

Pseudomonas aeruginosa is a leading cause of chronic respiratory infections in people with cystic fibrosis (CF), bronchiectasis or chronic obstructive pulmonary disease (COPD), and acute infections in immunocompromised individuals. The adaptability of this opportunistic pathogen has hampered the development of antimicrobial therapies, and consequently, it remains a major threat to public health. Due to its antimicrobial resistance, vaccines represent an alternative strategy to tackle the pathogen, yet despite over 50 years of research on anti-Pseudomonas vaccines, no vaccine has been licensed. Nevertheless, there have been many advances in this field, including a better understanding of the host immune response and the biology of P. aeruginosa. Multiple antigens and adjuvants have been investigated with varying results. Although the most effective protective response remains to be established, it is clear that a polarised Th2 response is sub-optimal, and a mixed Th1/Th2 or Th1/Th17 response appears beneficial. This comprehensive review collates the current understanding of the complexities of P. aeruginosa-host interactions and its implication in vaccine design, with a view to understanding the current state of Pseudomonal vaccine development and the direction of future efforts. It highlights the importance of the incorporation of appropriate adjuvants to the protective antigen to yield optimal protection.