Vaccine development for bacterial pathogens: Advances, challenges and prospects

The challenge of antimicrobial resistance in the Asia-Pacific: a pediatric perspective

PURPOSE OF REVIEW

The densely populated Asia Pacific region is home to 600 million children, and suffers from a significant burden of morbidity and mortality due to infections associated with antimicrobial resistance (AMR). We aimed to identify the drivers, challenges and potential opportunities to alter the burden of AMR within the region.

RECENT FINDINGS

Despite the high AMR burden borne by the Asia Pacific region, there are limited (and geographically imbalanced) published data to delineate the contemporary epidemiology of serious multidrug-resistant bacterial infections in children. Furthermore, the region is impacted by overcrowded and poorly resourced healthcare facilities, insufficient microbiological resources, and widespread community and environmental antibiotic use leading to limited efficacy for frequently prescribed antibiotics. Vaccine coverage is also inadequate and inequitable, further driving the burden of infectious disease (and antibiotic overuse) in children.

SUMMARY OF IMPLICATIONS

There are many challenges in implementing antimicrobial stewardship and infection prevention and control programs to reduce the excessive AMR disease burden in children across the Asia Pacific region, yet locally-driven strategies have successfully reduced antibiotic overuse in some settings, and should be replicated. Reducing the AMR disease burden will require improved healthcare resourcing, including better access to microbiological diagnosis, and multidisciplinary approaches to enhance infection prevention and antibiotic prescribing.

Advancing local manufacturing capacities for vaccines within Africa - Opportunities, priorities and challenges

Our viewpoint focuses on the paradox that Africa represents 25 % of total global vaccine usage, yet 99 % of these vaccines are manufactured overseas. In view of the iniquitous supply and distribution of COVID-19 vaccines to Africa during the pandemic, we emphasize the need for scaling up local vaccine manufacturing capacities across Africa. We review current vaccine manufacturing capacities within Africa, highlight priority vaccines needs, and describe opportunities and challenges of advancing local manufacturing capacities within Africa. Of 11 manufacturers in Africa, ten have operational formulation/fill/finish capacities. However, capacities to produce active vaccine components locally are very limited and leveraging of vaccine technology platforms such as live-attenuated virus, inactivated virus, and mRNA remain scanty. South Africa and Senegal are the only countries with end-to-end manufacturing capacities. Based on market demand, manufacturing complexity, target population, disease burden and vaccination regimen, the top 5 priority vaccines identified for local manufacturing in Africa were measles-rubella, yellow fever, cholera, rotavirus, and meningococcal vaccines. Enablers identified for Africa's vaccine manufacturing initiatives include: a preferential procurement of African-made vaccines for sustainable and reliable volumes through GAVI and UNICEF; deal preparation to target investments avoiding overproduction; technology transfers; regulatory systems strengthening; R&D capacities and infrastructure. Thus, African vaccine manufacturers and all stakeholders should focus taking forward the portfolio of activities required for continental vaccine manufacturing, including regulatory strengthening capacities, training and workforce development, rather than only focus on efforts that benefit a particular manufacturer or country. Optimism for advancing vaccine manufacturing in Africa comes from the announcement in December 2023 by GAVI for the establishment of the African Vaccine Manufacturing Accelerator, a financing mechanism of USD 1 billion aimed at creating a sustainable vaccine manufacturing industry in Africa. However, many challenges need to be overcome including that of having secure funding for sustaining what is developed.

mRNA vaccine platforms: linking infectious disease prevention and cancer immunotherapy

The advent of mRNA vaccines, accelerated by the global response to the COVID-19 pandemic, marks a transformative shift in vaccine technology. In this article, we discuss the development, current applications, and prospects of mRNA vaccines for both the prevention and treatment of infectious diseases and oncology. By leveraging the capacity to encode antigens within host cells directly, mRNA vaccines provide a versatile and scalable platform suitable for addressing a broad spectrum of pathogens and tumor-specific antigens. We highlight recent advancements in mRNA vaccine design, innovative delivery mechanisms, and ongoing clinical trials, with particular emphasis on their efficacy in combating infectious diseases, such as COVID-19, Zika, and influenza, as well as their emerging potential in cancer immunotherapy. We also address critical challenges, including vaccine stability, optimization of immune responses, and the broader issue of global accessibility. Finally, we review potential strategies for advancing next-generation mRNA vaccines, with the aim of overcoming current limitations in vaccine technology and enhancing both preventive and therapeutic approaches for infectious and oncological diseases.

Current innovations in mRNA vaccines for targeting multidrug-resistant ESKAPE pathogens

The prevalence of multidrug-resistant (MDR) ESKAPE pathogens, including Enterococcus faecium, Staphylococcus aureus, Klebsiella pneumoniae, Acinetobacter baumannii, and Pseudomonas aeruginosa, represents a critical global public health challenge. In response, mRNA vaccines offer an adaptable and scalable platform for immunotherapy against ESKAPE pathogens by encoding specific antigens that stimulate B-cell-driven antibody production and CD8+ T-cell-mediated cytotoxicity, effectively neutralizing these pathogens and combating resistance. This review examines recent advancements and ongoing challenges in the development of mRNA vaccines targeting MDR ESKAPE pathogens. We explore antigen selection, the nuances of mRNA vaccine technology, and the complex interactions between bacterial infections and antibiotic resistance. By assessing the potential efficacy of mRNA vaccines and addressing key barriers to their paraclinical implementation, this review highlights the promising function of mRNA-based immunization in combating MDR ESKAPE pathogens.

The role of asymmetric flow field-flow fractionation in drug development - From size separation to advanced characterization

Drug development is a complex multi-stage process that aims to deliver therapeutic products to the market. This process employs different analytical methods to separate and characterise compounds, monitor manufacturing, and validate the final drug products to ensure their safety, quality, and efficacy. However, advancements in modern drug development and discovery have led to new types of the therapeutical products of increasing complexity. As such, the capabilities of some traditional analytical techniques have become limited, and the demand for using advanced analytical techniques like field-flow fractionation (FFF) has been increasing. A special feature offered by the FFF family is a unique way of separation based on the analytes' specific physicochemical properties. As such, FFF is a powerful tool for analysing diverse analytes and complex mixtures. Herein, asymmetric flow field-flow fractionation (AF4) is the most frequently used technique within the FFF family in drug development. Therefore, this review aims to provide a general overview of the usage of AF4 technology in the drug development field.

Beyond Needles: Immunomodulatory Hydrogel-Guided Vaccine Delivery Systems

Vaccines are critical for combating infectious diseases, saving millions of lives worldwide each year. Effective immunization requires precise vaccine delivery to ensure proper antigen transport and robust immune activation. Traditional vaccine delivery systems, however, face significant challenges, including low immunogenicity and undesirable inflammatory reactions, limiting their efficiency. Encapsulating or binding vaccines within biomaterials has emerged as a promising strategy to overcome these limitations. Among biomaterials, hydrogels have gained considerable attention for their biocompatibility, ability to interact with biological systems, and potential to modulate immune responses. Hydrogels offer a materials science-driven approach for targeted vaccine delivery, addressing the shortcomings of conventional methods while enhancing vaccine efficacy. This review examines the potential of hydrogel-based systems to improve immunogenicity and explores their dual role as immunomodulatory adjuvants. Innovative delivery methods, such as microneedles, patches, and inhalable systems, are discussed as minimally invasive alternatives to traditional administration routes. Additionally, this review addresses critical challenges, including safety, scalability, and regulatory considerations, offering insights into hydrogel-guided strategies for eliciting targeted immune responses and advancing global immunization efforts.

Current Progress in the Development of mRNA Vaccines Against Bacterial Infections

Bacterial infections have accompanied humanity for centuries. The discovery of the first antibiotics and the subsequent golden era of their discovery temporarily shifted the balance in this confrontation to the side of humans. Nevertheless, the excessive and improper use of antibacterial drugs and the evolution of bacteria has gotten the better of humans again. Therefore, today, the search for new antibacterial drugs or the development of alternative approaches to the prevention and treatment of bacterial infections is relevant and topical again. Vaccination is one of the most effective strategies for the prevention of bacterial infections. The success of new-generation vaccines, such as mRNA vaccines, in the fight against viral infections has prompted many researchers to design mRNA vaccines against bacterial infections. Nevertheless, the biology of bacteria and their interactions with the host's immunity are much more complex compared to viruses. In this review, we discuss structural features and key mechanisms of evasion of an immune response for nine species of bacterial pathogens against which mRNA vaccines have been developed and tested in animals. We focus on the results of experiments involving the application of mRNA vaccines against various bacterial pathogens in animal models and discuss possible options for improving the vaccines' effectiveness. This is one of the first comprehensive reviews of the use of mRNA vaccines against bacterial infections in vivo to improve our knowledge.

Advancing Phage Therapy: A Comprehensive Review of the Safety, Efficacy, and Future Prospects for the Targeted Treatment of Bacterial Infections

BACKGROUND

Phage therapy, a treatment utilizing bacteriophages to combat bacterial infections, is gaining attention as a promising alternative to antibiotics, particularly for managing antibiotic-resistant bacteria. This study aims to provide a comprehensive review of phage therapy by examining its safety, efficacy, influencing factors, future prospects, and regulatory considerations. The study also seeks to identify strategies for optimizing its application and to propose a systematic framework for its clinical implementation.

METHODS

A comprehensive analysis of preclinical studies, clinical trials, and regulatory frameworks was undertaken to evaluate the therapeutic potential of phage therapy. This included an in-depth assessment of key factors influencing clinical outcomes, such as infection site, phage-host specificity, bacterial burden, and immune response. Additionally, innovative strategies-such as combination therapies, bioengineered phages, and phage cocktails-were explored to enhance efficacy. Critical considerations related to dosing, including inoculum size, multiplicity of infection, therapeutic windows, and personalized medicine approaches, were also examined to optimize treatment outcomes.

RESULTS

Phage therapy has demonstrated a favorable safety profile in both preclinical and clinical settings, with minimal adverse effects. Its ability to specifically target harmful bacteria while preserving beneficial microbiota underpins its efficacy in treating a range of infections. However, variable outcomes in some studies highlight the importance of addressing critical factors that influence therapeutic success. Innovative approaches, including combination therapies, bioengineered phages, expanded access to diverse phage banks, phage cocktails, and personalized medicine, hold significant promise for improving efficacy. Optimizing dosing strategies remains a key area for enhancement, with critical considerations including inoculum size, multiplicity of infection, phage kinetics, resistance potential, therapeutic windows, dosing frequency, and patient-specific factors. To support the clinical application of phage therapy, a streamlined four-step guideline has been developed, providing a systematic framework for effective treatment planning and implementation.

CONCLUSION

Phage therapy offers a highly adaptable, targeted, and cost-effective approach to addressing antibiotic-resistant infections. While several critical factors must be thoroughly evaluated to optimize treatment efficacy, there remains significant potential for improvement through innovative strategies and refined methodologies. Although phage therapy has yet to achieve widespread approval in the U.S. and Europe, its accessibility through Expanded Access programs and FDA authorizations for food pathogen control underscores its promise. Established practices in countries such as Poland and Georgia further demonstrate its clinical feasibility. To enable broader adoption, regulatory harmonization and advancements in production, delivery, and quality control will be essential. Notably, the affordability and scalability of phage therapy position it as an especially valuable solution for developing regions grappling with escalating rates of antibiotic resistance.

The Evolution of Vaccines Development across Salmonella Serovars among Animal Hosts: A Systematic Review

Salmonella is a significant zoonotic foodborne pathogen, and the global spread of multidrug-resistant (MDR) strains poses substantial challenges, necessitating alternatives to antibiotics. Among these alternatives, vaccines protect the community against infectious diseases effectively. This review aims to summarize the efficacy of developed Salmonella vaccines evaluated in various animal hosts and highlight key transitions for future vaccine studies. A total of 3221 studies retrieved from Web of Science, Google Scholar, and PubMed/Medline databases between 1970 and 2023 were evaluated. One hundred twenty-seven qualified studies discussed the vaccine efficacy against typhoidal and nontyphoidal serovars, including live-attenuated vaccines, killed inactivated vaccines, outer membrane vesicles, outer membrane complexes, conjugate vaccines, subunit vaccines, and the reverse vaccinology approach in different animal hosts. The most efficacious vaccine antigen candidate found was recombinant heat shock protein (rHsp60) with an incomplete Freund's adjuvant evaluated in a murine model. Overall, bacterial ghost vaccine candidates demonstrated the highest efficacy at 91.25% (95% CI = 83.69-96.67), followed by the reverse vaccinology approach at 83.46% (95% CI = 68.21-94.1) across animal hosts. More than 70% of vaccine studies showed significant production of immune responses, including humoral and cellular, against Salmonella infection. Collectively, the use of innovative methods rather than traditional approaches for the development of new effective vaccines is crucial and warrants in-depth studies.

Multimodal Mass Spectrometry Identifies a Conserved Protective Epitope in S. pyogenes Streptolysin O

An important element of antibody-guided vaccine design is the use of neutralizing or opsonic monoclonal antibodies to define protective epitopes in their native three-dimensional conformation. Here, we demonstrate a multimodal mass spectrometry-based strategy for in-depth characterization of antigen-antibody complexes to enable the identification of protective epitopes using the cytolytic exotoxin Streptolysin O (SLO) from Streptococcus pyogenes as a showcase. We first discovered a monoclonal antibody with an undisclosed sequence capable of neutralizing SLO-mediated cytolysis. The amino acid sequence of both the antibody light and the heavy chain was determined using mass-spectrometry-based de novo sequencing, followed by chemical cross-linking mass spectrometry to generate distance constraints between the antibody fragment antigen-binding region and SLO. Subsequent integrative computational modeling revealed a discontinuous epitope located in domain 3 of SLO that was experimentally validated by hydrogen-deuterium exchange mass spectrometry and reverse engineering of the targeted epitope. The results show that the antibody inhibits SLO-mediated cytolysis by binding to a discontinuous epitope in domain 3, likely preventing oligomerization and subsequent secondary structure transitions critical for pore-formation. The epitope is highly conserved across >98% of the characterized S. pyogenes isolates, making it an attractive target for antibody-based therapy and vaccine design against severe streptococcal infections.

Design of a multi-epitope-based vaccine candidate against Bovine Genital Campylobacteriosis using a reverse vaccinology approach

BACKGROUND

Bovine Genital Campylobacteriosis (BGC), a worldwide distributed venereal disease caused by Campylobacter fetus subsp. venerealis (Cfv), has a relevant negative economic impact in cattle herds. The control of BGC is hampered by the inexistence of globally available effective vaccines. The present in silico study aimed to develop a multi-epitope vaccine candidate against Cfv through reverse vaccinology.

RESULTS

The analysis of Cfv strain NCTC 10354 proteome allowed the identification of 9 proteins suitable for vaccine development. From these, an outer membrane protein, OmpA, and a flagellar protein, FliK, were selected for prediction of B-cell and T-cell epitopes. The top-ranked epitopes conservancy was assessed in 31 Cfv strains. The selected epitopes were integrated to form a multi-epitope fragment of 241 amino acids, which included 2 epitopes from OmpA and 13 epitopes from FliK linked by GPGPG linkers and connected to the cholera toxin subunit B by an EAAAK linker. The vaccine candidate was predicted to be antigenic, non-toxic, non-allergenic, and soluble upon overexpression. The protein structure was predicted and optimized, and the sequence was successfully cloned in silico into a plasmid vector. Additionally, immunological simulations demonstrated the vaccine candidate's ability to stimulate an immune response.

CONCLUSIONS

This study developed a novel vaccine candidate suitable for further in vitro and in vivo experimental validation, which may become a useful tool for the control of BGC.

Antimicrobial resistance containment in Africa: Moving beyond surveillance

Worldwide, infections caused by drug-resistant pathogens constitute a significant challenge threatening therapeutic efforts. According to the World Health Organization (WHO), antimicrobial resistance (AMR) ranks among the top 10 global public health threats. Organisms with a high rate of multiple host adaptivity, significant genetic diversity (multiple lineages), high virulence factors, and genetic exchange have been isolated from various sources (humans, animals, and the environment) even without exposure to prior antibiotics. Till now, the source of AMR and how resistant clones are selected in the environment remain largely elusive, and potential anthropogenic transmission has been reported in different studies. Various drug-resistant pathogens, lineages, resistant clones, outbreak clusters, plasmid replicates, and genes that play a critical role in resistance dissemination have been identified. Maintenance of certain multidrug-resistant (MDR) determinants has also been shown to enhance or support the propagation of MDR. So far, significant advances have been made in understanding the burden of AMR. However, overcoming AMR requires a holistic approach, as there is no single approach with sufficient precision to curb the threat. While strengthening AMR surveillance efforts is essential, as we have shown, there is also a need to intensify efforts to strengthen therapeutic interventions, especially in priority regions such as Africa. Herein, we discussed the burden of AMR and the dissemination of AMR in humans, animals, and the environment (non-medical drivers). We further delved into the big questions on Africa and discussed how therapeutic interventions involving vaccines and other viable biomaterials could be pivotal in reducing the burden of AMR to the barest minimum.

The Prevalence of Multidrug-Resistant Acinetobacter baumannii and Its Vaccination Status among Healthcare Providers

There is growing concern among healthcare providers worldwide regarding the prevalence of multidrug-resistant Acinetobacter baumannii (A. baumannii). Some of the worst hospital-acquired infections, often in intensive care units (ICUs), are caused by this bacterial pathogen. In recent years, the rise in multidrug-resistant A. baumannii has been linked to the overuse of antimicrobial drugs and the lack of adequate infection control measures. Infections caused by this bacterial pathogen are the result of prolonged hospitalization and ICU stays, and they are associated with increased morbidity and mortality. This review outlines the epidemiology, risk factors, and antimicrobial resistance associated with A. baumannii in various countries, with a special focus on the Kingdom of Saudi Arabia. In response to the growing concern regarding this drug-resistant bacteria, fundamental information about its pathology has been incorporated into the development of vaccines. Although these vaccines have been successful in animal models, their effectiveness in humans remains unproven. The review will discuss the development of A. baumannii vaccines, potential related obstacles, and efforts to find an effective strategy against this pathogen.