Innovative Approaches to Improve Anti-Infective Vaccine Efficacy

VFDB 2025: an integrated resource for exploring anti-virulence compounds

With the escalating crisis of bacterial multidrug resistance, anti-virulence therapeutic strategies have emerged as a highly promising alternative to conventional antibiotic treatments. Anti-virulence compounds are specifically designed to target virulence factors (VFs), disarming pathogens without affecting bacterial growth and thus reduce the selective pressure for resistance development. However, due to the complexity of bacterial pathogenesis, no anti-virulence small molecules have been approved for clinical use thus far, despite the documentation of hundreds of potential candidates. To provide valuable reference resources for drug design, repurposing, and target selection, the virulence factor database (VFDB, http://www.mgc.ac.cn/VFs/) has systematically collected public data on anti-virulence compounds through extensive literature mining, and further integrated this information with its existing knowledge of bacterial VFs. To date, the VFDB has curated a comprehensive dataset of 902 anti-virulence compounds across 17 superclasses reported by 262 studies worldwide. By cross-linking the current knowledge of bacterial VFs with information on relevant compounds (e.g. classification, chemical structure, molecular targets and mechanisms of action), the VFDB aims to bridge the gap between chemists and microbiologists, providing crucial insights for the development of innovative and effective antibacterial therapies to combat bacterial infections and address antibiotic resistance.

Staphylococcus aureus adaptive evolution: Recent insights on how immune evasion, immunometabolic subversion and host genetics impact vaccine development

Despite meritorious attempts, a S. aureus vaccine that prevents infection or mitigates severity has not yet achieved efficacy endpoints in prospective, randomized clinical trials. This experience underscores the complexity of host-S. aureus interactions, which appear to be greater than many other bacterial pathogens against which successful vaccines have been developed. It is increasingly evident that S. aureus employs strategic countermeasures to evade or exploit human immune responses. From entering host cells to persist in stealthy intracellular reservoirs, to sensing the environmental milieu and leveraging bacterial or host metabolic products to reprogram host immune responses, S. aureus poses considerable challenges for the development of effective vaccines. The fact that this pathogen causes distinct types of infections and can undergo transient genetic, transcriptional or metabolic adaptations in vivo that do not occur in vitro compounds challenges in vaccine development. Notably, the metabolic versatility of both bacterial and host immune cells as they compete for available substrates within specific tissues inevitably impacts the variable repertoire of gene products that may or may not be vaccine antigens. In this respect, S. aureus has chameleon phenotypes that have alluded vaccine strategies thus far. Nonetheless, a number of recent studies have also revealed important new insights into pathogenesis vulnerabilities of S. aureus. A more detailed understanding of host protective immune defenses versus S. aureus adaptive immune evasion mechanisms may offer breakthroughs in the development of effective vaccines, but at present this goal remains a very high bar. Coupled with the recent advances in human genetics and epigenetics, newer vaccine technologies may enable such a goal. If so, future vaccines that protect against or mitigate the severity of S. aureus infections are likely to emerge at the intersection of precision and personalized medicine. For now, the development of S. aureus vaccines or alternative therapies that reduce mortality and morbidity must continue to be pursued.

Immunosuppression in Glomerular Diseases: Implications for SARS-CoV-2 Vaccines and COVID-19

BACKGROUND

Glomerular diseases (GD) are chronic conditions that often involve immune dysfunction and require immunosuppressive therapy (IST) to control underlying pathogenesis. Unfortunately, such diseases appear to heighten risks of severe outcomes in COVID-19 and predispose to other infections that may be life-threatening. Thus, averting preventable infections is imperative in GD patients.

SUMMARY

The advent of vaccines demonstrated to be safe and efficacious against severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) has favorably impacted the COVID-19 pandemic epidemiology. However, patients on ISTs were excluded from initial vaccine clinical trials. Thus, only limited and incomplete data are available currently regarding the potential impact of immunosuppression on immune response to or efficacy of the SARS-CoV-2 vaccines. However, new insights are emerging from SARS-CoV-2 vaccine studies, and impacts of ISTs on conventional vaccines are useful to consider. Mechanisms of immunosuppressive agents commonly used in the treatment of GD are reviewed with respect to implications for immune responses induced by SARS-CoV-2 vaccines. ISTs discussed include corticosteroids; alkylating agents; antimetabolites; calcineurin or mammalian target of rapamycin inhibitors; CD38+, CD20+, or CD19+ cell depletion; and complement protein C5 inhibition.

KEY MESSAGES

Many immunosuppressive therapies may potentially attenuate or impair protective immunity of the SARS-CoV-2 vaccines. However, as vaccines currently in use employ mRNA or nonreplicative viral vectors, they appear to be safe in patients on immunosuppression, further favoring vaccination. Moreover, predominant SARS-CoV-2 vaccines are likely to afford at least partial protective immunity through one or more immune mechanisms even in patients on IST. Guidelines and emerging strategies are also considered to optimize vaccine protection from COVID-19.

Induction of mucosal immunity against pathogens by using recombinant baculoviral vectors: Mechanisms, advantages, and limitations

Over 90% of pathogens of medical importance invade the organism through mucosal surfaces, which makes it urgent to develop safe and effective mucosal vaccines and mucosal immunization protocols. Besides, parenteral immunization does not provide adequate protective immunity in mucosal surfaces. Effective mucosal vaccination could protect local and systemic compartments and favor herd immunity. Although various mucosal adjuvants and Ag-delivery systems have been developed, none has filled the gap to control diseases caused by complex mucosal pathogens. Among the strategies to counteract them, recombinant virions from the baculovirus Autographa californica multiple nucleopolyhedrovirus (rAcMNPV) are useful vectors, given their safety and efficacy to produce mucosal and systemic immunity in animal infection models. Here, we review the immunogenic properties of rAcMNPV virions from the perspectives of mucosal immunology and vaccinology. Some features, which are analyzed and extrapolated from studies with different particulate antigens, include size, shape, surface molecule organization, and danger signals, all needed to break the tolerogenic responses of the mucosal immune tissues. Also, we present a condensed discussion on the immunity provided by rAcMNPV virions against influenza virus and human papillomavirus in animal models. Through the text, we highlight the advantages and limitations of this experimental immunization platform.

Monoclonal IgM Antibodies Targeting Candida albicans Hyr1 Provide Cross-Kingdom Protection Against Gram-Negative Bacteria

Recent years have seen an unprecedented rise in the incidence of multidrug-resistant (MDR) Gram-negative bacteria (GNBs) such as Acinetobacter and Klebsiella species. In view of the shortage of novel drugs in the pipeline, alternative strategies to prevent, and treat infections by GNBs are urgently needed. Previously, we have reported that the Candida albicans hypha-regulated protein Hyr1 shares striking three-dimensional structural homology with cell surface proteins of Acinetobacter baumannii. Moreover, active vaccination with rHyr1p-N or passive immunization with anti-Hyr1p polyclonal antibody protects mice from Acinetobacter infection. In the present study, we use molecular modeling to guide design of monoclonal antibodies (mAbs) generated against Hyr1p and show them to bind to priority surface antigens of Acinetobacter and Klebsiella pneumoniae. The anti-Hyr1 mAbs block damage to primary endothelial cells induced by the bacteria and protect mice from lethal pulmonary infections mediated by A. baumannii or K. pneumoniae. Our current studies emphasize the potential of harnessing Hyr1p mAbs as a cross-kingdom immunotherapeutic strategy against MDR GNBs.

The Hyr1 protein from the fungus Candida albicans is a cross kingdom immunotherapeutic target for Acinetobacter bacterial infection

Different pathogens share similar medical settings and rely on similar virulence strategies to cause infections. We have previously applied 3-D computational modeling and bioinformatics to discover novel antigens that target more than one human pathogen. Active and passive immunization with the recombinant N-terminus of Candida albicans Hyr1 (rHyr1p-N) protect mice against lethal candidemia. Here we determine that Hyr1p shares homology with cell surface proteins of the multidrug resistant Gram negative bacterium, Acinetobacter baumannii including hemagglutinin (FhaB) and outer membrane protein A (OmpA). The A. baumannii OmpA binds to C. albicans Hyr1p, leading to a mixed species biofilm. Deletion of HYR1, or blocking of Hyr1p using polyclonal antibodies, significantly reduce A. baumannii binding to C. albicans hyphae. Furthermore, active vaccination with rHyr1p-N or passive immunization with polyclonal antibodies raised against specific peptide motifs of rHyr1p-N markedly improve survival of diabetic or neutropenic mice infected with A. baumannii bacteremia or pneumonia. Antibody raised against one particular peptide of the rHyr1p-N sequence (peptide 5) confers majority of the protection through blocking A. baumannii invasion of host cells and inducing death of the bacterium by a putative iron starvation mechanism. Anti-Hyr1 peptide 5 antibodies also mitigate A. baumannii /C. albicans mixed biofilm formation in vitro. Consistent with our bioinformatic analysis and structural modeling of Hyr1p, anti-Hyr1p peptide 5 antibodies bound to A. baumannii FhaB, OmpA, and an outer membrane siderophore binding protein. Our studies highlight the concept of cross-kingdom vaccine protection against high priority human pathogens such as A. baumannii and C. albicans that share similar ecological niches in immunocompromised patients.

Regulated Cell Death as a Therapeutic Target for Novel Antifungal Peptides and Biologics

The rise of microbial pathogens refractory to conventional antibiotics represents one of the most urgent and global public health concerns for the 21st century. Emergence of Candida auris isolates and the persistence of invasive mold infections that resist existing treatment and cause severe illness has underscored the threat of drug-resistant fungal infections. To meet these growing challenges, mechanistically novel agents and strategies are needed that surpass the conventional fungistatic or fungicidal drug actions. Host defense peptides have long been misunderstood as indiscriminant membrane detergents. However, evidence gathered over the past decade clearly points to their sophisticated and selective mechanisms of action, including exploiting regulated cell death pathways of their target pathogens. Such peptides perturb transmembrane potential and mitochondrial energetics, inducing phosphatidylserine accessibility and metacaspase activation in fungi. These mechanisms are often multimodal, affording target pathogens fewer resistance options as compared to traditional small molecule drugs. Here, recent advances in the field are examined regarding regulated cell death subroutines as potential therapeutic targets for innovative anti-infective peptides against pathogenic fungi. Furthering knowledge of protective host defense peptide interactions with target pathogens is key to advancing and applying novel prophylactic and therapeutic countermeasures to fungal resistance and pathogenesis.

Introduction to the Theme "New Methods and Novel Therapeutic Approaches in Pharmacology and Toxicology"

Major advances in scientific discovery and insights can result from the development and use of new techniques, as exemplified by the work of Solomon Snyder, who writes a prefatory article in this volume. The Editors have chosen "New Methods and Novel Therapeutic Approaches in Pharmacology and Toxicology" as the Theme for a number of articles in this volume. These include ones that review the development and use of new experimental tools and approaches (e.g., nanobodies and techniques to explore protein-protein interactions), new types of therapeutics (e.g., aptamers and antisense oligonucleotides), and systems pharmacology, which assembles (big) data derived from omics studies together with information regarding drugs and patients. The application of these new methods and therapeutic approaches has the potential to have a major impact on basic and clinical research in pharmacology and toxicology as well as on patient care.