Alanine Scanning Mutagenesis of the MEDI4893 (Suvratoxumab) Epitope Reduces Alpha Toxin Lytic Activity In Vitro and Staphylococcus aureus Fitness in Infection Models

Vaccines and Monoclonal Antibodies as Alternative Strategies to Antibiotics to Fight Antimicrobial Resistance

Antimicrobial resistance (AMR) is one of the most critical threats to global public health in the 21st century, causing a large number of deaths every year in both high-income and low- and middle-income countries. Vaccines and monoclonal antibodies can be exploited to prevent and treat diseases caused by AMR pathogens, thereby reducing antibiotic use and decreasing selective pressure that favors the emergence of resistant strains. Here, differences in the mechanism of action and resistance of vaccines and monoclonal antibodies compared to antibiotics are discussed. The state of the art for vaccine technologies and monoclonal antibodies are reviewed, with a particular focus on approaches validated in clinical studies. By underscoring the scope and limitations of the different emerging technologies, this review points out the complementary of vaccines and monoclonal antibodies in fighting AMR. Gaps in antigen discovery for some pathogens, as well as challenges associated with the clinical development of these therapies against AMR pathogens, are highlighted.

Mechanism of Action for an All-in-One Monoclonal Antibody Against Staphylococcus aureus Infection

Staphylococcus aureus is a major human pathogen associated with high mortality rates. The extensive use of antibiotics is associated with the rise of drug resistance, and exotoxins are not targeted by antibiotics. Therefore, monoclonal antibody (mAb) therapy has emerged as a promising solution to solve the clinical problems caused by refractory S aureus. Recent research suggests that the synergistic effects of several cytotoxins, including bicomponent toxins, are critical to the pathogenesis of S aureus. By comparing the amino acid sequences, researchers found that α-toxin and bicomponent toxins have high homology. Therefore, we aimed to screen an antibody, designated an all-in-one mAb, that could neutralize α-toxin and bicomponent toxins through hybridoma fusion. We found that this mAb has a significant pharmacodynamic effect within in vivo mouse models and in vitro experiments.

In Silico-Ex Vitro Iteration Strategy for Affinity Maturation of Anti-Ricin Peptides and the SPR Biosensing Application

The highly toxic plant toxin ricin is one of the most known threatening toxins. Accurate and sensitive biosensing methods for the first emergency response and intoxication treatment, are always pursued in the biodefense field. Screening affinity molecules is the fundamental mainstream approach for developing biosensing methods. Compared with common affinity molecules such as antibodies and oligonucleotide aptamers, peptides have great potential as biosensing modules with more accessible chemical synthesis capability and better batch-to-batch stability than antibodies, more abundant interaction sites, and robust sensing performance towards complex environments. However, anti-ricin peptides are so scant to be screened and discovered, and an advanced screening strategy is the utmost to tackle this issue. Here, we present a new in silico-in vitro iteration-assisted affinity maturation strategy of anti-ricin peptides. We first obtained affinity peptides targeting ricin through phage display with five panning rounds of "coating-elution-amplification-enrichment" procedures. The binding affinity and kinetic parameters characterized by surface plasmon resonance (SPR) showed that we had obtained four peptides owning dissociation constants (KD) around 2~35 μM, in which peptide PD-2-R5 has the lower KD of 4.7 μM and higher stable posture to interact with ricin. We then constructed a new strategy for affinity maturity, composing two rounds of in silico-in vitro iterations. Firstly, towards the single-site alanine scanning mutation peptide library, the molecular docking predictions match the SPR evaluation results well, laying a solid foundation for designing a full saturation mutated peptide library. Secondly, plenty of in silico saturation mutation prediction results guided the discovery of peptides PD2-R5-T3 and PD-2-R5-T4 with higher affinity from only a limited number of SPR evaluation experiments. Both evolved peptides had increased affinity by about 5~20 times, i.e., KD of 230 nM and 900 nM. A primary cellular toxicity assay indicated that both peptides could protect cells against ricin damage. We further established an SPR assay based on PD-2-R5-T3 and PD-2-R5-T4 elongated with an antifouling peptide linkage and achieved good linearity with a sensitivity of 1 nM and 0.5 nM, respectively. We hope this new affinity-mature strategy will find its favorable position in relevant peptide evolution, biosensing, and medical countermeasures for biotoxins to protect society's security and human life better.

Recent Advances in Monoclonal Antibody-Based Approaches in the Management of Bacterial Sepsis

Sepsis is a life-threatening condition characterized by an uncontrolled inflammatory response to an infectious agent and its antigens. Immune cell activation against the antigens causes severe distress that mediates a strong inflammatory response in vital organs. Sepsis is responsible for a high rate of morbidity and mortality in immunosuppressed patients. Monoclonal antibody (mAb)-based therapeutic strategies are now being explored as a viable therapy option for severe sepsis and septic shock. Monoclonal antibodies may provide benefits through two major strategies: (a) monoclonal antibodies targeting the pathogen and its components, and (b) mAbs targeting inflammatory signaling may directly suppress the production of inflammatory mediators. The major focus of mAb therapies has been bacterial endotoxin (lipopolysaccharide), although other surface antigens are also being investigated for mAb therapy. Several promising candidates for mAbs are undergoing clinical trials at present. Despite several failures and the investigation of novel targets, mAb therapy provides a glimmer of hope for the treatment of severe bacterial sepsis and septic shock. In this review, mAb candidates, their efficacy against controlling infection, with special emphasis on potential roadblocks, and prospects are discussed.

Molecular Targets for Antibody-Based Anti-Biofilm Therapy in Infective Endocarditis

Infective endocarditis (IE) is a heart disease caused by the infection of heart valves, majorly caused by Staphilococcus aureus. IE is initiated by bacteria entering the blood circulation in favouring conditions (e.g., during invasive procedures). So far, the conventional antimicrobial strategies based on the usage of antibiotics remain the major intervention for treating IE. Nevertheless, the therapeutic efficacy of antibiotics in IE is limited not only by the bacterial drug resistance, but also by the formation of biofilms, which resist the penetration of antibiotics into bacterial cells. To overcome these drawbacks, the development of anti-biofilm treatments that can expose bacteria and make them more susceptible to the action of antibiotics, therefore resulting in reduced antimicrobial resistance, is urgently required. A series of anti-biofilm strategies have been developed, and this review will focus in particular on the development of anti-biofilm antibodies. Based on the results previously reported in the literature, several potential anti-biofilm targets are discussed, such as bacterial adhesins, biofilm matrix and bacterial toxins, covering their antigenic properties (with the identification of potential promising epitopes), functional mechanisms, as well as the antibodies already developed against these targets and, where feasible, their clinical translation.

Anti-bacterial monoclonal antibodies: next generation therapy against superbugs

Prior to the nineteenth century, infectious disease was one of the leading causes of death. Human life expectancy has roughly doubled over the past century as a result of the development of antibiotics and vaccines. However, the emergence of antibiotic-resistant superbugs brings new challenges. The side effects of broad-spectrum antibiotics, such as causing antimicrobial resistance and destroying the normal flora, often limit their applications. Furthermore, the development of new antibiotics has lagged far behind the emergence and spread of antibiotic resistance. On the other hand, the genome complexity of bacteria makes it difficult to create effective vaccines. Therefore, novel therapeutic agents in supplement to antibiotics and vaccines are urgently needed to improve the treatment of infections. In recent years, monoclonal antibodies (mAbs) have achieved remarkable clinical success in a variety of fields. In the treatment of infectious diseases, mAbs can play functions through multiple mechanisms, including toxins neutralization, virulence factors inhibition, complement-mediated killing activity, and opsonic phagocytosis. Toxins and bacterial surface components are good targets to generate antibodies against. The U.S. FDA has approved three monoclonal antibody drugs, and there are numerous candidates in the preclinical or clinical trial stages. This article reviews recent advances in the research and development of anti-bacterial monoclonal antibody drugs in order to provide a valuable reference for future studies in this area. KEY POINTS: • Novel drugs against antibiotic-resistant superbugs are urgently required • Monoclonal antibodies can treat bacterial infections through multiple mechanisms • There are many anti-bacterial monoclonal antibodies developed in recent years and some candidates have entered the preclinical or clinical stages of development.

Bacterial keratitis: identifying the areas of clinical uncertainty

Bacterial keratitis is a common corneal infection that is treated with topical antimicrobials. By the time of presentation there may already be severe visual loss from corneal ulceration and opacity, which may persist despite treatment. There are significant differences in the associated risk factors and the bacterial isolates between high income and low- or middle-income countries, so that general management guidelines may not be appropriate. Although the diagnosis of bacterial keratitis may seem intuitive there are multiple uncertainties about the criteria that are used, which impacts the interpretation of investigations and recruitment to clinical studies. Importantly, the concept that bacterial keratitis can only be confirmed by culture ignores the approximately 50% of cases clinically consistent with bacterial keratitis in which investigations are negative. The aetiology of these culture-negative cases is unknown. Currently, the estimation of bacterial susceptibility to antimicrobials is based on data from systemic administration and achievable serum or tissue concentrations, rather than relevant corneal concentrations and biological activity in the cornea. The provision to the clinician of minimum inhibitory concentrations of the antimicrobials for the isolated bacteria would be an important step forward. An increase in the prevalence of antimicrobial resistance is a concern, but the effect this has on disease outcomes is yet unclear. Virulence factors are not routinely assessed although they may affect the pathogenicity of bacteria within species and affect outcomes. New technologies have been developed to detect and kill bacteria, and their application to bacterial keratitis is discussed. In this review we present the multiple areas of clinical uncertainty that hamper research and the clinical management of bacterial keratitis, and we address some of the assumptions and dogma that have become established in the literature.

Monoclonal Antibodies Against Infectious Microbes: So Long and Too Little!

Monoclonal antibodies (mAbs) as alternatives or more often as complementary to the conventional antimicrobials have been developed for the management of infectious conditions for the past two decades. These pharmacotherapeutic strategies are inevitable as the burden of antimicrobial resistance is far-reaching in recent times. MAbs are part of the targeted pharmacotherapy armamentarium with a high degree of specificity - hence, exert comparatively superior efficacy and tolerability than the conventional polyclonal antisera. So far, only five mAbs have been approved for the management of infectious states, since the marketing authorization (1998) given to palivizumab (Synagis®) for the prophylaxis of lower respiratory tract disease caused by a respiratory syncytial virus in pediatric patients. Ibalizumab-uiyk (Trogarzo™) used for the management of multidrug-resistant HIV-1 infection not yielding to at least 10 antiretroviral drugs, was approved recently. Among the three antibacterial mAbs, raxibacumab (ABthrax®/ Anthrin®) and obiltoxaximab (Anthim®) are indicated for the treatment and prophylaxis of inhalation anthrax due to Bacillus anthracis; bezlotoxumab (Zinplava®) is used to reduce the recurrence of Clostridium difficile infection. There are also around 30 and 15 mAbs in different phases of development for viral and bacterial conditions. As alternatives to the traditional antivirals and antibacterials, the antimicrobial mAbs are the need of the hour. These mAbs are more relevant to the management of conditions like emerging viral outbreaks wherein there is a lack of prophylactic vaccines. The current cutting-edge engineering technologies revolutionizing the production of mAbs include phagedisplayed antibody libraries, cloning from single-memory B cells or single-antibody-secreting plasma B cells, proteomics-directed cloning of mAbs from serum clubbed with high-throughput sequencing techniques. Yet, the cost of manufacture continues to be the main limiting factor. In this review, the different therapeutic monoclonal antibodies directed against the microbial pathogens are discussed.

Staphylococcus aureus Vaccine Research and Development: The Past, Present and Future, Including Novel Therapeutic Strategies

Staphylococcus aureus is one of the most important human pathogens worldwide. Its high antibiotic resistance profile reinforces the need for new interventions like vaccines in addition to new antibiotics. Vaccine development efforts against S. aureus have failed so far however, the findings from these human clinical and non-clinical studies provide potential insight for such failures. Currently, research is focusing on identifying novel vaccine formulations able to elicit potent humoral and cellular immune responses. Translational science studies are attempting to discover correlates of protection using animal models as well as in vitro and ex vivo models assessing efficacy of vaccine candidates. Several new vaccine candidates are being tested in human clinical trials in a variety of target populations. In addition to vaccines, bacteriophages, monoclonal antibodies, centyrins and new classes of antibiotics are being developed. Some of these have been tested in humans with encouraging results. The complexity of the diseases and the range of the target populations affected by this pathogen will require a multipronged approach using different interventions, which will be discussed in this review.

Identification and application of a neutralizing epitope within alpha-hemolysin using human serum antibodies elicited by vaccination

Staphylococcus aureus (SA), especially the methicillin-resistant variant (MRSA), is becoming a serious threat to human health in hospitals and communities, making the development of an effective vaccine urgent. Alpha-hemolysin (Hla) is a key virulence factor and also a good target for the development of SA vaccines. However, the epitopes in Hla recognized by human immunity are not characterized in detail, which hinders the design of epitope-based human vaccines against SA. In this study, we collected sera from volunteers in a phase 1b clinical trial of a novel recombinant five-antigen SA vaccine (NCT03966040). Using a Luminex-based assay, we characterized the human serologic response against Hla, and identified Hla_121-138 as a neutralizing epitope. In addition, we successfully produced ferritin nanoparticles carrying the neutralizing Hla_121-138 epitope (EpNP) in E. coli. EpNP presented as homogenous nanoparticles in aqueous solution. Immunization with EpNP elicited potent hemolysis-neutralizing antibodies and conferred significant protection in a mouse model of SA skin infection. Our data suggest that EpNP, carrying the neutralizing epitope Hla_121-138, is a good candidate for a vaccine against SA.

Antivirulence Strategies for the Treatment of Staphylococcus aureus Infections: A Mini Review

Staphylococcus aureus is a Gram-positive bacterium capable of infecting nearly all host tissues, causing severe morbidity and mortality. Widespread antimicrobial resistance has emerged among S. aureus clinical isolates, which are now the most frequent causes of nosocomial infection among drug-resistant pathogens. S. aureus produces an array of virulence factors that enhance in vivo fitness by liberating nutrients from the host or evading host immune responses. Staphylococcal virulence factors have been identified as viable therapeutic targets for treatment, as they contribute to disease pathogenesis, tissue injury, and treatment failure. Antivirulence strategies, or treatments targeting virulence without direct toxicity to the inciting pathogen, show promise as an adjunctive therapy to traditional antimicrobials. This Mini Review examines recent research on S. aureus antivirulence strategies, with an emphasis on translational studies. While many different virulence factors have been investigated as therapeutic targets, this review focuses on strategies targeting three virulence categories: pore-forming toxins, immune evasion mechanisms, and the S. aureus quorum sensing system. These major areas of S. aureus antivirulence research demonstrate broad principles that may apply to other human pathogens. Finally, challenges of antivirulence research are outlined including the potential for resistance, the need to investigate multiple infection models, and the importance of studying antivirulence in conjunction with traditional antimicrobial treatments.

Staphylococcus aureus alpha-toxin inhibits CD8+ T cell-mediated killing of cancer cells in cutaneous T-cell lymphoma

Staphylococcus aureus and its toxins have been linked to disease progression and mortality in advanced stages of cutaneous T-cell lymphoma (CTCL). CD8+ T cells play a crucial role in anti-cancer responses and high CD8+ T cell numbers in tumor lesions are associated with a favorable prognosis in CTCL. Here, we show that CD8+ T cells from both healthy donors and Sézary syndrome patients are highly susceptible to cell death induced by Staphylococcal alpha-toxin, whereas malignant T cells are not. Importantly, alpha-toxin almost completely blocks cytotoxic killing of CTCL tumor cells by peptide-specific CD8+ T cells, leading to their escape from induced cell death and continued proliferation. These findings suggest that alpha-toxin may favor the persistence of malignant CTCL cells in vivo by inhibiting CD8+ T cell cytotoxicity. Thus, we propose a novel mechanism by which colonization with Staphylococcus aureus may contribute to cancer immune evasion and disease progression in CTCL.

Monoclonal Antibodies as an Antibacterial Approach Against Bacterial Pathogens

In the beginning of the 21st century, the frequency of antimicrobial resistance (AMR) has reached an apex, where even 4th and 5th generation antibiotics are becoming useless in clinical settings. In turn, patients are suffering from once-curable infections, with increases in morbidity and mortality. The root cause of many of these infections are the ESKAPEE pathogens (Enterococcus species, Staphylococcus aureus, Klebsiella pneumoniae, Acinetobacter baumannii, Pseudomonas aeruginosa, Enterobacter species, and Escherichia coli), which thrive in the nosocomial environment and are the bacterial species that have seen the largest rise in the acquisition of antibiotic resistance genes. While traditional small-molecule development still dominates the antibacterial landscape for solutions to AMR, some researchers are now turning to biological approaches as potential game changers. Monoclonal antibodies (mAbs)—more specifically, human monoclonal antibodies (Hu-mAbs)—have been highly pursued in the anti-cancer, autoimmune, and antiviral fields with many success stories, but antibody development for bacterial infection is still just scratching the surface. The untapped potential for Hu-mAbs to be used as a prophylactic or therapeutic treatment for bacterial infection is exciting, as these biologics do not have the same toxicity hurdles of small molecules, could have less resistance as they often target virulence proteins rather than proteins required for survival, and are narrow spectrum (targeting just one pathogenic species), therefore avoiding the disruption of the microbiome. This mini-review will highlight the current antibacterial mAbs approved for patient use, the success stories for mAb development, and new Hu-mAb products in the antibacterial pipeline.

Identification and Application of Epitopes in EtMIC1 of Eimeria tenella Recognized by the Monoclonal Antibodies 1-A1 and 1-H2

Eimeria tenella microneme-1 protein (EtMIC1) has been proposed to be a transmembrane protein, but this characteristic has not yet been confirmed experimentally. Furthermore, despite EtMIC1 being an important candidate antigen, its key epitope has not been reported. Here, two linear B-cell epitopes of EtMIC1, 91LITFATRSK99 and 698ESLISAGE705, were identified by Western blotting using specific monoclonal antibodies (MAbs) and were named epitope I (located in the I-domain) and epitope CTR (located in the CTR domain), respectively. Sequence comparative analyses of these epitopes among Eimeria species that infect chickens showed that epitope I differs greatly across species, whereas epitope CTR is relatively conserved. Point mutation assay results indicate that all the amino acid residues of the epitopes recognized by MAb 1-A1 or 1-H2 are key amino acids involved in recognition. Comparative analyses of indirect immunofluorescence assay (IFA) results for MAbs 1-A1 and 1-H2 under both nonpermeabilization and permeabilization conditions indicate that epitope I is located on the outer side of the sporozoite surface membrane whereas epitope CTR is located on the inner side, together providing experimental evidence that EtMIC1 is a transmembrane protein. IFA also labeled the EtMIC1 protein on the parasitophorous vacuole membrane and on the surface of schizonts, which suggests that the EtMIC1 protein may play an important role in parasitophorous vacuole formation and E. tenella development. Immunoprotective efficacy experiments revealed that epitope I has good immunogenicity, as evidenced by its induction of high serum antibody levels, blood lymphocyte proliferation, and CD4+ blood lymphocyte percentage.

Monoclonal antibody-based therapies for bacterial infections

PURPOSE OF REVIEW

This review highlights recent developments in the development of monoclonal antibodies to treat bacterial disease, including preclinical advances and the status of current clinical trials.

RECENT FINDINGS

Monoclonal antibody (mAb) therapy is becoming increasingly promising in the infectious disease field. Though bacterial exotoxins continue to be a mainstay of mAb targets, searches for protein targets on the surface of bacteria have uncovered new mechanisms of antibody-mediated action against bacteria. Additionally, surveys of the polysaccharide serotype prevalence among antibiotic-resistant bacterial populations have yielded opportunities to leverage human selective pressures to our clinical advantage. Several mAb candidates are progressing through clinical development with great promise, especially those with structures altered to provide maximum benefit. Although other clinical trials have recently proved unsuccessful, these failures and lessons from immune profiling provide opportunities to understand how vulnerabilities of certain targets may change in different disease states.

SUMMARY

Despite the hurdles of identifying effective targets and understanding how mAbs provide protection within different infections, we show that the progress made in these fields is a positive indication of mAbs becoming more widely accepted as the future for treating bacterial infections.

Interaction of host and Staphylococcus aureus protease-system regulates virulence and pathogenicity

Staphylococcus aureus causes various health care- and community-associated infections as well as certain chronic TH2 driven inflammatory diseases. It is a potent pathogen with serious virulence and associated high morbidity. Severe pathogenicity is accredited to the S. aureus secreted virulence factors such as proteases and host protease modulators. These virulence factors promote adhesion and invasion of bacteria through damage of tight junction barrier and keratinocytes. They inhibit activation and transmigration of various immune cells such as neutrophils (and neutrophil proteases) to evade opsono-phagocytosis and intracellular bacterial killing. Additionally, they protect the bacteria from extracellular killing by disrupting integrity of extracellular matrix. Platelet activation and agglutination is also impaired by these factors. They also block the classical as well as alternative pathways of complement activation and assist in spread of infection through blood and tissue. As these factors are exquisite factors of S. aureus mediated disease development, we have focused on review of diversification of various protease-system associated virulence factors, their structural building, diverse role in disease development and available therapeutic counter measures. This review summarises the role of protease-associated virulence factors during invasion and progression of disease.