Determining the immunological characteristics of a novel human monoclonal antibody developed against staphylococcal enterotoxin B

A highly neutralizing human monoclonal antibody targeting a novel linear epitope on staphylococcal enterotoxin B

Staphylococcal Enterotoxin B (SEB), produced by Staphylococcus aureus (S. aureus), is a powerful superantigen that induces severe immune disruption and toxic shock syndrome (TSS) upon binding to MHC-II and TCR. Despite its significant impact on the pathogenesis of S. aureus, there are currently no specific therapeutic interventions available to counteract the mechanism of action exerted by this toxin. In this study, we have identified a human monoclonal antibody, named Hm0487, that specifically targets SEB by single-cell sequencing using PBMCs isolated from volunteers enrolled in a phase I clinical trial of the five-antigen S. aureus vaccine. X-ray crystallography studies revealed that Hm0487 exhibits high affinity for a linear B cell epitope in SEB (SEB138-147), which is located distantly from the site involved in the formation of the MHC-SEB-TCR ternary complex. Furthermore, in vitro studies demonstrated that Hm0487 significantly impacts the interaction of SEB with both receptors and the binding to immune cells, probably due to an allosteric effect on SEB rather than competing with receptors for binding sites. Moreover, both in vitro and in vivo studies validated that Hm0487 displayed efficient neutralizing efficacy in models of lethal shock and sepsis induced by either SEB or bacterial challenge. Our findings unveil an alternative mechanism for neutralizing the pathogenesis of SEB by Hm0487, and this antibody provides a novel strategy for mitigating both SEB-induced toxicity and S. aureus infection.

mRNA-based platform for preventing and treating Staphylococcus aureus by targeted staphylococcal enterotoxin B

Staphylococcus aureus (S. aureus) possesses numerous virulence factors, with the increasing prevalence of drug-resistant strains heightening the threat posed by this pathogen. Staphylococcal enterotoxin B (SEB), a highly conserved toxin secreted by S. aureus, is also recognized as a potential bioweapon with super-antigenic activity. SEB represents a promising target in efforts to combat infections caused by S. aureus. We developed mRNA-based vaccine and antibody targeting SEB for both prophylactic and therapeutic purposes in varying S. aureus infection conditions. The mSEB mRNA vaccine (10 μg per mouse) induces more robust and persistent immune responses, including higher antibody titers and specific cellular immune responses, compared to immunization with 30 μg of mSEB protein adjuvanted with aluminum phosphate. Additionally, the anti-SEB mRNA antibody maintains secretion of anti-SEB monoclonal antibody (mAb) with a dosage that is 10 times lower than purified protein administration. The mRNA-based antibody exhibits superior pharmacokinetic profiles compared to its protein counterparts, efficiently neutralizing SEB and clearing S. aureus from circulation. Both the mRNA vaccine and mRNA antibody demonstrate preventive and therapeutic effects by eliciting specific immune responses and generating high-affinity antibodies in mice. We have laid the groundwork for the development and evaluation of mRNA-based vaccines and antibodies targeting SEB produced by S. aureus. Our studies demonstrate that these approaches are more effective than traditional protein-based vaccines and antibodies in terms of inducing immune responses, pharmacokinetics, and their prophylactic or therapeutic efficacy against S. aureus infections.

Antibody-antibiotic conjugate targeted therapy for orthopedic implant-associated intracellular S. aureus infections

INTRODUCTION

Treating orthopedic implant-associated infections, especially those caused by Staphylococcus aureus (S. aureus), remains a significant challenge. S. aureus has the ability to invade host cells, enabling it to evade both antibiotics and immune responses during infection, which may result in clinical treatment failures. Therefore, it is critical to identify the host cell type of implant-associated intracellular S. aureus infections and to develop a strategy for highly targeted delivery of antibiotics to the host cells.

OBJECTIVES

Introduced an antibody-antibiotic conjugate (AAC) for the targeted elimination of intracellular S. aureus.

METHODS

The AAC comprises of a human monoclonal antibody (M0662) directly recognizes the surface antigen of S. aureus, Staphylococcus protein A, which is conjugated with vancomycin through cathepsin-sensitive linkers that are cleavable in the proteolytic environment of the intracellular phagolysosome. AAC, vancomycin and vancomycin combined with AAC were used in vitro intracellular infection and mice implant infection models. We then tested the effect of AAC in vivo and in vivo by fluorescence imaging, in vivo imaging, bacterial quantitative analysis and bacterial biofilm imaging.

RESULTS

In vitro, it was observed that AAC captured extracellular S. aureus and co-entered the cells, and subsequently released vancomycin to induce rapid elimination of intracellular S. aureus. In the implant infection model, AAC significantly improved the bactericidal effect of vancomycin. Scanning electron microscopy showed that the application of AAC effectively blocked the formation of bacterial biofilm. Further histochemical and micro-CT analysis showed AAC significantly reduced the level of bone marrow density (BMD) and bone volume fraction (BV/TV) reduction caused by bacterial infection in the distal femur of mice compared to vancomycin treatment alone.

CONCLUSIONS

The application of AAC in an implant infection model showed that it significantly improved the bactericidal effects of vancomycin and effectively blocked the formation of bacterial biofilms, without apparent toxicity to the host.

Immune Responses to Methicillin-Resistant Staphylococcus aureus Infections and Advances in the Development of Vaccines and Immunotherapies

Staphylococcus aureus (SA) is a major bacterial pathogen and causes a wide range of clinical infections in humans leading to severe outcomes including meningitis, endocarditis, and sepsis. This literature review examines studies on host immune responses after infections with SA and methicillin-resistant Staphylococcus aureus (MRSA) and their immune evasion mechanisms. Furthermore, information about vaccines and immunotherapies against SA and MRSA is reviewed. We found promising toxoid vaccine approaches, which deserve further research. We also found support for antitoxin therapies and immunomodulating therapies as high-potential research areas. Although many promising vaccines and immunotherapy candidates have been studied in animal models, more human clinical studies are needed to confirm their long-term safety and efficacy.

The SEB1741 Aptamer Is an Efficient Tool for Blocking CD4+ T Cell Activation Induced by Staphylococcal Enterotoxin B

Staphylococcal enterotoxin B (SEB) is a protein produced by Staphylococcus aureus, which is toxic to humans. It is well known for its ability to stimulate the exacerbated activation of proinflammatory CD4+ T cells (Th1 profile), and in vitro studies have been conducted to understand its mechanism of action and its potential use as an immune therapy. However, the efficiency of the SEB1741 aptamer in blocking SEB has not been experimentally demonstrated.

METHODS

Enrichment CD4+ T cells were stimulated with SEB, and as a blocker, we used the SEB1741 aptamer, which was previously synthesised by an "in silico" analysis, showing high affinity and specificity to SEB. The efficiency of the SEB1741 aptamer in blocking CD4+ T cell activation was compared with that of an anti-SEB monoclonal antibody. Flow cytometry and Bio-Plex were used to evaluate the T-cell function.

RESULTS

In vitro, SEB induced the activation of CD4+ T cells and favoured a Th1 profile; however, the SEB1741 aptamer was highly efficient in decreasing the frequency of CD4+ T cells positive to ki-67 and CD69 cells, this means that proliferation and activation of CD4+ T cells was decreased. Moreover, the production of interleukin 2 (IL-2) and interferon-gamma (IFN-γ) was affected, suggesting that the Th1 profile is not present when the SEB1441 aptamer is used. Thus, the SEB1741 function was similar to that of anti-SEB.

CONCLUSIONS

The SEB1741 aptamer is a valuable tool for blocking CD4+ T cell activation and the subsequent release of proinflammatory cytokines by SEB stimulation.

Contribution of Staphylococcal Enterotoxin B to Staphylococcus aureus Systemic Infection

Staphylococcal enterotoxin B (SEB), which is produced by the major human pathogen, Staphylococcus aureus, represents a powerful superantigenic toxin and is considered a bioweapon. However, the contribution of SEB to S. aureus pathogenesis has never been directly demonstrated with genetically defined mutants in clinically relevant strains. Many isolates of the predominant Asian community-associated methicillin-resistant S. aureus lineage sequence type (ST) 59 harbor seb, implying a significant role of SEB in the observed hypervirulence of this lineage. We created an isogenic seb mutant in a representative ST59 isolate and assessed its virulence potential in mouse infection models. We detected a significant contribution of seb to systemic ST59 infection that was associated with a cytokine storm. Our results directly demonstrate that seb contributes to S. aureus pathogenesis, suggesting the value of including SEB as a target in multipronged antistaphylococcal drug development strategies. Furthermore, they indicate that seb contributes to fatal exacerbation of community-associated methicillin-resistant S. aureus infection.

Pretargeted radioimmunoimaging with a biotinylated D-D3 construct and 99mTc-DTPA-biotin: strategies for early diagnosis of small cell lung cancer

Objective

Pro-gastrin releasing peptide (ProGRP) plays an oncogenic role in small cell lung cancer (SCLC). The anti-ProGRP_(31-98) monoclonal antibody D-D₃ can selectively accumulate in SCLC xenografts in nude mice. This study evaluated the effectiveness of a new pretargeting procedure for the early diagnosis of SCLC.

Methods

D-D₃ was radiolabeled with technetium-99m (^99mTc) using a three-step pretargeting method. Mice with SCLC xenografts were treated with different labeling regimens, and the biodistribution and radioimmunoimaging were explored. The percentage injected dose per gram (%ID/g) in various organs, tumor/non-tumor (T/NT) ratio, and tumor/background (T/B) ratio were also calculated.

Results

In vivo distribution experiments revealed that ^99mTc-DTPA-biotin was metabolized in the liver and kidney, with rapid elimination in the blood. The T/B ratio was highest in mice treated with biotinylated antibody D-D₃ + avidin + ^99mTc-DTPA-biotin. Single-photon emission computerized tomography imaging further confirmed that the T/B ratio was highest in this group at all time points.

Conclusions

In contrast to directly labeled D-D₃, pretargeting technology displayed specific enhancement and signal amplification in tumors, which could increase the target tumor uptake of ^99mTc and provide a new approach for the early diagnosis of SCLC.