Design and evaluation of mRNA encoding recombinant neutralizing antibodies for botulinum neurotoxin type B intoxication prophylaxis

Among all natural and synthetic toxins, botulinum neurotoxins (BoNTs), produced by Clostridium botulinum in an anaerobic environment, are the most toxic polymer proteins. Currently, the most effective modalities for botulism prevention and treatment are vaccination and antitoxin use, respectively. However, these modalities are associated with long response time for active immunization, side effects, and donor limitations. As such, the development of more promising botulism prevention and treatment modalities is warranted. Here, we designed an mRNA encoding B9-hFc - a heavy-chain antibody fused to VHH and human Fc that can neutralize BoNT serotype B (BoNT/B) effectively - and assessed its expression in vitro and in vivo. The results confirmed that our mRNA demonstrates good expression in vitro and in vivo. Moreover, a single mRNA lipid nanoparticle injection effectively prevents BoNT/B intoxication in vivo, with effects comparable to those of protein antibodies. In conclusion, we explored and clarified whether mRNA drugs encoding neutralizing antibodies prevent BoNT/B intoxication. Our results provide an efficient strategy for further research on the prevention and treatment of intoxication by botulinum toxin.

Isolation and characterization of Hc-targeting chimeric heavy chain antibodies neutralizing botulinum neurotoxin type B

Background

Botulinum neurotoxin (BoNT) produced by Clostridium botulinum is one of the most potent known toxins. Moreover, BoNT is classified as one of the most important biological warfare agents that threatens the biosafety of the world. Currently, the approved treatment for botulism in humans is the use of polyvalent horse serum antitoxins. However, they are greatly limited because of insufficient supply and adverse reactions. Thus, treatment of human botulism requires the development of effective toxin-neutralizing antibodies. Considering their advantages, neutralizing nanobodies will play an increasing role as BoNTs therapeutics.

Methods

Herein, neutralizing nanobodies binding to the heavy chain (Hc) domain of BoNT/B (BHc) were screened from a phage display library. Then, BoNT/B-specific clones were identified and fused with the human Fc fragment (hFc) to form chimeric heavy chain antibodies. Finally, the affinity, specificity, and neutralizing activity of antibodies against BoNT/B in vivo were evaluated.

Results

The B5-hFc, B9-hFc and B12-hFc antibodies demonstrated high affinity for BHc in the nanomolar range. The three antibodies were proven to have potent neutralizing activity against BoNT/B in vivo.

Conclusion

The results demonstrate that inhibiting toxin binding to the host receptor is an efficient strategy and the three antibodies could be used as candidates for the further development of drugs to prevent and treat botulism.

Reducing the Impact of Headache and Allodynia Score in Chronic Migraine: An Exploratory Analysis from the Real-World Effectiveness of Anti-CGRP Monoclonal Antibodies Compared to Onabotulinum Toxin A (RAMO) Study

BACKGROUND

Chronic migraine (CM) is a disabling and hard-to-treat condition, associated with high disability and high cost. Among the preventive treatments, botulinum toxin A (BoNT-a) and monoclonal antibodies against the calcitonin gene-related protein (anti-CGRP mAbs) are the only disease-specific ones. The assessment of the disease burden is complex, and among others, tools such as the allodynia symptoms checklist (ASC-12) and headache impact test (HIT-6) are very useful. This exploratory study analysed the impact of these two therapies on migraine burden.

METHODS

The RAMO study was a multicentre, observational, retrospective investigation conducted in two headache centres: the Fondazione IRCCS Istituto Neurologico Carlo Besta (Milan) and the Fondazione Policlinico Campus Bio-Medico (Rome). This study involved patients with chronic migraine treated with mAbs or BoNT-A. We conducted a subgroup exploratory analysis on HIT-6 and ASC-12 scores in the two groups. The Wilcoxon rank-sum test, Fisher's exact test, and ANOVA were performed.

RESULTS

Of 126 patients, 36 on mAbs and 90 on BoNT-A had at least one available follow-up. mAbs resulted in a mean reduction of -11.1 and -11.4 points, respectively, in the HIT-6 at 6 and 12 months, while BoNT-A was reduced -3.2 and -3.6 points, respectively; the mAbs arm resulted in mean reductions in ASC-12 at 6 and 12 months of follow-up of -5.2 and -6.0 points, respectively, while BoNT-A showed lesser mean changes of -0.5 and -0.9 points, respectively. The adjusted analysis confirmed our results.

CONCLUSIONS

In this exploratory analysis, anti-CGRP mAbs showed superior effectiveness for HIT-6 and ASC12 compared to BoNT-A. Reductions in terms of month headache days (MHD), migraine disability assessment test (MIDAS), and migraine acute medications (MAM) were clinically relevant for both treatments.

Sub-acute hypersensitive reaction to botulinum toxin type A following Covid-19 vaccination: Case report and literature review

RATIONALE

Botulinum toxin type A (BTA) is one of the most widely used injectable agents in cosmetic surgery. Corona virus disease 2019 (Covid-19) infection and vaccination, which can induce specific and nonspecific activation of the immune system, has been reported to induce delayed inflammatory reactions to previously injected hyaluronic acid fillers. However, there are no reports about the interaction between BTA and Covid-19. We aimed to report 2 sub-acute cases of allergic reactions to BTA in facial cosmesis following the Covid-19 vaccination.

PATIENT CONCERN

A 35-year-old and a 34-year-old female who has several previous BTA injections without any adverse effects experienced facial swelling, flu-like symptoms after BTA treatment following the Covid-19 vaccination.

DIAGNOSE

According to the typical clinical manifestation, a hypersensitive reaction to BTA was considered.

INTERVENTION

Corticosteroids and antihistamine were administered empirically.

OUTCOMES

The flu-like symptoms recovered over the next day, but the facial swelling gradually faded within 1 to 2 weeks.

LESSONS

A literature review was also conducted to summarize the hypersensitive actions to cosmesis related to Covid-19. We recommend BTA injection be administered at least 2 to 3 months after Covid-19 vaccination.

Can clinical and urodynamic parameters predict the occurrence of neutralizing antibodies in therapy failure of intradetrusor onabotulinumtoxin A injections in patients with spinal cord injury?

BACKGROUND

The aim of the study was to clarify whether clinical and/or urodynamic parameters could be used to infer the probability of neutralizing antibody (NAb) formation as a possible cause of therapy failure (non-response, NR) in patients with neurogenic detrusor overactivity (NDO) due to acquired spinal cord injury/disease (SCI/D) treated with intradetrusor botulinum neurotoxin A (BoNT-A) injections.

METHODS

A retrospective chart review was performed of all patients with SCI/D who underwent both intradetrusor onabotulinumtoxin A injections and the determination of neutralizing antibodies against BoNT-A between January 1, 2002, and December 31, 2018. NR was defined as urodynamically confirmed persistent or reappearing NDO.

RESULTS

A total of 2700 BoNT-A injections in 414 patients were ascertained. In 69 patients with primary NR after the first BoNT-A injection (n = 6) or with secondary NR after more than one BoNT-A injection (n = 63), an antibody analysis was performed. Antibody examination showed 36 (52.2%) negative, 5 (7.2%) borderline and 14 (each 20.3%) each of positive and highly positive values. Subgroup analysis indicated a correlation between NAb formation and the duration of BoNT-A therapy (p = 0.015), the mean number of BoNT-A injections (p = 0.011) and the time interval between BoNT-A applications (< 7 months, p = 0.022). Urodynamic data analysis indicate significant differences with cut-off values of MCC (< 225 ml, p = 0.038) and MDP (> 45 cmH2O, p = 0.040). However, in the regression analysis models, the predictive value for the occurrence of NAb was too low (MCC: ROC AUC 0.62, MDP: ROC AUC 0.52) to distinguish with sufficient certainty between NAb-positive and NAb-negative NR patients.

CONCLUSIONS

Despite significant correlations, clinical and urodynamic parameters are only partially suitable for predicting antibody formation against BoNT-A.

Fully Human Monoclonal Antibodies Effectively Neutralizing Botulinum Neurotoxin Serotype B

Botulinum neurotoxin (BoNT) is the most potent natural toxin known. Of the seven BoNT serotypes (A to G), types A, B, E, and F cause human botulism. Treatment of human botulism requires the development of effective toxin-neutralizing antibodies without side effects such as serum sickness and anaphylaxis. In this study, we generated fully human monoclonal antibodies (HuMAbs) against serotype B BoNT (BoNT/B1) using a murine–human chimera fusion partner cell line named SPYMEG. Of these HuMAbs, M2, which specifically binds to the light chain of BoNT/B1, showed neutralization activity in a mouse bioassay (approximately 10 i.p. LD₅₀/100 µg of antibody), and M4, which binds to the C-terminal of heavy chain, showed partial protection. The combination of two HuMAbs, M2 (1.25 µg) and M4 (1.25 µg), was able to completely neutralize BoNT/B1 (80 i.p. LD₅₀) with a potency greater than 80 i.p. LD₅₀/2.5 µg of antibodies, and was effective both prophylactically and therapeutically in the mouse model of botulism. Moreover, this combination showed broad neutralization activity against three type B subtypes, namely BoNT/B1, BoNT/B2, and BoNT/B6. These data demonstrate that the combination of M2 and M4 is promising in terms of a foundation for new human therapeutics for BoNT/B intoxication.

Effective long-term treatment with incobotulinumtoxin (Xeomin®) without neutralizing antibody induction: a monocentric, cross-sectional study

Background

Among the spectrum of licensed botulinum neurotoxin preparations incobotulinumtoxin (incoBoNT/A; Xeomin®) is the only one which does not contain complex proteins. Therefore, incoBoNT/A has been suggested to have a low antigenicity, but precise estimations on incidence and prevalence of neutralizing antibody formation during long-term treatment are outstanding so far.

Methods

For the present cross-sectional study, 59 patients having exclusively been treated with incoBoNT/A (mono group) and 32 patients having been treated with other BoNT/A preparations less than nine times and who were then switched to at least 14 sessions of incoBoNT/A treatment (switch group) were recruited from one botulinum toxin outpatient clinic. Side effects and doses were extracted from the charts, and the efficacy of treatment was assessed by the patients using a visual analogue scale (0–100). The prevalence of neutralizing antibodies was tested by means of the mouse hemi-diaphragm assay (MHDA).

Findings

None of the patients in the mono and only two in the switch group had a positive MHDA-test. Across all indications and patients, mean improvement exceeded 67%. Improvement did not depend on age at onset, sex, change of dose or duration of treatment, but on disease entity. In patients with cervical dystonia, improvement was about the same in the mono and switch subgroup, but the last dose was different.

Conclusions

The present study confirms the low antigenicity of incoBoNT/A, which has immediate consequences for patient management, and the use of higher doses and shorter durations of reinjection intervals in botulinum toxin therapy.

Camelid VHHs Fused to Human Fc Fragments Provide Long Term Protection Against Botulinum Neurotoxin A in Mice

The bacterium Clostridium botulinum is the causative agent of botulism-a severe intoxication caused by botulinum neurotoxin (BoNT) and characterized by damage to the nervous system. In an effort to develop novel C. botulinum immunotherapeutics, camelid single-domain antibodies (sdAbs, VHHs, or nanobodies) could be used due to their unique structure and characteristics. In this study, VHHs were produced using phage display technology. A total of 15 different monoclonal VHHs were selected based on their comlementarity-determining region 3 (CDR3) sequences. Different toxin lethal dose (LD50) challenges with each selected phage clone were conducted in vivo to check their neutralizing potency. We demonstrated that modification of neutralizing VHHs with a human immunoglobulin G (IgG)1 Fc (fragment crystallizable) fragment (fusionbody, VHH-Fc) significantly increased the circulation time in the blood (up to 14 days). At the same time, VHH-Fc showed the protective activity 1000 times higher than monomeric form when challenged with 5 LD50. Moreover, VHH-Fcs remained protective even 14 days after antibody administration. These results indicate that this VHH-Fc could be used as an effective long term antitoxin protection against botulinum type A.

IncobotulinumtoxinA: A Highly Purified and Precisely Manufactured Botulinum Neurotoxin Type A

Aesthetic dermatologic applications of botulinum neurotoxin (BoNT), including treatment of glabellar lines, horizontal forehead lines, and crow’s feet, were the most common non-surgical cosmetic procedures in the US in 2017, with high levels of subject satisfaction. Since the first BoNT type A (BoNT-A) formulation was approved in 1989, the number of formulations available on the world’s commercial markets has increased and new approvals are expected. BoNT is produced by Clostridium botulinum in nature as part of a large protein complex. However, the unnecessary clostridial proteins, which dissociate from BoNT under physiological conditions with a half-life of <1 minute, have no role in clinical applications. Data demonstrate that BoNT administration can elicit an immunological response, leading to production of neutralizing antibodies that can be associated with reduced efficacy or treatment non-response. As repeat treatments are required to maintain efficacy, clinicians should be aware of the possibility of antibody development and choose a BoNT with the lowest risk of immunogenicity. IncobotulinumtoxinA is manufactured using advanced technology to precisely isolate the pure BoNT without unnecessary clostridial proteins, and with low immunogenicity and high specific activity. In incobotulinumtoxinA clinical studies, no previously BoNT-naïve subjects developed neutralizing antibodies, and there was no secondary non-response to incobotulinumtoxinA treatment. Here we review the role of unnecessary clostridial proteins in BoNT-A and discuss the unique incobotulinumtoxinA manufacturing and purification process with a focus on the implications for use in aesthetic medicine. J Drugs Dermatol. 2019;18(1):52-57.

A Rapid, Sensitive, and Portable Biosensor Assay for the Detection of Botulinum Neurotoxin Serotype A in Complex Food Matrices

Botulinum neurotoxin (BoNT) intoxication can lead to the disease botulism, characterized by flaccid muscle paralysis that can cause respiratory failure and death. Due to the significant morbidity and mortality costs associated with BoNTs high toxicity, developing highly sensitive, rapid, and field-deployable assays are critically important to protect the nation’s food supply against either accidental or intentional contamination. We report here that the B-cell based biosensor assay CANARY^® (Cellular Analysis and Notification of Antigen Risks and Yields) Zephyr detects BoNT/A holotoxin at limits of detection (LOD) of 10.0 ± 2.5 ng/mL in assay buffer. Milk matrices (whole milk, 2% milk and non-fat milk) with BoNT/A holotoxin were detected at similar levels (7.4–7.9 ng/mL). BoNT/A complex was positive in carrot, orange, and apple juices at LODs of 32.5–75.0 ng/mL. The detection of BoNT/A complex in solid complex foods (ground beef, smoked salmon, green bean baby puree) ranged from 14.8 ng/mL to 62.5 ng/mL. Detection of BoNT/A complex in the viscous liquid egg matrix required dilution in assay buffer and gave a LOD of 171.9 ± 64.7 ng/mL. These results show that the CANARY^® Zephyr assay can be a highly useful qualitative tool in environmental and food safety surveillance programs.

An ambient temperature-stable antitoxin of nine co-formulated antibodies for botulism caused by serotypes A, B and E

Safe and effective antitoxins to treat and prevent botulism are needed for biodefense. We have developed recombinant antibody-based therapeutics for botulinum neurotoxin (BoNT) serotypes A, B, and E. The mechanism of action of this antitoxin requires that three mAbs bind one toxin molecule to achieve clearance. Here we present a co-formulation of an antitoxin to the three most important serotypes. Combining these antibodies obviates the need to identify the serotype causing intoxication prior to drug administration, which would facilitate administration. The lyophilized powder formulation contains nine mAbs, three mAbs for each of the three serotypes (A, B, E). The formulation was stored as a liquid and lyophilized powder for up to one year, and characterized by binding affinity and multiple physicochemical methods. No significant increase in soluble higher order aggregates, cleavage products, or change in charge isoforms was measured after storage as a lyophilized powder at 50°C for one year. Furthermore, toxin-domain binding ELISA data indicated that each of the individual antibodies in the lyophilized drug product showed essentially full binding capability to their respective toxin domains after being stored at 50°C for one year. Physicochemical characterization of the formulation demonstrated the nine individual mAbs were remarkably stable. This work demonstrates feasibility of lyophilized, oligoclonal antibody therapies for biodefense with ambient temperature stability, that would facilitate stockpiling, distribution, and administration.

[Myths and evidence on the use of botulinum toxin: neuropharmacology and dystonia]

INTRODUCTION

Botulinum toxin type A (BTA) is a bacterial endotoxin, whose therapeutic use has had a dramatic impact on different neurological disorders, such as dystonia and spasticity.

AIM

To analyze and summarize different questions about the use of BTA in our clinical practice.

DEVELOPMENT

A group of experts in neurology developed a list of topics related with the use of BTA. Two groups were considered: neuropharmacology and dystonia. A literature search at PubMed, mainly for English language articles published up to June 2016 was performed. The manuscript was structured as a questionnaire that includes those questions that, according to the panel opinion, could generate more controversy or doubt. The initial draft was reviewed by the expert panel members to allow modifications, and after subsequent revisions for achieving the highest degree of consensus, the final text was then validated. Different questions about diverse aspects of neuropharmacology, such as mechanism of action, bioequivalence of the different preparations, immunogenicity, etc. were included. Regarding dystonia, the document included questions about methods of evaluation, cervical dystonia, blepharospasm, etc.

CONCLUSION

This review does not pretend to be a guide, but rather a tool for continuous training of residents and specialists in neurology, about different specific areas of the management of BTA.

A mutated recombinant subunit vaccine protects mice and guinea pigs against botulinum type A intoxication

Botulinum neurotoxins (BoNTs) are the most potent toxins to mammals. A toxoid vaccine was previously used for prevention of botulinum intoxication; however, this vaccine is no longer available. Currently, no approved botulinum vaccines are available from the Food and Drug Administration (FDA). Recently, a recombinant host cell receptor-binding subunit created for use as a potential vaccine completed phase 2 clinical trials. The current study designed a vaccine candidate against BoNT type A (BoNT/A) using a structural design. Our vaccine candidate was the BoNT/A heavy chain C-terminal region (HCR) that contained the point mutation BA15 (R1269A) within the ganglioside-binding site. A Biacore affinity test showed that the affinity of BA15 for ganglioside GT1b was 100 times lower than that of the HCR. A SNAP25 cleavage assay revealed that immunized sera blocked SNAP25 cleavage of the BoNT/A toxin via BA15. In an in vivo experiment, mice and guinea pigs immunized with BA15 produced neutralizing antibodies that protected against 3,000 LD50 of BoNT/A. In conclusion, the results of both in vitro and in vivo assays showed that our BA15 vaccine candidate was similar to the recombinant host cell receptor-binding subunit vaccine. The inability of BA15to bind ganglioside shows that BA15 is a potential safe vaccine candidate.

Development of Germline-Humanized Antibodies Neutralizing Botulinum Neurotoxin A and B

Botulinum neurotoxins (BoNTs) are counted among the most toxic substances known and are responsible for human botulism, a life-threatening disease characterized by flaccid muscle paralysis that occurs naturally by food poisoning or colonization of the gastrointestinal tract by BoNT-producing clostridia. To date, 7 serologically distinct serotypes of BoNT (serotype A-G) are known. Due to the high toxicity of BoNTs the Centers for Disease Control and Prevention (CDC) have classified BoNTs as category A agent, including the six biological agents with the highest potential risk of use as bioweapons. Well tolerated antibodies neutralizing BoNTs are required to deal with the potential risk. In a previous work, we described the development of scFv and scFv-Fc (Yumab) from macaque origin (Macaca fascicularis) neutralizing BoNT/A and B by targeting the heavy and light chain of each serotype. In the present study, we humanized the macaque antibodies SEM120-IIIC1 (anti-BoNT/A light chain), A1HC38 (anti-BoNT/A heavy chain), BLC3 (anti-BoNT/B light chain) and B2-7 (anti-BoNT/B heavy chain) by germline-humanization to obtain a better potential immunotolerance in humans. We increased the Germinality Index (GI) of SEM120-IIIC1 to 94.5%, for A1HC38, to 95% for BLC3 and to 94.4% for B2-7. Furthermore, the neutralization efficacies of the germline-humanized antibodies were analyzed in lethal and non-lethal in vivo mouse assays as full IgG. The germline-humanized IgGs hu8SEM120-IIIC1, hu8A1HC38, hu8BLC3 and hu8B2-7 were protective in vivo, when anti-heavy and anti-light chain antibodies were combined. The synergistic effect and high humanness of the selected IgGs makes them promising lead candidates for further clinical development.

Induction of Acute Lung Injury after Intranasal Administration of Toxin Botulinum A Complex

The inhalation of aerozolized botulinum toxin may represent a potential significant hazard to both military and civilian personnel. Since the lung is the primary target organ for inhaled toxin, the investigation reported herein was conducted to examine lung function in mice exposed to botulinum toxin A complex by intranasal route. Data includes lethality, symptomatology, measurement of respiratory function (minute ventilation, respiratory frequency, and tidal volume), and histopathology of the lungs. The clinical signs of intoxication are similar to those observed in foodborne botulism. Plethysmography revealed severe impairment of all respiratory parameters tested from 7 hours postexposure. Severe lung lesions, possibly secondary to the intoxication, were observed in mice who survived 14 days after the toxin challenge. These included intra-alveolar hemorrhage and interstitial edema. Mice immunized by the pentavalent (ABCDE) toxoid were protected against the neurotoxin (4 LD50) as revealed by the decrease of lethality and severity of nervous signs of intoxication, but not against histopathological changes in the lungs. These effects are nonspecific and require further experiments in order to specify the relationships between the pathology and the inflammatory process in the lung due to mediators such as cytokines, and possibly permanent physiological sequelae.

Use of Monoclonal Antibodies in the Sensitive Detection and Neutralization of Botulinum Neurotoxin Serotype B

Botulinum neurotoxins (BoNT) are some of nature’s most potent toxins. Due to potential food contamination, and bioterrorism concerns, the development of detection reagents, therapeutics and countermeasures are of urgent interest. Recently, we have developed a sensitive electrochemiluminescent (ECL) immunoassay for BoNT/B, using monoclonal antibodies (mAbs) MCS6-27 and anti-BoNT/B rabbit polyclonal antibodies as the capture and detector. The ECL assay detected as little as 1 pg/mL BoNT/B in the buffer matrix, surpassing the detection sensitivities of the gold standard mouse bioassays. The ECL assay also allowed detection of BoNT/B in sera matrices of up to 100% sera with negligible matrix effects. This highly-sensitive assay allowed the determination of the biological half-lives of BoNT/B holotoxin in vivo. We further tested the toxin neutralization potential of our monoclonal antibodies using the mouse systemic and oral intoxication models. A combination of mAbs protected mice in both pre- and post-exposure models to lethal doses of BoNT/B. MAbs were capable of increasing survival of animals when administered even 10 h post-intoxication in an oral model, suggesting a likely time for BoNT/B complexes to reach the blood stream. More sensitive detection assays and treatments against BoNT intoxication will greatly enhance efforts to combat botulism.

Recommended Immunological Strategies to Screen for Botulinum Neurotoxin-Containing Samples

Botulinum neurotoxins (BoNTs) cause the life-threatening neurological illness botulism in humans and animals and are divided into seven serotypes (BoNT/A–G), of which serotypes A, B, E, and F cause the disease in humans. BoNTs are classified as “category A” bioterrorism threat agents and are relevant in the context of the Biological Weapons Convention. An international proficiency test (PT) was conducted to evaluate detection, quantification and discrimination capabilities of 23 expert laboratories from the health, food and security areas. Here we describe three immunological strategies that proved to be successful for the detection and quantification of BoNT/A, B, and E considering the restricted sample volume (1 mL) distributed. To analyze the samples qualitatively and quantitatively, the first strategy was based on sensitive immunoenzymatic and immunochromatographic assays for fast qualitative and quantitative analyses. In the second approach, a bead-based suspension array was used for screening followed by conventional ELISA for quantification. In the third approach, an ELISA plate format assay was used for serotype specific immunodetection of BoNT-cleaved substrates, detecting the activity of the light chain, rather than the toxin protein. The results provide guidance for further steps in quality assurance and highlight problems to address in the future.

In Vivo Toxicity and Immunological Characterization of Detoxified Recombinant Botulinum Neurotoxin Type A

PURPOSE

A double-mutant E224A/E262A full-length botulinum neurotoxin (BoNT) Type A with structural similarity to native BoNT/A but lacking the endopeptidase activity provides an ideal surrogate for testing pharmacokinetics and immunochemical characteristics of BoNT.

METHODS

We determined lethality (LD50) of deactivated recombinant botulinum neurotoxin (drBoNT/A) to be 24.0 μg by intraperitoneal route (i.p). The polypeptide drBoNT/A labeled with near infra-red dye 800 (NIR 800) was used to examine its distribution to different organs using whole body imaging when administered to mice via intravenous (i.v) or i.p route. Also, drBoNT/A was used to evaluate its immunogenicity in Balb/C mice model.

RESULTS

drBoNT/A was found to be highly immunogenic when tested under various in vivo conditions in Balb/C mice model. For the first time we have demonstrated that a full length 150 kDa drBoNT/A, by administering via inhalation route in mice model, has evoked both circulating immunoglobulin levels of IgG and secretory IgA at the mucosal surface. The immunoglobulin levels were sufficient enough to protect against the challenge dose of native BoNT toxin in mice model. Tissue distribution of drBoNT/A seems to be similar to that of native toxin.

CONCLUSIONS

Based on the characteristics described in this report this nontoxic holotoxin protein will assist us to explore the window of opportunity available for therapeutic treatment in case of unnatural poisoning, and also it can be an effective vaccine candidate.

Monoclonal Antibodies that Inhibit the Proteolytic Activity of Botulinum Neurotoxin Serotype/B

Existing antibodies (Abs) used to treat botulism cannot enter the cytosol of neurons and bind to botulinum neurotoxin (BoNT) at its site of action, and thus cannot reverse paralysis. However, Abs targeting the proteolytic domain of the toxin could inhibit the proteolytic activity of the toxin intracellularly and potentially reverse intoxication, if they could be delivered intracellularly. As such, antibodies that neutralize toxin activity could serve as potent inhibitory cargos for therapeutic antitoxins against botulism. BoNT serotype B (BoNT/B) contains a zinc endopeptidase light chain (LC) domain that cleaves synaoptobrevin-2, a SNARE protein responsible for vesicle fusion and acetylcholine vesicle release. To generate monoclonal Abs (mAbs) that could reverse paralysis, we targeted the protease domain for Ab generation. Single-chain variable fragment (scFv) libraries from immunized mice or humans were displayed on yeast, and 19 unique BoNT/B LC-specific mAbs isolated by fluorescence-activated cell sorting (FACS). The equilibrium dissociation constants (K_D) of these mAbs for BoNT/B LC ranged from 0.24 nM to 14.3 nM (mean K_D 3.27 nM). Eleven mAbs inhibited BoNT/B LC proteolytic activity. The fine epitopes of selected mAbs were identified by alanine-scanning mutagenesis, revealing that inhibitory mAbs bound near the active site, substrate-binding site or the extended substrate-binding site. The results provide mAbs that could prove useful for intracellular reversal of paralysis and identify epitopes that could be targeted by small molecules inhibitors.

Sheep monoclonal antibodies prevent systemic effects of botulinum neurotoxin A1

Botulinum neurotoxin (BoNT) is responsible for causing botulism, a potentially fatal disease characterized by paralysis of skeletal muscle. Existing specific treatments include polyclonal antisera derived from immunized humans or horses. Both preparations have similar drawbacks, including limited supply, risk of adverse effects and batch to batch variation. Here, we describe a panel of six highly protective sheep monoclonal antibodies (SMAbs) derived from sheep immunized with BoNT/A1 toxoid (SMAbs 2G11, 4F7) or BoNT/A1 heavy chain C-terminus (HcC) (SMAbs 1G4, 5E2, 5F7, 16F9) with or without subsequent challenge immunization with BoNT/A1 toxin. Although each SMAb bound BoNT/A1 toxin, differences in specificity for native and recombinant constituents of BoNT/A1 were observed. Structural differences were suggested by pI (5E2 = 8.2; 2G11 = 7.1; 4F7 = 8.8; 1G4 = 7.4; 5F7 = 8.0; 16F9 = 5.1). SMAb protective efficacy vs. 10,000 LD50 BoNT/A1 was evaluated using the mouse lethality assay. Although not protective alone, divalent and trivalent combinations of SMabs, IG4, 5F7 and/or 16F9 were highly protective. Divalent combinations containing 0.5–4 μg/SMAb (1–8 μg total SMAb) were 100% protective against death with only mild signs of botulism observed; relative efficacy of each combination was 1G4 + 5F7 > 1G4 + 16F9 >> 5F7 + 16F9. The trivalent combination of 1G4 + 5F7 + 16F9 at 0.25 μg/SMAb (0.75 μg total SMAb) was 100% protective against clinical signs and death. These results reflect levels of protective potency not reported previously.

Detection of botulinum neurotoxin serotypes A and B using a chemiluminescent versus electrochemiluminescent immunoassay in food and serum

Botulinum neurotoxins (BoNTs) are some of the most potent biological toxins. High-affinity monoclonal antibodies (mAbs) have been developed for the detection of BoNT serotypes A and B using a chemiluminescent capture enzyme-linked immunosorbent assay (ELISA). In an effort to improve toxin detection levels in complex matrices such as food and sera, we evaluated the performance of existing antitoxin mAbs using a new electrochemiluminescence (ECL) immunoassay platform developed by Meso Scale Discovery. In side-by-side comparisons, the limits of detection (LODs) observed for ELISA and the ECL immunoassay for BoNT/A were 12 and 3 pg/mL, and for BoNT/B, they were 17 and 13 pg/mL, respectively. Both the ELISA and the ECL method were more sensitive than the "gold standard" mouse bioassay. The ECL assay outperformed ELISA in detection sensitivity in most of the food matrices fortified with BoNT/A and in some foods spiked with BoNT/B. Both the ELISA and the ECL immunoassay platforms are fast, simple alternatives for use in the routine detection of BoNTs in food and animal sera.

New equine antitoxins to botulinum neurotoxins serotypes A and B

Hyperimmune monovalent antitoxins to botulinum neurotoxin serotypes A and B have been produced by immunizing horses with newly developed formalin toxoids. After primary immunization, horses developed acceptable prophylactic antibody titers (1-5 IU/mL). Three horses received additional toxoid booster injections to induce hyperimmune antibody titers with antitoxin-A and antitoxin-B titers reaching peaks of approximately 2000 IU/mL and 150-625 IU/mL, respectively. Titers were quantified throughout the process by antigen-capture ELISA and by in-vivo neutralization. ELISA titers and neutralization titers correlated (R² ∼0.62-0.92), however, unique correlations between in-vitro and in-vivo titers were observed for each horse. Monovalent antitoxin pools were made by combining plasma that had been collected twice via plasmaphoresis several months after primary immunization. Neutralizing units were established for each pool relative to the current US and WHO reference standards. Titers were determined at the L(+)/10 and L(+)/40 toxin dose for Toxin types A and B, respectively, and U.S. and international units were assigned to each monovalent antitoxin. Avidity of the new Anti-A pool was equivalent to the WHO Anti-A reference at the L(+), L(+)/10 and L(+)/30 dose. Each monovalent plasma pool failed to cross-neutralize other botulinum neurotoxin serotypes indicating a high degree of specificity of each antitoxin for the toxin serotype used during immunization.

[Development and optimization of immunoassays for the detection of botulinum toxins]

Monoparametric immunoassay tests for detecting botulinum toxins types A and B and multiparametric assays for simultaneous detection of botulinum toxins type A and B have been developed. It is shown that the sensitivity of assays is affected by the size of nanoparticles of colloidal gold used as a marker of antibodies, load intensity of antibodies of colloidal gold in conjugates, the type of analytical membranes, as well as the chemical composition of buffer solutions used for the storage of conjugates and immunoassay analysis. The detection limit of monoparametric immunoassay tests is 0.5 ng/ml; that of multiparametric assays, 5.0 ng/ml. The developed immunoassay can be used for rapid assay of product quality, for grade control of botulinum toxins in pharmaceuticals, and environmental monitoring.

Characterization of the monoclonal antibody response to botulinum neurotoxin type A in the complexed and uncomplexed forms

Clostridium botulinum produces large complex toxins, which include botulinum neurotoxin (BoNT) and auxiliary non-toxic proteins. We prepared monoclonal antibodies (mAbs) from mice that were immunized several times with BoNT/A after basal immunization with toxoid. We then examined the reactivities of these mAbs to BoNT and toxoid and showed that some mAbs reacted to only BoNT. This result indicates that the antigenicity of BoNT/A partially disappeared with formalin treatment. Some mAbs that specifically recognized either BoNT/A1 or BoNT/A2 were considered useful as detection antibodies specific for the BoNT/A subtype. Results of a neutralizing test with mAbs against either BoNT/A1 or BoNT/A2 showed that neutralizing antibody recognition sites were present in the light chain, heavy chain (N-terminal half), and heavy chain (C-terminal half) domains. Investigation of the different binding capabilities of the mAbs to BoNT and the complex toxin by immunoprecipitation suggested that the light chain of BoNT is exposed at the molecular surface of the complex toxin since there was no difference in the binding of light chain-specific mAb to BoNT and the complex toxin. The heavy chain is related to BoNT binding to non-toxic components, because the reactivity of the heavy chain to some mAbs was influenced by non-toxic components.