Botulinum Neurotoxin Serotype Research Articles

A versatile immunoassay based on functionalized nanoparticles for botulinum neurotoxin detection and sensor development

Botulinum neurotoxins (BoNTs) serotypes A and B are the two most common of the four BoNTs that cause the high mortality botulism disease in individuals consuming contaminated foods. The gold standard assay for BoNT detection is the live mouse bioassay, which has several major disadvantages, including tedious procedures and animal sacrifice requirements. In this study, we developed an immuno-based assay using magnetic streptavidin nanoparticles (mSNP) functionalized with specific synthetic biotinylated, 6xHis-tagged peptide substrates (Peptides A, PA and B, PB) designed for BoNT/A and BoNT/B proteolytic reactions, respectively. In the presence of active toxins that possess endopeptidase activity, upon cleavage, the released fragments with His-tag were dotted on a blotting membrane, ultimately producing color signals after incubation with anti-His antibody, alkaline phosphatase (AP)-conjugated antibody, and then AP substrates. The results showed that the efficiency of peptide-mSNP complex formation reached up to 81%, and the dot blot immunoassay allowed peptide detection from 10 ng of His-tagged peptides. Preliminary testing with the extracellular extracts from the isolated Clostridium botulinum strains indicated that the botulinum toxin in the 2020 botulism outbreak in Vietnam belonged to serotype A, the most potent BoNT. The established assay could be applied to construct a portable biosensor for BoNT detection and a high throughput device to screen potential BoNT inhibitors for drug development.

Evaluation of long-term immune response in cattle to botulism using a recombinant E. coli bacterin formulated with Montanide™ ISA 50 and aluminum hydroxide adjuvants

Botulism is a severe disease caused by potent botulinum neurotoxins (BoNTs) produced by Clostridium botulinum. This disease is associated with high-lethality outbreaks in cattle, which have been linked to the ingestion of preformed BoNT serotypes C and D, emphasizing the need for effective vaccines. The potency of current commercial toxoids (formaldehyde-inactivated BoNTs) is assured through tests in guinea pigs according to government regulatory guidelines, but their short-term immunity raises concerns. Recombinant vaccines containing the receptor-binding domain have demonstrated potential for eliciting robust protective immunity. Previous studies have demonstrated the safety and effectiveness of recombinant E. coli bacterin, eliciting high titers of neutralizing antibodies against C. botulinum and C. perfringens in target animal species. In this study, neutralizing antibody titers in cattle and the long-term immune response against BoNT/C and D were used to assess the efficacy of the oil-based adjuvant compared with that of the aluminum hydroxide adjuvant in cattle. The vaccine formulation containing Montanide™ ISA 50 yielded significantly higher titers of neutralizing antibody against BoNT/C and D (8.64 IU/mL and 9.6 IU/mL, respectively) and induced an immune response that lasted longer than the response induced by aluminum, extending between 30 and 60 days. This approach represents a straightforward, cost-effective strategy for recombinant E. coli bacterin, enhancing both the magnitude and duration of the immune response to botulism.

Botulinum neurotoxin X lacks potency in mice and in human neurons.

The family of botulinum neurotoxins comprises the most potent toxins known to humankind. New members of this family of protein toxins as well as more distantly related homologs are being identified. The discovery of BoNT/X via bioinformatic screen in 2017 as a putative new BoNT serotype raised concern about its potential as a pathogenic agent with no available countermeasures. This study for the first time assessed both recombinantly produced and native purified BoNT/X for its vertebrate neurotoxicity.

Botulinum Neurotoxin Induces Neurotoxic Microglia Mediated by Exogenous Inflammatory Responses.

Botulinum neurotoxin serotype A (BoNT/A) is widely used in therapeutics and cosmetics. The effects of multi-dosed BoNT/A treatment are well documented on the peripheral nervous system (PNS), but much less is known on the central nervous system (CNS). Here, the mechanism of multi-dosed BoNT/A leading to CNS neurodegeneration is explored by using the 3D human neuron-glia model. BoNT/A treatment reduces acetylcholine, triggers astrocytic transforming growth factor beta, and upregulates C1q, C3, and C5 expression, inducing microglial proinflammation. The disintegration of the neuronal microtubules is escorted by microglial nitric oxide, interleukin 1β, tumor necrosis factor α, and interleukin 8. The microglial proinflammation eventually causes synaptic impairment, phosphorylated tau (pTau) aggregation, and the loss of the BoNT/A-treated neurons. Taking a more holistic approach, the model will allow to assess therapeutics for the CNS neurodegeneration under the prolonged use of BoNT/A.

Closed genome sequence of Clostridium botulinum type B1 strain isolated from an infant botulism case in the United States.

We present the closed genome sequence of the Clostridium botulinum BT-22100019 strain isolated from the stool specimen of an infant diagnosed with botulism. With 4.33-Mb genome size and 28.0% G + C content, the bont/B1 gene encoded for botulinum neurotoxin serotype B was found on a 262 kb plasmid arranged in a ha+ orfx - cluster.

Abstract B112: SNAP23-dependent SNARE complex is a novel molecular target in AL Amyloidosis and Multiple Myeloma by blocking free light chain secretion and triggering a terminal unfolded protein response

Abstract The goal of this study was to investigate whether SNARE proteins are necessary for immunoglobulin (Ig) free light chain (FLC) secretion, thus representing a yet unexplored therapeutic target in AL amyloidosis (AL) and Multiple myeloma (MM). Both these disorders are incurable, and in the former, pathogenesis is invariably related to deposition of Ig FLC fibrils in target organs. The molecular mechanisms underlying FLC folding/secretion have not been studied, and no therapies directly target this intrinsic vulnerability. We hypothesize that FLC secretion is at least in part mediated by SNARE proteins, and their inhibition would block FLC exocytosis, causing retention of FLC-loaded vesicles, leading to activation of a terminal unfolded protein response (UPR) and apoptosis. We therefore hypothesized that novel, effective targets for MM and AL therapy could be identified within SNAREs. As a tool to study SNARE function, we stably expressed 7 distinct, tetracycline-inducible botulinum neurotoxin (BoNT) serotypes (BoNT/A-F) in FLC-secreting AL (ALMC1, ALMC2) and MM (U266, KMS11) cell lines. To monitor BoNT expression, a bicistronic lentiviral vector with a P2A-GFP was used. Upon doxycycline administration, we performed growth competition assay in polyclonally transduced cells and assessed kinetics of GFP expression over time and apoptosis via flow cytometry in monoclones. Western blot (WB) was used to assess cleavage of SNAREs upon expression of each BoNT. We used WB and ELISA to assess FLC secretion on a per-cell base upon BoNT expression. We used TurboID proximity labeling followed by mass spectrometry to identify cytotoxic BoNT interacting partners and CRISPR-Cas9 gene editing to validate putative BoNT targets. By querying the IFM170 gene expression database of newly diagnosed MM patients, we identified VAMP2, VAMP3, SYNTAXIN4, and SNAP23 as the top expressed SNARE and confirmed their high expression in a panel of AL and MM cell lines. Expression of all BoNT serotypes, except BoNT B, led to rapid apoptosis of AL and MM cells, with BoNT F standing out for extent and rapidity of cytotoxicity. Concurrent cleavage of SNAP23, VAMP3, and SYNTAXIN4 correlated with cytotoxicity of BoNT in AL and MM cell lines. Mechanistically, we showed that cytotoxic BoNTs, but not BoNT B, blocked FLC secretion and triggered the PERK-mediated terminal UPR with induction of CHOP and GADD34 followed by massive apoptosis. We identified SNAP23 as an interacting partner of cytotoxic BoNT F, but not BoNT B. Single SNAP23 KO did not completely recapitulate cytotoxic BoNT phenotype, as it was only partially cytotoxic. Based on our preliminary data, we hypothesize SYNTAXIN4 and VAMP3 to be synthetic lethal with SNAP23. Our data provide proof of concept that blocking FLC secretion in AL and MM cells is feasible and results in rapid cell apoptosis by triggering a terminal UPR, thus representing a promising, novel therapeutic approach. Using BoNT as a biological tool, we identified SNAP23 as a critical component of FLC exocytosis, paving the way for the design of novel therapeutics. Citation Format: Emre Karayol, Maria Moscvin, Tianzeng Chen, Peter G. Czarnecki, Annamaria Gulla, Kenneth C. Anderson, Giada Bianchi. SNAP23-dependent SNARE complex is a novel molecular target in AL Amyloidosis and Multiple Myeloma by blocking free light chain secretion and triggering a terminal unfolded protein response [abstract]. In: Proceedings of the AACR-NCI-EORTC Virtual International Conference on Molecular Targets and Cancer Therapeutics; 2023 Oct 11-15; Boston, MA. Philadelphia (PA): AACR; Mol Cancer Ther 2023;22(12 Suppl):Abstract nr B112.

A SNAP23-Dependent SNARE Complex Mediates Free Light Chain Secretion in AL Amyloidosis and Multiple Myeloma and Its Blockade Triggers a Terminal Unfolded Protein Response and Massive Apoptosis

Background AL amyloidosis (AL) is an incurable plasma cell (PC) disorder with only one FDA-approved therapy. Deposition of immunoglobulin free light chain (FLC) fibrils in target organs is the sole pathogenic mechanism in AL. However, therapeutic strategies directly targeting FLC secretion are not available. SNARE proteins, the specific targets of botulinum neurotoxin (BoNT), mediate the docking and fusion of secretory vesicles. We hypothesized that targeting specific sets of SNAREs via BoNT will block FLC exocytosis, causing retention of FLC-loaded vesicles and triggering a terminal unfolded protein response (UPR) and apoptosis in AL cells. We postulate that SNAREs are potential novel targets in AL and other plasma cell disorders. Materials and Methods We stably expressed 7 distinct, inducible BoNT serotypes (BoNT/A-F) in FLC-secreting AL (ALMC1 and ALMC2) and multiple myeloma (MM, KMS11) cell lines via tetracycline-inducible (Tet-On) bicistronic lentiviral vectors with a P2A-GFP which allowed us to use GFP as a biomarker of BoNT expression. We established monoclones of successfully transduced cells for each BoNT. We performed flow cytometry to assess the kinetics of GFP induction and assess for apoptosis via AnnexinV/DAPI staining. Western blot (WB) was used to assess the cleavage of SNAREs upon expression of each BoNT serotype. We used WB and ELISA to assess FLC secretion per cell upon expression of each BoNT serotype. We used TurboID proximity labeling followed by mass spectrometry to identify cytotoxic BoNT interacting partners and used co-IP for confirmation. We used RNP-based CRISPR-Cas9 gene editing to knock out (KO) putative BoNT targets. Results By querying the IFM170 gene expression database of newly diagnosed MM patients, we identified VAMP2, VAMP3, SNAP23, and SYNTAXIN4 as the top expressed SNAREs. Their high expression was retained in a large panel of AL and MM cell lines. Expression of all BoNT serotypes, except for BoNT B, led to rapid apoptosis of AL and MM cells, with BoNT F standing out for the extent and rapidity of cytotoxicity. Dual cleavage of SNAP23 and VAMP3 correlated with cytotoxicity of BoNT in AL and MM cell lines. Mechanistically, we showed that cytotoxic BoNTs, but not non-toxic BoNT B, led to decreased FLC secretion and increased FLC retention and triggered the PERK pathway of the UPR with increased expression of CHOP and GADD34, preceding the onset of apoptosis. We identified SNAP23 as an interacting partner of highly cytotoxic BoNT F, but not non-toxic BoNT B. KO experiment showed single SNAP23 KO to be partially toxic for AL and MM cell lines but did not recapitulate the effects of cytotoxic BoNTs entirely. Based on our preliminary data, we hypothesize VAMP3 and SYNTAXIN4 to be synthetic lethal with SNAP23. Conclusions Our data provide proof of concept that blocking FLC secretion in AL and MM cells is feasible and results in rapid cell apoptosis by triggering a terminal UPR, thus representing a promising, novel therapeutic approach. By using BoNT as a biological tool, we identified SNAP23 as a critical component of FLC exocytosisin AL cell lines, thus representing a novel, promising molecular target in AL amyloidosis and multiple myeloma.

Single-Domain Antibody Multimers for Detection of Botulinum Neurotoxin Serotypes C, D, and Their Mosaics in Endopep-MS.

Botulinum neurotoxins (BoNTs) are highly toxic proteins that require high-affinity immunocapture reagents for use in endopeptidase-based assays. Here, 30 novel and 2 earlier published llama single-domain antibodies (VHHs) against the veterinary-relevant BoNT serotypes C and D were yeast-produced. These VHHs recognized 10 independent antigenic sites, and many cross-reacted with the BoNT/DC and CD mosaic variants. As VHHs are highly suitable for genetically linking to increase antigen-binding affinity, 52 VHH multimers were produced and their affinity for BoNT/C, D, DC, and CD was determined. A selection of 15 multimers with high affinity (KD < 0.1 nM) was further shown to be resilient to a high salt wash that is used for samples from complex matrices and bound native BoNTs from culture supernatants as shown by Endopep-MS. High-affinity multimers suitable for further development of a highly sensitive Endopep-MS assay include four multimers that bind both BoNT/D and CD with KD of 14-99 pM, one multimer for BoNT/DC (65 pM) that also binds BoNT/C (75 pM), and seven multimers for BoNT/C (<1-19 pM), six of which also bind BoNT/DC with lower affinity (93-508 pM). In addition to application in diagnostic tests, these VHHs could be used for the development of novel therapeutics for animals or humans.

Generation and characterization of a monoclonal antibody against FGFR3 that protects mice from BoNT/A

Botulinum neurotoxin serotype A (BoNT/A) can cause flaccid paralysis of muscles, an illness fatal to human, by entering neurons and blocking neurotransmitter release. The process was mediated by three receptors. A specific monoclonal antibody anti-D23, designated as ML419, targeting the ectodomain (D23) of fibroblast growth factor receptor 3 (FGFR3), one of the three receptors, was screened and capable of disturbing the recognition of BoNT/A and FGFR3. ML419 was screened from 14 stable positive hybridoma cell lines, and was subcloned, sequenced, and classified as IgG2a(κ) subclass. ML419 binds the D23 domain of FGFR3 with high affinity (KD∼0.26 nM), and prevents the BoNT/A from entering Neuro-2a cells effectively. In vivo data showed that, 200 μg of ML419 could completely protect all the mice against with 5 MLD50 BoNT/A, while 100 μg of ML419 could protected 60% of the mice. Collectively, our results indicated that ML419 served as a good candidate for further development of therapeutics for BoNT/A.

Crystal Structure of the Catalytic Domain of a Botulinum Neurotoxin Homologue from Enterococcus faecium: Potential Insights into Substrate Recognition.

Clostridium botulinum neurotoxins (BoNTs) are the most potent toxins known, causing the deadly disease botulism. They function through Zn2+-dependent endopeptidase cleavage of SNARE (soluble N-ethylmaleimide-sensitive factor attachment protein receptor) proteins, preventing vesicular fusion and subsequent neurotransmitter release from motor neurons. Several serotypes of BoNTs produced by Clostridium botulinum (BoNT/A-/G and/X) have been well-characterised over the years. However, a BoNT-like gene (homologue of BoNT) was recently identified in the non-clostridial species, Enterococcus faecium, which is the leading cause of hospital-acquired multi-drug resistant infections. Here, we report the crystal structure of the catalytic domain of a BoNT homologue from Enterococcus faecium (LC/En) at 2.0 Å resolution. Detailed structural analysis in comparison with the full-length BoNT/En AlphaFold2-predicted structure, LC/A (from BoNT/A), and LC/F (from BoNT/F) revealed putative subsites and exosites (including loops 1-5) involved in recognition of LC/En substrates. LC/En also appears to possess a conserved autoproteolytic cleavage site whose function is yet to be established.

Biology activity and characterization of the functional L-HN fragment derivative of botulinum neurotoxin serotype E

ObjectivesThe mature botulinum neurotoxin (BoNT) is a long peptide chain consisting of a light chain (L) and a heavy chain (H) linked by a disulfide bond, where the heavy chain is divided into a translocation domain and an acceptor binding domain (Hc). In this study, we further explored the biology activity and characteristics of recombinant L-HN fragment (EL-HN) composed of the L and HN domains of BoNT/E in vivo and in vitro. MethodsNeurotoxicity of L-HN fragments from botulinum neurotoxins was assessed in mice. Cleavage of dichain EL-HN in vitro and in neuro-2a cells was assessed and compared with that of single chain EL-HN. Interaction of HN domain and the receptor synaptic vesicle glycoprotein 2C (SV2C) was explored in vitro and in neuro-2a cells only expressing SV2C. ResultsWe found that the 50% mouse lethal dose of the nicked dichain EL-HN fragment (EL–HN–DC) was 0.5 μg and its neurotoxicity was the highest among the L-HN's of the four serotypes of BoNT (A/B/E/F). The cleavage efficiency of EL–HN–DC toward synaptosome associated protein 25 (SNAP25) in vitro was 3-fold higher than that of the single chain at the cellular level, and showed 200-fold higher animal toxicity. The EL–HN–DC fragment might enter neuro-2a cells via binding to SV2C to efficiently cleave SNAP25. ConclusionsThe EL-HN fragment showed good biological activities in vivo and in vitro, and could be used as a drug screening model and to further explore the molecular mechanism of its transmembrane transport.

Botulinum neurotoxins: Future innovations.

Botulinum neurotoxins (BoNTs) are multi-domain proteins whose potent and selective actions on nerve endings have led to innovations in both basic and clinical science. The various BoNT domains are responsible for binding to gangliosides and proteins associated with nerve cell membranes, internalization into the cell, and cleavage of one or more SNARE (soluble N-ethylmaleimide sensitive factor attachment protein receptor) proteins necessary for vesicle docking and fusion. Novel modifications to BoNT molecules, such as the creation of chimeras, helped identify the protein domains responsible for various aspects of BoNT action, such as localized effects. Other molecular modifications have been introduced in attempts to increase the specificity of BoNTs for autonomic or sensory neurons, with the ultimate goal of optimizing therapeutic selectivity. This research, in turn, has led to the development of BoNT-based proteins that can target non-SNARE substrates such as phosphatase and tensin homolog (PTEN). Still others are developing different BoNT serotypes, subtypes, or variants that are longer- or shorter-acting or have faster onset for various clinical purposes. New formulations of BoNTs that provide convenience for both patients and physicians are under investigation. Novel clinical uses are being evaluated for onabotulinumtoxinA, including in the prevention of post-operative atrial fibrillation. All these innovations capitalize on the unique properties of BoNTs, which continue to intrigue scientists and clinicians across numerous fields of study.

A Three-Monoclonal Antibody Combination Potently Neutralizes BoNT/G Toxin in Mice.

Equine-derived antitoxin (BAT®) is the only treatment for botulism from botulinum neurotoxin serotype G (BoNT/G). BAT® is a foreign protein with potentially severe adverse effects and is not renewable. To develop a safe, more potent, and renewable antitoxin, humanized monoclonal antibodies (mAbs) were generated. Yeast displayed single chain Fv (scFv) libraries were prepared from mice immunized with BoNT/G and BoNT/G domains and screened with BoNT/G using fluorescence-activated cell sorting (FACS). Fourteen scFv-binding BoNT/G were isolated with KD values ranging from 3.86 nM to 103 nM (median KD 20.9 nM). Five mAb-binding non-overlapping epitopes were humanized and affinity matured to create antibodies hu6G6.2, hu6G7.2, hu6G9.1, hu6G10, and hu6G11.2, with IgG KD values ranging from 51 pM to 8 pM. Three IgG combinations completely protected mice challenged with 10,000 LD50s of BoNT/G at a total mAb dose of 6.25 μg per mouse. The mAb combinations have the potential for use in the diagnosis and treatment of botulism due to serotype G and, along with antibody combinations to BoNT/A, B, C, D, E, and F, provide the basis for a fully recombinant heptavalent botulinum antitoxin to replace the legacy equine product.

Cloning the gene fragment encoding botulinum neurotoxin serotype A and establishment of a detection method for Clostridium botulinum using LAMP technique

The neurotoxins produced by Clostridium botulinum are lethal in minute amounts. Botulinum neurotoxin serotype A accounts for approximately 60% of botulism cases worldwide. Bacterial and toxin detection methods including the gold standard mouse bioassay and routine culture both require tedious procedures and need days to obtain results. Importantly, the development of a rapid and accurate technique to identify the toxin-encoding gene is crucial for timely diagnosis and treatment. This study aimed to clone a gene fragment encoding botulinum neurotoxin serotype A to serve as a positive control and establish a method based on the loop-mediated isothermal amplification (LAMP) technique to rapidly detect the encoding bont/A gene. The LAMP reaction was performed at the optimized temperature of 65˚C for 30 minutes with the in-house recombinant plasmid carrying a 250-bp fragment as the positive control. The developed method showed positive results for all strains provided by the National Institute of Hygiene and Epidemiology, consistent with the conventional polymerase chain reaction (PCR) results using the Vietnam standard with a total time roughly four times faster than the PCR amplification.

Biological and Immunological Characterization of a Functional L-HN Derivative of Botulinum Neurotoxin Serotype F.

Botulinum neurotoxins (BoNTs) can cause nerve paralysis syndrome in mammals and other vertebrates. BoNTs are the most toxic biotoxins known and are classified as Class A biological warfare agents. BoNTs are mainly divided into seven serotypes A-G and new neurotoxins BoNT/H and BoNT/X, which have similar functions. BoNT proteins are 150 kDa polypeptide consisting of two chains and three domains: the light chain (L, catalytic domain, 50 kDa) and the heavy chain (H, 100 kDa), which can be divided into an N-terminal membrane translocation domain (HN, 50 kDa) and a C-terminal receptor binding domain (Hc, 50 kDa). In current study, we explored the immunoprotective efficacy of each functional molecule of BoNT/F and the biological characteristics of the light chain-heavy N-terminal domain (FL-HN). The two structure forms of FL-HN (i.e., FL-HN-SC: single chain FL-HN and FL-HN-DC: di-chain FL-HN) were developed and identified. FL-HN-SC could cleave the vesicle associated membrane protein 2 (VAMP2) substrate protein in vitro as FL-HN-DC or FL. While only FL-HN-DC had neurotoxicity and could enter neuro-2a cells to cleave VAMP2. Our results showed that the FL-HN-SC had a better immune protection effect than the Hc of BoNT/F (FHc), which indicated that L-HN-SC, as an antigen, provided the strongest protective effects against BoNT/F among all the tested functional molecules. Further in-depth research on the different molecular forms of FL-HN suggested that there were some important antibody epitopes at the L-HN junction of BoNT/F. Thus, FL-HN-SC could be used as a subunit vaccine to replace the FHc subunit vaccine and/or toxoid vaccine, and to develop antibody immune molecules targeting L and HN domains rather than the FHc domain. FL-HN-DC could be used as a new functional molecule to evaluate and explore the structure and activity of toxin molecules. Further exploration of the biological activity and molecular mechanism of the functional FL-HN or BoNT/F is warranted.

Structural basis of botulinum neurotoxin serotype A1 binding to human SV2A or SV2C receptors

Botulinum neurotoxin A1 (BoNT/A1) is the most potent natural poison in human. BoNT/A1 recognize the luminal domain of SV2A (LD-SV2A) and its glycosylation at position N573 (N573g) or the luminal domain of SV2C (LD-SV2C) and its glycosylation at position N559 (N559g) to bind neural membrane. Our computational data suggest that the N-glycan at position 480 (N480g) in the luminal domain of SV2C (LD-SV2C) indirectly enhanced the contacts of the neurotoxin surface with the second N-glycan at position 559 (N559g) by acting as a shield to prevent N559g to interact with residues of LD-SV2C. The absence of an N-glycan homologous to N480g in LD-SV2A leads to a decrease of the binding of N573g to the surface of BoNT/A1. Concerning the intermolecular interactions between BoNT/A and the protein part of LD-SV2A or LD-SV2C, we showed that the high affinity of the neurotoxin for binding LD-SV2C are mediated by a better compaction of its F557–F562 part provided by a π-π network mediated by residues F547, F552, F557 and F562 coupled with the presence of two aromatic residues at position 563 and 564 that optimize the binding of BoNT/A1 via cation-pi and CH-pi interaction. Finally, in addition to the well-known ganglioside binding site which accommodates a ganglioside on the surface of BoNT/A1, we identified a structure we coined the ganglioside binding loop defined by the sequence 1253-HQFNNIAK-1260 that is conserved across all subtypes of BoNT/A and is predicted to has a high affinity to interact with gangliosides. These data solved the puzzle generated by mutational studies that could be only partially understood with crystallographic data that lack both a biologically relevant membrane environment and a full glycosylation of SV2.

Dual-Toxin ("Bivalent") Infant Botulism in California, 1976-2020: Epidemiologic, Clinical, and Laboratory Aspects.

To assess the consequences of infant botulismthat result from Clostridium botulinum strains that produce 2 botulinum toxin serotypes, termed "bivalent." Epidemiologic investigations used a standard questionnaire. Clostridium botulinum strains were isolated by standard methods. Botulinum neurotoxin (BoNT) serotypes and the relative amounts of toxins produced were identified using the standard mouse bioassay. BoNT subtypes and genomic locations were identified by DNA nucleotide sequencing. Thirty bivalent cases of infant botulism occurred in the 45years (1976-2020), representing 2.0% of all California infant botulism cases, in the 3 geographic regions of southern California, the southern Central Valley, and mid-northern California. Toxin serotype combinations were Ba (n=22), Bf (n=7), and Ab (n=1). More patients with illness caused by bivalent C botulinum Ba and Bf strains needed endotracheal intubation at hospital admission, 60.0% (18/30), than did patients with illness caused by monovalent BoNT/B strains, 34.3% (152/443). The Cbotulinum Ba and Bf strains produced BoNT/B5 and either BoNT/A4 or /F2. The Ab strain produced BoNT/A2 and /B1. All toxin gene clusters were on plasmids. Infant botulism caused by bivalent Cbotulinum strains occurs sporadically and in diverse locations in California. Affected patients with bivalent Ba and Bf strains lacked distinguishing epidemiological features but appeared to be more severely paralyzed at hospital presentation than patients with illness caused by only BoNT/B. These bivalent strains produced BoNT subtypes A2, A4, B1, B5, and F2, and all toxin gene clusters were on plasmids.

Functional Deimmunization of Botulinum Neurotoxin Protease Domain via Computationally Driven Library Design and Ultrahigh-Throughput Screening.

Botulinum neurotoxin serotype A (BoNT/A) is a widely used cosmetic agent that also has diverse therapeutic applications; however, adverse antidrug immune responses and associated loss of efficacy have been reported in clinical uses. Here, we describe computational design and ultrahigh-throughput screening of a massive BoNT/A light-chain (BoNT/A-LC) library optimized for reduced T cell epitope content and thereby dampened immunogenicity. We developed a functional assay based on bacterial co-expression of BoNT/A-LC library members with a Förster resonance energy transfer (FRET) sensor for BoNT/A-LC enzymatic activity, and we employed high-speed fluorescence-activated cell sorting (FACS) to identify numerous computationally designed variants having wild-type-like enzyme kinetics. Many of these variants exhibited decreased immunogenicity in humanized HLA transgenic mice and manifested in vivo paralytic activity when incorporated into full-length toxin. One variant achieved near-wild-type paralytic potency and a 300% reduction in antidrug antibody response in vivo. Thus, we have achieved a striking level of BoNT/A-LC functional deimmunization by combining computational library design and ultrahigh-throughput screening. This strategy holds promise for deimmunizing other biologics with complex superstructures and mechanisms of action.

Recombinant botulinum toxin as a new stage in the development of botulinum toxin therapy. Possibilities and perspectives of use in neurological practice

Currently, eight natural serotypes of botulinum neurotoxin (BNT-A-G, -X) are known. The mechanism of action of all BNT serotypes is presynaptic blockade of SNARE transport proteins (Soluble N-ethylmaleimide-sensitive factor [NSF] Attachment Protein Receptor), as a result of which the release of acetylcholine into the synaptic cleft is disrupted and neuromuscular transmission is blocked. Each botulinum toxin serotype selectively binds to its own presynaptic membrane receptor and causes cleavage of its own SNARE protein. These differences determine the neuronal specificity and activity of botulinum toxins, which leads to their unique pharmacological properties, such as activity, duration of action, and time to onset of action. In the international clinical practice, only two BNT serotypes (A and B) are allowed to be used, however, in recent years, a large number of studies on the efficacy and safety of other BNT serotypes (E, C, F) have been carried out, and technologies for changing their natural properties have been developed. One of the indications for the use of botulinum therapy in neurology is the correction of post-stroke spasticity. Currently, BNT-A is used for this purpose, clinical improvement after its injection occurs after 2 weeks, the therapeutic effect persists for 3 months, and then the symptoms of spasticity increase again, which worsens the patient's quality of life and reduces the possibility of medical rehabilitation. The use of fast-acting recombinant botulinum toxins for this purpose could help overcome this disadvantage of BNT-A therapy. Currently the LANTIMA study, supported by IPSEN company, is going on to evaluate the safety profile and level of efficacy of modified recombinant botulinum toxin type AB in the treatment of upper limb spasticity in adults.

A Thermostable Dissolving Microneedle Vaccine with Recombinant Protein of Botulinum Neurotoxin Serotype A.

As a Class A bioterrorism agent, botulinum neurotoxin serotype A (BoNT/A) carries the risk of being used by terrorists to cause mass poisoning. The microneedle (MN) patch has a great potential for application as a novel vaccine delivery method. The aim of this study is to develop a thermally stable, dissolving microneedle patch for the delivery of a recombinant protein vaccine using a recombinant C-terminal heavy chain of BoNT/A (Hc of BoNT/A, AHc) to prevent botulism. Fish gelatin, a natural non-toxic and bacteriostatic material, was selected as the microneedle matrix for the preparation of the dissolving microneedle vaccine. Subsequently, the mechanical performance, bacteriostatic properties, vaccination effect, and stability of the microneedle patches were evaluated using instruments such as the displacement-force test station and optical coherence tomography (OCT) scanner. Fish gelatin matrix at high concentrations has good bacteriostatic properties, and excellent mechanical performance and vaccination effect, meeting the necessities of a vaccine. In both in vivo and in vitro neutralization experiments, MN vaccines containing different antigen doses achieved the same protective efficacy as subcutaneous vaccinations, protecting mice against 106 LD50 of BoNT/A injected intraperitoneally. Thermal stability analysis of the MN vaccines revealed that the fish gelatin matrix protected the AHc vaccine from protein denaturation even after 7 days of storage at 37 °C and enabled the vaccine patches to maintain good immunogenicity and protective efficacy even after 6 months of storage at room temperature. In this study, we successfully prepared a bacteriostatic MN patch using a fish gelatin matrix that not only has a good vaccination effect, but also obviates the need for a cold chain for the AHc vaccine, providing the possibility of rapid, painless, and large-scale vaccination.