Characterization of neutralizing chimeric heavy-chain antibodies against tetanus toxin.

Tetanus toxin (TeNT) is one of the most toxic proteins. Neutralizing antibodies against TeNT are effective in prevention and treatment. In this study, 14 anti-tetanus nanobodies were obtained from a phage display nanobody library by immunizing a camel with the C-terminal receptor-binding domain of TeNT (TeNT-Hc) as the antigen. After fusion with the human Fc fragment, 11 chimeric heavy-chain antibodies demonstrated nanomolar binding toward TeNT-Hc. The results of toxin neutralization experiments showed that T83-7, T83-8, and T83-13 completely protected mice against 20 × the median lethal dose (LD50) at a low concentration. The neutralizing potency of T83-7, T83-8, and T83-13 against TeNT is 0.4 IU/mg, 0.4 IU/mg and 0.2 IU/mg, respectively. In the prophylactic setting, we found that 5 mg/kg of T83-13 provided the mice with full protection from tetanus, even when they were injected 14 days before exposure to 20 × LD50 TeNT. T83-7 and T83-8 were less effective, being fully protective only when challenged 7 or 10 days before exposure, respectively. In the therapeutic setting, 12 h after exposure to TeNT, 1 ~ 5 mg/kg of T83-7, and T83-8 could provide complete protection for mice against 5 × LD50 TeNT, while 1 mg/kg T83-13 could provide complete protection 24 h after exposure to 5 × LD50 TeNT. Our results suggested that these antibodies represent prophylactic and therapeutic activities against TeNT in a mouse model. The T83-7, T83-8, and T83-13 could form the basis for the subsequent development of drugs to treat TeNT toxicity.

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.

A potential broad-spectrum neutralizing antibody against Betacoronavirus.

Three pandemics caused by human Betacoronavirus had broken out in the past two decades. Severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) was one of the novel epidemic strains which caused the third pandemic, coronavirus disease 2019 (COVID-19), a global public health crisis. So far, more than millions of people have been infected. Considering the public health and economic impact of Betacoronavirus pandemic, drugs with broad-spectrum activity against these coronaviruses are urgently needed. In this study, two monoclonal antibodies targeting SARS-CoV-2 spike protein receptor-binding domain (RBD) with good neutralizing activity were used to construct a novel immunoglobulin-like bispecific antibody BI31. The neutralizing effect of BI31 against the pseudovirus and the authentic virus is better than that of its parent antibodies alone and in combination. What surprised us most was that the newly constructed bispecific antibody also had the neutralizing activity against SARS-CoV and Middle East respiratory syndrome coronavirus (MERS-CoV) that the parent antibodies did not have. These suggested that the BI31 can not only be developed as a therapeutic drug against COVID-19 but it could also become a broad-spectrum therapeutic antibody against Betacoronavirus.

A human bispecific antibody neutralizes botulinum neurotoxin serotype A.

Botulinum neurotoxin (BoNT) shows high lethality and toxicity, marking it as an important biological threat. The only effective post-exposure therapy is botulinum antitoxin; however, such products have great potential for improvement. To prevent or treat BoNT, monoclonal antibodies (mAbs) are promising agents. Herein, we aimed to construct a bispecific antibody (termed LUZ-A1-A3) based on the anti-BoNT/A human monoclonal antibodies (HMAb) A1 and A3. LUZ-A1-A3 binds to the Hc and L-HN domains of BoNT/A, displaying potent neutralization activity against BoNT/A (124 × higher than that of HMAb A1 or HMAb A3 alone and 15 × higher than that of the A1 + A3 combination). LUZ-A1-A3 provided effective protection against BoNT/A in an in vivo mouse model. Mice were protected from infection with 500 × LD50 of BoNT/A by LUZ-A1-A3 from up to 7 days before intraperitoneal administration of BoNT/A. We also demonstrated the effective therapeutic capacity of LUZ-A1-A3 against BoNT/A in a mouse model. LUZ-A1-A3 (5 µg/mouse) neutralized 20 × LD50 of BoNT/A at 3 h after intraperitoneal BoNT/A administration and complete neutralized 20 × LD50 of BoNT/A at 0.5 h after intraperitoneal BoNT/A administration. Thus, LUZ-A1-A3 is a promising agent for the pre-exposure prophylaxis and post-exposure treatment of BoNT/A.

Immunogenicity and immunoprotection of the functional TL-HN fragment derived from tetanus toxin.

Tetanus toxin (TeNT) is a protein toxin produced by Clostridium tetani bacteria, which causes hyperreflexia and rhabdomyolysis by spastic paralysis. Like botulinum neurotoxin, TeNT comprises a heavy chain (HC) and a light chain (LC) linked via an interchain disulfide bond, which include the following three functional domains: a receptor-binding domain (Hc), a translocation domain (HN), and a catalytic domain (LC). Herein, we produced and characterized three functional domains of TeNT and three types of TeNT-derived L-HN fragments (TL-HN, TL-GS-HN and TL-2A-HN), which contained L and HN domains but lacked the Hc domain. The immunological effects of these different functional domains or fragments of TeNT were explored in an animal model. Our investigations showed the TL-HN functional fragment provided the best immunoprotection among all the TeNT functional domains. The TL-HN fragment, as a protective antigen, induced the highest levels of neutralizing antibodies, indicating that it might contain some crucial epitopes. Further experiments revealed that the protective effect of TL-HN was superior to that of the THc, TL, or THN fragments, either individually or in combination. Therefore, the TL-HN fragment exerts an important function in immune protection against tetanus toxin, providing a good basis for the development of TeNT vaccines or antibodies, and could serve as a promising subunit vaccine to replace THc or tetanus toxoid (TT).

Tetanus toxin and botulinum neurotoxin-derived fusion molecules are effective bivalent vaccines.

Tetanus toxin (TeNT) and botulinum neurotoxins (BoNTs) are neuroprotein toxins, with the latter being the most toxic known protein. They are structurally similar and contain three functional domains: an N-terminal catalytic domain (light chain), an internal heavy-chain translocation domain (HN domain), and a C-terminal heavy chain receptor binding domain (Hc domain or RBD). In this study, fusion functional domain molecules consisting of the TeNT RBD (THc) and the BoNT/A RBD (AHc) (i.e., THc-Linker-AHc and AHc-Linker-THc) were designed, prepared, and identified. The interaction of each Hc domain and the ganglioside receptor (GT1b) or the receptor synaptic vesicle glycoprotein 2 (SV2) was explored in vitro. Their immune response characteristics and protective efficacy were investigated in animal models. The recombinant THc-linker-AHc and AHc-linker-THc proteins with the binding activity had the correct size and structure, thus representing novel subunit vaccines. THc-linker-AHc and AHc-linker-THc induced high levels of specific neutralizing antibodies, and showed strong immune protective efficacy against both toxins. The high antibody titers against the two novel fusion domain molecules and against individual THc and AHc suggested that the THc and AHc domains, as antigens in the fusion functional domain molecules, do not interact with each other and retain their full key epitopes responsible for inducing neutralizing antibodies. Thus, the recombinant THc-linker-AHc and AHc-linker-THc molecules are strong and effective bivalent biotoxin vaccines, protecting against two biotoxins simultaneously. Our experimental design will be valuable to develop recombinant double-RBD fusion molecules as potent bivalent subunit vaccines against bio-toxins. KEY POINTS: • Double-RBD fusion molecules from two toxins had the correct structure and activity. • THc-linker-AHc and AHc-linker-THc efficiently protected against both biotoxins. • Such bivalent biotoxin vaccines based on the RBD are a valuable experimental design.

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

OBJECTIVES: The 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. METHODS: Neurotoxicity 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. RESULTS: We 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. CONCLUSIONS: The 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.

A humanized anti-human adenovirus 55 monoclonal antibody with good neutralization ability.

Background: Human adenovirus type 55 (HAdV55) has a re-emerged as pathogen causing an acute respiratory disease presenting as a severe lower respiratory illness that can cause death. To date, there is no HAdV55 vaccine or treatment available for general use. Methods: Herein, a monoclonal antibody specific for HAdV55, mAb 9-8, was isolated from an scFv-phage display library derived from mice immunized with the purified inactived-HAdV55 virions. By using ELISA and a virus micro-neutralization assay, we evaluated the binding and neutralizing activity of mAb 9-8 following humanization. Western blotting analysis and antigen-antibody molecular docking analysis were used to identify the antigenic epitopes that the humanized monoclonal antibody 9-8-h2 recognized. After that, their thermal stability was determined. Results: MAb 9-8 showed potent neutralization activity against HAdV55. After humanization, the humanized neutralizing monoclonal antibody (9-8-h2) was identified to neutralize HAdV55 infection with an IC50 of 0.6050 nM. The mAb 9-8-h2 recognized HAdV55 and HAdV7 virus particles, but not HAdV4 particles. Although mAb 9-8-h2 could recognize HAdV7, it could not neutralize HAdV7. Furthermore, mAb 9-8-h2 recognized a conformational neutralization epitope of the fiber protein and the crucial amino acid residues (Arg 288, Asp 157, and Asn 200) were identified. MAb 9-8-h2 also showed favorable general physicochemical properties, including good thermostability and pH stability. Conclusions: Overall, mAb 9-8-h2 might be a promising molecule for the prevention and treatment of HAdV55.

Characterization of a novel tetravalent botulism antitoxin based on receptor-binding domain of BoNTs.

Botulinum neurotoxin (BoNTs; serotypes A, B, E, and F) cause botulism disease in humans, which could be effectively treated using antitoxins. Herein, we established a novel receptor-binding domain (RBD)-based antitoxin using recombinant C terminal heavy chain (Hc) domains of BoNTs as immunogens. Immunization of horses with these recombinant Hc domains allowed the purification and digestion of IgGs from hyper-immune sera to produce high-quality and high-efficiency monovalent botulism antitoxin F(ab')2 against each BoNT (M-BATs). However, these M-BATs could not bind or neutralize other serotypes of BoNTs, and that there were no cross-protective effects among these M-BATs. This suggested the need to prepare tetravalent antitoxins to neutralize the four BoNTs simultaneously. Thus, these M-BATs were formulated into a novel tetravalent botulism antitoxin (T-BAT), in which a 10-ml volume contained 10000 IU of BoNT/A and 5000 IU of BoNT/B, BoNT/E, and BoNT/F antitoxins. The novel antitoxin preparation could prevent and treat the four mixed botulinum neurotoxins simultaneously in vivo, representing strong efficacy in an animal poisoning model. Moreover, these antibodies in T-BAT could bind the RBD, whereas conventional antitoxins based on inactivated toxins mainly bind the light chain or heavy chain translocation domain (HN) and weakly bind the important RBD in current experimental conditions. The high levels of RBD-specific novel antitoxins can efficiently bind the RBD and neutralize natural or recombinant toxins containing this RBD. The findings of the present study experimentally support the use of RBD-specific antitoxins to treat BoNT serotype A, B, E, and F-mediated botulism. This study demonstrated the concept of developing potent novel multivalent antitoxins against all BoNTs or other toxins, using the RBD of these toxins as an alternative antigen to inactivated toxins. KEY POINTS: • Antitoxins based on the receptor-binding domains of botulinum neurotoxins were made. • Novel antitoxin binds RBD; traditional antitoxin mainly binds light chain or HN domain. • A tetravalent antitoxin could prevent and treat the four mixed neurotoxins in vivo.

Humanization and characterization of a murine monoclonal neutralizing antibody against human adenovirus 7.

Human adenovirus type 7 (HAdV7) is commonly associated with febrile acute respiratory disease (ARD) outbreaks. We have reported that 10G12, a mouse monoclonal antibody (mAb) specifically recognizing and neutralizing HAdV7, is a promising candidate for humanization. In this study, we engineered the six variants of 10G12 with increased degree of humanization and investigated their biological activity. The humanized monoclonal antibody (mAb) 10G12-M2 was shown to retain the parental antibody's high binding affinity, specificity and potent efficacy of viral suppression. The mAb 10G12-M2 recognized a conformational neutralization epitope of the hexon protein. Complex structure-based molecular docking simulation showed that the hexon protein formed several interactions with 10G12-M2, including hydrogen bonds and salt bridges interaction. Physicochemical properties analysis of 10G12-M2 demonstrated that it is stable and desirable lead candidate. In general, 10G12-M2 had excellent biological activity after humanization combined with the potential for use in prophylactic or therapeutic applications against HAdV7.

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.

A Single Amino Acid Replacement Boosts the Analgesic Activity of α-Conotoxin AuIB through the Inhibition of the GABABR-Coupled N-Type Calcium Channel.

α-conotoxin AuIB is the only one of the 4/6 type α-conotoxins (α-CTxs) that inhibits the γ-aminobutyric acid receptor B (GABABR)-coupled N-type calcium channel (CaV2.2). To improve its inhibitory activity, a series of variants were synthesized and evaluated according to the structure-activity relationships of 4/7 type α-CTxs targeting GABABR-coupled CaV2.2. Surprisingly, only the substitution of Pro7 with Arg results in a 2-3-fold increase in the inhibition of GABABR-coupled CaV2.2 (IC50 is 0.74 nM); substitutions of position 9-12 with basic or hydrophobic amino acid and the addition of hydrophobic amino acid Leu or Ile at the second loop to mimic 4/7 type α-CTxs all failed to improve the inhibitory activity of AuIB against GABABR-coupled CaV2.2. Interestingly, the most potent form of AuIB[P7R] has disulfide bridges of "1-4, 2-3" (ribbon), which differs from the "1-3, 2-4" (globular) in the isoforms of wildtype AuIB. In addition, AuIB[P7R](globular) displays potent analgesic activity in the acetic acid writhing model and the partial sciatic nerve injury (PNL) model. Our study demonstrated that 4/6 type α-CTxs, with the disulfide bridge connectivity "1-4, 2-3," are also potent inhibitors for GABABR-coupled CaV2.2, exhibiting potent analgesic activity.

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

BACKGROUND: 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. METHODS: 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. RESULTS: 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. CONCLUSION: 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.

Rapid and sensitive detection of botulinum toxin type A in complex sample matrices by AlphaLISA.

Botulinum toxin A(BoNT/A) is a neurotoxin produced by the bacteria Clostridium botulinum, which can cause serious food poisoning and is recognized as a potential biological warfare agent. BoNT/A is does not degrade easily and can remain in the complex matrix for a long time. Meanwhile, the poisonous dose of botulinum toxin exceptionally low and intravenous human lethal doses estimated at 1-3 ng/kg. Therefore, sensitive and accurate detection methods suitable for testing a wide range of complex samples are urgently needed. To this end, the "amplified luminescent proximity homogeneous assay linked immunosorbent assay" (AlphaLISA) was established for the detection of BoNT/A and its detection efficacy in plasma, beverage, food, and other complex samples was evaluated. The results showed that this method can very effectively resist matrix interference. The detection time is rapid, reaching a detection limit for all samples of up to 0.1 ng/mL in only 30 min. BoNT/A can also be accurately detected in vomit samples of patients with clinical food poisoning. This study demonstrates that AlphaLISA is an effective tool for the detection of BoNT/A in complex samples and can potentially be developed for commercial use in the future.

A human monoclonal antibody to neutralize all four serotypes of dengue virus derived from patients at the convalescent phase of infection.

Dengue virus (DENV) is a prevalent mosquito-transmitted human pathogen, causing about 100 million cases of acute dengue fever and 21,000 deaths annually worldwide. Therapeutic neutralizing antibodies against dengue virus might be effective to treat severe dengue fever. Here, we showed that human monoclonal antibody (HMAb) 9C7 bound to all four intact serotypes of DENV but not to the recombinant envelope protein, suggesting HMAb 9C7 recognized a conformational epitope of the envelope protein. Taken together our results suggested that HMAb 9C7 neutralized all four serotypes of DENV in vitro and, for DENV-1, indicated activity at the pre- and post-attachment steps in the viral life cycle. HMAb 9C7 potently protected suckling mice from lethal challenge with all four serotypes of DENV. FcγRII-mediated uptake of immune complexes and antibody-dependent enhancement at low doses of the antibody were abolished by two Leu-to-Ala (9C7-LALA) mutations or deletion of nine amino acids (9C7-9del) in HMAb 9C7 Fc. Therefore, HMAb 9C7 represented a promising prophylactic and therapeutic agent against all four serotypes of DENV.

Synthesis and activity evaluation of selenazole-coupled CPI-1 irreversible bifunctional inhibitors for botulinum toxin A light chain.

A series of novel conjugates of benzoselenazole or selenazole and CPI-1 were designed, synthesized, and evaluated for inhibitory activities against the botulinum neurotoxin A (BoNT/A) light chain (LC) and BoNT/A in vivo. The results show that these compounds exhibit potent inhibitory activities to the LC with IC50 of 0.5-4.1 µM. The reaction kinetics and the mass spectra of the reaction products of LC with benzoselenazole- or selenazole- coupled CPI-1 demonstrate that the benzoselenazole group of most inhibitors is coupled to the LC of BoNT/A. These data indicate that the CPI-1 conjugates can inhibit both the active center of BoNT/A LC as well as Cys165, therefore functioning as irreversible bifunctional inhibitors. The detoxification activities in vivo show that one of the benzoselenazole-CPI-1 compounds prolongs the survival time of mice challenged by 2 × LD50 of BoNT/A. This work provides a new strategy to design potent antidotes of BoNT/A.

Generation and characterization of humanized synergistic neutralizing antibodies against SARS-CoV-2.

The emerging coronavirus, severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), is the causative agent of coronavirus disease 2019 (COVID-19), which has become a severe threat to global public health and local economies. In this study, several single-chain antibody fragments that bind to the receptor-binding domain (RBD) of the SARS-CoV-2 spike (S) protein were identified and used to construct human-mouse chimeric antibodies and humanized antibodies. These antibodies exhibited strong binding to RBD and neutralization activity towards a SARS-CoV-2 pseudovirus. Moreover, these antibodies recognize different RBD epitopes and exhibit synergistic neutralizing activity. These provide candidate to combination use or bispecific antibody to potential clinical therapy for COVID-19.

Development and evaluation of a tetravalent botulinum vaccine.

Botulinum neurotoxins (BoNTs) are the most toxic known proteins. Naturally occurring botulism in humans is caused by botulinum serotypes A, B, E, and F. Vaccination is an effective strategy to prevent botulism. In this study, a tetravalent botulinum vaccine (TBV) that can prevent serotypes A, B, E, and F was developed using the C-terminal receptor-binding domain of BoNT (Hc) as an antigen. To develop a suitable vaccine formulation, in vitro binding experiments of antigens and aluminum adjuvant in different buffers, and in vivo experiments of TBV at different antigen concentrations, were conducted. Our results showed that the optimal vaccine formulation buffer was a pH 6.0 phosphate buffer, and the suitable antigen concentration was 40 or 80 µg/ml of each antigen. A pilot-scale TBV was then prepared and evaluated for immunogenicity and stability. The results showed that TBV could elicit strong protective efficacy against each BoNT in mice, and remain effective after two years of storage at 4ºC, indicating that the preparation was stable and highly effective. Adsorption experiments also showed that the antigens could be well adsorbed by the aluminum adjuvant after 2 years of storage. Our results provide valuable experimental data supporting the development of a tetravalent botulinum vaccine, which is a promising candidate for the prevention of botulinum serotypes A, B, E, and F.

Functional EL-HN Fragment as a Potent Candidate Vaccine for the Prevention of Botulinum Neurotoxin Serotype E.

Clostridium botulinum produces botulinum neurotoxin (BoNT), which is the most toxic known protein and the causative agent of human botulism. BoNTs have similar structures and functions, comprising three functional domains: catalytic domain (L), translocation domain (HN), and receptor-binding domain (Hc). In the present study, BoNT/E was selected as a model toxin to further explore the immunological significance of each domain. The EL-HN fragment (L and HN domains of BoNT/E) retained the enzymatic activity without in vivo neurotoxicity. Extensive investigations showed EL-HN functional fragment had the highest protective efficacy and contained some functional neutralizing epitopes. Further experiments demonstrated the EL-HN provided a superior protective effect compared with the EHc or EHc and EL-HN combination. Thus, the EL-HN played an important role in immune protection against BoNT/E and could provide an excellent platform for the design of botulinum vaccines and neutralizing antibodies. The EL-HN has the potential to replace EHc or toxoid as the optimal immunogen for the botulinum vaccine.