Isolation and characterization of a neutralizing antibody specific to internalization domain of Clostridium botulinum neurotoxin type B

Botulinum neurotoxins (BoNTs), the causative agents for life-threatening human disease botulism, have been recognized as biological warfare agents. In this study, a neutralizing mouse monoclonal antibody against botulinum neurotoxin serotype B (BoNT/B), named BTBH-N1, was developed from mice immunized with BoNT/B toxoid without non-toxic components, which are generally associated with the toxin. Western blot analysis, using recombinant toxin fragments containing light (L), N-terminal half of heavy (HN) and C-terminal half of heavy chains, indicated that BTBH-N1 recognizes linear epitopes located on the HN domain. An in vivo neutralization assay with mice, was conducted to characterize the neutralization capacity of the BTBH-N1. Only 10 microg of BTBH-N1 completely neutralized 20 units (1 unit = one 50% lethal dose) of BoNT/B. Even though the Mab (up to 100 microg) failed to protect mice challenged with 100 units, it significantly prolonged the time to death in a dose dependent manner. BTBH-N1, the first neutralizing antibody against BoNT/B, could be further developed as effective biological therapeutics for preventing and treating botulism, as well as other diseases caused by BoNT/B.

Roads from vaccines to therapies

Over the past decade, we have demonstrated that various recombinant fragments of botulinum neurotoxin are highly immunogenic, stimulating notable levels of protective antibodies in mice, guinea pigs, and nonhuman primates. One of the fragments evaluated, the fragment C, is a potential next-generation vaccine candidate to replace the current pentavalent botulinum toxoid vaccine. Synthetic genes encoding the carboxyl-terminal regions (approximately 50 kDa) of toxin types A, B, C1, E, and F were expressed in Pichia pastoris, and manufacturing processes were developed for producing highly purified vaccines. These vaccines were shown to be safe, highly efficacious, stable, and amenable to high-level industrial production. Recombinant vaccines are now being produced in accordance with current Good Manufacturing Practices for use in future clinical trials. As our discovery-based program on vaccine development is diminishing, it is concurrently being replaced with a program focused on developing therapeutic interventions to botulism. Synthetic genes encoding the light chains of botulinum toxin have been expressed in Escherichia coli, and purified. These proteolytically active light chains are being used in high-throughput assays to screen for inhibitors of its catalytic activity. Other resources developed as part of the vaccine initiative, likewise, are finding utility in the quest to develop therapies for botulism.

Medical management of biological warfare and bioterrorism: place of the immunoprevention and the immunotherapy

Biological weapons are considered as mass destruction and terror weapons. Terrorism including bioterrorism is the major threat in the future conflicts for our nations. The aim of bioterrorism is more related to the potential disorganisation of the society than to the lethal effects of the agents used. The dramatic consequences cannot be discarded, especially if contagious agents such viral are used. The preparation of specific defence measures is a major challenge for our countries. The knowledge acquired from the struggle against natural infectious diseases and recent events are essential to improve behaviours to face the biological weapon threats. The defence attitude is based on the anticipation of the threat, the management of the victims, and the restoration of the operational capabilities. This global defence attitude implies six important functions: (i) alert, (ii) detection and diagnosis, (iii) availability of pharmaceutical countermeasures such as vaccine, sera and anti-infectious medicine and products, (iv) medical management of victims, (v) training and information, (vi) research and development. Passive and active immunoprevention and immuntherapy belong to the approaches discussed in the context of bioterrorism countermeasures. Further researches might be focused on these topics.

[Clinical and epidemiological analysis of patients with botulism hospitalized at the Department of Infectious Disease, Medical University of Lublin in 1990-2000]

In the paper we presented results of clinical and epidemiological analysis of 32 patients with botulism hospitalized at the Department of Infectious Diseases, Medical University of Lublin in 1990-2000. In the studied group, the relationships between botulism incidence and sex and place of residence were not significant. The incubation period ranged from 7 hours to 5 days (average 36 hrs). The clinical manifestations of botulism were typical in all cases. In one female patient the course of disease was complicated. She developed right-sided bronchopneumonia and left-sided purulent parotitis. The type B botulinum toxin occurred more frequently than the other types and the cases without serological confirmation (Chi 2 = 6.125 p = 0.01). It was found in serum of 23 patients (in 2 cases together with the type A toxin). The type E toxin was found in serum of one patient. The presence of toxin in serum was not detected in 8 patients. In all patients trivalent (types A, B and E) equine antitoxin was administered. The dose ranged from 50 to 150 cm3. Symptomatic treatment was given in all cases. Nobody required mechanical ventilation. The duration of hospitalization ranged from 5 to 28 days (average 16.6 days). A few patients complained of long-lasting blurred vision or dry mouth.

Vaccines for Category A bioterrorism diseases

Vaccination programmes are very successful as a preventive strategy against many infectious diseases which have had a major impact on human morbidity and mortality. One of these diseases, smallpox, has been eliminated as a natural infection. The recent concern about biological attacks has turned attention to the use of an immunisation programme to prevent infection with what are considered the most significant potentially harmful biowarfare pathogens. This review puts into perspective the available information on current immunisation and newer vaccine options for anthrax, smallpox, tularaemia, plague and botulism.

Investigation of repeated vaccination as a possible cause of glomerular disease in mink

The search for antigens capable of causing immune-complex-mediated glomerulonephritis continues. Modified live-virus vaccines commercially available for veterinary use are a possible source. In this study, repeated vaccination of mink with live-virus vaccines was investigated as a model for vaccine-induced glomerular injury. Three groups of 10-wk-old mink, 15 per group, were vaccinated once with 4-way vaccine against distemper, Pseudomonas aeruginosa infection, botulism and mink viral enteritis. Subsequently, all mink in each group each were vaccinated either with the 4-way vaccine, a monovalent canine distemper vaccine, or saline. Glomerular function was assessed at 2-wk intervals by determining the urinary protein:creatinine (P:C) ratio. Kidney sections taken at necropsy, 20 wk after the 1st vaccination, were examined by light and immunofluorescent microscopy for deposition of immunoglobulin and complement. There was no statistically significant difference between the treated and control groups based on average urinary P:C ratio medians. Light microscopic changes were detected in glomeruli, but Fisher's exact test showed no significant differences between any of the treatment groups. Deposition of immunoglobulin but not complement was significantly more frequent (P < 0.05) in the glomeruli of animals that received multiple injections of the 4-way vaccine than in the glomeruli of those given only the monovalent canine distemper vaccine or saline. These findings suggest that repeated vaccination may increase the glomerular deposition of immunoglobulin. Further studies are required to determine if the increased deposition of immunoglobulin contributes to the development of glomerular damage and to identify the antigens driving production of the deposited immunoglobulin.

Production and immunogenic efficacy of botulinum tetravalent (A, B, E, F) toxoid

A tetravalent (type A, B, E and F) toxoid was produced and its efficacy and safety were assessed. The toxoid preparation was inoculated from two to five times to 15 healthy adult volunteers participating in botulinum toxin research. The serum samples taken from the toxoid recipients were titrated for the antitoxin potencies by enzyme-linked immunosorbent assay (ELISA) and the neutralization test. The neutralizing and ELISA titers were too low to correlate each other. The mean neutralization titer of four recipients in 9 months after three doses of toxoid was about 0.1IU/ml for each of the four types, whereas, the one receiving five doses possessed a higher titer. Since the amount of the toxin handled in laboratory work is usually not so large, three or more doses of the present toxoid will bestow sufficient immunity on the workers participating in botulinum research. Nevertheless booster injections might be desirable to those at higher risk, handling the toxin of a high concentration.

Genetic and immunological comparison of anti-botulinum type A antibodies from immune and non-immune human phage libraries

Understanding the antibody response in botulinum intoxication is important for vaccine design and passive prophylaxis. To investigate this activity, we have studied the immune response to BoNT/A (botulinum neurotoxin serotype A) binding domain (HC) at the molecular level using phage display. The scFv antibodies were isolated from V-gene repertoires prepared from (a) human volunteer immunized with pentavalent botulinum toxoid and (b) non-immune human peripheral blood lymphocytes and spleenocytes. A large panel of serotype specific phage expressing botulinum binding scFv could be selected from both libraries. Epitope mapping of immune scFv binders towards BoNT/A HC revealed surprisingly a limited number of scFv recognizing conformational epitopes that corresponded to two distinct groups, clusters I and II. Only scFv from cluster I exhibited neutralizing activity in the mouse hemidiaphragm assay. Anti- BoNT/A HC clones derived from a non-immune library could be conveniently grouped into clusters III-XI and appeared to share no overlapping epitopes with cluster I or II. In addition they showed no neutralization of toxin at biologically significant concentrations. We therefore suggest that a vaccine based on the pentavalent botulinum toxoid directs the humoral immune response to a limited number of immunodominant epitopes exposed on the binding domain HC.

Cross-species vaccination in wild and exotic animals

These are two examples of organisms which may cause morbidity and/or mortality among numerous unrelated species. Since it is cost prohibitive in most instances to have a biological licensed for wild or exotic species, it remains a challenge to the zoo or wildlife veterinarian to determine if a licensed vaccine for other species is safe and efficacious for a particular exotic species.

Development of vaccines for prevention of botulism

Botulism is a potentially lethal disease caused by one of seven homologous neurotoxic proteins usually produced by the bacterium, Clostridium botulinum. This neuromuscular disorder occurs through an exquisite series of molecular events, ultimately ending with the arrest of acetylcholine release and hence, flaccid paralysis. The development of vaccines that protect against botulism dates back to the 1940s. Currently, a pentavalent vaccine that protects against BoNT serotypes A-E and a separate monovalent vaccine that protects against BoNT serotype F are available as Investigational New Drugs. However, due to the numerous shortcomings associated with the toxoid vaccines, several groups have efforts towards developing next-generation vaccines. Identifying a synthetic peptide that harbors a neutralizing epitope is one approach to a BoNT vaccine, while another employs the use of a Venezuelan equine encephalitis virus replicon vector to produce protective antigens in vivo against BoNT. The strategy used in our laboratory is to design synthetic genes encoding non-toxic, carboxy-terminal fragments of the C. botulinum neurotoxins (rBoNT(H(C))). The gene products are expressed in the yeast, Pichia pastoris, and purified to greater than 98% with yields typically ranging from 200-500 mg per kg of wet cells. Protective immunity to the purified products against high-level challenges of neurotoxin is elicited in mice and in non-human primates. A pre-Investigational New Drug meeting was held with the Food and Drug Administration, and the next milestone for the vaccine candidates will be clinical trials.

Immunization of ducks for type C botulism

A single subcutaneous immunization with a vaccine used for protecting ranch mink (Mustela vison) against type C botulism reduced morbidity and mortality in mallard (Anas platyrhynchos) and northern pintail (Anas acuta) ducks challenged with approximately 4.5 x 10(4) and 2.25 x 10(4) mouse lethal doses (MLD50), respectively, of botulinum toxin at 10 and 15 days post-immunization (pi). There was no significant protection at 5 days pi. Protection persisted in mallards for 90 days pi. To simulate use of vaccine as a part of treatment of sick birds in the field, mallards were exposed to toxin and, when clinical signs were evident, each bird was treated by intraperitoneal injection of type C botulinum antitoxin and one-half of the birds were immunized. Immunization had no significant effect on recovery from intoxication. At 10 days posttreatment, all birds were challenged with toxin. Clinical signs and mortality were significantly less frequent among immunized birds than among non-immunized birds after the second exposure. Immunization might be useful as part of the treatment regimen in botulism outbreaks.

Development of in vitro assays for the detection of botulinum toxins in foods

Currently the only accepted method for the detection of botulinum neurotoxin in contaminated samples is the mouse bioassay. Although highly sensitive this test has a number of drawbacks: it is expensive to perform, lacks specificity and involves the use of animals. With increasing resistance to such animal tests there is a need to replace the bioassay with a reliable in vitro test. Over the past six years it has been demonstrated that all the botulinum neurotoxins act intracellularly as highly specific zinc endoproteases, cleaving proteins involved in the control of secretion of neurotransmitters. In the work described, this enzymatic activity has been utilised in assay formats for the detection in foods of neurotoxin of the serotypes involved in food-borne outbreaks in man. These assays have been shown to have a greater sensitivity, speed and specificity than the mouse bioassay. It is envisaged that such assays will prove realistic alternatives to animal-based tests.

Comparative immunogenicity of two bivalent botulinum vaccines

OBJECTIVE

To compare the ability of a new single-dose botulinum vaccine containing a non-mineral oil adjuvant with a single dose of a conventional botulinum vaccine product to produce antibody to Clostridium botulinum types C and D in cattle in Northern Australia.

DESIGN AND PROCEDURE

One hundred and fifty Brahman steer weaners were randomly divided into two groups receiving either a single dose of CSL Bivalent Botulinum vaccine or Websters Singvac. Blood samples were collected at 0, 8 and 24 weeks and tested by antibody ELISA. The final samples were also tested by the toxin neutralisation test, to test titres of neutralising antibody.

RESULTS

Six months after inoculation, cattle vaccinated with Websters Singvac had ELISA antibody response twice that of CSL conventional product. However, this difference was only evident for neutralising antibody to type C botulinum toxin. Both products produced similar titres of type D neutralising antibody after a single dose.

CONCLUSION

Websters' Singvac produces a greater neutralising antibody response to type C botulism upon single inoculation than a conventional vaccine. The product produces an equivalent neutralising antibody response to type D.

Development of recombinant vaccines for botulinum neurotoxin

Synthetic genes encoding non-toxic, carboxyl-terminal regions (approximately 50 kDa) of botulinum neurotoxin (BoNT) serotypes A and B (referred to as fragment C or HC) were constructed and cloned into the methylotropic yeast, Pichia pastoris. Genes specifying BoNTA(HC) and BoNTB(HC) were expressed as both intracellular and secreted products. Recombinants, expressed intracellularly, yielded products with the expected molecular weight as judged by SDS PAGE and Western blot (immunoblot) analysis, while secreted products were larger due to glycosylation. Gene products were used to vaccinate mice and evaluated for their ability to elicit protective antibody titers in vivo. Mice given three intramuscular vaccinations with yeast supernatant containing glycosylated BoNTA(HC) were protected against an intraperitoneal challenge of 10(6) 50% mouse lethal doses (MLD50) of serotype A neurotoxin, a result not duplicated by its BoNTB(HC) counterpart. Vaccinating mice with cytoplasmically produced BoNTA(HC) and BoNTB(HC) protected animals from a challenge of 10(6) MLD50 of serotype A and B toxins, respectively. Because of the glycosylation encountered with secreted BoNT(HC), our efforts focused on the production and purification of products from intracellular expression.

Endogenous antibody production to botulinum toxin in an adult with intestinal colonization botulism and underlying Crohn's disease

A patient with obstruction of the terminal ileum from Crohn's disease developed complete paralysis in week 1 of hospitalization. Features initially suggested Guillain-Barre syndrome, but botulinum toxin was identified in serum and stool specimens from week 1 and type A toxin-producing Clostridium botulinum in stool specimens from weeks 3 to 19, confirming botulism due to intestinal colonization. In week 19, the inflamed small bowel was resected, and C. botulinum disappeared from the stool. In week 31, the patient was able to breath without assistance. Testing for an active immune response with neutralizing antibodies to C. botulinum at week 19 was positive; these antibodies remained at a protective level for >1 year. Intestinal colonization botulism, rare in adults, should be considered for patients with descending paralysis, especially those with a preceding alteration in small bowel function. An active immune response to botulinum toxin with production of protective antibodies has not been demonstrated previously in a patient with botulism and may have contributed to this patient's recovery.

Use of enzyme-linked immunoassays for antibody to types C and D botulinum toxins for investigations of botulism in cattle

The development of specific enzyme-linked immunosorbent assays (ELISA) for antibody to types C and D Clostridium botulinum toxins for investigation of botulism in cattle is described. Partially purified type C and D toxins were used as antigens to develop these ELISAs. Specificity of the ELISAs was evaluated on sera from 333 adult beef and dairy cattle from areas with no history or evidence of botulism in animals or water birds. The test was also evaluated on sera from 41 herds that included herds vaccinated against botulism, confirmed botulism cases and herds from areas where the disease is considered endemic. The ELISAs detected the presence of antibody to botulinum toxins in samples from vaccinated cattle and both convalescent and clinically normal animals from unvaccinated herds with outbreaks of botulism. Antibody was also found in unvaccinated animals from herds in which there had been no diagnosed botulism cases in areas where botulism was considered endemic. Sera from some unvaccinated cattle with high ELISA reactivity was shown to be protective for mice in botulinum toxin neutralisation tests. The use of these tests in investigations of botulism in cattle is discussed.

Botulism: the present status of the disease

The main form of human botulism throughout the world is the classic foodborne intoxication. Would botulism is very rare, and most of the documented cases have been found in the United States. While infant botulism remains rare throughout the world, it has become the most frequent form of the disease in the United States in recent years. On very rare occasions botulism results from growth and toxin production in humans other than infants. Botulism occurs in animals with much higher frequency. The causative organisms constitute a diverse group of clostridia, resulting in nomenclature problems. Human botulism is largely limited to toxin types A, B, and E, while type C botulism predominates in avian and nonhuman mammalian species. The diagnosis of botulism is made on the basis of the neurologic signs and symptoms that it causes in humans and animals. The diagnosis is confirmed by tests that identify the toxin and toxigenic organisms in patient and food specimens. Treatment includes supportive intensive care and use of therapeutic antitoxin.

The mechanism of botulism

Botulism is induced by botulinum toxin and the mechanism of the disease is unknown. In another study, a fatal autoimmune disease was produced in animals by immunization with a fraction of choline acetyltransferase. When these two syndromes are compared, numerous similarities are observed. It is postulated that botulism toxin acts as an initiator for the autoimmune disease by catalyzing in vivo the formation of the pathogenic fraction of choline acetyltransferase.

Antimuscle antibody in infantile botulism

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Serum antibody response to Clostridium botulinum toxin in infant botulism

A serum antibody response has not been previously demonstrated after infection with Clostridium botulinum. We developed an enzyme immunoassay for measuring serum antibody to C. botulinum toxins A, B, and E. This assay system detected a specific immunoglobulin G and immunoglobulin M antibody response to C. botulinum toxin in two patients with infant botulism.

Experimental toxicoinfection in infant mice challenged with spores of Clostridium botulinum type E

Conventionally raised suckling mice were given 10(7) spores of a strain of Clostridium botulinum type E. Most but not all infant mice aged 8 through 19 days at the time of administration died after developing symptoms typical of botulism. However, none of the infant mice challenged with the spores at dose levels lower than 10(6) spores/mouse developed illness.

Susceptibility to enteric botulinum colonization of antibiotic-treated adult mice

The relationship between the indigenous intestinal microflora of adults and their resistance to the enteric botulinum infection of infant botulism was studied. Orogastric challenges of 10(5) type A Clostridium botulinum spores were given to adult mice whose gut flora had been altered by feedings of a mixture of erythromycin and kanamycin sulfate. From 80 to 100% of mice became infected when challenged 15 to 60 h after antibiotic administration. The mean infective dose of 2 X 10(4) spores per mouse for challenges given 23 h after antibiotic administration contrasted with the failure of 10(6) spores to infect control mice. Botulinum-colonized mice remained asymptomatic, although colonization lasted up to 5 days, and total botulinum toxin in the gut on days 3 and 4 postchallenge averaged 3,400 and 2,200 mouse intraperitoneal mean lethal doses. The mean infective dose for inocula placed in the colon of antibiotic-treated mice was 10(3) spores per mouse, and C. botulinum multiplied in the cecum as well as in the colon.