Botulinum toxin type A and other botulinum toxin serotypes: a comparative review of biochemical and pharmacological actions

Botulinum toxin type A is an important therapeutic agent for the treatment of movement and other disorders. As the clinical uses of botulinum toxin type A expand, it is increasingly important to understand the biochemical and pharmacological actions of this toxin, as well as those of other botulinum toxin serotypes (B-G). Botulinum neurotoxin serotypes exhibit differences in neurotoxin complex protein size, percentage of neurotoxin in the activated or nicked form, intracellular protein target, and potency. These properties differ even between preparations that contain the same botulinum toxin serotype due to variations in product formulations. As demonstrated in preclinical and clinical studies, these differences result in a unique combination of efficacy, duration of action, safety, and antigenic potential for each botulinum neurotoxin preparation.

Pharmacology and immunology of botulinum toxin serotypes

Botulinum toxin preparations can provide patients with a therapeutic modality that may improve both their medical condition and quality of life. The mechanism of action of the various botulinum toxin preparations and serotypes is similar: they all block neurotransmitter release. The majority of clinical conditions treated are based upon the targeted temporary chemodenervation of the selected organ. The antinociceptive effects of botulinum toxin type A (BTX-A), based on preclinical studies and clinical experiences in treating movement disorders and other painful conditions, will also be reviewed to illustrate how this compound may act as it alleviates the discomfort associated with various conditions. Chronic therapies with preparations with the lowest amount of neurotoxin protein provide the best chance for long-term therapy by minimizing the potential of the patient to form neutralizing antibodies. Differences in formulations or serotypes impart unique efficacy and safety profiles and thus does not support a simple dose ratio conversion between products.

Epitope mapping of neutralizing botulinum neurotoxin A antibodies by phage display

Single-chain antibodies neutralize activity and bind nonoverlapping epitopes of botulinum A neurotoxin. Two phage display epitope libraries were constructed from the 1.3 kb of binding domain cDNA. The minimal epitopes selected against the single-chain Fv-Fc antibodies correspond to conformational epitopes with amino acid residues 1115 to 1223 (S25), 1131 to 1264 (3D12), and 889 to 1294 (C25).

Candidate vaccine against botulinum neurotoxin serotype A derived from a Venezuelan equine encephalitis virus vector system

A candidate vaccine against botulinum neurotoxin serotype A (BoNT/A) was developed by using a Venezuelan equine encephalitis (VEE) virus replicon vector. This vaccine vector is composed of a self-replicating RNA containing all of the VEE nonstructural genes and cis-acting elements and also a heterologous immunogen gene placed downstream of the subgenomic 26S promoter in place of the viral structural genes. In this study, the nontoxic 50-kDa carboxy-terminal fragment (H(C)) of the BoNT/A heavy chain was cloned into the replicon vector (H(C)-replicon). Cotransfection of BHK cells in vitro with the H(C)-replicon and two helper RNA molecules, the latter encoding all of the VEE structural proteins, resulted in the assembly and release of propagation-deficient, H(C) VEE replicon particles (H(C)-VRP). Cells infected with H(C)-VRP efficiently expressed this protein when analyzed by either immunofluorescence or by Western blot. To evaluate the immunogenicity of H(C)-VRP, mice were vaccinated with various doses of H(C)-VRP at different intervals. Mice inoculated subcutaneously with H(C)-VRP were protected from an intraperitoneal challenge of up to 100,000 50% lethal dose units of BoNT/A. Protection correlated directly with serum enzyme-linked immunosorbent assay titers to BoNT/A. The duration of the immunity achieved was tested at 6 months and at 1 year postvaccination, and mice challenged at these times remained refractory to challenge with BoNT/A.

Characterization of neutralizing antibodies and identification of neutralizing epitope mimics on the Clostridium botulinum neurotoxin type A

Clostridium botulinum neurotoxin type A (BTx-A) is known to inhibit the release of acetylcholine at the neuromuscular junctions and synapses and to cause neuroparalysis and death. In this study, we have identified two monoclonal antibodies, BT57-1 and BT150-3, which protect ICR mice against lethal doses of BTx-A challenge. The neutralizing activities for BT57-1 and BT150-3 were 10(3) and 10(4) times the 50% lethal dose, respectively. Using immunoblotting analysis, BT57-1 was recognized as a light chain and BT150-3 was recognized as a heavy chain of BTx-A. Also, applying the phage display method, we investigated the antibodies' neutralizing B-cell epitopes. These immunopositive phage clones displayed consensus motifs, Asp-Pro-Leu for BT57-1 and Cys-X-Asp-Cys for BT150. The synthetic peptide P4M (KGTFDPLQEPRT) corresponded to the phage-displayed peptide selected by BT57-1 and was able to bind the antibodies specifically. This peptide was also shown by competitive inhibition assay to be able to inhibit phage clone binding to BT57-1. Aspartic acid (D(5)) in P4M was crucial to the binding of P4M to BT57-1, since its binding activity dramatically decreased when it was changed to lysine (K(5)). Finally, immunizing mice with the selected phage clones elicited a specific humoral response against BTx-A. These results suggest that phage-displayed random-peptide libraries are useful in identifying the neutralizing epitopes of monoclonal antibodies. In the future, the identification of the neutralizing epitopes of BTx-A may provide important information for the identification of the BTx-A receptor and the design of a BTx-A vaccine.

Botulinum toxin type A: history and current cosmetic use in the upper face

This article reviews the cosmetic use of botulinum toxin in upper face from both the historic and clinical viewpoints. The published literature and our current experience are outlined. Botulinum toxin type A in the upper face has become an extremely poplular cosmetic procedure and is outstandingly safe.

Complications and adverse reactions with the use of botulinum toxin

Botulinum toxins are the causative agents of the severe food-borne illness botulism. With lethal doses approximating 10(-9) g/kg body weight, these neurotoxins represent some of the most toxic naturally occurring substances. Regardless, botulinum toxin is considered a safe therapy for inappropriate muscle spasms with adverse effects being typically self-limited. This article deals with some of the complications that have occurred with these treatments. The greatest concern with the use of BOTOX is probably the formation of blocking antibodies leading to nonresponse of subsequent treatment. Prevalence of resistance is less than 5%. Most complications associated with its aesthetic use are few and anecdotal. Nevertheless, the common problems and pitfalls associated with aesthetic treatment of the various areas of the face and neck with botulinum toxin are discussed. Also included are recommendations as to how to avoid these very undesirable, yet common, problems.

Detection of Clostridium botulinum neurotoxin type A using immuno-PCR

AIMS

An immuno-polymerase chain reaction (immuno-PCR) has been developed for the sensitive detection of antigens, which greatly extends the detection limits of immunoassays. In the current study, the method was applied to the detection of Clostridium botulinum neurotoxin type A (BTx-A).

METHODS AND RESULTS

Anti-BTx-A antibody-DNA conjugates were synthesized using a heterobifunctional cross-linker reagent to covalently link the reporter DNA and the antibodies. The antibody-DNA conjugates with antigens were amplified by PCR, and dose-dependent relationships for each analyte were demonstrated. Detection limits of immuno-PCR for BTx-A (3.33 x 10(-17) mol) exceeded the conventional enzyme-linked immunosorbent assay (3.33 x 10(-14) mol) by a 1000-fold enhancement in detection sensitivity.

CONCLUSION

Detection of BTx-A antigens by immuno-PCR demonstrated 100% sensitivity and 100% specificity in 100-fold magnitude below the detection limit of ELISA.

SIGNIFICANCE AND IMPACT OF THE STUDY

It is concluded that the immuno-PCR method could be used to detect a very low level of BTx-A for clinical diagnosis.

Anomalous enhancement of botulinum toxin type A neurotoxicity in the presence of antitoxin

The neutralization of botulinum toxin serotype A with polyclonal equine antitoxin was studied in isolated mouse hemidiaphragms and compared to the same action in live mice. The biological activity of the toxin in the isolated muscle could be markedly reduced with excess antitoxin, estimated as 3:1 molar ratios of IgG Ab:toxin or better. Toxin neutralization in vivo required higher ratios of Ab:toxin, ranging from 30:1 at high toxin doses and increasing to 100:1 at 10xLD50 toxin. At equimolar Ab to toxin ratios in the isolated muscle, the biological activity of the toxin underwent a statistically significant increase. This paradoxical effect of the polyclonal antisera was serotype selective and independent of the presence or absence of hemagglutinin in the toxin. The enhancement of toxin activity was subsequently localized to occupancy of one of four epitopes on the toxin using monoclonal antibodies to mimic the effect of the antitoxin. The enhancement of toxin activity suggests that botulinum toxin may undergo a conformational change upon binding antibodies to certain domains. This phenomenon could contribute to the observed concentration dependent changes in neutralization efficacy with antitoxin in vivo.

[Treatment of focal dystonia with botulinum toxin A]

Local injections with Botulinum toxin A (BtxA) are safe and effective in the treatment of focal dystonia. In cervical dystonia and blepharospasm, BtxA injections have become the treatment of choice. However, good results have also been reported with oromandibular dystonia, spasmodic dysphonia and writer's cramp. In cervical dystonia, muscles for injection are selected by clinical presentation or in complex forms with EMG guidance. Several studies have shown that 500 units Dysport are safe and effective in the treatment of cervical dystonia. In blepharospasm, injections are performed in the periorbital part of the orbicularis oculi muscle with good results for 12-14 weeks. The most frequently employed starting dose is 120 units Dysport per eye, divided in three periorbital injection sites. In case of levator inhibition, the pretarsal part of the orbicularis oculi muscle should be injected in a lower dose. EMG guidance is not necessary. By contrast, BtxA treatment of spasmodic dysphonia and writer's cramp require EMG-guided injections in order to avoid side-effects. Dose recommendations for the various types of dystonia are given in the text. In up to 5% of patients with dystonia, the development of neutralising antibodies is reported following repetitive injections with BtxA. Patients with antibodies had a shorter interval between injections, more "boosters", a higher dose per 3-month interval, and a higher total dose injected. In case of neutralizing antibodies against the A toxin, the treatment with Botulinum toxin B (Neurobloc) is a possible alternative.

Immunological properties of Hn-33 purified from type A Clostridium botulinum

Type A botulinum neurotoxin is produced along with 6-7 neurotoxin associated proteins to form a complex in addition to the neurotoxin. Immunological reactivity of type A botulinum complex and purified hemagglutinin (Fu et al., 1998) to polyclonal antibody raised against the complex have been investigated using ELISA. In competitive ELISA, 50% inhibition of the binding of IgG antibody against complex A is observed at 78 ng/ml of complex and hemagglutinin-33, suggesting that the hemagglutinin-33 accounts for most of the immunogenic response of the complex. Considering the fact that the complex consists of a group of proteins with a cumulative molecular weight of 900 kDa, hemagglutinin-33 may be one of the major immunoreactive proteins present in the type A neurotoxin complex.

Botulinum toxin antibody testing: comparison between the mouse protection assay and the mouse lethality assay

Conventionally, the standard test for detection of antibodies against botulinum toxin (BT-A) has been the mouse lethality assay (MLA). Because this test has a number of disadvantages, a novel mouse protection assay (MPA) was recently introduced. We sought to compare the results of both tests. Forty-three samples from 38 patients with cervical dystonia and complete or partial subjective BT-A therapy failure underwent simultaneous MPA and MLA testing. Twenty-seven samples showed concordant results in both tests. Eleven of them were MPA- and MLA-positive and 16 MPA- and MLA-negative, resulting in a significant association of the dichotomous test results (Fisher exact test, p <0.01). Sixteen samples showed discordant results. All of those were MPA-positive and MLA-negative. This excess of MPA-positive results was also significant (Wilcoxon signed-rank test, p <0.001). Of the patients with MPA-positive samples, 62% had complete and 38% had partial therapy failure. Of the patients with MLA-positive samples, 90% had complete and 10% had partial therapy failure. MPA and MLA results show significant association. Statistical analysis and predominance of partial therapy failure in MPA-positive patients demonstrate higher sensitivity of MPA. With its methodologic advantages, its test parameter being more relevant to BT-A therapy, and its higher sensitivity, the MPA appears to be superior to the MLA.

Production and purification of the heavy chain fragment C of botulinum neurotoxin, serotype A, expressed in the methylotrophic yeast Pichia pastoris

A recombinant H(C) fragment of botulinum neurotoxin, serotype A (rBoNTA(H(C))), has been successfully expressed in a Mut(+) strain of the methylotrophic yeast Pichia pastoris for use as an antigen in a proposed human vaccine. Fermentation employed glycerol batch, glycerol-fed batch, and methanol-fed batch phases to achieve high cell density. Induction times were short to maximize rBoNTA(H(C)) production while minimizing proteolytic degradation. Concentration of rBoNTA(H(C)) in yeast cell lysates was generally 1-2% of the total protein based on ELISA analysis. The H(C) fragment was purified from cell lysates using a multistep ion-exchange (IEC) chromatographic process, including SP, Q, and HS resins. The zwitterionic detergent Chaps was included in the buffer system to combat possible interactions, such as protein-protein or protein-DNA interactions. Following IEC was a hydrophobic interaction chromatography (HIC) polishing step, using phenyl resin. The H(C) fragment was purified to >95% purity with yields up to 450 mg/kg cells based on ELISA and Bradford protein assay. The purified H(C) fragment of serotype A was stable, elicited an immune response in mice, and was protected upon challenge with native botulinum type A neurotoxin.

Vaccination of mice with DNA encoding a large fragment of botulinum neurotoxin serotype A

The potential utility of using DNA vaccination to protect mice from the microbial neurotoxin, botulinum toxin type A, was evaluated. A synthetically derived gene encoding a carboxyl-terminal 50 kDa fragment of the toxin was placed in two sites in the DNA inoculation vehicle pCMVint-BL (Vical), one predicted to lead to MHC I processing (pJT-1 construct) and the other to direct MHC II processing (pJT-2 construct). Mice were then inoculated at 3 week intervals with these two constructs and with the vehicle alone and evaluated for protection from botulinum toxin by i.p. challenges with various toxin doses. Protection was observed at about week 10-11 from toxin doses of 25-100 LD(50). Only animals inoculated with pJT-2 exhibited protection. In dose-response experiments, 50 micrograms of DNA was the minimal dose required to elicit a protective response against serotype A, while protection against serotypes B or E was not obtained. With standard ELISA testing, a relationship was observed between the level of protection and the level of ELISA reactive antibody. Our results support the concept that DNA vaccination is a viable methodology to use in cases where protection from toxins is the goal.

Alternatives to the use of animals for bacterial toxins and antitoxins

The potency of several novel botulinum toxin-derived biological therapeutic products now in routine medical use is determined exclusively by in vivo methods. In addition, large numbers of animals continue to be used for the potency and safety testing of therapeutic antitoxins and toxoid vaccines. There is thus an increasing need to develop acceptable alternative assays for toxicity testing of clostridia neurotoxins which could be applied to different toxin derived therapeutic agents, including vaccines. Scientific advances in the understanding of the mode of action of clostridial neurotoxins have now provided the basis for improving conventional testing procedures.

Sudomotor testing discriminates between subjects with and without antibodies against botulinum toxin A--a preliminary observation

With an increasing number of patients being treated with botulinum toxin A (BTX A), the incidence of neutralizing anti-BTX antibodies (ABA) is rising. Because BTX A is known to inhibit sweating, sudometry seems to be a promising tool to test the efficacy of BTX A. We injected BTX A subcutaneously in normal control subjects and four patients with spasmodic torticollis, two responders and two nonresponders with proven ABA. Sweating was visualized using iodine starch staining and quantified used capacitance hygrometry. BTX A inhibited sweating completely at the injection site in both control subjects and all responders without evidence for ABA. However, continued sweating was recorded when the nonresponders with proven ABA were tested. We conclude that sudomotor testing is able to discriminate between subjects with and without clinically important ABA.

DNA vaccination using the fragment C of botulinum neurotoxin type A provided protective immunity in mice

Botulinum neurotoxin (BoNT) is one of the most toxic substances known to produce severe neuromuscular paralysis. The currently used vaccine is prepared mainly from biohazardous toxins. Thus, we studied an alternative method and demonstrated that DNA immunization provided sufficient protection against botulism in a murine model. A plasmid of pBoNT/A-Hc, which encodes the fragment C gene of type A botulinum neurotoxin, was constructed and fused with an Igkappa leader sequence under the control of a human cytomegalovirus promoter. After 10 cycles of DNA inoculation with this plasmid, mice survived lethal doses of type A botulinum neurotoxin challenges. Immunized mice also elicited cross-protection to the challenges of type E botulinum neurotoxin. This is the first study demonstrating the potential use of DNA vaccination for botulinum neurotoxins.

Aerobic growth and toxigenicity of Clostridium botulinum types A and B

Clostridium botulinum types A and B cultured in association with avian skin flora, had similar growth patterns under both aerobic and anaerobic conditions. The selective "C. botulinum isolation" (CBI) medium was found to be especially useful for the recovery and quantitation of small numbers of type A or type B organisms from the mixed cultures. Enzyme immunoassay in conjunction with conventional mouse bioassay provided a practical means for the quantitation of toxigenicity of C. botulinum in avian skin cultures. The amount of toxin produced by type A was always higher than that produced by type B strains. The aerobically incubated type A or type B cultures appeared to be less toxigenic than cultures incubated anaerobically.

Comparison of mouse bioassay and immunoprecipitation assay for botulinum toxin antibodies

OBJECTIVE

To compare a recently developed immunoprecipitation assay (IPA) to the mouse protection bioassay (MPB), currently considered the "gold standard", for detecting antibodies against botulinum toxin A (BTX-A) and to correlate these assay results with clinical responses to BTX-A injections.

METHODS

MPB and IPA assays were performed on serum samples from 83 patients (38 non-responders, 45 responders) who received BTX-A injections. Six non-responders had serum tested on two separate occasions. Some patients also received a "test" injection into either the right eyebrow (n=29) or right frontalis (n=19).

RESULTS

All patients antibody positive (Ab+) by MPB were also Ab+ by IPA, whereas an additional 19 patients (17 with reduced or no clinical response) who were MPB Ab- were Ab+, with low titres, by IPA. Two of these 19 patients (non-responders) were initially MPB Ab- but later became MPB Ab+. Similar to previous studies, the sensitivity for the MPB was low; 50% for clinical, 38% for eyebrow, and 30% for frontalis responses whereas the IPA sensitivity was much higher at 84% for clinical (p<0.001), 77% for eyebrow (p=0.111, NS) and 90% for frontalis responses (p<0.02). The IPA specificity was 89% for clinical, 81% for eyebrow, and 89% for frontalis responses, whereas the MPB specificity was 100% for all three response types, which were all non-significant differences.

CONCLUSIONS

Both assays had high specificity although the sensitivity of the IPA was higher than the MPB. In addition, the IPA seems to display positivity earlier than the MPB, and as such, it may prognosticate future non-responsiveness. Eyebrow and frontalis "test" injections correlated well with clinical and immunological results and are useful in the assessment of BTX non-responders.

Depletion of neutralising antibodies resensitises a secondary non-responder to botulinum A neurotoxin

The objective was to evaluate whether removal of neutralising antibodies potentially resensitises a secondary non-responder to botulinum neurotoxin A (BoNT/A). Neutralising antibodies directed against BoNT/A are produced during long term treatment with BoNT/A-hemagglutinin complex in up to 10% of patients with cervical dystonia. These patients become secondary non-responders. Other serotypes of BoNT are not yet generally available and may also bear the risk of inducing antibody formation. Plasma exchange (PE) (one treatment cycle) and immunoadsorption on a protein A column (IA-PA; three treatment cycles) was employed over 15 months to remove neutralising antibodies from a severely disabled secondary non-responder with cervical dystonia. After plasma exchange or IA-PA, BoNT/A was reinjected. Antibodies were measured with a sensitive functional toxin neutralising test. Repeated use of plasma exchange and IA-PA depleted neutralising antibodies to below the detection limit and subsequently allowed successful BoNT/A injection into dystonic muscles. No serious side effects were found related to the depletion of IgG. In conclusion PE or IA-PA performed before BoNT/A readministration may provide an alternative strategy in treating selected secondary non-responders who are severely disabled.

Identifying the principal protective antigenic determinants of type A botulinum neurotoxin

The neurotoxins from Clostridium botulinum (BoNT serotypes A-G) exert their lethal effect by preventing the release of acetylcholine at the neuromuscular junction. As with tetanus toxin, immunization with a non-toxic fragment, the 50 kDa C-terminal portion of BoNT/A (Hc; residues 861-1296), protects mice against lethal challenges with the intact toxin. To locate the neutralizing epitopes, several protective monoclonal antibodies (mAbs) against BoNT/A-Hc were isolated and cloned. Specific binding of the mAbs to BoNT/A-Hc was demonstrated by surface plasmon resonance, with Kas in the range of 10(-10) to 10(-11) M. These antibodies recognized a genetically engineered polypeptide (1150-1289) that was previously shown to induce protective immunity. Prior to the determination of the X-ray crystal structure of the tetanus neurotoxin Hc fragment, molecular modelling studies indicated that it contained two highly solvent-exposed loops. Based on these predictions, two 25-mer Hc-peptides corresponding to these two regions were synthesized and were demonstrated to bind the neutralizing mAbs. Mice immunized with the Hc-peptides had high levels of antibodies that recognized BoNT/A-Hc. However, immunizations with only one of the Hc peptides protected when mice were challenged with BoNT/A. On the basis of these analyses, it should be possible to develop small peptides that could be useful in the design of future vaccines against these neurotoxins.

A radioimmuno-precipitation assay for antibodies to botulinum A

We quantified antibodies to botulinum A (anti-BTx) by immunoprecipitation of 125I-BTx. We tested seven bioassay-positive sera and 68 coded samples, including 18 from patients who had ceased to respond to BTx treatment. Compared with values from healthy control subjects and 42 neurologic control subjects, all bioassay-positive sera were positive (range, 258 to 2,809 pM) and 49 of 50 patients who continued to respond to BTx were negative (<130 pM). This simple, specific, sensitive, and quantitative assay should prove helpful in the investigation of BTx resistance.

Negative chronotropic effect of botulinum toxin on neonatal rat cardiac myocytes

We demonstrated that botulinum neurotoxin attenuated the spontaneous beating rate of cultured cardiac myocytes. Primary cultured cardiac myocytes were prepared from the ventricles of neonatal Wistar rats (1-3 days old). On 7 days after cell seeding, botulinum toxin type A incorporated into liposomes was added to the culture medium. At a final concentration of 5.0 micrograms/ml, botulinum toxin markedly attenuated the beating rate of cardiac myocytes within 2-4 hours. These results demonstrated the effect of SNARE-complex proteins on the spontaneous beating of cardiac myocytes.

Antibodies and T cells against synthetic peptides of the C-terminal domain (Hc) of botulinum neurotoxin type A and their cross-reaction with Hc

Seventeen peptides containing T cell and/or antibody (Ab) epitopes previously localized on Hc of botulinum neurotoxin type A were used in SJL and BALB/c mice as immunogens either individually or as an equimolar mixture of groups that contained epitopes of T cells, Abs or both, to determine their abilities to generate T cells and/or Abs that recognize intact Hc. In SJL, peptide 897-915 which included both T cell and Ab epitopes, elicited Abs that cross-reacted very strongly with Hc. In BALB/c, peptides 869-887, 883-901, 981-999 and 1275-1296 which contained Ab epitopes generated Abs that cross-reacted strongly with Hc. A mixture of peptides that contained T cell and Ab epitopes was effective in both strains in eliciting T cells and Abs that cross-reacted with Hc. This mixture form gave a quicker rise (after two injections) in cross-reactive (with Hc) Ab titer as compared to other peptide mixtures or the individual peptides, and sustained in BALB/c a high Ab titer upon further booster injections. Some of the regions that elicited crossreactive immunity to Hc have sequence similarity to other clostridial toxins, suggesting that one or more of these synthetic peptides might provide cross-protection against those toxins.

Variability of the immunologic and clinical response in dystonic patients immunoresistant to botulinum toxin injections

Immunoresistance (Ab+) to botulinum toxin type A (BTX-A) has been a serious concern since the introduction of BTX-A in the treatment of dystonia and other disorders associated with abnormal muscle contractions. We studied seven patients who developed Ab+ and later reverted to antibody-negative (Ab-) status. These seven patients, six women (mean age, 56 years; range, 41-80 years), with an average duration of dystonia for all patients of 197 months (range, 84-360 months), received a total mean cumulative dose of 1659 units (U) (range, 810-1975 U), with an average dose of 207 U per visit. All of these patients became unresponsive to BTX-A treatment and became Ab+ as determined by mouse bioassay. Their response to BTX-A after they reverted to Ab- was analyzed. The average latency between the initial BTX-A treatment and development of Ab+ was 27 months (range, 1543 months). The average duration between the detection of Ab+ status and subsequent reversal to Ab- status was 30 months (range, 10-78 months). Six of these Ab- patients were reinjected with BTX-A, and all six benefited from repeat injections comparable with their earlier response. Three patients lost their clinical response to subsequent injections and were found to be again Ab+. Two of the five patients who became immunoresistant to BTX-A received botulinum toxin type F (BTX-F) injections and one patient received a single session of BTX-B with improvement in their symptoms. In conclusion, this unique group of patients who were Ab+ and became Ab- responded favorably to repeat BTX-A injections, but some lost the benefit with subsequent injections. These observations suggest that the anamnestic immunologic response to BTX-A can wane, but can be reactivated by repeat BTX-A treatments. The presence of antibodies did not interfere with the response to BTX-F or BTX-B injections, thus confirming the antigenic specificity of various BTX serotypes.

Immune recognition of botulinum neurotoxin type A: regions recognized by T cells and antibodies against the protective H(C) fragment (residues 855-1296) of the toxin

Botulism toxicity is caused by botulinum neurotoxins (BoNTs), a group of protein neurotoxins produced by Clostridium botulinum. Recent studies have shown that immunization with a C-terminal fragment [H(C), residues 855-1296] of BoNT type A (BoNT/A) affords excellent protection against BoNT/A toxicity. The present work was carried out in order to map the molecular and cellular immunological recognition of H(C). We have previously described the synthesis of 31 overlapping peptides encompassing the entire H(C)-fragment of BoNT/A. These peptides were employed in this study to localize the continuous regions recognized by T cells and by antibodies (Abs) generated in two mouse strains against H(C). T cells from SJL that had been primed with H(C) gave a strong proliferative response to challenge in vitro with each of the six peptides spanning residues 897-985 and a lower response to peptide 1051- 1069. While H(C)-primed T cells of BALB/c recognized three regions residing within residues 939-957, 1009-1027 and 1135-1153 (strong). Recognition regions by Abs in SJL or BALB/c anti-H(C) antisera essentially overlapped. However, the level of Abs bound to each region differed between the two strains. These common or similar recognition regions by the two strains were: 855-915 (SJL) or 855-901 (BALB/c); 939-957; 967-1013 (BALB/c) or 981-1013 (SJL); 1051-1069; 1079-1111 (BALB/c) or 1093-1125 (SJL); 1177-1195; and 1275-1296. In addition, BALB/c recognized region 1135-1153. Some of these regions show considerable sequence similarity in BoNT types B and E and, therefore, H(C) of these two BoNTs might offer protection against the correlate clostridial toxins.

Molecular characterization of murine humoral immune response to botulinum neurotoxin type A binding domain as assessed by using phage antibody libraries

To produce antibodies capable of neutralizing botulinum neurotoxin type A (BoNT/A), the murine humoral immune response to BoNT/A binding domain (H(C)) was characterized at the molecular level by using phage antibody libraries. Mice were immunized with BoNT/A H(C), the spleens were harvested, and single-chain Fv (scFv) phage antibody libraries were constructed from the immunoglobulin heavy and light chain variable region genes. Phage expressing BoNT/A binding scFv were isolated by selection on immobilized BoNT/A and BoNT/A H(C). Twenty-eight unique BoNT/A H(C) binding scFv were identified by enzyme-linked immunosorbent assay and DNA sequencing. Epitope mapping using surface plasmon resonance in a BIAcore revealed that the 28 scFv bound to only 4 nonoverlapping epitopes with equilibrium constants (Kd) ranging from 7.3 x 10(-8) to 1.1 x 10(-9) M. In a mouse hemidiaphragm assay, scFv binding epitopes 1 and 2 significantly prolonged the time to neuroparalysis, 1.5- and 2.7-fold, respectively, compared to toxin control. scFv binding to epitopes 3 and 4 showed no protection against neuroparalysis. A combination of scFv binding epitopes 1 and 2 had an additive effect on time to neuroparalysis, which increased to 3.9-fold compared to the control. The results suggest that there are two "productive" receptor binding sites on H(C) which lead to toxin internalization and toxicity. Blockade of these two epitopes with monoclonal antibodies may provide effective immunoprophylaxis or therapy against BoNT/A intoxication.

Botulinum A toxin therapy: neutralizing and nonneutralizing antibodies--therapeutic consequences

Although muscle-relaxant doses of botulinum A toxin (BoNT/A) are generally lower than doses stimulating the immune system, specific antibodies are raised in a substantial number of patients. As a rule, this necessitates the termination of treatment. Therefore, a reliable determination of specific anti-BoNT/A antibodies is helpful and we introduced, for this purpose, a novel in vitro toxin-neutralizing assay based on a nerve-muscle preparation. We measured the antibody titers in four groups of subjects: Group 1 comprised 75 randomly selected patients of a total of 295 who responded to treatment with Dysport in our local clinic. Five patients, in group 2, were nonresponders. Group 3 consisted of 32 untreated volunteers and group 4 of 8 subjects immunized with a toxoid more than 10 years ago. Two of the responders had marginal titers of neutralizing antibodies, while they were present in all nonresponders. The sera of all responders were also tested for nonneutralizing antibodies by ELISA. Their occurrence, however, was of no consequence to the therapeutic success. The blood samples of volunteers were free from specific antibodies, whereas antibodies persisted in the immunized subjects for longer than a decade. Patients from various clinics who had been treated unsuccessfully with the toxin-14 patients had received BOTOX, 7 had been treated with Dysport, and 7 with both products-all had neutralizing antibodies. Whether there was an antibody response depended on the amount of toxin administered. We believe, however, the effective toxin dose can be reduced by so much as to make antibody production highly improbable.

Localization of the regions on the C-terminal domain of the heavy chain of botulinum A recognized by T lymphocytes and by antibodies after immunization of mice with pentavalent toxoid

We have mapped the regions recognized by T and/or B cells (Abs) on the C-terminal domain (Hc) of the heavy chain of botulinum neurotoxin serotype A (BoNT/A) after immunization of two inbred mouse strains with pentavalent toxoid (BoNTs A, B, C, D and E). Using a set of synthetic overlapping peptides, encompassing the entire Hc domain (residues 855-1296), we demonstrated that T cells of Balb/c (H-2d) mice, primed with one injection of toxoid, recognized two major regions within residues 897-915 and 939-957. After multiple inoculations with toxoid, T cells of Balb/c expanded their recognition ability and responded very well to challenge with peptide 1261-1279 and moderately to stimulation with peptide 1149-1167. Unlike Balb/c T cells, those of toxoid-primed SJL (H-2s) mice exhibited a more complex profile and responded to challenge with a large number of overlapping peptides. After one toxoid injection, however, three peptides, 897-915, 939-957/953-971 overlap and 1051-1069, were the most potent T cells stimulators. After three toxoid injections, peptides 897-915 and 1051-1069 remained immunodominant while the third region was shifted upstream to 925-943/939-957 overlap. The immunodominant epitope within peptide 897-915 was recognized exclusively by T cells, since no Abs were detected against this region. The Ab binding profiles of the two mouse strains were quite similar, showing only small quantitative differences. Both, Balb/c and SJL anti-toxoid Abs displayed strong binding mainly to peptide 1177-1195, followed by peptides 869-887/883-901 overlap and 1275-1296. In addition, a significant amount of Balb/c anti-toxoid Abs was bound to peptide 1135-1153. Unlike Balb/c Abs, that interacted weakly with peptides 995-1013 and 1051-1069, the anti-toxoid Abs of SJL mice exhibited strong binding toward both peptides. The results showed that, in a given strain, the regions recognized by anti-toxoid Abs and T cells may coincide or may be uniquely B or T cell determinants.

Antibody mapping to domains of botulinum neurotoxin serotype A in the complexed and uncomplexed forms

The domain organization of the botulinum neurotoxin serotype A was studied by using antibody mapping of 44 monoclonal single-chain variable fragments. The analysis was carried out on (i) the individual domains of botulinum neurotoxin holotoxin (binding, translocation, and catalytic), (ii) botulinum neurotoxin holotoxin, (iii) the botulinum neurotoxin holotoxin in complex with the nontoxic portion, and (iv) botulinum neurotoxin holotoxin and nontoxic portion of the complex recombined in vitro. All 44 antibodies mapped to individual domains of botulinum neurotoxin. Forty of the 44 single-chain variable fragments bound the botulinum neurotoxin holotoxin relative to the isolated domains, suggesting that 4 epitopes are covered when the individual domains are in the holotoxin form. Only 20 of the antibodies showed a positive reaction to the toxin while in complex with the nontoxic portion. All of the covered epitopes were mapped to the binding domain of botulinum neurotoxin, which suggested that the binding domain is in direct contact with the nontoxic portion in the complex. Based on the antibody mapping to the different domains of the botulinum neurotoxin holotoxin and the entire complex, a model of the botulinum neurotoxin complex is proposed.

Sensitive assay for measurement of antibodies to Clostridium botulinum neurotoxins A, B, and E: use of hapten-labeled-antibody elution to isolate specific complexes

The measurement of chicken and human antibodies to Clostridium botulinum neurotoxins A, B, and E was accomplished by affinity isolation of complexes containing these antibodies. By this approach, a mixture of toxin with the test antibody, fluoresceinated antibody, and enzyme (Russell's viper venom factor X activator)-labeled antibody is allowed to form a complex in solution phase. This complex is then bound to a matrix containing antifluorescein antibody. All components not bound to the matrix are washed off, and the complex is isolated intact by elution with fluorescein, which competes with the complex for binding to the antifluorescein matrix. The eluted complex is then bound to a matrix which specifically binds the test antibody (anti-chicken immunoglobulin Y [IgY] or anti-human IgG), and the bound complex is measured by using the enzyme label. Using this approach, we were able to measure as little as 1 ng of specific antibody per ml from affinity-isolated, monospecific chicken antibody preparations and to measure antibody specifically from IgY fractions of monospecific chicken antibody preparations. Human antibodies from subjects immunized with pentavalent toxoid preparations were detectable at dilutions as great as 24,300-fold, and undiluted serum from most control subjects showed no measurable antibody. Antibody was also measured in 65 subjects who were receiving preparations of neurotoxin A (BOTOX) for the treatment of spastic disorders. Eighteen of them had toxin-specific antibody reactive with toxin B, and two of them had toxin-specific antibody reactive with toxin A. The two patients having antibody to toxin A were refractory to treatment with this toxin. This approach of isolation of hapten-labeled immune complexes under nondenaturing conditions with hapten is broadly applicable to the specific measurement of antibodies present at very low concentrations in serum.

The EBD test--a clinical test for the detection of antibodies to botulinum toxin type A

Approximately 5 to 10% of patients with cervical, segmental or multifocal dystonia receiving repetitive local injections with botulinum toxin A (BTX A) are estimated to develop secondary loss of treatment benefit (nonresponding) because of the formation of circulating serum antibodies against the neurotoxin. Because other reasons may account for loss of benefit during the course of treatment, the group of secondary nonresponders because of antibody formation need to be separated from the antibody-negative group by appropriate testing. We present an easy clinical antibody test based on a test injection of BTX A into an indicator muscle, the extensor digitorum brevis (EDB), combined with amplitude measurements of compound muscle action potentials (CMAPs) elicited by electrical nerve stimulation of the peroneal nerve before and after the injection. The results show that in a group of clinically defined secondary nonresponders, who were serologically proven to be antibody negative, a marked decrease in CMAP amplitude can consistently be detected in the injected EDB 4 weeks after BTX A injection. In contrast, antibody-positive patients are characterized by a lack of such decrease in amplitude. In all cases, results of the EDB test were in keeping with the standard mouse bioassay test. We conclude that the EDB test is a useful tool for clinicians faced with the question of whether a secondary nonresponding patient has in fact developed antibodies to BTX A.

Mapping of protective and cross-reactive domains of the type A neurotoxin of Clostridium botulinum

The purpose of this study was to identify the location of domains within the serotype A neurotoxin of Clostridium botulinum (BoNT/A) that conferred protection against botulism. The BoNT/A gene was subcloned into a series of 10 overlapping fragments that were expressed in Escherichia coli. The expressed proteins were partially purified and used to immunize mice. The resulting antisera were screened by immunoblotting analysis for the presence of BoNT/A-specific antibody. All fragments, except one, elicited antibody that recognized BoNT/A in an immunoblot. Serological screening identified several fragment-specific cross-reactive epitopes that were shared by heterologous serotypes of BoNT. Most of these epitopes immunoreactive by enzyme-linked immunosorbent assay, but not by immunoblot. Only two fragments were shown to confer protection against BoNT/A intoxication. Both of these proteins were derived from segments of the heavy chain and encoded amino acid residues H455-661 and H1150-1289 of BoNT/A.