Mucosal vaccine targeting improves onset of mucosal and systemic immunity to botulinum neurotoxin A

Absence of suitable mucosal adjuvants for humans prompted us to consider alternative vaccine designs for mucosal immunization. Because adenovirus is adept in binding to the respiratory epithelium, we tested the adenovirus 2 fiber protein (Ad2F) as a potential vaccine-targeting molecule to mediate vaccine uptake. The vaccine component (the host cell-binding domain to botulinum toxin (BoNT) serotype A) was genetically fused to Ad2F to enable epithelial binding. The binding domain for BoNT was selected because it lies within the immunodominant H chain as a beta-trefoil (Hcbetatre) structure; we hypothesize that induced neutralizing Abs should be protective. Mice were nasally immunized with the Hcbetatre or Hcbetatre-Ad2F, with or without cholera toxin (CT). Without CT, mice immunized with Hcbetatre produced weak secretory IgA (sIgA) and plasma IgG Ab response. Hcbetatre-Ad2F-immunized mice produced a sIgA response equivalent to mice coimmunized with CT. With CT, Hcbetatre-Ad2F-immunized mice showed a more rapid onset of sIgA and plasma IgG Ab responses that were supported by a mixed Th1/Th2 cells, as opposed to mostly Th2 cells by Hcbetatre-dosed mice. Mice immunized with adjuvanted Hcbetatre-Ad2F or Hcbetatre were protected against lethal BoNT serotype A challenge. Using a mouse neutralization assay, fecal Abs from Hcbetatre-Ad2F or Hcbetatre plus CT-dosed mice could confer protection. Parenteral immunization showed that the inclusion of Ad2F enhances anti-Hcbetatre Ab titers even in the absence of adjuvant. This study shows that the Hcbetatre structure can confer protective immunity and that use of Hcbetatre-Ad2F gives more rapid and sustained mucosal and plasma Ab responses.

Secondary nonresponsiveness to botulinum toxin A in cervical dystonia: the role of electromyogram-guided injections, botulinum toxin A antibody assay, and the extensor digitorum brevis test

We studied 20 patients with cervical dystonia who had started to respond poorly to botulinum toxin A (BTXA) injections after an initial good response. All patients had extensor digitorum brevis (EDB) tests performed in addition to BTXA immunoprecipition assay (IPA) and mouse bioassay (MBA) antibody testing. The patients were reexamined and then treated with carefully placed electromyogram (EMG)-guided BTXA. Nine patients had a good clinical response to EMG-guided injections and all of these patients showed an obvious decrement on the EDB test. All were BTXA blocking antibodies (Abs)-negative via IPA and MBA (apart from one patient who had low BTXA antibodies titers using IPA but no antibodies by MBA). In the other 11 patients, there was a poor clinical response to EMG-guided BTXA injections. Seven of these 11 had small EDB decrement and BTXA antibodies using IPA, suggesting resistance to BTXA. Of the remaining four patients, two had obvious EDB decrement and low antibody titers via IPA (one of them had no antibodies via MBA), while the other two patients showed obvious decrement on the EDB test and no antibodies via IPA. This study shows that the EDB test correlates better with the clinical response than the antibody assays and that EDB decrement does not always correlate quantitatively with the BTXA antibody titers. In patients with secondary nonresponsiveness, it is recommended that an EDB test is the initial investigation of choice. In those patients where the EDB test does not demonstrate resistance to BTXA, a reexamination of the patients and carefully placed injections under EMG guidance may improve results.

The management of cervical dystonia

Cervical dystonia (CD), also known as 'spasmodic torticollis', is the most common form of adult-onset focal dystonia. It is a chronic disorder for which there is no curative treatment. Proposed interventions only have a symptomatic effect that is directed at controlling the intensity of the dystonic contractions and their associated symptoms. Both serotypes of botulinum toxin (BtA and BtB) have shown efficacy for the treatment of CD, and they constitute the first-line therapy for CD. BtB constitutes the best medical treatment for secondary failures to BtA. The efficacy of all other proposed medications, including anticholinergics, should be considered unknown due to the lack of good-quality trials. This lack of evidence applies also to all physical rehabilitation treatments. Although the authors have concluded that all surgical procedures for CD should still be considered investigational, the best data supporting benefit of surgery comes from case series of selective peripheral denervation and pallidal deep brain stimulation.

Comparative Membrane Channel Size and Activity of Botulinum Neurotoxins A and E

In an effort to compare the molecular basis of differential toxic activity of botulinum neurotoxin A (BoNT/A) and BoNT/E, we have analyzed their membrane channel activity by measuring calcein release from liposomes. Both BoNT/A and /E showed a same level of membrane channel activity that was specifically blocked by IgG specific to the neurotoxins. With the use of fluorescein-labeled dextran, we determined that the size of the channel is at least 24.2 A which is appropriate for the translocation of a protein of 50 kDa (the light chain of BoNT). These findings would suggest that the difference in the toxicity level of the two BoNT serotypes might reflect differences in either endopeptidase activity or their binding to receptor(s).

Secondary non-response due to antibody formation in a child after three injections of botulinum toxin B into the salivary glands

Botulinum toxin (BTX) offers a new treatment option to reduce drooling in adults and children. Antibody formation against BTX is known to be one reason for clinical secondary non-response to this treatment. This is a case report on the development of secondary non-response to BTX type B (BTX-B) in a 15-year-old male, with bilateral dyskinetic cerebral palsy (Gross Motor Function Classification System Level IV) with additional learning disability* and microcephaly, treated for the indication of drooling. After three successful treatment sessions, the fourth and fifth injections showed no clinical response. This was associated with the presence of antibodies against BTX-B as determined using the mouse diaphragm assay. Thus, formation of neutralizing antibodies against BTX-B appears to be an important issue, not only in patients treated for cervical dystonia but also in children treated for drooling. Subsequent injections with an adequate dose of BTX type A (BTX-A) did not show any clinical response either, although no antibodies to BTX-A were detected. Besides the unanswered questions of dosing and distribution, a second possible explanation could be that BTX-B gave rise to non-neutralizing antibodies that cross-react with BTX-A. The resulting immune complexes could be taken up by phagocytes and, thereby, impede clinical response.

Molecular evolution of antibody cross-reactivity for two subtypes of type A botulinum neurotoxin

Broadening antibody specificity without compromising affinity should facilitate detection and neutralization of toxin and viral subtypes. We used yeast display and a co-selection strategy to increase cross-reactivity of a single chain (sc) Fv antibody to botulinum neurotoxin type A (BoNT/A). Starting with a scFv that binds the BoNT/A1 subtype with high affinity (136 pM) and the BoNT/A2 subtype with low affinity (109 nM), we increased its affinity for BoNT/A2 1,250-fold, to 87 pM, while maintaining high-affinity binding to BoNT/A1 (115 pM). To find the molecular basis for improved cross-reactivity, we determined the X-ray co-crystal structures of wild-type and cross-reactive antibodies complexed to BoNT/A1 at resolutions up to 2.6 A, and measured the thermodynamic contribution of BoNT/A1 and A2 amino acids to wild-type and cross-reactive antibody binding. The results show how an antibody can be engineered to bind two different antigens despite structural differences in the antigen-antibody interface and may provide a general strategy for tuning antibody specificity and cross-reactivity.

Fine and domain-level epitope mapping of botulinum neurotoxin type A neutralizing antibodies by yeast surface display

Botulinum neurotoxin (BoNT), the most poisonous substance known, causes naturally occurring human disease (botulism) and is one of the top six biothreat agents. Botulism is treated with polyclonal antibodies produced in horses that are associated with a high incidence of systemic reactions. Human monoclonal antibodies (mAbs) are under development as a safer therapy. Identifying neutralizing epitopes on BoNTs is an important step in generating neutralizing mAbs, and has implications for vaccine development. Here, we show that the three domains of BoNT serotype A (BoNT/A) can be displayed on the surface of yeast and used to epitope map six mAbs to the toxin domains they bind. The use of yeast obviates the need to express and purify each domain, and it should prove possible to display domains of other BoNT subtypes and serotypes for epitope mapping. Using a library of yeast-displayed BoNT/A binding domain (H(C)) mutants and selecting for loss of binding, the fine epitopes of three neutralizing BoNT/A mAbs were identified. Two mAbs bind the C-terminal subdomain of H(C), with one binding near the toxin sialoganglioside binding site. The most potently neutralizing mAb binds the N-terminal subdomain of H(C), in an area not previously thought to be functionally important. Modeling the epitopes shows how all three mAbs could bind BoNT/A simultaneously and may explain, in part, the dramatic synergy observed on in vivo toxin neutralization when these antibodies are combined. The results demonstrate how yeast display can be used for domain-level and fine mapping of conformational BoNT antibody epitopes and the mapping results identify three neutralizing BoNT/A epitopes.

A peptide-based immunoassay for antibodies against botulinum neurotoxin A

Cervical dystonia (CD) is due to neck-muscle spasms that cause pain and involuntary contractions resulting in abnormal neck movements and posture. Symptoms can be relieved by injecting the affected muscle with a botulinum neurotoxin (BoNT, usually type A or type B). The therapeutic benefits are impermanent and toxin injections need to be repeated every 3-6 months. In a very small percentage of patients (less with BoNT/A than with BoNT/B) the treatment elicits blocking anti-toxin antibodies (Abs), which reduce or terminate the patient's responsiveness to further treatment. We have recently mapped (Dolimbek et al., 2006) the CD sera Ab-binding profile using a panel of 60, 19-residue peptides that encompassed the entire H chain sequence 449-1296 and overlapped consecutively by 5 residues. Abs in CD sera bound to one or more of the peptides N25, C10, C15, C20, and C31. This suggested the possibility that binding to these peptides could be used for assay of Abs in CD sera. Data analysis reported here found that Ab binding to these regions showed very significant deviations from the control responses. Of these four peptides, C10 showed the most significant level of separation between patient and control groups (p = 5 x 10(-7)) and the theoretical resolution (i.e., ability to distinguish CD patients from control, see full definition under 'Statistical analysis' in Methods), 84%, was about 4% higher than the least resolved response, C31 (p = 6 x 10(-6), resolution 80%). Since the amounts of Abs bound to a given peptide varied with the patient and not all the patients necessarily recognized all four peptides, there was the possibility that binding to combinations of two or more peptides might give a better discriminatory capability. Using two peptides, C10 plus C31, the resolution improved to 87% (p = 4 x 10(-8)). These two peptides appeared to compliment each other and negate the lower resolution of C31. Combination of three peptides gave resolutions that ranged from 85 (N25 + C15 + C31; p = 2 x 10(-7)) to 88% (C10 + C15 + C31; p = 1 x 10(-8)). Finally, using the data of all four peptides, N25 + C10 + C15 + C31, gave a resolution of 86% (p = 1 x 10(-7)). Although these levels of resolution are somewhat lower than that obtained with whole BoNT/A (resolution 97%; p = 6 x 10(-12)), it may be concluded that the two-peptide combination C10 + C31, or the three-peptide combination C10 + C15 + C31 (affording resolutions of 87 and 88%, respectively) provide a good diagnostic, toxin-free procedure for assay of total specific anti-toxin Abs in BoNT/A-treated CD patients.

Immunological aspects of Botox, Dysport and Myobloc/NeuroBloc

In some patients treated with botulinum toxin (BT), antibodies are produced in association with certain treatment parameters, patient characteristics and immunological properties of the BT preparation used. Therapeutic BT preparations are comprised of botulinum neurotoxin, non-toxic proteins and excipients. Antibodies formed against botulinum neurotoxin can block BT's biological activity. The antigenicity of a BT preparation depends on the amount of botulinum neurotoxin presented to the immune system. This amount is determined by the specific biological activity, the relationship between the biological activity and the amount of botulinum neurotoxin contained in the preparation. For Botox the specific biological activity is 60 MU-EV/ng neurotoxin, for Dysport 100 MU-EV/ng neurotoxin and for Myobloc/NeuroBloc 5 MU-EV/ng neurotoxin. For Myobloc/NeuroBloc this translates into an antibody-induced therapy failure rate of 44% in patients treated for cervical dystonia, whereas for BT type A preparations this figure is approximately 5%. No obvious differences in antigenicity of BT type A preparations have been detected thus far. For the current formulation of Botox, the rate of antibody-induced therapy failure is reportedly less than 1%. To determine the antigenicity of different BT preparations in more detail, prospective studies on large series of unbiased patients with sensitive and specific BT antibody tests are necessary.

Mapping of the regions on the heavy chain of botulinum neurotoxin A (BoNT/A) recognized by antibodies of cervical dystonia patients with immunoresistance to BoNT/A

The purpose of this work was to map the entire recognition profile of the H chain of botulinum neurotoxin A (BoNT/A) by Abs in sera that have protective anti-BoNT/A Abs by the mouse protection assay (MPA) from cervical dystonia (CD) patients who had been treated with botulinum neurotoxin, serotype A (BOTOX). In previous studies we found that human anti-tetanus neurotoxin (TeNT) Abs cross-react with BoNT/A and BoNT/B. In the present work we devised an assay procedure for measuring specific anti-BoNT/A Abs in human sera by absorbing out or inhibiting the anti-TeNT Abs with TeNT before analyzing the sera for the anti-BoNT/A Abs. The sera were obtained from 28 CD patients who had become unresponsive to treatment with BoNT/A and the sera were found to protect mice against a lethal dose of BoNT/A. For localization of the Ab-binding regions on the H chain we employed a set of sixty, 19-residue synthetic peptides (except for peptide C31 which was 22 residues) that encompassed the entire H chain sequence 449-1296 and overlapped consecutively by five residues. The pattern of Ab recognition varied from patient to patient, but a very limited set of peptides were recognized by most of the patients. These were, in decreasing amounts of Ab binding, peptide N25 (H chain residues 785-803), C9/C10 (967-985/981-999), C31 (1275-1296), C15 (1051-1069), C20 (1121-1139), N16 (659-677), N22 (743-761), and N4 (491-509). But not every serum recognized all these peptides. The finding that the binding profile was not the same for all the patients is consistent with previous observations that immune responses to protein antigens are under genetic control and that the response to each epitope within a protein is under separate genetic control. Except for the region within C9/C10, the other regions either coincided (N16 and C31), or overlapped (N4, N22, N25, C15 and C20), with the recently mapped synaptosomes (snps)-binding regions on the H chain. The molecular and clinical implications of these findings are discussed.

Expression of an anti-botulinum toxin A neutralizing single-chain Fv recombinant antibody in transgenic tobacco

Botulinum neurotoxins (BoNTs) are the most poisonous substances known and are thus classified as high-risk threats for use as bioterror agents. To examine the potential of transgenic plants as bioreactors for the production of BoNT antidotes, we transformed tobacco with an optimized, synthetic gene encoding a botulinum neurotoxin A (BoNT/A) neutralizing single-chain Fv (scFv) recombinant antibody fragment. In vitro mouse muscle twitch assays demonstrated the functional utility of this scFv extracted from tobacco for neutralizing the paralytic effects of BoNT/A at neuromuscular junctions. Based on the efficiency of the scFv capture process and the dose required to antidote a human being, 1-2 ha of this tobacco could yield up to 4 kg of scFv, which would be enough to contribute to the manufacture of 1,000,000 therapeutic doses of a monoclonal antibody (mAb) cocktail capable of neutralizing the effects of BoNT poisoning. Transgenic plants could provide an inexpensive production platform for expression of multiple mAbs toward the creation of polyclonal therapies (i.e. pooled mAbs) as the next improvement in recombinant antibody therapy.

Inhibition by human sera of botulinum neurotoxin-A binding to synaptosomes: A new assay for blocking and non-blocking antibodies

The mouse protection assay (MPA), which is an in vivo assay, is currently the most widely used method for monitoring blocking antibodies (Abs) in botulinum neurotoxin (BoNT)-treated patients. In recent studies we found that a number of the regions on the heavy (H) subunit of BoNT/A that bind blocking mouse Abs coincided, or overlapped, with the regions that bind to mouse synaptosomes (snps). This suggested that blocking anti-BoNT/A Abs would be expected to inhibit BoNT/A binding to snps. In the present work, we analyzed sera from 58 cervical dystonia (CD) patients who had been treated with BOTOX (a preparation of BoNT/A serotype) for blocking Abs by MPA and by their abilities to inhibit in vitro the binding of 125I-labeled active BoNT/A or inactive toxin (toxoid) to mouse brain snps. With active 125I-labeled BoNT/A-snps binding, the MPA-positive sera (n = 30) displayed inhibition levels that were distinctly higher (mean = 21.1 +/- 5.8) than those obtained with MPA-negative sera (n = 28) (mean = -1.3 +/- 3.9; p < 0.0001) or control sera (n = 19) (mean = -3.4 +/- 2.8; p < 0.0001). Similarly, inhibition levels by MPA-positive sera of 125I-labeled toxoid snp-binding (mean = 48.6 +/- 8.7) were distinctly higher than inhibition by MPA-negative sera (mean=10.0+/-7.6; p < 0.0001) or control sera (mean = 1.8 +/- 6.9; p < 0.0001). Thus, using labeled active toxin or toxoid, the inhibition assay correlated very well with the MPA. The inhibitory activity of the non-protective sera generally correlated with the duration of survival after toxin challenge (correlation coefficients of inhibition: active toxin = 0.445; p = 0.0167; inactive toxoid = 0.774; p < 0.0001). It is concluded that the snp-inhibition assay reported here is reliable, reproducible and correlates very well with the MPA. It requires much less serum (0.75% of the amount needed for the MPA) and is considerably less costly than the MPA. With either 125I-labeled active toxin or toxoid, it is possible to distinguish CD sera that have blocking Abs from those that lack such Abs. Since the results with the toxoid were as discriminating as those of the active toxin, it would not even be necessary to use active toxin in these assays.

Human botulism immune globulin for the treatment of infant botulism

BACKGROUND

We created the orphan drug Human Botulism Immune Globulin Intravenous (Human) (BIG-IV), which neutralizes botulinum toxin, and evaluated its safety and efficacy in treating infant botulism, the intestinal-toxemia form of human botulism.

METHODS

We performed a five-year, randomized, double-blind, placebo-controlled trial statewide, in California, of BIG-IV in 122 infants with suspected (and subsequently laboratory-confirmed) infant botulism (75 caused by type A Clostridium botulinum toxin, and 47 by type B toxin); treatment was given within three days after hospital admission. We subsequently performed a 6-year nationwide, open-label study of 382 laboratory-confirmed cases of infant botulism treated within 18 days after hospital admission.

RESULTS

As compared with the control group in the randomized trial, infants treated with BIG-IV had a reduction in the mean length of the hospital stay, the primary efficacy outcome measure, from 5.7 weeks to 2.6 weeks (P<0.001). BIG-IV treatment also reduced the mean duration of intensive care by 3.2 weeks (P<0.001), the mean duration of mechanical ventilation by 2.6 weeks (P=0.01), the mean duration of tube or intravenous feeding by 6.4 weeks (P<0.001), and the mean hospital charges per patient by 88,600 dollars (in 2004 U.S. dollars; P<0.001). There were no serious adverse events attributable to BIG-IV. In the open-label study, infants treated with BIG-IV within seven days of admission had a mean length of hospital stay of 2.2 weeks, and early treatment with BIG-IV shortened the mean length of stay significantly more than did later treatment.

CONCLUSIONS

Prompt treatment of infant botulism type A or type B with BIG-IV was safe and effective in shortening the length and cost of the hospital stay and the severity of illness.

The use of botulinum toxin type-B in the treatment of patients who have become unresponsive to botulinum toxin type-A -- initial experiences

The increasing use of botulinum toxin type-A, especially for focal dystonia and spasticity has highlighted the issue of secondary non-responsiveness. Within the last few years botulinum toxin type-B (Myobloc/Neurobloc) has become commercially available as an alternative to type-A. This paper discusses our initial experience of botulinum toxin type-B in a total of 63 individuals who attended our botulinum clinic. Thirty-six patients had cervical dystonia and a secondary non-response to type-A toxin. Thirteen of these patients (36%) had a reasonable clinical response to Neurobloc and continue to have injections. The other 23 patients either had no response, or a poor response, or had unacceptable side effects and ceased treatment. A small number of people with blepharospasm, hemifacial spasm and foot dystonia also had a disappointing response to injection. Twenty patients with spasticity were also type-A resistant. Seven of these show some continuing response to type-B, without unacceptable side effects. These findings demonstrate that botulinum toxin type-B has a place in the management of patients who have become non-responsive to type-A, but overall the responses to type-B toxin were disappointing.

Sequence variation within botulinum neurotoxin serotypes impacts antibody binding and neutralization

The botulinum neurotoxins (BoNTs) are category A biothreat agents which have been the focus of intensive efforts to develop vaccines and antibody-based prophylaxis and treatment. Such approaches must take into account the extensive BoNT sequence variability; the seven BoNT serotypes differ by up to 70% at the amino acid level. Here, we have analyzed 49 complete published sequences of BoNTs and show that all toxins also exhibit variability within serotypes ranging between 2.6 and 31.6%. To determine the impact of such sequence differences on immune recognition, we studied the binding and neutralization capacity of six BoNT serotype A (BoNT/A) monoclonal antibodies (MAbs) to BoNT/A1 and BoNT/A2, which differ by 10% at the amino acid level. While all six MAbs bound BoNT/A1 with high affinity, three of the six MAbs showed a marked reduction in binding affinity of 500- to more than 1,000-fold to BoNT/A2 toxin. Binding results predicted in vivo toxin neutralization; MAbs or MAb combinations that potently neutralized A1 toxin but did not bind A2 toxin had minimal neutralizing capacity for A2 toxin. This was most striking for a combination of three binding domain MAbs which together neutralized >40,000 mouse 50% lethal doses (LD(50)s) of A1 toxin but less than 500 LD(50)s of A2 toxin. Combining three MAbs which bound both A1 and A2 toxins potently neutralized both toxins. We conclude that sequence variability exists within all toxin serotypes, and this impacts monoclonal antibody binding and neutralization. Such subtype sequence variability must be accounted for when generating and evaluating diagnostic and therapeutic antibodies.

Characterization of the antibody response to the receptor binding domain of botulinum neurotoxin serotypes A and E

Clostridium botulinum neurotoxins (BoNTs) are the most toxic proteins for humans. The current clostridial-derived vaccines against BoNT intoxication have limitations including production and accessibility. Conditions were established to express the soluble receptor binding domain (heavy-chain receptor [HCR]) of BoNT serotypes A and E in Escherichia coli. Sera isolated from mice and rabbits immunized with recombinant HCR/A1 (rHCR/A1) from the classical type A-Hall strain (ATCC 3502) (BoNT/A1) and rHCR/E from BoNT serotype E Beluga (BoNT/E(B)) neutralized the homologous serotype of BoNT but displayed differences in cross-recognition and cross-protection. Enzyme-linked immunosorbent assay and Western blotting showed that alpha-rHCR/A1 recognized epitopes within the C terminus of the HCR/A and HCR/E, while alpha-rHCR/E recognized epitopes within the N terminus or interface between the N and C termini of the HCR proteins. alpha-rHCR/E(B) sera possessed detectable neutralizing capacity for BoNT/A1, while alpha-rHCR/A1 did not neutralize BoNT/E. rHCR/A was an effective immunogen against BoNT/A1 and the Kyoto F infant strain (BoNT/A2), but not BoNT serotype E Alaska (BoNT/E(A)), while rHCR/E(B) neutralized BoNT/E(A), and under hyperimmunization conditions protected against BoNT/A1 and BoNT/A2. The protection elicited by rHCR/A1 to BoNT/A1 and BoNT/A2 and by rHCR/E(B) to BoNT/E(A) indicate that immunization with receptor binding domains elicit protection within sub-serotypes of BoNT. The protection elicited by hyperimmunization with rHCR/E against BoNT/A suggests the presence of common neutralizing epitopes between the serotypes E and A. These results show that a receptor binding domain subunit vaccine protects against serotype variants of BoNTs.

Submolecular recognition profiles in two mouse strains of non-protective and protective antibodies against botulinum neurotoxin A

We have used a set of synthetic overlapping peptides encompassing the entire heavy (H) chain of botulinum neurotoxin serotype A (BoNT/A) to map, in two mouse strains (BALB/c, H2d, and SJL, H2S), the regions on the H-chain recognized by Abs in the last bleed of non-protective anti-BoNT/A antisera and in the bleed of protective antisera immediately following it in the bleeding schedule. Although the protective antisera bound slightly higher amounts of total (IgG+IgM) Abs, non-protective and protective BALB/c antisera showed similar peptide-binding profiles involving peptides N6/N7, N25, C2/C3, C9/C10/C11, C15, C18, C24, C30, and C31 and, at lower amounts of bound Abs, peptides N19, C6/C7, and C28. IgG+IgM antibodies of the protective SJL antisera recognized peptides N5, N22, and C21, and these peptides were only slightly recognized (N22, C21) or unrecognized (N5) by the non-protective antisera. Additionally, peptides N7/N8, N25, C11, C15, and less so N27/N28 bound two-fold or more Abs from the SJL protective antisera than the non-protective antisera. The Abs bound to peptides C4 and C29 were of relatively lower affinity. Peptides C2/C3, C7, C18/C19, C24, C30, and C31 bound higher amounts of Abs in the SJL protective versus the non-protective antisera, but the differences were less than double. We also mapped the binding profiles of the IgG Abs in these sera. BALB/c and SJL had 13-36-fold higher of IgG Abs that bound to BoNT/A in the protective antisera relative to non-protective antisera. The IgG Abs in the protective antisera of each mouse haplotype bound to the same peptides that bound total Abs in the correlate antiserum. But in both mouse strains, the non-protective Abs showed little or no IgG Abs that bound to these peptides. In the SJL haplotype, the IgG response to peptide N5 was transient, appearing strongly in early protective Abs and disappearing by day 70. It is not clear whether the response to region N5 plays a role in initiating and contributing to the protective activity of the toxin in the SJL strain in the early stages but is not needed in later hyperimmune stages of the Ab response. It is concluded that the switch in BALB/c and SJL mice from non-protective to protective Abs is not associated with major changes in the epitope-recognition profiles. Although some slight differences between non-protective and protective antisera appeared in their levels of Abs that were bound by some peptides, these differences are not sufficient to explain differences in the protection properties. Protection was mostly associated with the immunoglobulin class of the antibodies. IgM antibodies were non-protective, while IgG Abs produced after the switch were protective.

Formulation of botulinum neurotoxin heavy chain fragments for vaccine development: mechanisms of adsorption to an aluminum-containing adjuvant

Heavy chain fragments of botulinum neurotoxin serotypes A and B are being developed as a bivalent vaccine for botulism. To potentiate the immune response, an aluminum containing adjuvant will be formulated with the two antigens. The adsorption mechanisms of each antigen to aluminum phosphate and aluminum hydroxide adjuvants were studied. The adsorption of the serotype A antigen to each adjuvant, and the serotype B antigen to aluminum phosphate adjuvant, is dependent on electrostatic attractive forces. The serotype A antigen is basic, and pretreatment with phosphate anions is required for favorable adsorption conditions to aluminum hydroxide adjuvant. In contrast, the serotype B antigen displays a high affinity to aluminum hydroxide adjuvant even when the two species possess the same charge. It is proposed that the serotype B antigen is adsorbed to aluminum hydroxide adjuvant by a ligand exchange mechanism.

[Recombinant design and expression of human three-domain antibody against BoNTa]

VH and Vkappa genes were amplified from human ScFv B17 specific against botulinum neurotoxin serotype A (BoNTa). Gene sequence encoding 5'-terminal 12 amino acid of heavy chain constant region CH1, as a linker, linked VH and Vkappa to construct a new three-domain antibody molecule VH/Vkappa. VH/Vkappa was expressed at high level over 34% of total host cell proteins in E. coli. Recombinant protein were purified up to 95% by affinity column. As a result, recombinant VH/Vkappa could recognize and bind specific to BoNTa in ELISA. However, comparing with its parent ScFv, VH/Vkappa has higher relative affinity and stability.

A novel neurotoxoid vaccine prevents mucosal botulism

The threat posed by botulism, classically a food- and waterborne disease with a high morbidity and mortality, has increased exponentially in an age of bioterrorism. Because botulinum neurotoxin (BoNT) could be easily disseminated by terrorists using an aerosol or could be used to contaminate the food or water supply, the Centers for Disease Control and Prevention and the National Institute of Allergy and Infectious Diseases has classified it as a category A agent. Although clearly the development of a safe and effective mucosal vaccine against this toxin should be a high priority, essentially no studies to date have assessed mucosal immune responses to this disease. To bridge this gap in our knowledge, we immunized mice weekly for 4 wk with nasal doses of BoNT type A toxoid and a mutant of cholera toxin termed E112K. We found elevated levels of BoNT-specific IgG Abs in plasma and of secretory IgA Abs in external secretions (nasal washes, saliva, and fecal extracts). When mice given nasal BoNT vaccine were challenged with 4 x 10(3) LD50 of BoNT type A (BoNT/A) via the i.p. route, complete protection was seen, while naive mice given the same dosage died within 2 h. To further confirm the efficacy of this nasal BoNT vaccine, an oral LD50 was determined. When mice were given an oral challenge of 5 microg (2 x oral LD50) of progenitor BoNT/A, all immunized mice survived beyond 5 days, while nonimmunized mice did not. The fecal extract samples from nasally vaccinated mice were found to contain neutralizing secretory IgA Abs. Taken together, these results show that nasal BoNT/A vaccine effectively prevents mucosal BoNT intoxication.