Protective efficacy of recombinant bacterin vaccine against botulism in cattle

Botulism is a paralytic disease caused by the intoxication of neurotoxins produced by Clostridium botulinum. Among the seven immunologically distinct serotypes of neurotoxins (BoNTs A − G), serotypes C and D, or a chimeric fusion termed C/D or D/C, are responsible for animal botulism. The most effective way to prevent botulism in cattle is through vaccination; however, the commercially available vaccines produced by detoxification of native neurotoxins are time-consuming and hazardous. To overcome these drawbacks, a non-toxic recombinant vaccine was developed as an alternative. In this study, the recombinant protein vaccine was produced using an Escherichia coli cell-based system. The formaldehyde-inactivated E. coli is able to induce 7.45 ± 1.77 and 6.6 ± 1.28 IU/mL neutralizing mean titers against BoNTs C and D in cattle, respectively, determined by mouse neutralization bioassay, and was deemed protective by the Brazilian legislation. Moreover, when the levels of anti-BoNT/C and D were compared with those achieved by the recombinant purified vaccines, no significant statistical difference was observed. Cattle vaccinated with the commercial vaccine developed 1.33 and 3.33 IU/mL neutralizing mean titers against BoNT serotypes C and D, respectively. To the best of our knowledge, this study is the first report on recombinant E. coli bacterin vaccine against botulism. The vaccine was safe and effective in generating protective antibodies and, thus, represents an industry-friendly alternative for the prevention of cattle botulism.     

Oral vaccination with an adenovirus-vectored vaccine protects against botulism

We have previously shown that an adenovirus vectored vaccine delivered intramuscularly or intranasally was effective in protection against botulism in a mouse model. The adenoviral vector encodes a human codon-optimized heavy chain C-fragment (H_C50) of botulinum neurotoxin type C (BoNT/C). Here, we evaluate the same vaccine candidate as an oral vaccine against BoNT/C in a mouse model. To elicit protective immunity, the mice were orally vaccinated with a single dose of 1 × 10⁴ to 1 × 10⁷ plaque forming units (pfu) of the adenoviral vector. The immune sera, collected six weeks after oral vaccination with 2 × 10⁷ pfu adenovirus, have shown an ability to neutralize the biological activity of BoNT/C in vitro. Additionally, animals receiving a single dose of 2 × 10⁶ pfu adenovirus or greater were completely protected against challenge with 100 × MLD₅₀ of BoNT/C. The data demonstrated the feasibility to develop an adenovirus-based oral vaccine against botulism.     

Potent tetravalent replicon vaccines against botulinum neurotoxins using DNA-based Semliki Forest virus replicon vectors

Human botulism is commonly associated with botulinum neurotoxin (BoNT) serotypes A, B, E and F. This suggests that the greatest need is for a tetravalent vaccine that provides protection against all four of these serotypes. In current study, we investigated the feasibility of generating several tetravalent vaccines that protected mice against the four serotypes. Firstly, monovalent replicon vaccine against BoNT induced better antibody response and protection than that of corresponding conventional DNA vaccine. Secondly, dual-expression DNA replicon pSCARSE/FHc or replicon particle VRP-E/FHc vaccine was well resistant to the challenge of BoNT/E and BoNT/F mixture as a combination vaccine composed of two monovalent replicon vaccines. Finally, the dual-expression DNA replicon or replicon particle tetravalent vaccine could simultaneously and effectively neutralize and protect the four BoNT serotypes. Protection correlated directly with serum ELISA titers and neutralization antibody levels to BoNTs. Therefore, replicon-based DNA or particle might be effective vector to develop BoNT vaccines, which might be more desirable for use in clinical application than the conventional DNA vaccines. Our studies demonstrate the utility of combining dual-expression DNA replicon or replicon particle vaccines into multi-agent formulations as potent tetravalent vaccines for eliciting protective responses to four serotypes of BoNTs.     

Enhancing toxin-based vaccines against botulism

Botulinum neurotoxins (BoNT) are the most toxic proteins for humans. BoNTs are single chain proteins with an N-terminal light chain (LC) and a C-terminal heavy chain (HC). HC comprises a translocation domain (HC_N) and a receptor binding domain (HC_C). Currently, there are no approved vaccines against botulism. This study tests a recombinant, full-length BoNT/A1 versus LCHC_N/A1 and HC_C/A1 as vaccine candidates against botulism. Recombinant, full-length BoNT/A1 was detoxified by engineering 3-amino acid mutations (E224A/R363A/Y366F) (M-BoNT/A1) into the LC to eliminate catalytic activity, which reduced toxicity in a mouse model of botulism by >10⁶-fold relative to native BoNT/A1. As a second step to improve vaccine safety, an additional mutation (W1266A) was engineered in the ganglioside binding pocket, resulting in reduced receptor binding, to produce M-BoNT/A1^W. M-BoNT/A1^W vaccination protected against challenge by 10⁶ LD₅₀ Units of native BoNT/A1, while M-BoNT/A1 or M-BoNT/A1^W vaccination equally protected against challenge by native BoNT/A2, a BoNT subtype. Mice vaccinated with M-BoNT/A1^W surviving BoNT challenge had dominant antibody responses to the LCHC_N domain, but varied antibody responses to HC_C. Sera from mice vaccinated with M-BoNT/A1^W also neutralized BoNT/A1 action on cultured neuronal cells. The cell- and mouse-based assays measured different BoNT-neutralizing antibodies, where M-BoNT/A1^W elicited a strong neutralizing response in both assays. Overall, M-BoNT/A1^W, with defects in multiple toxin functions, elicits a potent immune response to BoNT/A challenge as a vaccine strategy against botulism and other toxin-mediated diseases.     

Botulism: cause, effects, diagnosis, clinical and laboratory identification, and treatment modalities

Botulism is a neuroparalytic disease caused by neurotoxins produced by the bacteria Clostridium botulinum. Botulinum neurotoxins (BoNTs) are among the most potent naturally occurring toxins and are a category A biological threat agent. The 7 toxin serotypes of BoNTs (serotypes A-G) have different toxicities, act through 3 different intracellular protein targets, and exhibit different durations of effect. Botulism may follow ingestion of food contaminated with BoNT, from toxin production of C botulinum present in the intestine or wounds, or from inhalation of aerosolized toxin. Intoxication classically presents as an acute, symmetrical, descending flaccid paralysis. Early diagnosis is important because antitoxin therapy is most effective when administered early. Confirmatory testing of botulism with BoNT assays or C botulinum cultures is time-consuming, and may be insensitive in the diagnosis of inhalational botulism and in as many as 32% of food-borne botulism cases. Therefore, the decision to initiate botulinum antitoxin therapy is primarily based on symptoms and physical examination findings that are consistent with botulism, with support of epidemiological history and electrophysiological testing. Modern clinical practice and antitoxin treatment has reduced botulism mortality rates from approximately 60% to < or =10%. The pentavalent botulinum toxoid is an investigational product and has been used for more than 45 years in at-risk laboratory workers to protect against toxin serotypes A to E. Due to declining immunogenicity and potency of the pentavalent botulinum toxoid, novel vaccine candidates are being developed.     

Production of catalytically inactive BoNT/A1 holoprotein and comparison with BoNT/A1 subunit vaccines against toxin subtypes A1, A2, and A3

A recombinant, catalytically inactive Clostridium botulinum neurotoxin A1 holoprotein (ciBoNT/A1 HP) was constructed by introducing amino acid substitutions H223A, E224A, and H227A in the active site to ablate proteolytic activity. ciBoNT/A1 HP was produced in the yeast Pichia pastoris and the purified product was evaluated as a vaccine candidate by comparison against recombinant BoNT/A1 LC, LC-belt, LC-H_n, and H_c antigens and a LC-H_n + H_c combination in mouse potency and efficacy bioassays when challenged with BoNT/A subtypes /A1, /A2, and /A3. A single dose of ciBoNT/A1 HP provided equivalent or greater protective immunity, not only against the homologous toxin, but also against two distinct toxin subtypes with significant amino acid divergence. Only the LC-H_n + H_c combination provided comparable protection against /A1; however, it was less effective against subtypes /A2 and /A3. Differences in protective immunity diminished after multiple vaccinations with either ciBoNT/A1 HP or BoNT/A1 H_c, and the survival rates were more comparable at the toxin levels used to challenge.     

Vaccination with recombinant Clostridium perfringens toxoids α and β promotes elevated antepartum and passive humoral immunity in swine

Due to the increasingly restricted use of antimicrobials in animal production systems, the prevention and control of Clostridium perfringens type A- and C-induced diarrhea in piglets should be based on passive immunization via the prepartum vaccination of sows. Given the current obstacles in the production of conventional clostridial vaccines, the use of recombinant proteins has been considered to represent a promising alternative. In the present study, the neutralizing antibody response of immunized sows and their litters to a bivalent vaccine containing the C. perfringens recombinant toxoids alpha (rTA) and beta (rTB) produced in Escherichia coli was assessed. Rabbits (n = 8) and pregnant sows (n = 7) were immunized with 200 μg of each recombinant antigen using Al(OH)₃ as adjuvant. The alpha and beta antitoxin titer detected in the rabbits’ serum pool was 9.6 and 20.4 IU/mL, respectively. The mean alpha and beta antitoxin titers in the sows’ sera were 6.0 ± 0.9 IU/mL and 14.5 ± 2.2 IU/mL, and the corresponding individual coefficients of variation (CV) were 16.04% and 14.91%, respectively. The mean alpha and beta antitoxin titers in the litters’ serum pools were 4.2 ± 0.4 IU/mL and 10.9 ± 1.7 IU/mL, and the CV between litters was 9.23% and 9.85%, respectively. The results showed that the rTA and rTB proteins produced and tested in the present study induced an immune response and can be regarded as candidates for the development of a commercial vaccine against C. perfringens type A- and C-induced diarrhea in pigs.     

Immunogenicity of candidate chimeric DNA vaccine against tuberculosis and leishmaniasis

Mycobacterium tuberculosis and Leishmania donovani are important intracellular pathogens, especially in Indian context. In India and other South East Asian countries, both these infections are highly endemic and in about 20% cases co-infection of these pathogens is reported. For both these pathogens cell mediated immunity plays most important role. The available treatment of these infections is either prolonged or cumbersome or it is ineffective in controlling the outbreaks and spread. Therefore, potentiation of a common host defense mechanism can be used to prevent both the infections simultaneously. In this study we have developed a novel chimeric DNA vaccine candidate comprising the esat-6 gene of M. tuberculosis and kinesin motor domain gene of L. donovani. After developing this novel chimera, its immunogenicity was studied in mouse model. The immune response was compared with individual constructs of esat-6 and kinesin motor domain. The results showed that immunization with chimeric DNA vaccine construct resulted in stronger IFN-γ and IL-2 response against kinesin (3012 ± 102 and 367.5 ± 8.92 pg/ml) and ESAT-6 (1334 ± 46.5 and 245.1 ± 7.72 pg/ml) in comparison to the individual vaccine constructs. The reciprocal immune response (IFN-γ and IL-2) against individual construct was lower (kinesin motor domain: 1788 ± 36.48 and 341.8 ± 9.801 pg/ml and ESAT-6: 867.0 ± 47.23 and 170.8 ± 4.578 pg/ml, respectively). The results also suggest that using the chimeric construct both proteins yielded a reciprocal adjuvant affect over each other as the IFN-γ production against chimera vaccination is statistically significant (p < 0.0001) than individual construct vaccination. From this pilot study we could envisage that the chimeric DNA vaccine construct may offer an attractive strategy in controlling co-infection of leishmaniasis and tuberculosis and have important implication in future vaccine design.     

Potency against enterotoxemia of a recombinant Clostridium perfringens type D epsilon toxoid in ruminants

Enterotoxemia, a disease that affects domestic ruminants, is caused mainly by the epsilon toxin from Clostridium perfringens type D. Its eradication is virtually impossible, control and prophylaxis are based on systematic vaccination of herds with epsilon toxoids that are efficient in inducing protective antibody production. The use of recombinant toxins is one of the most promising of these strategies. This work evaluates the potency of a Cl. perfringens type D epsilon toxoid expressed by Escherichia coli administered to goats, sheep, and cattle. The etx gene was cloned into the pET-11a plasmid of E. coli strain BL21 to produce the recombinant toxin. Rabbits (n = 8), goats, sheep, and cattle (n = 5 for each species) were immunized with 0.2 mg of the insoluble recombinant protein fraction to evaluate vaccine potency of the epsilon toxoid studied. Antibody titers were 40, 14.3, 26, and 13.1 IU/mL in the rabbit, goat, sheep, and cattle serum pools, respectively. The epsilon toxoid produced and tested in this work is adequate for immunization of ruminants against enterotoxemia.     

The effect of anti-TNF treatment on the immunogenicity and safety of the 7-valent conjugate pneumococcal vaccine in children with juvenile idiopathic arthritis

Our aim was to study the effect of anti-TNF treatment on immunogenicity and safety of the 7-valent conjugate pneumococcal vaccine in children with juvenile idiopathic arthritis. Thirty-one children (mean age:12.9 ± 4.6 years) treated with anti-TNFs plus Disease Modifying Anti-Rheumatic Drugs (DMARDs) and 32 age-matched children treated only with DMARDs were vaccinated with two doses of PCV7. After the first vaccine dose geometric mean titers (GMTs) were significantly increased for all vaccine serotypes (p < 0.0001) in both groups and were found to be protective (>0.35 μg/ml) in 87–100% of all children, depending on the serotype. Children receiving anti-TNFs achieved a significantly lower GMTs against serotypes 4, 14 and 23F (p < 0.05). A ≥4-fold increase of the baseline titers to ≥5 vaccine serotypes was observed in 50% and 75% of the anti-TNF and control patients, respectively (p = 0.0697). No patient developed vaccine-associated serious adverse events or disease flares.     

Individual and bivalent vaccines against botulinum neurotoxin serotypes A and B using DNA-based Semliki Forest virus vectors

We evaluated individual and bivalent replicon vaccines against Clostridiumbotulinum neurotoxin serotypes A (BoNT/A) or B (BoNT/B). The DNA replicon vaccine (pSCARSBHc) encoding the Hc domain of BoNT/B (BHc) induced better responses and protection against BoNT/B mouse challenge than conventional DNA vaccine. The dual-expressing DNA vaccine (pSCARSA/BHc) protected similarly to a DNA replicon vaccine mixture (pSCARSAHc + pSCARSBHc). Additionally, recombinant SFV particles, VRP-AHc or VRP-BHc, protected mice from high-dose BoNT/A or BoNT/B challenge, respectively. Mice given either dual-expressing VRP-A/BHc or mixture of VRP-AHc and VRP-BHc were protected from challenge with serotype A/B mixtures. These data justify further testing in other animals or humans.     

Strong protection induced by an experimental DIVA subunit vaccine against bluetongue virus serotype 8 in cattle

Bluetongue virus (BTV) infections in ruminants pose a permanent agricultural threat since new serotypes are constantly emerging in new locations. Clinical disease is mainly observed in sheep, but cattle were unusually affected during an outbreak of BTV seroype 8 (BTV-8) in Europe. We previously developed an experimental vaccine based on recombinant viral protein 2 (VP2) of BTV-8 and non-structural proteins 1 (NS1) and NS2 of BTV-2, mixed with an immunostimulating complex (ISCOM)–matrix adjuvant. We demonstrated that bovine immune responses induced by this vaccine were as good or superior to those induced by a classic commercial inactivated vaccine. In this study, we evaluated the protective efficacy of the experimental vaccine in cattle and, based on the detection of VP7 antibodies, assessed its DIVA compliancy following virus challenge. Two groups of BTV-seronegative calves were subcutaneously immunized twice at a 3-week interval with the subunit vaccine (n = 6) or with adjuvant alone (n = 6). Following BTV-8 challenge 3 weeks after second immunization, controls developed viremia and fever associated with other mild clinical signs of bluetongue disease, whereas vaccinated animals were clinically and virologically protected. The vaccine-induced protection was likely mediated by high virus-neutralizing antibody titers directed against VP2 and perhaps by cellular responses to NS1 and NS2. T lymphocyte responses were cross-reactive between BTV-2 and BTV-8, suggesting that NS1 and NS2 may provide the basis of an adaptable vaccine that can be varied by using VP2 of different serotypes. The detection of different levels of VP7 antibodies in vaccinated animals and controls after challenge suggested a compliancy between the vaccine and the DIVA companion test. This BTV subunit vaccine is a promising candidate that should be further evaluated and developed to protect against different serotypes.     

Subunit vaccine efficacy against Botulinum neurotoxin subtypes

Botulinum neurotoxins (BoNT) are classified into 7 serotypes (A-G) based upon neutralization by serotype-specific anti-sera. Several recombinant serotype-specific subunit BoNT vaccines have been developed, including a subunit vaccine comprising the receptor binding domain (HCR) of the BoNTs. Sequencing of the genes encoding BoNTs has identified variants (subtypes) that possess up to 32% primary amino acid variation among different BoNT serotypes. Studies were conducted to characterize the ability of the HCR of BoNT/A to protect against challenge by heterologous BoNT/A subtypes (A1-A3). High dose vaccination with HCR/A subtypes A1-A4 protected mice from challenge by heterologous BoNT/A subtype A1-A3, while low dose HCR vaccination yielded partial protection to heterologous BoNT/A subtype challenge. Absolute IgG titers to HCRs correlated to the dose of HCR used for vaccination, where HCR/A1 elicited an A1 subtype-specific IgG response, which was not observed with HCR/A2 vaccination. Survival of mice challenged to heterologous BoNT/A2 following low dose HCR/A1 vaccination correlated with elevated IgG titers directed to the denatured C-terminal sub-domain of HCR/A2, while survival of mice to heterologous BoNT/A1 following low dose HCR/A2 vaccination correlated to elevated IgG titers directed to native HCRc/A1. This implies that low dose vaccinations with HCR/A subtypes elicit unique IgG responses, and provides a basis to define how the host develops a neutralizing immune response to BoNT intoxication. These results may provide a reference for the development of pan-BoNT vaccines.     

Cattle immune response to botulinum type D toxoid: results of a vaccination study

Cattle botulism is a food-borne intoxication caused by the ingestion of preformed botulinum neurotoxins (BoNT) of serotypes B, C, or D. Protection in cattle against botulinum intoxication is based on the presence of specific serum neutralizing antibodies upon exposure. Outbreaks in vaccinated cattle have raised concerns about vaccine quality and efficacy. To this end, three different immunization protocols and the effect of maternal anti-BoNT/D antibodies, at the priming dose, were analyzed in 2-month-old dairy calves. Based on previously determined protective anti-BoNT/D antibody levels analyzed in field outbreaks, the immune response to type D toxoids was analyzed using an in-house ELISA system. Here we show that using the current vaccination strategy of using a priming dose in 2-month-old calves followed by booster doses after 4 weeks and annually thereafter, did not result in continuous protective levels of anti-BoNT/D antibodies. As a result of this vaccination protocol, only 15-31% of cattle in parities 1-3 were protected at the time of the annual booster. Vaccination study in calves indicated that adding a 6-month booster dose to the current protocol resulted in continuous protective levels of anti-BoNT/D antibodies well above the cut-off protective levels. The presence of maternally derived anti-BoNT/D antibodies did not interfere with the immune response to toxoids that can be administered to 2-month-old calves.     

Improvement of the immunity of pig to Hog cholera vaccine by recombinant plasmid with porcine interleukin-6 gene and CpG motifs

In order to observe the dosage-effect of recombinant pig interleukin-6 gene and CpG motifs on the immune responses of swine to vaccine, a novel recombinant eukaryotic VPIL6C plasmid was packed with chitosan nanoparticles (CNP) prepared by ionic cross linkage, which contains pig interleukin-6 gene and immunostimulatory sequence consisted of 11 CpG motifs. CNP-VRIL6C was then utilized to inoculate 30-day-old piglets intramuscularly at the dosage of 0.5, 1.0 and 1.5 mg/per capita, respectively. Meanwhile, the piglets were injected with attenuated classical Hog cholera vaccine and designated as A1, A2 and A3 group. The blood was weekly collected from the piglets after vaccination to detect the changes of immunoglobulins, specific antibody, interleukins, IFN-γ and immune cells. The results were found that compared to those of the control piglets injected with VR1020-CNP, the content of IgG, IgA and IgM, specific antibodies, IL-2, IL-6 and IFN-γ significantly increased in the sera from the treated three groups from 14 to 70 days after vaccination (P < 0.05); the number of T_H, T_C and CD3⁺ positive T cells raised obviously in the blood of VPIL6C treated piglets (P < 0.05). Also the above immune indexes of A1 group were significantly lower to different extent in comparison with those of A2 and A3 group from 14 to 56 days post inoculation (P > 0.05). Moreover, the lymphocytes also remarkably elevated in the treated groups (P < 0.05). These indicate that VPIL6C entrapped with CNP is a novel effective adjuvant to boost the humoral and cellular immunity of pig to Hog cholera, implying it's potentiality to enhance the resistance of pig against infectious diseases.     

Quantitative anti-F1 and anti-V IgG ELISAs as serological correlates of protection against plague in female Swiss Webster mice

A recombinant fusion protein composed of Yersinia pestis fraction 1 capsule (F1) and virulence-associated V antigen (V) (F1–V) has been developed as the next-generation vaccine against plague. In this study, female Swiss Webster mice received a single intramuscular vaccination with one of eight doses of the F1–V vaccine and exposed 4 weeks later to either Y. pestis CO92 or C12 organisms by the subcutaneous or aerosol routes of infection. Quantitative anti-F1 and anti-V immunoglobulin G (IgG) ELISAs were used to examine the relationship between survival outcome and antibody titers to F1 and V. Results suggested that each 1 log₁₀ increase in week 4 quantitative anti-F1 and anti-V IgG ELISA titers were associated with a 1.7-fold (p = 0.0051) and 2.5-fold (p = 0.0054) increase in odds of survival, respectively, against either bubonic or pneumonic plague and may serve as serological correlates of protection.     

Heterologous protection against alpha toxins of Clostridium perfringens and Staphylococcus aureus induced by binding domain recombinant chimeric protein

Clostridium perfringens and Staphylococcus aureus are the two important bacteria frequently associated with majority of the soft tissue infections. The severity and progression of the diseases caused by these pathogens are attributed primarily to the alpha toxins they produce. Previously, we synthesized a non-toxic chimeric molecule r-αCS encompassing the binding domains of C. perfringens and S. aureus alpha toxins and demonstrated that the r-αCS hyperimmune polysera reacts with both the native wild type toxins. In the present report, we evaluated efficacy of r-αCS in conferring protection against C. perfringens and S. aureus alpha toxin infections in murine model. Immunization of BALB/c with r-αCS was effective in inducing both high titers of serum anti-r-αCS antibodies after three administrations. Sub-typing the antibody pool revealed high proportions of IgG1 indicating a Th2-polarized immune response. The r-αCS stimulated the proliferation of splenocytes from the immunized mice upon re-induction by the antigen, in vitro. The levels of interleukin-10 increased while TNF-α was found to be downregulated in the r-αCS induced splenocytes. Mice immunized with r-αCS were protected against intramuscular challenge with 5 × LD₁₀₀ doses of C. perfringens and S. aureus alpha toxins with >80% survival, which killed control animals within 48–72 h. Passive immunization of mice with anti-r-αCS serum resulted in 50–80% survival. Our results indicate that r-αCS is a remarkable antigen with protective efficacy against alpha toxin mediated C. perfringens and S. aureus soft tissue co-infections.     

Vaccine induced antibodies to the first variable loop of human immunodeficiency virus type 1 gp120, mediate antibody-dependent virus inhibition in macaques

The role of antibodies directed against the hyper variable envelope region V1 of human immunodeficiency virus type 1 (HIV-1), has not been thoroughly studied. We show that a vaccine able to elicit strain-specific non-neutralizing antibodies to this region of gp120 is associated with control of highly pathogenic chimeric SHIV_89.6P replication in rhesus macaques. The vaccinated animal that had the highest titers of antibodies to the amino terminus portion of V1, prior to challenge, had secondary antibody responses that mediated cell killing by antibody-dependent cellular cytotoxicity (ADCC), as early as 2 weeks after infection and inhibited viral replication by antibody-dependent cell-mediated virus inhibition (ADCVI), by 4 weeks after infection. There was a significant inverse correlation between virus level and binding antibody titers to the envelope protein, (R = −0.83, p = 0.015), and ADCVI (R = −0.84 p = 0.044). Genotyping of plasma virus demonstrated in vivo selection of three SHIV_89.6P variants with changes in potential N-linked glycosylation sites in V1. We found a significant inverse correlation between virus levels and titers of antibodies that mediated ADCVI against all the identified V1 virus variants. A significant inverse correlation was also found between neutralizing antibody titers to SHIV_89.6 and virus levels (R = −0.72 p = 0.0050). However, passive inoculation of purified immunoglobulin from animal M316, the macaque that best controlled virus, to a naïve macaque, resulted in a low serum neutralizing antibodies and low ADCVI activity that failed to protect from SHIV_89.6P challenge. Collectively, while our data suggest that anti-envelope antibodies with neutralizing and non-neutralizing Fc(R-dependent activities may be important in the control of SHIV replication, they also demonstrate that low levels of these antibodies alone are not sufficient to protect from infection.     

Immune response of horses to vaccination with the recombinant Hc domain of botulinum neurotoxin types C and D

Botulinum neurotoxins, predominantly serotypes C and D, cause equine botulism through forage poisoning. The C-terminal part of the heavy chain of botulinum neurotoxin types C and D (HcBoNT/C and D) was expressed in Escherichia coli and evaluated as a recombinant mono- and bivalent vaccine in twelve horses in comparison to a commercially available toxoid vaccine. A three-dose subcutaneous immunization of adult horses elicited robust serum antibody response in an ELISA using the immunogen as a capture antigen. Immune sera showed dose-dependent high potency in neutralizing specifically the active BoNT/C and D in the mouse protection assay. The aluminium hydroxide based mono- and bivalent recombinant HcBoNT/C and D vaccines were characterized by good compatibility and the ability to elicit protective antibody titers similar or superior to the commercially available toxoid vaccine.     

Dual-route targeted vaccine protects efficiently against botulinum neurotoxin A complex

Clostridium botulinum readily persists in the soil and secretes life-threatening botulinum neurotoxins (BoNTs) that are categorized into serotypes A to H, of which, serotype A (BoNT/A) is the most commonly occurring in nature. An efficacious vaccine with high longevity against BoNT intoxication is urgent. Herein, we developed a dual-route vaccine administered over four consecutive weeks by mucosal and parenteral routes, consisting of the heavy chain (Hc) of BoNT/A targeting dendritic cell peptide (DCpep) expressed by Lactobacillus acidophilus as a secretory immunogenic protein. The administered dual-route vaccine elicited robust and long-lasting memory B cell responses comprising germinal center (GC) B cells and follicular T cells (Tfh) that fully protected mice from lethal oral BoNT/A fatal intoxication. Additionally, passively transferring neutralizing antibodies against BoNT/A into naïve mice induced robust protection against BoNT/A lethal intoxication. Together, a targeted vaccine employing local and systemic administrative routes may represent a novel formulation eliciting protective B cell responses with remarkable longevity against threatening biologic agents such as BoNTs.