Cattle and goats' humoral response to vaccination with Clostridium perfringens type D purified epsilon toxoids.

Herd vaccination is an important preventive measure against enterotoxemia in ruminants. Vaccination in goats should be performed every four months, and recent studies have shown that immunity in cattle lasts for less than one year. One of the mechanisms for increasing the duration of the immune response is to use purified toxoids as immunogens. The aim of the present study was to evaluate the humoral response in cattle and goats after vaccination with purified and semi-purified Clostridium perfringens type D epsilon toxoid. The following three different vaccines were used: vaccine 1 (V1), a semi-purified toxoid adsorbed to aluminum hydroxide; vaccine 2 (V2), a purified toxoid adsorbed to aluminum hydroxide; and vaccine (V3), a purified toxoid adsorbed on chitosan microparticles. Groups of cattle (n = 6-7) and goats (n = 6-7) were vaccinated on days 0 and 30, and serum samples for antitoxin titration were collected every 30 days for one-year post-vaccination. Goats were revaccinated on day 360, and their serum was evaluated on days 367 and 374. The antibody peaks ranged between 6.90 and 11.47 IU/mL in cattle and from 1.11 to 4.40 IU/mL in goats. In cattle administered with the V1 and V2 vaccines, we observed that the antibody titers were maintained above 0.2 IU/mL until the end of the experiment. In goats, V2 elicited long-lasting antibodies, and all animals maintained the protective titers for 210 days after the first dose. In conclusion, the purified toxoid vaccine with aluminum hydroxide adjuvant was able to induce strong and long-lasting humoral responses in both species and could be an alternative for improving the immunization schedule against enterotoxemia in goats and cattle.

Humoral Immune Response Evaluation in Horses Vaccinated with Recombinant Clostridium perfringens Toxoids Alpha and Beta for 12 Months.

In horses, Clostridium perfringens is associated with acute and fatal enterocolitis, which is caused by a beta toxin (CPB), and myonecrosis, which is caused by an alpha toxin (CPA). Although the most effective way to prevent these diseases is through vaccination, specific clostridial vaccines for horses against C. perfringens are not widely available. The aim of this study was to pioneer the immunization of horses with three different concentrations (100, 200 and 400 µg) of C. perfringens recombinant alpha (rCPA) and beta (rCPB) proteins, as well as to evaluate the humoral immune response over 360 days. Recombinant toxoids were developed and applied to 50 horses on days 0 and 30. Those vaccines attempted to stimulate the production of alpha antitoxin (anti-CPA) and beta antitoxin (anti-CPB), in addition to becoming innocuous, stable and sterile. There was a reduction in the level of neutralizing anti-CPA and anti-CPB antibodies following the 60th day; therefore, the concentrations of 200 and 400 µg capable of inducing a detectable humoral immune response were not determined until day 180. In practical terms, 200 µg is possibly the ideal concentration for use in the veterinary industry's production of vaccines against the action of C. perfringens in equine species.

Safety of Diphtheria and Tetanus Toxoids and Acellular Pertussis (DTaP) Vaccine in Adults in Japan.

Tetanus toxoid, reduced diphtheria toxoid, and acellular pertussis (Tdap) vaccine is generally used for booster vaccination of infants in Europe and the United States to avoid increased reactogenicity after diphtheria and tetanus toxoids and acellular pertussis (DTaP) vaccination. However, Japan has extended the use of additional DTaP vaccination without reducing the antigen dose for diphtheria and pertussis in adolescents and adults, despite limited reports on its safety in adults. This prospective, observational, questionnaire-based study investigated the occurrence of adverse events (AEs) following DTaP vaccination between June 2018 and June 2019 in participants aged 10 years or older. Of the 250 eligible participants, 235 (94%) responded regarding AEs. Among them, 133 (56.6%) reported AEs, of which 39 reported systemic AEs (16.6%) and 120 reported local AEs (51.1%) attributed to DTaP vaccination. The incidence of local AEs was markedly higher with DTaP vaccination than with non-DTaP vaccination (51.1% vs. 10.5%), and AEs appeared later (P < 0.01) and lasted longer (P < 0.01) with DTaP vaccination. However, more than 75% of these AEs resolved within 7 days. DTaP vaccination was not associated with any serious AEs. These results indicate that the DTaP vaccine can be widely used as a booster in adults as an alternative to the Tdap vaccine.

Virus-like particle-display of the enterotoxigenic Escherichia coli heat-stable toxoid STh-A14T elicits neutralizing antibodies in mice.

Enterotoxigenic Escherichia coli (ETEC) causes diarrhoea by secreting enterotoxins into the small intestine. Human ETEC strains may secrete any combination of three enterotoxins: the heat-labile toxin (LT) and the heat-stable toxins (ST), of which there are two variants, called human ST (STh) and porcine ST (STp). Strains expressing STh, either alone or in combination with LT and/or STp, are among the four most important diarrhoea-causing pathogens affecting children in low- and middle-income countries. ST is therefore an attractive target for ETEC vaccine development. To produce a safe ST-based vaccine, several challenges must be solved. ST must be rendered immunogenic and non-toxic, and antibodies elicited by an ST vaccine should neutralize ST but not cross-react with the endogenous ligands uroguanylin and guanylin. Virus-like particles (VLPs) tend to be highly immunogenic and are increasingly being used as carriers for presenting heterologous antigens in new vaccines. In this study, we have coupled native STh and the STh-A14T toxoid to the coat protein of Acinetobacter phage AP205 by using the SpyCatcher system and immunized mice with these VLPs without the use of adjuvants. We found that both STs were efficiently coupled to the VLP, that both the STh and STh-A14T VLPs were immunogenic in mice, and that the resulting serum antibodies could completely neutralize the toxic activities of native STh. The serum antibodies showed a high degree of immunological cross-reaction to STp, while there was little or no unwanted cross-reaction to uroguanylin and guanylin. Moreover, compared to native STh, the STh-A14T mutation did not seem to negatively impact the immunogenicity of the construct or the neutralizing ability of the resulting sera. Taken together, these findings demonstrate that VLPs are suitable carriers for making STs immunogenic, and that the STh-A14T-coupled AP205 VLP represents a promising ETEC vaccine candidate.

Humoral responses in cattle to commercial vaccines containing Clostridium perfringens epsilon toxoid and C. botulinum types C and D toxoids last less than a-year.

The aim of this study was to evaluate the titers of neutralizing antibodies in cattle inoculated with multivalent commercial clostridial vaccines containing C. botulinum type C (BoNTC), C. botulinum type D (BoNTD), and C. perfringens epsilon (ETX) toxoids for a period of one year. Cattle (Bos taurus), aged 4-6 months and not previously immunized, were vaccinated under four different protocols at days 0 and 30 and followed over one year. Individual serum titration was performed by a serum neutralization test in mice or in MDCK cells. The number of animals with detectable neutralizing antibodies ranged from 40.6% to 78.1%, but only 12.5% of animals showed neutralizing antibodies against all tested antigens. Neutralizing antibodies were found only until 60 days for ETX, 120 days for BoNTC, and 180 days for BoNTD. The absence of detectable neutralizing antibodies against the three antigens before 360 days, suggests that cattle remained unprotected for a long period before the recommended booster vaccination.

Evaluation of Adenylate Cyclase Toxoid Antigen in Acellular Pertussis Vaccines by Using a Bordetella pertussis Challenge Model in Mice.

Bordetella pertussis is the primary causative agent of pertussis (whooping cough), which is a respiratory infection that leads to a violent cough and can be fatal in infants. There is a need to develop more effective vaccines because of the resurgence of cases of pertussis in the United States since the switch from the whole-cell pertussis vaccines (wP) to the acellular pertussis vaccines (aP; diphtheria-tetanus-acellular-pertussis vaccine/tetanus-diphtheria-pertussis vaccine). Adenylate cyclase toxin (ACT) is a major virulence factor of B. pertussis that is (i) required for establishment of infection, (ii) an effective immunogen, and (iii) a protective antigen. The C-terminal repeats-in-toxin domain (RTX) of ACT is sufficient to induce production of toxin-neutralizing antibodies. In this study, we characterized the effectiveness of vaccines containing the RTX antigen against experimental murine infection with B. pertussis RTX was not protective as a single-antigen vaccine against B. pertussis challenge, and adding RTX to 1/5 human dose of aP did not enhance protection. Since the doses of aP used in murine studies are not proportionate to mouse/human body masses, we titrated the aP from 1/20 to 1/160 of the human dose. Mice receiving 1/80 human aP dose had bacterial burden comparable to those of naive controls. Adding RTX antigen to the 1/80 aP base resulted in enhanced bacterial clearance. Inclusion of RTX induced production of antibodies recognizing RTX, enhanced production of anti-pertussis toxin, decreased secretion of proinflammatory cytokines, such as interleukin-6, and decreased recruitment of total macrophages in the lung. This study shows that adding RTX antigen to an appropriate dose of aP can enhance protection against B. pertussis challenge in mice.

Enterotoxigenic Escherichia coli Adhesin-Toxoid Multiepitope Fusion Antigen CFA/I/II/IV-3xSTaN12S-mnLTG192G/L211A-Derived Antibodies Inhibit Adherence of Seven Adhesins, Neutralize Enterotoxicity of LT and STa Toxins, and Protect Piglets against Diarrhea.

Enterotoxigenic Escherichia coli (ETEC) strains are a leading cause of children's diarrhea and travelers' diarrhea. Vaccines inducing antibodies to broadly inhibit bacterial adherence and to neutralize toxin enterotoxicity are expected to be effective against ETEC-associated diarrhea. 6×His-tagged adhesin-toxoid fusion proteins were shown to induce neutralizing antibodies to several adhesins and LT and STa toxins (X. Ruan, D. A. Sack, W. Zhang, PLoS One 10:e0121623, 2015, https://doi.org/10.1371/journal.pone.0121623). However, antibodies derived from His-tagged CFA/I/II/IV-2xSTaA14Q-dmLT or CFA/I/II/IV-2xSTaN12S-dmLT protein were less effective in neutralizing STa enterotoxicity and were not evaluated in vivo for efficacy against ETEC diarrhea. Additionally, His-tagged proteins are considered less desirable for human vaccines. In this study, we produced a tagless adhesin-toxoid MEFA (multiepitope fusion antigen) protein, enhanced anti-STa immunogenicity by including a third copy of STa toxoid STaN12S, and examined antigen immunogenicity in a murine model. Moreover, we immunized pregnant pigs with the tagless adhesin-toxoid MEFA protein and evaluated passive antibody protection against STa+ or LT+ ETEC infection in a pig challenge model. Results showed that tagless adhesin-toxoid MEFA CFA/I/II/IV-3xSTaN12S-mnLTR192G/L211A induced broad antiadhesin and antitoxin antibody responses in the intraperitoneally immunized mice and the intramuscularly immunized pigs. Mouse and pig serum antibodies significantly inhibited adherence of seven colonization factor antigen (CFA) adhesins (CFA/I and CS1 to CS6) and effectively neutralized both toxins. More importantly, suckling piglets born to the immunized mothers acquired antibodies and were protected against STa+ ETEC and LT+ ETEC diarrhea. These results indicated that tagless CFA/I/II/IV-3xSTaN12S-mnLTR192G/L211A induced broadly protective antiadhesin and antitoxin antibodies and demonstrate that this adhesin-toxoid MEFA is a potential antigen for developing broadly protective ETEC vaccines.

Toxoid Vaccination against Bacterial Infection Using Cell Membrane-Coated Nanoparticles.

As nanoparticles exhibit unique properties attractive for vaccine development, they have been progressively implemented as antigen delivery platforms and immune potentiators. Recently, cell membrane-coated nanoparticles have provided a novel approach for intercepting and neutralizing bacterial toxins by leveraging their natural affinity to cellular membranes. Such toxin-nanoparticle assemblies, termed nanotoxoids, allow rapid loading of different types of toxins and have been investigated for their ability to effectively confer protection against bacterial infection. This topical review will cover the current progress in antibacterial vaccine nanoformulations and highlight the nanotoxoid platform as a novel class of nanoparticulate vaccine. We aim to provide insights into the potential of nanotoxoids as a platform that is facile to implement and can be broadly applied to help address the rising threat of super pathogens.

A Recombinant Probiotic, Lactobacillus casei, Expressing the Clostridium perfringens α-toxoid, as an Orally Vaccine Candidate Against Gas Gangrene and Necrotic Enteritis.

The alpha-toxin is one of the virulence factors of Clostridium perfringens for gas gangrene in humans and animals or necrotic enteritis in poultry. The C-terminal domain of this toxin ( cpa 247-370 ) was synthesized and cloned into pT1NX vector to construct the pT1NX-alpha plasmid. This surface-expressing plasmid was electroporated into Lactobacillus casei ATCC 393, generating the recombinant L. casei strain expressing alpha-toxoid (LC-α strain). Expression of this modified alpha-toxoid was confirmed by SDS-PAGE, immunoblotting, and direct immunofluorescence microscopy. BALB/c mice, immunized orally by the recombinant LC-α strain, elicited mucosal and significantly humoral immune responses (p < 0.05) and developed a protection against 900 MLD/mL of the standard alpha-toxin. This study showed that this recombinant LC-α strain could be a promising vaccine candidate against gas gangrene and necrotic enteritis.

Clinical Study of New Tetravalent (Type A, B, E, and F) Botulinum Toxoid Vaccine Derived from M Toxin in Japan.

Botulinum toxin is the most poisonous substance known, and is believed to be a highly lethal as a biological weapon; researchers of the toxin are exposed to this hazard. Botulinum toxoid vaccines have been produced and used in Japan. However, since clinical studies involving these vaccines were conducted before establishment of the Ethical Guidelines for Clinical Research in Japan, their immunogenicity and safety were not systematically assessed. In this study, we produced a new tetravalent (type A, B, E, and F) botulinum toxoid vaccine, the first ever to be derived from M toxin, and conducted quality control tests with reference to the Minimum Requirements in Japan for adsorbed tetanus toxoid vaccine. Subsequently, a clinical study using the new vaccine in 48 healthy adult volunteers was conducted according to the guidelines in Japan. No clinically serious adverse event was noted. Neutralizing antibody titers for each type of toxin in the participants' sera, 1 month after the 4th injection were more than 0.25 IU/mL, indicating sufficient protection. This study demonstrated that the vaccine has marked immunogenicity and is safe for use in humans.

Active immunization of cattle with a bothropic toxoid does not abrogate envenomation by Bothrops asper venom, but increases the likelihood of survival.

This study assessed the protective effect of active immunization of cattle to prevent the envenomation induced by B. asper venom. Two groups of oxen were immunized with a bothropic toxoid and challenged by an intramuscular injection of either 10 or 50 mg B. asper venom, to induce moderate or severe envenomations, respectively. Non-immunized oxen were used as controls. It was found that immunized oxen developed local edema similar to those observed in non-immunized animals. However, systemic effects were totally prevented in immunized oxen challenged with 10 mg venom, and therefore antivenom treatment was not required. When immunized oxen were challenged with 50 mg venom, coagulopathy was manifested 3-16 h later than in non-immunized oxen, demonstrating a delay in the onset of systemic envenomation. In these animals, active immunization did not eliminate the need for antivenom treatment, but increased the time lapse in which antivenom administration is still effective. All experimentally envenomed oxen completely recovered after a week following venom injection. Our results suggest that immunization of cattle with a bothropic toxoid prevents the development of systemic effects in moderate envenomations by B. asper, but does not abrogate these effects in severe envenomation.

Preclinical evaluation of a chemically detoxified pneumolysin as pneumococcal vaccine antigen.

The use of protein antigens able to protect against the majority of Streptococcus pneumoniae serotypes is envisaged as stand-alone and/or complement to the current capsular polysaccharide-based pneumococcal vaccines. Pneumolysin (Ply) is a key virulence factor that is highly conserved in amino acid sequence across pneumococcal serotypes, and therefore may be considered as a vaccine target. However, native Ply cannot be used in vaccines due to its intrinsic cytolytic activity. In the present work a completely, irreversibly detoxified pneumolysin (dPly) has been generated using an optimized formaldehyde treatment. Detoxi-fication was confirmed by dPly challenge in mice and histological analysis of the injection site in rats. Immunization with dPly elicited Ply-specific functional antibodies that were able to inhibit Ply activity in a hemolysis assay. In addition, immunization with dPly protected mice against lethal intranasal challenge with Ply, and intranasal immunization inhibited nasopharyngeal colonization after intranasal challenge with homologous or heterologous pneumococcal strain. Our findings supported dPly as a valid candidate antigen for further pneumococcal vaccine development.

PLGA nano/micro particles encapsulated with pertussis toxoid (PTd) enhances Th1/Th17 immune response in a murine model.

Poly(lactic-co-glycolic acid) (PLGA) based nano/micro particles were investigated as a potential vaccine platform for pertussis antigen. Presentation of pertussis toxoid as nano/micro particles (NP/MP) gave similar antigen-specific IgG responses in mice compared to soluble antigen. Notably, in cell line based assays, it was found that PLGA based nano/micro particles enhanced the phagocytosis of fluorescent antigen-nano/micro particles by J774.2 murine monocyte/macrophage cells compared to soluble antigen. More importantly, when mice were immunised with the antigen-nano/micro particles they significantly increased antigen-specific Th1 cytokines INF-γ and IL-17 secretion in splenocytes after in vitro re-stimulation with heat killed Bordetalla pertussis, indicating the induction of a Th1/Th17 response. Also, presentation of pertussis antigen in a NP/MP formulation is able to provide protection against respiratory infection in a murine model. Thus, the NP/MP formulation may provide an alternative to conventional acellular vaccines to achieve a more balanced Th1/Th2 immune response.

Recent advances in nontoxic Escherichia coli heat-labile toxin and its derivative adjuvants.

INTRODUCTION: The nontoxic heat-labile enterotoxin (LT) of Escherichia coli and the B subunit of LT (LTB) have been extensively studied as potent vaccine adjuvants. Areas covered: This review covers the area of enterotoxin based vaccine adjuvant and summarizes the development of nontoxic LT mutant (mLT) and LTB and their potency as oral, parenteral and injection adjuvants. Recent evidences indicated that the mechanism of LTB adjuvanticity was to enhance the turnover of dendritic cells (DCs) in spleen and increase DCs capacity to perform as antigen presentation cells (APCs) encountered with T cells. LTB also induces B and T cells clustering and delay/arrest in T-cell division following endocytosis or B-cell receptor (BCR) uptaking of antigen in a ganglioside-mediated manner. Expert commentary: It is pointed out that the immunogenicity of LTB (or LT) is more important than the receptor binding property (or ADP-ribosylation activity) for the adjuvanticity of LT toxoid. The immunogenicity of LTB (or LT) might confer unknown characteristics to maintain LT toxoid adjuvanticity.

Defining the optimal formulation and schedule of a candidate toxoid vaccine against Clostridium difficile infection: A randomized Phase 2 clinical trial.

BACKGROUND: Clostridium difficile, a major cause of nosocomial and antibiotic-associated diarrhea, carries a significant disease and cost burden. This study aimed to select an optimal formulation and schedule for a candidate toxoid vaccine against C. difficile toxins A and B. METHODS: Randomized, placebo-controlled, two-stage, Phase 2 study in a total of 661 adults aged 40-75 years. Stage I: low (50 µg antigen) or high (100 µg antigen) dose with or without aluminum hydroxide (AlOH) adjuvant, or placebo, administered on Days 0-7-30. Stage II: Days 0-7-30, 0-7-180, and 0-30-180, using the formulation selected in Stage I through a decision tree defined a priori and based principally on a bootstrap ranking approach. Administration was intramuscular. Blood samples were obtained on Days 0, 7, 14, 30, 60 (Stage I and II), 180, and 210 (Stage II); IgG to toxins A and B was measured by ELISA and in vitro functional activity was measured by toxin neutralizing assay (TNA). Safety data were collected using diary cards. RESULTS: In Stage I the composite immune response against toxins A and B (percentage of participants who seroconverted for both toxins) was highest in the high dose+adjuvant group (97% and 92% for Toxins A and B, respectively) and was chosen for Stage II. In Stage II the immune response profile for this formulation through Day 180 given on Days 0-7-30 ranked above the other two administration schedules. There were no safety issues. CONCLUSIONS: The high dose+adjuvant (100 µg antigen+AlOH) formulation administered at 0-7-30 days elicited the best immune response profile, including functional antibody responses, through Day 180 and was selected for use in subsequent clinical trials.

Oral immunization of mice against Clostridium perfringens epsilon toxin with a Lactobacillus casei vector vaccine expressing epsilon toxoid.

Clostridium perfringens type D infects ruminants and causes the enterotoxemia disease by ε-toxin. A mutated ε-toxin gene lacking toxicity was designed, synthesized, and cloned into the pT1NX vector and electroporated into Lactobacillus casei competent cells to yield LC-pT1NX-ε recombinant strain. BALB/c mice, immunized orally with this strain, highly induced mucosal, humoral, and cell-mediated immune responses and developed a protection against 200 MLD/ml of the activated ε-toxin. This study showed that the LC-pT1NX-ε could be a promising vaccine candidate against the enterotoxemia disease.

A phase 1, placebo-controlled, randomized study of the safety, tolerability, and immunogenicity of a Clostridium difficile vaccine administered with or without aluminum hydroxide in healthy adults.

INTRODUCTION: Clostridium difficile is a significant cause of morbidity and mortality in hospitals, nursing homes, and long-term care facilities. The bacteria can produce 3 toxins, of which the C. difficile toxin A and C. difficile toxin B are the principal virulence factors for C. difficile-associated disease. METHODS: A phase 1, first-in-human, placebo-controlled, dose-escalation study was performed to assess the safety and immunogenicity of an investigational vaccine candidate consisting of genetically and chemically detoxified, purified toxins A and B. The toxoids, either alone or in combination with aluminum hydroxide (Al(OH)3), were administered to healthy adults 50-85 years of age at antigen dose levels of 50, 100, or 200 µg in a 3-dose regimen administered at 0, 1, and 6 months. RESULTS: Overall, the C. difficile vaccine formulations and doses administered were generally well tolerated. Local reactions and systemic events were predominantly mild to moderate, were more common in the 50-64-year age cohort, and comprised mostly injection site pain, headache, and fatigue. In subjects who received the vaccine formulations, both the toxin A- and toxin B-specific neutralizing antibody geometric mean concentrations increased substantially at 1 month after Dose 2 and after Dose 3 compared to baseline. In the 50-64-year age cohort, geometric mean fold rises (GMFRs) in toxin A-specific neutralizing antibodies from baseline at Month 7 ranged from 59.19 to 149.23 in the vaccine groups compared to 2.47 in the control group. For toxin-B specific neutralizing antibodies, the GMFRs from baseline at Month 7 ranged from 116.67 to 2503.75 in the vaccine groups compared to 2.48 in the control group. In the 65-85-year age cohort, GMFRs in toxin A-specific neutralizing antibodies from baseline at Month 7 ranged from 42.73 to 254.77 in the vaccine groups compared to 2.03 in the control group. For toxin-B specific neutralizing antibodies, the GMFRs from baseline at Month 7 ranged from 136.12 to 4922.80 in the vaccine groups compared to 1.58 in the control group. Potent antitoxin neutralizing responses were still evident in immunized subjects in both age groups at Month 12. Although there was no clear dose-level response pattern, the data suggest that both the antitoxin A- and B-specific neutralizing responses were trending higher in the toxoid-only groups compared to the toxoid+Al(OH)3 groups. Furthermore, the magnitude of the immune response was similar in the 2 age cohorts. CONCLUSION: The vaccine formulations studied in this phase 1 study were immunogenic and well tolerated. The results presented support further development of the C. difficile vaccine candidate in a larger population of subjects to determine the optimal dose and immunization schedule. CLINICAL TRIAL REGISTRY: NCT01706367.

Vaccination during pregnancy: Today's need in India.

Immunization during pregnancy is a simple and effective way to protect the mother and child from certain infections. The immunological changes occur during pregnancy which may be responsible for the susceptibility of certain infectious diseases that increases the risk of more serious outcomes. Vaccination of pregnant women can protect to mother against vaccine-preventable infections, and in so doing potentially protect the fetus. Immunization during pregnancy can also directly protect the fetus and infant via transferred of antibodies from the mother to the fetus. This is why vaccinations during pregnancy are so important. Vaccination during pregnancy is a cost-effective strategy to improve pregnancy outcomes in India. Globally, no scientific study exist which shows the risk of fetus after vaccination of pregnant women with inactivated vaccines or bacterial vaccines or toxoids. Even live vaccines causing risk to fetus is theoretical. Vaccination with inactivated virus, bacterial or toxoid in pregnancy is risk to a developing fetus during pregnancy is theoretical. But definitely the live vaccine poses a theoretical risk to a developing fetus. Therefore, all live vaccines should be avoided during pregnancy. The developing country like India where the people can't afford these vaccines, the government should be included these vaccines in routine immunization program.

Enhancement of long-lasting immunoprotective effect against Androctonus australis hector envenomation using safe antigens: Comparative role of MF59 and Alum adjuvants.

Envenomation is a public health problem in many regions of the world. The only available treatment is the serotherapy that has limited efficiency due to the delay of its administration. The goal of this study is to provide a new and more efficient alternative to this treatment. A comparative study of the effects of two adjuvants in their ability to enhance the efficiency of the detoxified and safe antigens to produce a long lasting immunoprotection is undertaken using Aluminum Hydroxide adjuvant (Alum) or the water-in-oil MF59 adjuvant mixed with Androctonus australis hector (Aah) detoxified venom, and compare their effects on the immune system. Immunization schedule was performed with two groups of rabbits, which were injected with attenuated venom and Alum or MF59 adjuvant preparations, once a month during three months. Blood samples were collected each week for cell count, evaluation of myeloperoxidase (MPO) and eosinoperoxydase (EPO) activities and antibody titer. After four months from the last immunization, rabbits were challenged with increased doses of native Aah venom. Results showed that MF59 effect was immediate in the first 24h post-immunization by activating the recruitment of lymphocytes, monocytes and neutrophils, while Alum adjuvant effect seems to be delayed, and appeared in the second week after immunization. An important cell infiltration was observed with Alum preparation, due to its specific local depot effect. However, immunized animals with MF59 preparation challenged with the native venom showed a protective effect against its toxicity until 6 LD50 compared to those immunized with Alum preparation which are only protected at 4 LD50. One week after challenge, only immunized animals with Alum preparation present an increase in cell infiltration, MPO and EPO activities. These results are correlated with the ability of MF59 adjuvant to induce a potent immunoprotective effect against Aah venom compared to Alum adjuvant.

Divalent toxoids loaded stable chitosan-glucomannan nanoassemblies for efficient systemic, mucosal and cellular immunostimulatory response following oral administration.

The present study reports dual tetanus and diphtheria toxoids loaded stable chitosan-glucomannan nanoassemblies (sCh-GM-NAs) formulated using tandem ionic gelation technique for oral mucosal immunization. The stable, lyophilized sCh-GM-NAs exhibited ~152 nm particle size and ~85% EE of both the toxoids. The lyophilized sCh-GM-NAs displayed excellent stability in biomimetic media and preserved chemical, conformation and biological stability of encapsulated toxoids. The higher intracellular APCs uptake of sCh-GM-NAs was concentration and time dependent which may be attributed to the receptor mediated endocytosis via mannose and glucose receptor. The higher Caco-2 uptake of sCh-GM-NAs was further confirmed by ex vivo intestinal uptake studies. The in vivo evaluation revealed that sCh-GM-NAs posed significantly (p<0.001) higher humoral, mucosal and cellular immune response than other counterparts by eliciting complete protective levels of anti-TT and anti-DT (~0.1 IU/mL) antibodies. Importantly, commercial 'Dual antigen' vaccine administered through oral or intramuscular route was unable to elicit all type of immune response. Conclusively, sCh-GM-NAs could be considered as promising vaccine adjuvant for oral mucosal immunization.