Frequent nasal administrations of recombinant cholera toxin B subunit (rCTB)-containing tetanus and diphtheria toxoid vaccines induced antigen-specific serum and mucosal immune responses in the presence of anti-rCTB antibodies

Development of safe, effective and immunogenic vaccine candidate for diarrheagenic Escherichia coli main pathotypes in a mouse model

Background

Enteric and diarrheal diseases are important causes of childhood death in the developing world. These diseases are responsible for more than 750 thousand deaths in children under 5 years old worldwide, ranking second cause of death, after lower respiratory diseases, in this age group. Among the major causative agents of diarrhea is Escherichia coli. There are several vaccine trials for diarrheagenic E. coli. However, diarrheagenic E. coli has seven pathotypes and vaccines are directed for one or two of the five main pathotypes-causing diarrhea. Currently, there are no combined vaccines available in the market for all five diarrheagenic E. coli pathotypes. Therefore, we aimed to develop a low-cost vaccine candidate combining the five main diarrheagenic E. coli to offer wide-spectrum protection. We formulated a formalin-killed whole-cell mixture of enteroaggregative, enteropathogenic, enteroinvasive, enterohemorrhagic, and enterotoxigenic E. coli pathotypes as a combined vaccine candidate.

Results

We immunized Balb/C mice subcutaneously with 10⁹ CFU of combined vaccine candidate and found a significant increase in survival rate post challenge compared to unimmunized controls (100 % survival). Next we aimed to determine the immunological response of mice to the combined vaccine candidate compared to each pathotype immunization. To do so, we immunized mice groups with combined vaccine candidate and monitored biomarkers levels over 6 weeks as well as measured responses post challenge with relevant living E. coli. We found significant increase in specific systemic antibodies (IgG), interferon gamma (IFNγ) and interleukin 6 (IL-6) levels elicited by combined vaccine candidate especially in the first 2 weeks after mice immunization compared to controls (p < 0.05). We also evaluated alum and cholera toxin B subunit (CTB) as potential adjuvant systems for our candidate vaccine. We found that CTB-adjuvanted combined vaccine candidate showed significantly higher IgG and IFNγ levels than alum.

Conclusions

Overall, our combined vaccine candidate offered protection against the five main diarrheagenic E. coli pathotypes in a single vaccine using mouse model. To the best of our knowledge, this is the first combined vaccine against the five main diarrheagenic E. coli pathotypes that is cost-effective with promise for further testing in humans.

Electronic supplementary material

The online version of this article (doi:10.1186/s13104-016-1891-z) contains supplementary material, which is available to authorized users.

Progress toward development of an inhalation vaccine against botulinum toxin

The looming threat of bioterrorism has enhanced interest in the development of vaccines against agents such as botulinum toxin. This in turn has stimulated efforts to create vaccines that are effective by the oral and inhalation routes. Recently, considerable progress has been made in creating an inhalation vaccine against botulism. This work stems from the discovery that a polypeptide that represents a third of the toxin molecule retains the ability to be adsorbed from the airway and to evoke an immune response but retains none of the adverse effects of the native toxin. Interestingly, this polypeptide can also serve as a carrier molecule in the creation of inhalation vaccines against other pathogens.

High level expression of a functionally active cholera toxin B: rabies glycoprotein fusion protein in tobacco seeds

A synthetic DNA construct containing cholera toxin B subunit, genetically fused to the surface glycoprotein of rabies virus was expressed in tobacco plants from a seed specific (legumin) promoter. Seed specific expression was monitored by real-time PCR, GM1-ELISA and Western blot analyses. The fusion protein accumulated in tobacco seeds at up to 1.22% of the total seed protein. It was functionally active in binding to the GM1-ganglioside receptors, suggesting its assembly into pentamers in seeds of the transgenic plants. Immunoblot analysis confirmed that the approximately 80.6 kDa monomeric fusion polypeptide was expressed in tobacco seeds and accumulated as an approximately 403 kDa pentamer. Evaluation of its immunoprotective ability against rabies and cholera is to be examined.

Plants as bioreactors for the production of vaccine antigens

Plants have been identified as promising expression systems for commercial production of vaccine antigens. In phase I clinical trials several plant-derived vaccine antigens have been found to be safe and induce sufficiently high immune response. Thus, transgenic plants, including edible plant parts are suggested as excellent alternatives for the production of vaccines and economic scale-up through cultivation. Improved understanding of plant molecular biology and consequent refinement in the genetic engineering techniques have led to designing approaches for high level expression of vaccine antigens in plants. During the last decade, several efficient plant-based expression systems have been examined and more than 100 recombinant proteins including plant-derived vaccine antigens have been expressed in different plant tissues. Estimates suggest that it may become possible to obtain antigen sufficient for vaccinating millions of individuals from one acre crop by expressing the antigen in seeds of an edible legume, like peanut or soybean. In the near future, a plethora of protein products, developed through ‘naturalized bioreactors’ may reach market. Efforts for further improvements in these technologies need to be directed mainly towards validation and applicability of plant-based standardized mucosal and edible vaccines, regulatory pharmacology, formulations and the development of commercially viable GLP protocols. This article reviews the current status of developments in the area of use of plants for the development of vaccine antigens.

Nasal immunization with a recombinant HIV gp120 and nanoemulsion adjuvant produces Th1 polarized responses and neutralizing antibodies to primary HIV type 1 isolates

Epidemiological and experimental data suggest that both robust neutralizing antibodies and potent cellular responses play important roles in controlling primary HIV-1 infection. In this study we have investigated the induction of systemic and mucosal immune responses to HIV gp120 monomer immunogen administered intranasally in a novel, oil-in-water nanoemulsion (NE) adjuvant. Mice and guinea pigs intranasally immunized by the application of recombinant HIV gp120 antigen mixed in NE demonstrated robust serum anti-gp120 IgG, as well as bronchial, vaginal, and serum anti-gp120 IgA in mice. The serum of these animals demonstrated antibodies that cross-reacted with heterologous serotypes of gp120 and had significant neutralizing activity against two clade-B laboratory strains of HIV (HIVBaL and HIVSF162) and five primary HIV-1 isolates. The analysis of gp120-specific CTL proliferation, INF-gamma induction, and prevalence of anti-gp120 IgG2 subclass antibodies indicated that nasal vaccination in NE also induced systemic, Th1-polarized cellular immune responses. This study suggests that NE should be evaluated as a mucosal adjuvant for multivalent HIV vaccines.

Induction of mucosal and systemic immune responses following oral immunization of mice with Lactococcus lactis expressing human papillomavirus type 16 L1

Human papillomavirus type 16 L1 (HPV16 L1) has shown considerable promise as a parenteral vaccine for prevention of cervical cancers. Here, we report the possibility of oral vaccination for HPV16 L1 using Lactococcus lactis (L. lactis) as a live vector. L. lactis MG1363 was transformed with two types of HPV16 L1-encoding plasmids for intracellular expression or secretion. L. lactis transformed with HPV16 L1-encoding plasmids retained biochemical lactic acid production capability. The mucosal and systemic immune responses were affected by the cellular location of expressed HPV16 L1 proteins in L. lactis. Serum IgG responses were induced after oral immunizations of L. lactis secreting HPV16 L1. Vaginal IgA immune responses were observed following oral immunization with L. lactis expressing HPV16 L1 in an intracellular form, but not with L. lactis secreting HPV16 L1. Furthermore, induction of HPV16 L1-specific mucosal immune responses was affected by immunization frequency. Six immunizations over 5 weeks were required to induce vaginal immune responses. The levels of HPV16 L1-specific vaginal IgA were maintained until 12 weeks after the first vaccination. These results suggest the feasibility of L. lactis as an oral vaccine vehicle of HPV16 L1 and demonstrate the importance of cellular loci of expressed antigen for induction of vaginal and systemic immune responses.

Induction of protective and mucosal immunity against diphtheria by a immune stimulating complex (ISCOMS) based vaccine

There is increasing concern over the efficacy of existing vaccines for diphtheria and there is interest in the development of a mucosally active formulation which might improve local protection. Lipophilic immune stimulating complexes (ISCOMS) containing Quil A are active by both parenteral and mucosal routes and here we have established methods for incorporating palmitified diphtheria toxoid (DT) into ISCOMS. The resulting formulation was immunogenic by the subcutaneous, oral and intranasal routes, with very low doses of DT inducing systemic humoral immune responses, as well as cell mediated immunity including both gammaIFN and IL5 production. Intranasal immunisation with DT in ISCOMS also stimulated significant local antibody production in tracheal washes, as well as cellular immunity in draining lymphoid tissues and serum neutralising antibodies. Finally, subcutaneous immunisation of guinea pigs with DT in ISCOMS primed protective immunity against challenge with diphtheria holotoxin more efficiently than the equivalent doses of DT in the conventional alum vaccine. ISCOMS based vaccines may provide a novel strategy for mucosal and systemic immunisation against diphtheria.

Induction of systemic and mucosal cross-clade neutralizing antibodies in BALB/c mice immunized with human immunodeficiency virus type 1 clade A virus-like particles administered by different routes of inoculation

We have recently developed a candidate human immunodeficiency virus type 1 (HIV-1) vaccine model, based on virus-like particles (VLPs) expressing gp120 from a Ugandan HIV-1 isolate of clade A (HIV-VLP(A)s), which shows the induction of neutralizing antibodies as well as cytotoxic T lymphocytes (CTL) in BALB/c mice by intraperitoneal (i.p.) administration. In the present study, immunization experiments based on a multiple-dose regimen have been performed with BALB/c mice to compare different routes of administration. i.p. and intranasal (i.n.), but not oral, administration induce systemic as well as mucosal (vaginal and intestinal) immunoglobulin G (IgG) and IgA responses. These immune sera exhibit >50% ex vivo neutralizing activity against both autologous and heterologous primary isolates. Furthermore, the administration of HIV-VLP(A)s by the i.n. immunization route induces a specific CTL activity, although at lower efficiency than the i.p. route. The HIV-VLP(A)s represent an efficient strategy to stimulate both arms of immunity; furthermore, the induction of specific humoral immunity at mucosal sites, which nowadays represent the main port of entry for HIV-1 infection, is of great interest. All these properties, and the possible cross-clade in vivo protection, could make these HIV-VLP(A)s a good candidate for a mono- and multicomponent worldwide preventive vaccine approach not restricted to high-priority regions, such as sub-Saharan countries.

Mucosal adjuvant properties of mutant LT-IIa and LT-IIb enterotoxins that exhibit altered ganglioside-binding activities

LT-IIa and LT-IIb, the type II heat-labile enterotoxins of Escherichia coli, are closely related in structure and function to cholera toxin and LT-I, the type I heat-labile enterotoxins of Vibrio cholerae and E. coli, respectively. Recent studies from our group demonstrated that LT-IIa and LT-IIb are potent systemic and mucosal adjuvants. To determine whether binding of LT-IIa and LT-IIb to their specific ganglioside receptors is essential for adjuvant activity, LT-IIa and LT-IIb enterotoxins were compared with their respective single-point substitution mutants which have no detectable binding activity for their major ganglioside receptors [e.g., LT-IIa(T34I) and LT-IIb(T13I)]. Both mutant enterotoxins exhibited an extremely low capacity for intoxicating mouse Y1 adrenal cells and for inducing production of cyclic AMP in a macrophage cell line. BALB/c female mice were immunized by the intranasal route with the surface adhesin protein AgI/II of Streptococcus mutans alone or in combination with LT-IIa, LT-IIa(T34I), LT-IIb, or LT-IIb(T13I). Both LT-IIa and LT-IIb potentiated strong mucosal and systemic immune responses against AgI/II. Of the two mutant enterotoxins, only LT-IIb(T13I) had the capacity to strongly potentiate mucosal anti-AgI/II and systemic anti-AgI/II antibody responses. Upon boosting with AgI/II, however, both LT-IIa(T34I) and LT-IIb(T13I) enhanced humoral memory responses to AgI/II. Flow cytometry demonstrated that LT-IIa(T34I) had no affinity for cervical lymph node lymphocytes. In contrast, LT-IIb(T13I) retained binding activity for T cells, B cells, and macrophages, indicating that this immunostimulatory mutant enterotoxin interacts with one or more unknown lymphoid cell receptors.

Recombinant cholera toxin B subunit (rCTB) as a mucosal adjuvant enhances induction of diphtheria and tetanus antitoxin antibodies in mice by intranasal administration with diphtheria-pertussis-tetanus (DPT) combination vaccine

Recombinant cholera toxin B subunit (rCTB) which is produced by Bacillus brevis carrying pNU212-CTB acts as a mucosal adjuvant capable of enhancing host immune responses specific to unrelated, mucosally co-administered vaccine antigens. When mice were administered intranasally with diphtheria-pertussis-tetanus (DPT) combination vaccine consisting of diphtheria toxoid (DTd), tetanus toxoid (TTd), pertussis toxoid (PTd), and formalin-treated filamentous hemagglutinin (fFHA), the presence of rCTB elevated constantly high values of DTd- and TTd-specific serum ELISA IgG antibody titres, and protective levels of diphtheria and tetanus toxin-neutralizing antibodies but the absence of rCTB did not. Moreover, the addition of rCTB protected all mice against tetanic symptoms and deaths. DPT combination vaccine raised high levels of serum anti-PT IgG antibody titres regardless of rCTB and protected mice from Bordetella pertussis challenge. These results suggest that co-administration of rCTB as an adjuvant is necessary for induction of diphtheria and tetanus antitoxin antibodies on the occasion of intranasal administration of DPT combination vaccine.

Immunological tools for the assessment of both humoral and cellular immune responses in Foxes (Vulpes vulpes) using ovalbumin and cholera toxin B as an antigenic model

The immune response in the fox (Vulpes vulpes), despite the success of the oral rabies vaccine is not well characterized, and specific immunological tools are needed. To investigate both the humoral and cellular immune response, we used ovalbumin (OVA) and cholera toxin B (CTB) as an antigenic model to set-up ELISA and ELISPOT antibodies secreting cells (ASC) assays in the fox model. Identification of antibodies that cross-react with fox immunoglobulin was performed by Western blot, and their use was adapted for both the ELISA and ELISPOT ASC assay. The humoral and cellular specific immune responses were assessed after intra-muscular or intra-nasal immunization. Intra-muscular immunization resulted in the development of both cellular and humoral anti-OVA and anti-CTB responses in peripheral blood mononuclear cells (PBMCs). Immunization via the intra-nasal route resulted in the development of a cellular and humoral response against CTB in PBMCs. This immune response was confirmed using splenocytes from immunized animals by ELISPOT assay at euthanasia. Females immunized via the intra-nasal route developed specific anti-CTB IgM, IgA and IgG in vaginal fluids after the initial boost (day 26) showing that mucosal immunization produces a vaginal immune response in foxes. These immunological tools developed here are now available to be adapted to other antigenic models to facilitate further immune studies in foxes.