Enhanced Immune Response to DNA Vaccine Encoding Bacillus anthracis PA-D4 Protects Mice against Anthrax Spore Challenge

The use of electroporation to deliver DNA-based vaccines

INTRODUCTION

Nucleic acids represent a promising platform for creating vaccines. One disadvantage of this approach is its relatively low immunogenicity. Electroporation (EP) is an effective way to increase the DNA vaccines immunogenicity. However, due to the different configurations of devices used for EP, EP protocols optimization is required not only to enhance immunogenicity, but also to ensure greater safety and tolerability of the EP procedure.

AREA COVERED

An data analysis for recent years on the DNA vaccines delivery against viral and parasitic infections using EP was carried out. The study of various EP physical characteristics, such as frequency, pulse duration, pulse interval, should be considered along with the immunogenic construct design and the site of delivery of the vaccine, through the study of the immunogenic and protective characteristics of the latter.

EXPERT OPINION

Future research should focus on regulating the humoral and cellular response required for protection against infectious agents by modifying the EP protocol. Significant efforts will be directed to establishing the possibility of redirecting the immune response toward the Th1 or Th2 response by changing the EP physical parameters. It will allow for an individual selective approach during EP, depending on the pathogen type of an infectious disease.

BA3338, a surface layer homology domain possessing protein augments immune response and protection efficacy of protective antigen against Bacillus anthracis in mouse model

AIM

Category A classified Bacillus anthracis is highly fatal pathogen that causes anthrax and creates challenges for global security and public health. In this study, development of a safe and ideal next-generation subunit anthrax vaccine has been evaluated in mouse model.

METHOD AND RESULTS

Protective antigen (PA) and BA3338, a surface layer homology (SLH) domain possessing protein were cloned, expressed in heterologous system and purified by IMAC. Recombinant PA and BA3338 with alum were administered in mouse alone or in combination. The humoral and cell-mediated immune response was measured by ELISA and vaccinated animals were challenged with B. anthracis spores via intraperitoneal route. The circulating IgG antibody titre of anti-PA and anti-BA3338 was found significantly high in the first and second booster sera. A significant enhanced level of IL-4, IFN-γ and IL-12 was observed in antigens stimulated supernatant of splenocytes of PA + BA3338 vaccinated animals. A combination of PA and BA3338 provided 80% protection against 20 LD₅₀ lethal dose of B. anthracis spores.

CONCLUSION

Both antigens induced admirable humoral and cellular immune response as well as protective efficacy against B. anthracis spores.

SIGNIFICANCE AND IMPACT OF THE STUDY

This study has been evaluated for the first time using BA3338 as a vaccine candidate alone or in combination with well-known anthrax vaccine candidate PA. The findings of this study demonstrated that BA3338 could be a co-vaccine candidate for development of dual subunit vaccine against anthrax.

Immunogenicity and Biodistribution of Anthrax DNA Vaccine Delivered by Intradermal Electroporation

PURPOSE

Anthrax is a lethal bacterial disease caused by gram-positive bacterium Bacillus anthracis and vaccination is a desirable method to prevent anthrax infections. In the present study, DNA vaccine encoding a protective antigen of Bacillus anthracis was prepared and we investigated the influence of DNA electrotransfer in the skin on the induced immune response and biodistribution.

METHODS AND RESULTS

The tdTomato reporter gene for the whole animal in vivo imaging was used to assess gene transfer efficiency into the skin as a function of electrical parameters. Compared to that with 25 V, the transgene expression of red fluorescent protein increased significantly when a voltage of 90 V was used. Delivery of DNA vaccines expressing Bacillus anthracis protective antigen domain 4 (PAD4) with an applied voltage of 90 V induced robust PA-D4-specific antibody responses. In addition, the in vivo fate of anthrax DNA vaccine was studied after intradermal administration into the mouse. DNA plasmids remained at the skin injection site for an appropriate period of time after immunization. Intradermal administration of DNA vaccine resulted in detection in various organs (viz., lung, heart, kidney, spleen, brain, and liver), although the levels were significantly reduced.

CONCLUSION

Our results offer important insights into how anthrax DNA vaccine delivery by intradermal electroporation affects the immune response and biodistribution of DNA vaccine. Therefore, it may provide valuable information for the development of effective DNA vaccines against anthrax infection.

Development of a multiple-antigen protein fusion vaccine candidate that confers protection against Bacillus anthracis and Yersinia pestis

Bacillus anthracis and Yersinia pestis are zoonotic bacteria capable of causing severe and sometimes fatal infections in animals and humans. Although considered as diseases of antiquity in industrialized countries due to animal and public health improvements, they remain endemic in vast regions of the world disproportionally affecting the poor. These pathogens also remain a serious threat if deployed in biological warfare. A single vaccine capable of stimulating rapid protection against both pathogens would be an extremely advantageous public health tool. We produced multiple-antigen fusion proteins (MaF1 and MaF2) containing protective regions from B. anthracis protective antigen (PA) and lethal factor (LF), and from Y. pestis V antigen (LcrV) and fraction 1 (F1) capsule. The MaF2 sequence was also expressed from a plasmid construct (pDNA-MaF2). Immunogenicity and protective efficacy were investigated in mice following homologous and heterologous prime-boost immunization. Antibody responses were determined by ELISA and anthrax toxin neutralization assay. Vaccine efficacy was determined against lethal challenge with either anthrax toxin or Y. pestis. Both constructs elicited LcrV and LF-specific serum IgG, and MaF2 elicited toxin-neutralizing antibodies. Immunizations with MaF2 conferred 100% and 88% protection against Y. pestis and anthrax toxin, respectively. In contrast, pDNA-MaF2 conferred only 63% protection against Y. pestis and no protection against anthrax toxin challenge. pDNA-MaF2-prime MaF2-boost induced 75% protection against Y. pestis and 25% protection against anthrax toxin. Protection was increased by the molecular adjuvant CARDif. In conclusion, MaF2 is a promising multi-antigen vaccine candidate against anthrax and plague that warrants further investigation.

Anthrax and plague are ancient infectious diseases that continue to affect people living in poor, endemic regions and to threaten industrialized nations due to their potential use in biowarfare. Candidate vaccines need improvement to minimize non-desirable effects and increase their efficacy. The purpose of this work was to develop and evaluate a single subunit vaccine capable of conferring protection against Bacillus anthracis and Yersinia pestis. To this end, specific regions from their genome or key protective protein sequences from both microorganisms were combined to obtain either recombinant plasmids or recombinant proteins and tested as vaccine candidates in mice. The recombinant protein MaF2 induced specific antibody responses and afforded full and partial protection against Y. pestis and B. anthracis, respectively. Meanwhile, the DNA vaccine equivalent to MaF2 conferred only partial protection against Y. pestis, which increased when combined with an MaF2 protein boost. MaF2 emerged as a promising dual pathogen recombinant vaccine that warrants further investigation.

Vaccines against anthrax based on recombinant protective antigen: problems and solutions

Introduction: Anthrax is a dangerous bio-terror agent because Bacillus anthracis spores are highly resilient and can be easily aerosolized and disseminated. There is a threat of deliberate use of anthrax spores aerosol that could lead to serious fatal diseases outbreaks. Existing control measures against inhalation form of the disease are limited. All of this has provided an impetus to the development of new generation vaccines. Areas сovered: This review is devoted to challenges and achievements in the design of vaccines based on the anthrax recombinant protective antigen (rPA). Scientific databases have been searched, focusing on causes of PA instability and solutions to this problem, including new approaches of rPA expression, novel rPA-based vaccines formulations as well as the simultaneous usage of PA with other anthrax antigens. Expert opinion: PA is a central anthrax toxin component, playing a key role in the defense against encapsulated and unencapsulated strains. Subunit rPA-based vaccines have a good safety and protective profile. However, there are problems of PA instability that are greatly enhanced when using aluminum adjuvants. New adjuvant compositions, dry formulations and resistant to proteolysis and deamidation mutant PA forms can help to handle this issue. Devising a modern anthrax vaccine requires huge efforts.

Phylogenetic affiliation and determination of bioactive compounds of bacterial population associated with organs of mud crab, Scylla olivacea

Mud crab belongs to the genus Scylla is an economically valuable and preferred species for costal aquaculture in Asian countries, including India. In recent years, there has been a tremendous expansion of Scylla farming, which has led to increasing research on its habit and habitats. However, there has been no study undertaken to understand the role of the bacterial population associated with the different organs of the mud crab, Scylla olivacea. In total, 43 isolates were recovered from four selected parts of the crab (carapace, n = 18; abdomen n = 11; leg, n = 8; and hand, n = 6), and the 16S rRNA gene was used to identify the bacterial isolates. The antimicrobial potential along with the detection of modular polyketide synthase (PKSI), cytochrome P450 hydroxylase (CYP) and non-ribosomal peptide synthetase (NRPS) gene clusters were investigated to show a relationship among the biosynthetic genes with their useful aspects. Additionally, the potential three strains (BPS_CRB12, BPS_CRB14 and BPS_CRB41), which showed significant antimicrobial activities, also showed the presence of twenty volatile compounds (VOCs) using GC-MS analysis. We conclude that the strain Aneurinibacillus aneurinilyticus BPS_CRB41 could be source for the production of bioactive compounds.

Intradermal immunization with botulinum neurotoxin serotype E DNA vaccine induces humoral and cellular immunity and protects against lethal toxin challenge

Botulinum neurotoxins (BoNTs) produced by the spore-forming, gram-positive, anaerobic bacterium Clostridium botulinum are the most toxic substances known and cause botulism, flaccid paralysis, or death. Owing to their high lethality, BoNTs are classified as category A agents by the Centers for Disease Control (CDC). Currently, there are no vaccines available to protect against BoNTs, so the rapid development of a safe and effective vaccine is important. DNA-based vaccines have recently drawn great attention because they can be developed quickly and can be applied in mass vaccination strategies to prevent disease outbreaks. Here, we report on the immunogenic and protective efficacy of a DNA vaccine, encoding a 50-kDa carboxy-terminal fragment of the BoNT serotype E heavy chain, which is delivered via an intradermal route. This plasmid DNA vaccine induced robust humoral and cellular BoNT/E-specific immune responses and completely protected animals against lethal challenge with BoNT/E. These results not only indicate that DNA vaccines could be further developed as safe and effective candidates for vaccines against BoNTs but also suggest a possible approach for developing vaccines that protect against bio-threat toxins.

Enhancement of anti-tumor effect of plasmid DNA-carrying MUC1 by the adjuvanticity of FLT3L in mouse model

AIM

DNA vaccines have emerged as a promising strategy for cancer immunotherapy; however, their immunogenicity is weak. Fms-like tyrosine kinase 3-ligand (Flt3L) has been exploited for its ability to increase the proliferation of dendritic cells (DCs). The aim of the present study was to investigate whether co-administration of an adjuvant plasmid expressing mouse Flt3L and a DNA vaccine of the Mucin 1 (MUC1) antigen enhances immune responses.

METHODS

The recombinant plasmids pVAX1-MUC1 and pVAX1-Flt3L were constructed and injected into mice intramuscularly (i.m.), followed by electroporation. The humoral and cellular immune responses after immunization were examined by enzyme linked immunosorbent assay (ELISA) and enzyme-linked immunospot assay (ELISPOT), respectively. To evaluate the anti-tumor efficacy of the plasmids, a mouse model of MUC1-expressing tumors was established.

RESULTS

The results showed that co-administration of an adjuvant plasmid and a DNA vaccine stimulated the production of higher titers of specific antibodies and a T cell response and suppressed the growth of subcutaneous tumors expressing MUC1. Collectively, our results indicate that a plasmid expressing murine Flt3L could stimulate stronger immune responses.

CONCLUSION

These observations emphasize the potential of Flt3L as an adjuvant for colon cancer DNA vaccines.

Antitumor immunity of DNA vaccine based on CTLA-4 fused with HER2 against colon carcinoma

Cytotoxic T-lymphocyte-associated protein 4 (CTLA-4) negatively regulates the T cell activation and competes with CD28 in binding with B7.1/B7.2 molecules. Fusion of the extracellular region of CTLA-4 and a specific antigen is an effective method for improving the immune efficacy of DNA vaccines. This study aimed to investigate the effects of DNA vaccine of human epidermal growth factor receptor-2 (HER2) fused with CTLA-4 on the development of colon carcinoma in mice and to identify the potential immune mechanisms underlying its effects. We constructed recombinant plasmids corresponding to the control group, individual antigen group, and fusion antigen group. Then, mice were intramuscularly injected with the corresponding plasmids and exposed to electrical pulses. Immunogenicity was evaluated at 2 weeks after the last immunization. Furthermore, to investigate the antitumor immune effects of the recombinant plasmid, we established a mouse model of HER2 expression in transplanted tumors. Experimental results showed that the recombinant plasmids expressing fusion antigen induced a stronger cellular immune response. Inoculation of the HER2-CTLA-4 plasmid exerted the strongest inhibitory effect on HER2 expression-mediated tumor growth in mice. These results highlight the potential of the CTLA-4 fusion DNA vaccine as a therapeutic vaccine against colon cancer based on HER2 and CTLA-4.

DNA vaccines against leptospirosis: A literature review

Leptospirosis is an infectious disease caused by pathogenic Leptospira species. The vaccines that are currently available for leptospirosis are composed of whole-cell preparations and suffer from limitations such as low efficacy, multiple side-effects, poor immunological memory and lack of cross-protection against different serovars of Leptospira spp. In light of the global prevalence of this disease, the development of a more effective vaccine against leptospirosis is of paramount importance. Genetic immunization is a promising alternative to conventional vaccine development. In the last 25years, several novel strategies have been developed for increasing the efficacy of DNA vaccines. Examples of such strategies include the introduction of novel plasmid vectors, adjuvants, alternate delivery routes, and prime-boost regimens. Herein we discuss the latest and most promising advances that have been made in developing DNA vaccines against leptospirosis. We also deliberate over the future directions that must be undertaken in order to improve results in this field.

Novel recombinant DNA vaccine candidates for human respiratory syncytial virus: Preclinical evaluation of immunogenicity and protection efficiency

The development of safe and potent vaccines for human respiratory syncytial virus (HRSV) is still a challenge for researchers worldwide. DNA-based immunization is currently a promising approach that has been used to generate human vaccines for different age groups. In this study, novel HRSV DNA vaccine candidates were generated and preclinically tested in BALB/c mice. Three different versions of the codon-optimized HRSV fusion (F) gene were individually cloned into the pPOE vector. The new recombinant vectors either express full-length (pPOE-F), secretory (pPOE-TF), or M2_82-90 linked (pPOE-FM2) forms of the F protein. Distinctive expression of the F protein was identified in HEp-2 cells transfected with the different recombinant vectors using ELISA and immunofluorescence. Mice immunization verified the potential for recombinant vectors to elicit significant levels of neutralizing antibodies and CD8⁺ T-cell lymphocytes. pPOE-TF showed higher levels of gene expression in cell culture and better induction of the humoral and cellular immune responses. Following virus challenge, mice that had been immunized with the recombinant vectors were able to control virus replication and displayed lower inflammation compared with mice immunized with empty pPOE vector or formalin-inactivated HRSV vaccine. Moreover, pulmonary cytokine profiles of mice immunized with the 3 recombinant vectors were similar to those of the mock infected group. In conclusion, recombinant pPOE vectors are promising HRSV vaccine candidates in terms of their safety, immunogenicity and protective efficiency. These data encourage further evaluation in phase I clinical trials.

A novel staphylococcal enterotoxin B subunit vaccine candidate elicits protective immune response in a mouse model

Staphylococcal enterotoxin B (SEB), produced by the gram-positive bacterium Staphylococcus aureus, is responsible for food poisoning and toxic shock syndrome, and is considered a potential bioterrorism agent. Unfortunately, still now no approved vaccines are available against SEB. In this study, we constructed a series of nontoxic SEB mutants (mSEBs) and examined whether these mSEBs provide protective immunity against SEB challenge. These mSEB vaccine candidates did not demonstrate superantigen activity in mouse splenocyte cultures. Immunization with the vaccine candidates triggered the production of IgG-antibodies with neutralizing activity. In addition, increased production of IgG1 and IgG3 was observed after immunization, which signifies both Th1- and Th2-induced immune responses. Among the vaccine candidates tested, S9, a double mutant (N23A and Y90A) and S19, a quadruple mutant (N23A, Y90A, R110A, and F177A), demonstrated complete protection against a lethal SEB challenge. Altogether, our results strongly suggest that these mSEBs could be an effective recombinant SEB vaccine candidates for further/future preclinical and clinical studies.

Screening a Phage Display Library for Two Novel OmpU-Binding Peptides with Adhesion Antagonistic Activity against Vibrio mimicus

Vibrio mimicus is a pathogen that causes ascites disease in fish. We have previously demonstrated that the outer membrane protein U (OmpU) is an important adhesin in V. mimicus. Here eight specific OmpU-binding phage clones, which presented three different OmpU-binding peptides (designated P1, P2, P3), were screened from a commercially available phage displayed 12-mer peptide library using rOmpU protein as target. Then, synthetic OmpU-binding peptides were measured for their adhesion antagonistic activity and binding affinity via adhesion inhibition test and non-competitive ELISA, respectively. The results showed that after co-incubated with the mixture of rOmpU and P3, visible green fluorescence could be observed on the epithelioma papulosum cyprinidi (EPC) cells surface; while the EPC cells co-incubated with the mixture of rOmpU and P1/P2 exhibited little green fluorescence. The average adhesion number of V. mimicus 04–14 isolate before and after treatment with peptide was 21.4 ± 1.5, 20.8 ± 0.8 (irrelevant peptide), 20.2 ± 0.5 (P3), 5.1 ± 0.7 (P1) and 3.4 ± 0.8 (P2), respectively. There was a significant decrease in the adhesive level of 04–14 isolate treated with P1/ P2 compared to the untreated isolate (p<0.01). The affinity constants of P1 and P2 were (6.17 ± 0.19) × 10⁸ L/mol and (1.24 ± 0.56) × 10⁹ L/mol, respectively. Furthermore, protective effects of P1 and P2 on grass carps challenged with V. mimicus were preliminary detected. It was found there was delayed death of fish in the groups treated with P1/P2, and the survival rate of challenged fish improved with the increase of the dose of adhesion antagonistic peptide. Taken together, two novel OmpU-binding peptides, which possessed adhesion antagonistic activity, high affinity and a certain degree of antibacterial activity against V. mimicus, were screened and identified.

The increasingly anti-tumor effect of a colonic carcinoma DNA vaccine carrying HER2 by the adjuvanticity of IL-12

The present study aimed to determine the effect of recombinant DNA vaccine-based human epidermal growth factor receptor-2 (HER2) and Interleukin 12 (IL-12) on the development of colonic carcinoma in mice and the potential immune mechanisms involved. Recombinant plasmids pVAX1-HER2, pVAX1-IL-12 and pVAX1-HER2-IL-12 were constructed, and injected into female mice intramuscularly (i.m.) followed by an electric pulse. The humoral and cellular immune responses after immunization were examined by enzyme linked immunosorbent assay (ELISA) and enzyme-linked immunospot assay (ELISPOT), respectively. To evaluate the anti-tumor efficacy of the plasmids, a mouse model with a HER2-expressing tumor was designed. Mice vaccinated with the HER2-IL-12 plasmid generated the strongest inhibition efficacy on the growth of HER2-expressing tumors and prolonged mouse survival. These observations emphasized the potential of IL-12 as an adjuvant for DNA vaccines and of vaccines based on HER2 and IL-12 as a promising treatment for colonic carcinoma.