Simultaneous GeneGun immunisation with plasmids encoding antigen and GM-CSF: significant enhancement of murine antivenom IgG1 titres

Innovative Immunization Strategies for Antivenom Development

Snakes, scorpions, and spiders are venomous animals that pose a threat to human health, and severe envenomings from the bites or stings of these animals must be treated with antivenom. Current antivenoms are based on plasma-derived immunoglobulins or immunoglobulin fragments from hyper-immunized animals. Although these medicines have been life-saving for more than 120 years, opportunities to improve envenoming therapy exist. In the later decades, new biotechnological tools have been applied with the aim of improving the efficacy, safety, and affordability of antivenoms. Within the avenues explored, novel immunization strategies using synthetic peptide epitopes, recombinant toxins (or toxoids), or DNA strings as immunogens have demonstrated potential for generating antivenoms with high therapeutic antibody titers and broad neutralizing capacity. Furthermore, these approaches circumvent the need for venom in the production process of antivenoms, thereby limiting some of the complications associated with animal captivity and venom collection. Finally, an important benefit of innovative immunization approaches is that they are often compatible with existing antivenom manufacturing setups. In this review, we compile all reported studies examining venom-independent innovative immunization strategies for antivenom development. In addition, a brief description of toxin families of medical relevance found in snake, scorpion, and spider venoms is presented, as well as how biochemical, bioinformatic, and omics tools could aid the development of next-generation antivenoms.

High-throughput immuno-profiling of mamba (Dendroaspis) venom toxin epitopes using high-density peptide microarrays

Snakebite envenoming is a serious condition requiring medical attention and administration of antivenom. Current antivenoms are antibody preparations obtained from the plasma of animals immunised with whole venom(s) and contain antibodies against snake venom toxins, but also against other antigens. In order to better understand the molecular interactions between antivenom antibodies and epitopes on snake venom toxins, a high-throughput immuno-profiling study on all manually curated toxins from Dendroaspis species and selected African Naja species was performed based on custom-made high-density peptide microarrays displaying linear toxin fragments. By detection of binding for three different antivenoms and performing an alanine scan, linear elements of epitopes and the positions important for binding were identified. A strong tendency of antivenom antibodies recognizing and binding to epitopes at the functional sites of toxins was observed. With these results, high-density peptide microarray technology is for the first time introduced in the field of toxinology and molecular details of the evolution of antibody-toxin interactions based on molecular recognition of distinctive toxic motifs are elucidated.

Direct Delivery of Antigens to Dendritic Cells via Antibodies Specific for Endocytic Receptors as a Promising Strategy for Future Therapies

Dendritic cells (DCs) are the most potent professional antigen presenting cells and are therefore indispensable for the control of immunity. The technique of antibody mediated antigen targeting to DC subsets has been the basis of intense research for more than a decade. Many murine studies have utilized this approach of antigen delivery to various kinds of endocytic receptors of DCs both in vitro and in vivo. Today, it is widely accepted that different DC subsets are important for the induction of select immune responses. Nevertheless, many questions still remain to be answered, such as the actual influence of the targeted receptor on the initiation of the immune response to the delivered antigen. Further efforts to better understand the induction of antigen-specific immune responses will support the transfer of this knowledge into novel treatment strategies for human diseases. In this review, we will discuss the state-of-the-art aspects of the basic principles of antibody mediated antigen targeting approaches. A table will also provide a broad overview of the latest studies using antigen targeting including addressed DC subset, targeted receptors, outcome, and applied coupling techniques.

A Heterologous Multiepitope DNA Prime/Recombinant Protein Boost Immunisation Strategy for the Development of an Antiserum against Micrurus corallinus (Coral Snake) Venom

Background

Envenoming by coral snakes (Elapidae: Micrurus), although not abundant, represent a serious health threat in the Americas, especially because antivenoms are scarce. The development of adequate amounts of antielapidic serum for the treatment of accidents caused by snakes like Micrurus corallinus is a challenging task due to characteristics such as low venom yield, fossorial habit, relatively small sizes and ophiophagous diet. These features make it difficult to capture and keep these snakes in captivity for venom collection. Furthermore, there are reports of antivenom scarcity in USA, leading to an increase in morbidity and mortality, with patients needing to be intubated and ventilated while the toxin wears off. The development of an alternative method for the production of an antielapidic serum, with no need for snake collection and maintenance in captivity, would be a plausible solution for the antielapidic serum shortage.

Methods and Findings

In this work we describe the mapping, by the SPOT-synthesis technique, of potential B-cell epitopes from five putative toxins from M. corallinus, which were used to design two multiepitope DNA strings for the genetic immunisation of female BALB/c mice. Results demonstrate that sera obtained from animals that were genetically immunised with these multiepitope constructs, followed by booster doses of recombinant proteins lead to a 60% survival in a lethal dose neutralisation assay.

Conclusion

Here we describe that the genetic immunisation with a synthetic multiepitope gene followed by booster doses with recombinant protein is a promising approach to develop an alternative antielapidic serum against M. corallinus venom without the need of collection and the very challenging maintenance of these snakes in captivity.

Coral snakes are a group of deadly venomous snakes that exhibit a characteristic red, yellow/white, and black coloured banding pattern. Accidents involving these snakes tend to be very severe or even lethal, causing peripheral nervous system depression with muscle paralysis and vasomotor instability. The only acceptable medical treatment for snakebite accidents is the administration of an antivenom, generally produced by immunising horses with the snake venom. Nonetheless, for what concerns the antielapidic serum production in Brazil, the total amount of venom available for horse immunisations is insufficient. This is mainly due to the small size of coral snake glands, their underground life style, combined with its very low survival rates in captivity. Moreover, cases of patients being intubated and ventilated as a consequence of antivenom shortage in USA have also been registered. In this work, we present an alternative method for the development of antielapidic serum, which does not rely upon snake capture. This serum was produced by a heterologous DNA prime—with a multiepitope DNA string coding for the most reactive epitopes from the most abundant toxins of M. corallinus, a coral snake which occupy highly populated areas in Brazil—followed by recombinant multiepitope protein boost immunisation of mice.

Effect of Cytokine-Encoding Plasmid Delivery on Immune Response to Japanese Encephalitis Virus DNA Vaccine in Mice

We have previously shown that immunization of mice with plasmid pMEa synthesizing Japanese encephalitis virus (JEV) envelope protein induced anti-JEV humoral and cellular immune responses. We now show that intra-muscular co-administration of mice with pMEa and pGM-CSF, encoding murine granulocyte-macrophage colony-stimulating factor or pIL-2, encoding murine interleukin-2 given 4 days after pMEa, augmented anti-JEV antibody titers. This did not enhance the level of protection in immunized mice against JEV. However, intra-dermal co-administration of pMEa and pGM-CSF in mice using the gene gun, enhanced anti-JEV antibody titers resulting in an increased level of protection in mice against lethal JEV challenge.

Neutralization of venom-induced hemorrhage by equine antibodies raised by immunization with a plasmid encoding a novel P-II metalloproteinase from the lancehead pitviper Bothrops asper

In this work, the cDNA encoding a novel P-II type metalloproteinase from Bothrops asper venom glands was cloned, sequenced and used for DNA immunization of animals with accelerated DNA-coated tungsten microparticles and the helius Gene Gun system. Specific antibodies against B. asper venom antigens were induced in mice co-immunized with the plasmid encoding the P-II metalloproteinase together with an expression plasmid encoding the murine IL-2. Similarly, specific antibodies against B. asper venom antigens were also induced in a horse co-immunized with the plasmid encoding the P-II metalloproteinase, together with a plasmid encoding the equine IL-6. The equine antibodies induced by immunization with the P-II metalloproteinase encoding plasmid cross react with several proteins of B. asper, Crotalus durissus durissus, and Lachesis stenophrys venoms in western blot, demonstrating antigenic similarity between the cloned metalloproteinase and other metalloproteinases present in these venoms. Furthermore, the equine antibodies induced by immunization with the P-II metalloproteinase encoding plasmid completely neutralized the hemorrhagic activity of the whole B. asper venom and partially the hemorrhagic activity of C. durissus durissus venom. The neutralizing ability of the produced antibodies raises, for the first time, the possibility of developing therapeutic antivenoms in horses by DNA immunization using tungsten microparticles.

Bioinformatics and multiepitope DNA immunization to design rational snake antivenom

BACKGROUND

Snake venom is a potentially lethal and complex mixture of hundreds of functionally diverse proteins that are difficult to purify and hence difficult to characterize. These difficulties have inhibited the development of toxin-targeted therapy, and conventional antivenom is still generated from the sera of horses or sheep immunized with whole venom. Although life-saving, antivenoms contain an immunoglobulin pool of unknown antigen specificity and known redundancy, which necessitates the delivery of large volumes of heterologous immunoglobulin to the envenomed victim, thus increasing the risk of anaphylactoid and serum sickness adverse effects. Here we exploit recent molecular sequence analysis and DNA immunization tools to design more rational toxin-targeted antivenom.

METHODS AND FINDINGS

We developed a novel bioinformatic strategy that identified sequences encoding immunogenic and structurally significant epitopes from an expressed sequence tag database of a venom gland cDNA library of Echis ocellatus, the most medically important viper in Africa. Focusing upon snake venom metalloproteinases (SVMPs) that are responsible for the severe and frequently lethal hemorrhage in envenomed victims, we identified seven epitopes that we predicted would be represented in all isomers of this multimeric toxin and that we engineered into a single synthetic multiepitope DNA immunogen (epitope string). We compared the specificity and toxin-neutralizing efficacy of antiserum raised against the string to antisera raised against a single SVMP toxin (or domains) or antiserum raised by conventional (whole venom) immunization protocols. The SVMP string antiserum, as predicted in silico, contained antibody specificities to numerous SVMPs in E. ocellatus venom and venoms of several other African vipers. More significantly, the antiserum cross-specifically neutralized hemorrhage induced by E. ocellatus and Cerastes cerastes cerastes venoms.

CONCLUSIONS

These data provide valuable sequence and structure/function information of viper venom hemorrhagins but, more importantly, a new opportunity to design toxin-specific antivenoms-the first major conceptual change in antivenom design after more than a century of production. Furthermore, this approach may be adapted to immunotherapy design in other cases where targets are numerous, diverse, and poorly characterized such as those generated by hypermutation or antigenic variation.

Jararhagin and its multiple effects on hemostasis

Jararhagin is a 52 kDa hemorrhagic P-III metalloproteinase isolated from the venom of the medically important Brazilian pit-viper Bothrops jararaca. It is a member of the reprolysin family of zinc metalloproteinases containing a catalytic metalloproteinase domain followed by a disintegrin-like and a cysteine-rich domain. The impact of jararhagin on hemostasis has been extensively studied using in vitro and in vivo model systems as well as in clinical studies. Jararhagin-induced hemorrhage is the result of the degradation of sub-endothelial matrix proteins leading to the disruption of the blood vessel endothelium, with accompanying disturbances in platelet function. The versatility of jararhagin is further demonstrated by its direct action on von Willebrand factor, the degradation of fibrinogen, by its inhibition of platelet adhesion to collagen and by its inability to be affected by the plasma inhibitor alpha(2)-macroglobulin. Collagen-induced platelet aggregation is inhibited by jararhagin though the binding of the molecule to the alpha(2) subunit I domain of the platelet surface alpha(2)beta(1) integrin (collagen receptor). Jararhagin also cleaves the beta(1) subunit of the same integrin, inhibiting platelet interaction and ultimately causing impairment of signal transduction. The effect of jararhagin on cell systems other than platelets is evaluated; in fibroblasts, jararhagin functions as a collagen-mimetic substrate and, in endothelial cells, it causes apoptosis and indirectly inhibits cell proliferation by release of angiostatin-like compounds. Jararhagin induces a strong pro-inflammatory response characterized by intense leukocyte accumulation at the site of the injection. Although hemorrhage and edema are a response to the direct effect of jararhagin, jararhagin-induced inflammation and necrosis are dependent on macrophages and key pro-inflammatory cytokines or their receptors. Some data also indicate that the toxin possesses anti-tumorgenic properties. Methods for inhibiting jararhagin are reviewed; this encompasses the use of synthetic peptides to the isolation of naturally occurring mammalian peptides and the development of toxin-specific antibodies through DNA immunisation and monoclonal antibody technologies. The availability of jararhagin makes it an important tool for research into the mechanisms of action of similar toxins, for insights into cellular interactions and for clinical investigations into the treatment of envenomings from B. jararaca.

Antibody zymography: a novel adaptation of zymography to determine the protease-neutralising potential of specific antibodies and snake antivenoms

A common problem in the development of antibody-based therapeutics is the selection, usually from a large population, of specific antibodies with the desired function. One of our research objectives is to identify antibodies capable of neutralising the most important haemorrhagic and haemostasis-disruptive proteases from viper venom. Here, we describe a modification of conventional gelatin-zymography that permits the identification of antibodies capable of neutralising gelatinolytic proteases. We demonstrate that the gelatinolytic activity of viper venom proteases is neutralised by addition of viper antivenom to the matrix of conventional gelatin-zymograms. Venom protein gelatinolytic activity was unaffected by inclusion of antibody from control, non-immunised animals or immunoglobulin-depleted serum. The application of this antibody zymogram technique for future research on snake venoms is evaluated in the context of identified limitations.

Immobilisation of GM-CSF onto particulate vaccine carrier systems

Physical connection of vaccine carriers with immunostimulating cytokines may provide an interesting possibility to enhance the immune response of protective or therapeutic vaccines. As a first evaluation, various aluminium hydroxide adjuvants and poly(D,L-lactide-co-glycolide) (PLGA) microparticulates with modified positively and negatively charged surfaces were prepared to adsorb granulocyte-macrophage colony-stimulating factor (GM-CSF) under different pH conditions. Negatively charged surfaces were chosen to resemble physiological binding of GM-CSF to extracellular glycosaminoglycans, while modified positively charged surfaces may enhance GM-CSF adsorption due to electrostatic interaction. Release of GM-CSF was checked in vitro in a simulated interstitial environment. Anionic and cationic surfaces efficiently attracted GM-CSF to the carrier surface independently of the pH, while the composition of the carrier largely influenced the release of GM-CSF over time. Thus, the adsorption of GM-CSF to aluminium hydroxide adjuvants and PLGA microparticulates provides a simple and efficient possibility to physically connect the cytokine with these commonly used and potential vaccine carriers and may enable its localised delivery to the side of action.

Development of venom toxin-specific antibodies by DNA immunisation: rationale and strategies to improve therapy of viper envenoming

DNA vaccination induces potent cellular immune responses against infectious and parasitic intracellular pathogens. This paper illustrates that DNA immunisation protocols can be adapted to induce high titre antibody responses with potential to improve the treatment of systemic snake envenoming that kills 20000 people annually in Africa. Envenoming by the saw-scaled vipers and puff adders are responsible for the majority of these deaths. DNA sequences encoding haemorrhagic, pro- and anti-coagulant and other haemostasis-disruptive venom toxins from these vipers showed extensive cross-specific and cross-generic sequence and structural similarities. The predicted antigenic profiles of these toxin sequences are utilised to design DNA immunisation constructs to generate toxin-specific antibodies with potential to polyspecifically neutralise venoms from the most medically-important African vipers.

Cloning of a prothrombin activator-like metalloproteinase from the West African saw-scaled viper, Echis ocellatus

Systemic envenoming by the saw-scaled viper, Echis ocellatus, is responsible for more deaths than any other snake in West Africa. Despite its medical importance, there have been few investigations into the toxin composition of the venom of this viper. Here we describe the isolation of E. ocellatus venom gland cDNAs encoding a protein of 514 amino acids that showed 91% sequence similarity to Ecarin, a prothrombin-activating metalloproteinase from the venom of the East African viper, E. pyramidum leakeyi, that induces severe consumption coagulopathy. Structural similarities between the E. ocellatus metalloproteinase and analogues in venoms of related vipers suggest that antibodies raised to phylogenetically conserved E. ocellatus metalloproteinase domains may have potential for cross-specific and cross-generic neutralisation of analogous venom toxins.

Novel sequences encoding venom C-type lectins are conserved in phylogenetically and geographically distinct Echis and Bitis viper species

Envenoming by Echis saw scaled vipers and Bitis arietans puff adders is the leading cause of death and morbidity in Africa due to snake bite. Despite their medical importance, the composition and constituent functionality of venoms from these vipers remains poorly understood. Here, we report the cloning of cDNA sequences encoding seven clusters or isoforms of the haemostasis-disruptive C-type lectin (CTL) proteins from the venom glands of Echis ocellatus, E. pyramidum leakeyi, E. carinatus sochureki and B. arietans. All these CTL sequences encoded the cysteine scaffold that defines the carbohydrate-recognition domain of mammalian CTLs. All but one of the Echis and Bitis CTL sequences showed greater sequence similarity to the beta than alpha CTL subunits in venoms of related Asian and American vipers. Four of the new CTL clusters showed marked inter-cluster sequence conservation across all four viper species which were significantly different from that of previously published viper CTLs. The other three Echis and Bitis CTL clusters showed varying degrees of sequence similarity to published viper venom CTLs. Because viper venom CTLs exhibit a high degree of sequence similarity and yet exert profoundly different effects on the mammalian haemostatic system, no attempt was made to assign functionality to the new Echis and Bitis CTLs on the basis of sequence alone. The extraordinary level of inter-specific and inter-generic sequence conservation exhibited by the Echis and Bitis CTLs leads us to speculate that antibodies to representative molecules should neutralise the biological function of this important group of venom toxins in vipers that are distributed throughout Africa, the Middle East and the Indian subcontinent.

Molecular cloning of phospholipases A(2) from venom glands of Echis carpet vipers

Venom toxin-specific antibodies offer a more rational treatment of snake envenoming than conventional antivenom. Here, we describe novel cDNAs encoding phospholipase A(2) (PLA(2)) isoforms from venom gland RNA of Echis pyramidum leakeyi (Epl), Echis sochureki (Es) and Echis ocellatus (Eo). The deduced amino acid sequences of these cDNAs encoded proteins with high overall sequence identity to the viper group II PLA(2) protein family, including the 14 cysteine residues capable of forming seven disulphide bonds that characterize this group of PLA(2) enzymes. Comparison of the PLA(2) sequences from Echis with those from related vipers failed to make significant geographic, taxonomic or PLA(2)-function distinctions between these Echis PLA(2) isoforms. However, their deduced hydrophilicity profiles revealed a conserved tertiary structure that we will exploit, by epidermal DNA immunization, to generate PLA(2)-neutralizing antibodies with polyspecific potential.

The conserved structure of snake venom toxins confers extensive immunological cross-reactivity to toxin-specific antibody

We have demonstrated previously that antisera from mice immunised with DNA encoding the carboxy-terminal domain (JD9) of a potent haemorrhagic metalloproteinase, jararhagin, neutralised over 70% of the haemorrhagic activity of the whole Bothrops jararaca venom. Here, we demonstrate that the JD9-specific antibody possesses extensive immunological reactivity to venom components in snakes of distinct species and genera. The polyspecific immunological reactivity of the antibody showed a correlation with amino acid sequence identity and with predicted antigenic domains of JD9-analogues in venoms of snakes with closest phylogenetic links to B. jararaca. This study further promotes the potential of DNA immunisation to generate toxin-specific antibodies with polyspecific cover. An analysis of the reactivity of the JD9-specific antisera to B. atrox complex venoms that exhibited intraspecific variation in the venom proteome revealed, however, that the toxin-specific approach to antivenom development requires a more in-depth knowledge of the target molecules than is required for conventional antivenoms.

Unmasking venom gland transcriptomes in reptile venoms

While structural studies of reptile venom toxins can be achieved using lyophilized venom samples, until now the cloning of precursor cDNAs required sacrifice of the specimen for dissection of the venom glands. Here we describe a simple and rapid technique that unmasks venom protein mRNAs present in lyophilized venom samples. To illustrate the technique we have RT-PCR-amplified a range of venom protein transcripts from cDNA libraries derived from the venoms of a hemotoxic snake, the Chinese copperhead (Deinagkistrodon acutus), a neurotoxic snake, the black mamba (Dendroaspis polylepis), and a venomous lizard, the Gila monster (Heloderma suspectum). These include a metalloproteinase and phospholipase A2 from D. acutus, a potassium channel blocker, dendrotoxin K, from D. polylepis, and exendin-4 from H. suspectum. These findings imply that the apparent absence and/or lability of mRNA in complex biological matrices is not always real and paves the way for accelerated acquisition of molecular genetic data on venom toxins for scientific and potential therapeutic purposes without sacrifice of endangered herpetofauna.