Oral immunization of BALB/c mice by intragastric delivery of Streptococcus gordonii-expressing Giardia cyst wall protein 2 decreases cyst shedding in challenged mice

Conserved Candidate Antigens and Nanoparticles to Develop Vaccine against Giardia intestinalis

Giardia intestinalis (Giardia lambia, Giardia duodenalis) infections in humans may be asymptomatic or symptomatic and associated with diarrhea (without blood), abdominal cramps, bloating, flatulence, and weight loss. The protozoan Giardia is the third most common cause of diarrhea and death in children under five, preceded only by rotavirus and by Cryptosporidium parvum and C. hominis infections. Antimicrobial drugs, particularly 5-nitroimidazole (5-NIs), are used to treat giardiasis in humans. Immunologically naive or immunocompromised host are more vulnerable to Giardia infection, whereas a degree of resistance to this protozoan is present in humans living in endemic areas. This suggests that vaccination may be a potential and appropriate means to control this parasitic disease outbreak and protect the human population. This review discusses Giardia antigens related to vaccine development. Additionally, based on the latest development of nanoparticle technology, a combination of methods for future research and development is proposed for the design of the next generation of powerful immunogens and an effective vaccine against Giardia.

Genetic variation in potential Giardia vaccine candidates cyst wall protein 2 and α1-giardin

Giardia is a prevalent intestinal parasitic infection. The trophozoite structural protein a1-giardin (a1-g) and the cyst protein cyst wall protein 2 (CWP2) have shown promise as Giardia vaccine antigen candidates in murine models. The present study assesses the genetic diversity of a1-g and CWP2 between and within assemblages A and B in human clinical isolates. a1-g and CWP2 sequences were acquired from 15 Norwegian isolates by PCR amplification and 20 sequences from German cultured isolates by whole genome sequencing. Sequences were aligned to reference genomes from assemblage A2 and B to identify genetic variance. Genetic diversity was found between assemblage A and B reference sequences for both a1-g (90.8% nucleotide identity) and CWP2 (82.5% nucleotide identity). However, for a1-g, this translated into only 3 amino acid (aa) substitutions, while for CWP2 there were 41 aa substitutions, and also one aa deletion. Genetic diversity within assemblage B was larger; nucleotide identity 92.0% for a1-g and 94.3% for CWP2, than within assemblage A (nucleotide identity 99.0% for a1-g and 99.7% for CWP2). For CWP2, the diversity on both nucleotide and protein level was higher in the C-terminal end. Predicted antigenic epitopes were not affected for a1-g, but partially for CWP2. Despite genetic diversity in a1-g, we found aa sequence, characteristics, and antigenicity to be well preserved. CWP2 showed more aa variance and potential antigenic differences. Several CWP2 antigens might be necessary in a future Giardia vaccine to provide cross protection against both Giardia assemblages infecting humans.

Vaccination of domestic animals with a novel oral vaccine prevents Giardia infections, alleviates signs of giardiasis and reduces transmission to humans

Giardia lamblia is a human intestinal parasite and one of the most frequent enteric pathogen of companion animals. Clinical manifestations of giardiasis, such as diarrhoea, anorexia, weight loss and lethargy, have been associated with Giardia infections in both domestic and farm animals. A few anti-parasitic drugs are routinely used to treat giardiasis, but re-infections are common and drug-resistant strains have already been reported. Unfortunately, efficient vaccines against Giardia are not available. Giardia undergoes antigenic variation; through this mechanism, parasites can avoid the host’s immune defenses, causing chronic infections and/or re-infections. Antigenic variation is characterised by a continuous switch in the expression of members of a homologous family of genes encoding surface antigens. In a previous report, we indicated that in Giardia, the mechanism responsible for the exchange of variant-specific surface proteins (VSPs) involves the RNA interference (RNAi) pathway. From a repertoire of ~200 VSP genes, only one is expressed on the surface of single trophozoites; however, RNAi machinery disruption generates trophozoites that express the complete VSP repertoire. We also demonstrated that gerbils orally immunised with VSPs isolated from these altered parasites showed high levels of protection. Here we tested this vaccine in cats and dogs, and found that it is highly efficient in preventing new infections and reducing chronic giardiasis in domestic animals both in experimental and natural infections. Remarkably, immunisation of dogs in a highly endemic area strongly decreased the percentage of infected children in the community, suggesting that this vaccine would block the zoonotic transmission of the disease.

Development of a gene delivery system in Streptococcus gordonii using thymidylate synthase as a selection marker

Streptococcus gordonii, a commensal bacterium of the human oral cavity, is a potential live vaccine vector. In this study, we have developed a system that delivers a vaccine antigen gene onto the chromosome of S. gordonii. The system consisted of a recipient strain, that is a thymidine auxotroph constructed by deletion of a portion of thyA gene, and a linear gene delivery construct, composed of the functional thyA gene, the vaccine antigen gene, and a DNA fragment immediately downstream of thyA. The construct is assembled by a ligation and polymerase chain reaction strategy. Upon introduction into the thyA mutant, the vaccine antigen gene integrated into the chromosome via a double crossing-over event. Using the above strategy, a test vaccine antigen gene coding for a fusion protein composed of the Bordetella pertussis filamentous hemagglutinin type I domain and the single chain antibody against complement receptor 1 was successfully delivered to S. gordonii. The resulting S. gordonii expressed the fusion protein and the delivered gene was stable in the bacterium in vitro and in a mouse colonization experiment. Mice colonized by the fusion protein-expressing S. gordonii developed antibodies that recognized the native filamentous hemagglutinin protein suggesting that an immune response was elicited.

Lactic acid bacteria: reviewing the potential of a promising delivery live vector for biomedical purposes

Lactic acid bacteria (LAB) have a long history of safe exploitation by humans, being used for centuries in food production and preservation and as probiotic agents to promote human health. Interestingly, some species of these Gram-positive bacteria, which are generally recognized as safe organisms by the US Food and Drug Administration (FDA), are able to survive through the gastrointestinal tract (GIT), being capable to reach and colonize the intestine, where they play an important role. Besides, during the last decades, an important effort has been done for the development of tools to use LAB as microbial cell factories for the production of proteins of interest. Given the need to develop effective strategies for the delivery of prophylactic and therapeutic molecules, LAB have appeared as an appealing option for the oral, intranasal and vaginal delivery of such molecules. So far, these genetically modified organisms have been successfully used as vehicles for delivering functional proteins to mucosal tissues in the treatment of many different pathologies including GIT related pathologies, diabetes, cancer and viral infections, among others. Interestingly, the administration of such microorganisms would suppose a significant decrease in the production cost of the treatments agents since being live organisms, such vectors would be able to autonomously amplify and produce and deliver the protein of interest. In this context, this review aims to provide an overview of the use of LAB engineered as a promising alternative as well as a safety delivery platform of recombinant proteins for the treatment of a wide range of diseases.

Mucosal vaccination and therapy with genetically modified lactic acid bacteria

Lactic acid bacteria (LAB) have proved to be effective mucosal delivery vehicles that overcome the problem of delivering functional proteins to the mucosal tissues. By the intranasal route, both live and killed LAB vaccine strains have been shown to elicit mucosal and systemic immune responses that afford protection against infectious challenges. To be effective via oral administration, frequent dosing over several weeks is required but new targeting and adjuvant strategies have clearly demonstrated the potential to increase the immunogenicity and protective immunity of LAB vaccines. Oral administration of Lactococcus lactis has been shown to induce antigen-specific oral tolerance (OT) to secreted recombinant antigens. LAB delivery is more efficient at inducing OT than the purified antigen, thus avoiding the need for purification of large quantities of antigen. This approach holds promise for new therapeutic interventions in allergies and antigen-induced autoimmune diseases. Several clinical and research reports demonstrate considerable progress in the application of genetically modified L. lactis for the treatment of inflammatory bowel disease (IBD). New medical targets are on the horizon, and the approval by several health authorities and biosafety committees of a containment system for a genetically modified L. lactis that secretes Il-10 should pave the way for new LAB delivery applications in the future.

Lactococci and lactobacilli as mucosal delivery vectors for therapeutic proteins and DNA vaccines

Food-grade Lactic Acid Bacteria (LAB) have been safely consumed for centuries by humans in fermented foods. Thus, they are good candidates to develop novel oral vectors, constituting attractive alternatives to attenuated pathogens, for mucosal delivery strategies. Herein, this review summarizes our research, up until now, on the use of LAB as mucosal delivery vectors for therapeutic proteins and DNA vaccines. Most of our work has been based on the model LAB Lactococcus lactis, for which we have developed efficient genetic tools, including expression signals and host strains, for the heterologous expression of therapeutic proteins such as antigens, cytokines and enzymes. Resulting recombinant lactococci strains have been tested successfully for their prophylactic and therapeutic effects in different animal models: i) against human papillomavirus type 16 (HPV-16)-induced tumors in mice, ii) to partially prevent a bovine β-lactoglobulin (BLG)-allergic reaction in mice and iii) to regulate body weight and food consumption in obese mice. Strikingly, all of these tools have been successfully transposed to the Lactobacillus genus, in recent years, within our laboratory. Notably, anti-oxidative Lactobacillus casei strains were constructed and tested in two chemically-induced colitis models. In parallel, we also developed a strategy based on the use of L. lactis to deliver DNA at the mucosal level, and were able to show that L. lactis is able to modulate the host response through DNA delivery. Today, we consider that all of our consistent data, together with those obtained by other groups, demonstrate and reinforce the interest of using LAB, particularly lactococci and lactobacilli strains, to develop novel therapeutic protein mucosal delivery vectors which should be tested now in human clinical trials.

Cyst and encystment in protozoan parasites: optimal targets for new life-cycle interrupting strategies?

Certain protozoan parasites use survival strategies to reside outside the host such as the formation of cysts. This dormant and resistant stage results from the complex process of encystment that involves diverse molecular and cellular modifications. The stimuli and changes associated with cyst biogenesis are a matter of ongoing studies in human and animal protozoan parasites such as amoeba and Giardia species because blocking every step in the encystment pathway should, in theory, interrupt their life cycles. The present review thoroughly examines this essential process in those protozoan parasites and discusses the possibility of using that information to develop new kinds of anti-parasite specific and life cycle-interrupting drugs, aimed at holding back the dissemination of these infections.

Giardia duodenalis: the double-edged sword of immune responses in giardiasis

Giardiasis is one of the most common intestinal protozoan infections worldwide. The etiological agent, Giardia duodenalis (syn. Giardia lamblia, Giardia intestinalis), is a flagellated, binucleated protozoan parasite which infects a wide array of mammalian hosts (Adam, 2001). The symptoms of giardiasis include abdominal cramps, nausea, and acute or chronic diarrhea, with malabsorption and failure of children to thrive occurring in both sub-clinical and symptomatic disease (Thompson et al., 1993). Infections are transmitted by cysts which are excreted in the feces of infected humans and animals. Human giardiasis is distributed worldwide, with rates of detection between 2-5% in the developed world and 20-30% in the developing nations (Farthing, 1994). There is significant variation in the outcome of Giardia infections. Most infections are self-limiting, although re-infection is common in endemic areas and chronic infections also occur. Moreover, some individuals suffer from severe cramps, nausea and diarrhea while others escape these overt symptoms. This review will describe recent advances in parasite genetics and host immunity that are helping to shed light on this variability.

Utilisation des bactéries lactiques comme vecteurs vaccinaux

Aujourd’hui, nous disposons de données suffisantes qui confortent l’intérêt d’utiliser des bactéries lactiques (BL), notamment des souches des lactocoques et lactobacilles, pour le développement de nouvelles stratégies de vaccination mucosale. Les BL sont des bactéries à Gram positif utilisées depuis des millénaires dans la production d’aliments fermentés. Elles sont donc de bonnes candidates pour le développement de nouvelles stratégies de vectorisation orale et constituent des alternatives attractives aux stratégies vaccinales basées sur des bactéries pathogènes atténuées dont l’utilisation présente des risques sanitaires. Ce chapitre passe en revue la recherche et les progrès les plus récents dans l’utilisation des BL comme vecteurs de délivrance de protéines d’intérêt médical pour développer de nouveaux vaccins.

Is Giardia a significant pathogen in production animals?

Although Giardia duodenalis is recognised worldwide as the most important parasitic cause of gastro-intestinal disorder in human patients, the relevance of infection in production animals is prone to debate. Since the 1980s, clinical disease has been associated with giardiasis in production animals, both in natural conditions and in experimental studies. However, most Giardia research is focussed on the relevance of production animals as a reservoir for zoonotic transmission. In this study, the current knowledge on clinical relevance of giardiasis in production animals is reviewed, along with the diagnosis, treatment and control of infection. Furthermore, future research objectives are discussed.

Encystation of Giardia lamblia: a model for other parasites

To colonize the human small intestine, Giardia lamblia monitors a dynamic environment. Trophozoites attach to enterocytes that mature and die. The parasites must 'decide' whether to re-attach or differentiate into cysts that survive in the environment and re-activate when ingested. Other intestinal parasites face similar challenges. Study of these parasites is limited because they do not encyst in vitro. Giardia trophozoites were persuaded to encyst in vitro by mimicking physiological stimuli. Cysts are dormant, yet 'spring-loaded for action' to excyst upon ingestion. Giardial encystation has been studied from morphological, cell biological, biochemical, and molecular viewpoints. Yet important gaps remain and the mechanisms that co-ordinate responses to external signals remain enigmatic.

Mucosal delivery of a transmission-blocking DNA vaccine encoding Giardia lamblia CWP2 by Salmonella typhimurium bactofection vehicle

In this study, we investigated the use of Salmonella typhimurium (STM1 strain) as a bactofection vehicle to deliver a transmission-blocking DNA vaccine (TBDV) plasmid to the intestinal immune system. The gene encoding the full length cyst wall protein-2 (CWP2) from Giardia lamblia was subcloned into the pCDNA3 mammalian expression vector and stably introduced into S. typhimurium STM1. Eight-week-old female BALB/c mice were orally immunized every 2 weeks, for a total of three immunizations. Vaccinated and control mice were sacrificed 1 week following the last injection. Administration of the DNA vaccine led to the production of CWP2-specific cellular immune responses characterized by a mixed Th1/Th2 response. Using ELISA, antigen-specific IgA and IgG antibodies were detected in intestinal secretions. Moreover, analysis of sera demonstrated that the DNA immunization also stimulated the production of CWP2-specific IgG antibodies that were mainly of the IgG2a isotype. Finally, challenge infection with live Giardia muris cysts revealed that mice receiving the CWP2-encoding DNA vaccine were able to reduce cyst shedding by approximately 60% compared to control mice. These results demonstrate, for the first time, the development of parasite transmission-blocking immunity at the intestinal level following the administration of a mucosal DNA vaccine delivered by S. typhimurium STM1.

Characterization of the local immune response to cyst antigens during the acute and elimination phases of primary murine giardiasis

During the course of a giardial infection, the host's immune system is presented with a variety of Giardia antigens as trophozoites differentiate, through encysting cells, to form the infective cysts. Previous studies examining the host's immune response during giardial infections have focused on trophozoite-derived antigens (Ags). In this study, we were interested to determine if the host's immune system reacts to cyst Ags during the acute and elimination phases, when there is cyst shedding. For this purpose, we used antigenic extracts from trophozoites (Troph), encysting cells (ENC), and purified giardial cyst walls (PCW), as well as purified recombinant cyst wall protein 2 (rCWP2). Comparative analysis of the parasite extracts using SDS-PAGE analysis and surface-enhanced laser desorption/ionization time of flight mass spectrometry resulted in the detection of 175 protein entities, of which 26 were Troph-specific proteins, 17 ENC-specific proteins, and 31 were PCW-specific proteins. On the other hand, we detected 34 proteins shared between Troph and ENC, 19 proteins that were shared between ENC and PCW, and 29 proteins that were common to Troph and PCW. Finally, we detected 19 proteins that were shared by all three extract samples. BALB/c mice were infected with 10(5)Giardia muris cysts and sacrificed either at the acute or elimination phases of infection (days 12 and 40, respectively), and lymphocytes were isolated from the Peyer's patches (PP). Using flow cytometry, we detected significant increases in the number of PP-derived CD4(+) and CD19(+), but not CD8(+) lymphocytes. Quantification of the number of mucosal IL-4 and IFN-gamma secreting T-lymphocytes by enzyme-linked immunosorbent spot assay showed that these cells reacted by secreting similar levels of IL-4 and IFN-gamma, regardless of the Ag or the phase of infection. Analysis of intestinal humoral immune responses by ELISA resulted in the detection of Ag-specific IgA and IgG intestinal antibodies. Regardless of the Ag tested, a trend was consistently observed where the concentration of local antibodies was found to be slightly increased by the acute phase, where we detected approximately 200microg/mg of specific IgA and approximately 300ng/ml of specific IgG in intestinal lavage of infected mice. By the elimination phase, the amount of specific antibodies was found to increase to approximately 600microg/mg of specific IgA and approximately 1300ng/ml of specific IgG antibodies. Finally, we tested the biological activity of these antibodies and found that they were able to reduce the ability of trophozoites to differentiate into cysts in vitro. Collectively, we believe these results demonstrate for the first time the existence of significant cellular and humoral immune responses against Giardia cyst Ags that may contribute to the reduction of cyst shedding in infected animals.