Ascaris suum--vaccination of mice with liposome encapsulated antigen

Getting around the roundworms: Identifying knowledge gaps and research priorities for the ascarids

The ascarids are a large group of parasitic nematodes that infect a wide range of animal species. In humans, they cause neglected diseases of poverty; many animal parasites also cause zoonotic infections in people. Control measures include hygiene and anthelmintic treatments, but they are not always appropriate or effective and this creates a continuing need to search for better ways to reduce the human, welfare and economic costs of these infections. To this end, Le Studium Institute of Advanced Studies organized a two-day conference to identify major gaps in our understanding of ascarid parasites with a view to setting research priorities that would allow for improved control. The participants identified several key areas for future focus, comprising of advances in genomic analysis and the use of model organisms, especially Caenorhabditis elegans, a more thorough appreciation of the complexity of host-parasite (and parasite-parasite) communications, a search for novel anthelmintic drugs and the development of effective vaccines. The participants agreed to try and maintain informal links in the future that could form the basis for collaborative projects, and to co-operate to organize future meetings and workshops to promote ascarid research.

A historical and systematic overview of Ascaris vaccine development

Ascariasis is the most prevalent helminth infection in the world and leads to significant, life-long morbidity, particularly in young children. Current efforts to control and eradicate ascariasis in endemic regions have been met with significant challenges including high-rates of re-infection and potential development of anthelminthic drug resistance. Vaccines against ascariasis are a key tool that could break the transmission cycle and lead to disease eradication globally. Evolution of the Ascaris vaccine pipeline has progressed, however no vaccine product has been brought to human clinical trials to date. Advancement in recombinant protein technology may provide the first step in generating an Ascaris vaccine as well as a pan-helminthic vaccine ready for human trials. However, several roadblocks remain and investment in new technologies will be important to develop a successful human Ascaris vaccine that is critically needed to prevent significant morbidity in Ascaris-endemic regions around the world.

Vaccination with chimeric protein induces protection in murine model against ascariasis

An estimated 400 million people are infected by parasites of the genus Ascaris and the existing control measures are inefficient. Vaccine development using B cell antigens is a promising strategy for increased protection against this parasite. The present study aimed at developing a chimeric protein capable of conferring protection against infection by Ascaris sp. For this purpose, we performed B-cell epitope predictions on previously described vaccine candidate proteins from Ascaris suum and the corresponding peptides were used to construct a chimeric protein. Female BALB / c mice were immunized subcutaneously in three doses at 10 day intervals with a vaccine formulation comprised of the chimeric protein together with monophosphoryl lipid A (MPLA). Control groups included protein alone, MPLA, or PBS. After challenge infection, animals vaccinated with chimeric protein plus MPLA showed a reduction of 73.54% of larval load in the lung compared to control group animals. Animals immunized with chimeric protein plus MPLA also display higher IgG response and a reduction in lung inflammation. Our study highlights how chimeric proteins containing more than one B cell epitope can enhance immune protection against helminthic infection and offer new approaches to the development of Ascaris vaccines.

IgG Induced by Vaccination With Ascaris suum Extracts Is Protective Against Infection

Human ascariasis has a global and cosmopolitan distribution, and has been characterized as the most prevalent neglected tropical disease worldwide. The development of a preventive vaccine is highly desirable to complement current measures required for this parasitic infection control and to reduce chronic childhood morbidities. In the present study, we describe the mechanism of protection elicited by a preventive vaccine against ascariasis. Vaccine efficacy was evaluated after immunization with three different Ascaris suum antigen extracts formulated with monophosphoryl lipid A (MPLA) as an adjuvant: crude extract of adult worm (ExAD); crude extract of adult worm cuticle (CUT); and crude extract of infective larvae (L3) (ExL3). Immunogenicity elicited by immunization was assessed by measuring antibody responses, cytokine production, and influx of tissue inflammatory cells. Vaccine efficacy was evaluated by measuring the reductions in the numbers of larvae in the lungs of immunized BALB/c mice that were challenged with A. suum eggs. Moreover, lung physiology and functionality were tested by spirometry to determine clinical efficacy. Finally, the role of host antibody mediated protection was determined by passive transfer of serum from immunized mice. Significant reductions in the total number of migrating larvae were observed in mice immunized with ExL3 61% (p < 0.001), CUT 59% (p < 0.001), and ExAD 51% (p < 0.01) antigens in comparison with non-immunized mice. For the Ascaris antigen-specific IgG antibody levels, a significant and progressive increase was observed with each round of immunization, in association with a marked increase of IgG1 and IgG3 subclasses. Moreover, a significant increase in concentration of IL-5 and IL-10 (pre-challenge) in the blood and IL-10 in the lung tissue (post-challenge) was induced by CUT immunization. Finally, ExL3 and CUT-immunized mice showed a marked improvement in lung pathology and tissue fibrosis as well as reduced pulmonary dysfunction induced by Ascaris challenge, when compared to non-immunized mice. Moreover, the passive transfer of specific IgG antibodies from ExL3, CUT, and ExAD elicited a protective response in naïve mice, with significant reductions in parasite burdens in lungs of 65, 64, and 64%, respectively. Taken together, these studies indicated that IgG antibodies contribute to protective immunity.

Advancing a multivalent 'Pan-anthelmintic' vaccine against soil-transmitted nematode infections

Ascaris lumbricoides

The Sabin Vaccine Institute Product Development Partnership is developing a Pan-anthelmintic vaccine that simultaneously targets the major soil-transmitted nematode infections, in other words, ascariasis, trichuriasis and hookworm infection. The approach builds off the current bivalent Human Hookworm Vaccine now in clinical development and would ultimately add both a larval Ascaris lumbricoides antigen and an adult-stage Trichuris trichiura antigen from the parasite stichosome. Each selected antigen would partially reproduce the protective immunity afforded by UV-attenuated Ascaris eggs and Trichuris stichosome extracts, respectively. Final antigen selection will apply a ranking system that includes the evaluation of expression yields and solubility, feasibility of process development and the absence of circulating antigen-specific IgE among populations living in helminth-endemic regions. Here we describe a five year roadmap for the antigen discovery, feasibility and antigen selection, which will ultimately lead to the scale-up expression, process development, manufacture, good laboratory practices toxicology and preclinical evaluation, ultimately leading to Phase 1 clinical testing.

Ascaris suum enolase is a potential vaccine candidate against ascariasis

Ascariasis caused by Ascaris is the most common parasite problem in humans and pigs worldwide. No vaccines are available for the prevention of Ascaris infections. In the present study, the gene encoding Ascaris suum enolase (As-enol-1) was amplified, cloned and sequenced. Amino acid sequence alignment indicated that As-enol-1 was highly conserved between different nematodes and shared the highest identity (87%) with enolase from Anisakis simplex s.l. The recombinant pVAX-Enol was successfully expressed in Marc-145 cells. The ability of the pVAX-Enol for inducing immune protective responses against challenge infection with A. suum L3 was evaluated in Kunming mice. The immune response was evaluated by lymphoproliferative assay, cytokine and antibody measurements, and the reduction rate of recovery larvae. The results showed that the mice immunized with pVAX-Enol developed a high level of specific antibody responses against A. suum, a strong lymphoproliferative response, and significant levels of IFN-γ, IL-2, IL-4 and IL-10 production, compared with the other groups immunized with empty plasmid or blank controls, respectively. There was a 61.13% reduction (P<0.05) in larvae recovery compared with that in the blank control group. Our data indicated that A. suum enolase is a potential vaccine candidate against A. suum infection.

Vaccination with recombinant Ascaris suum 24-kilodalton antigen induces a Th1/Th2-mixed type immune response and confers high levels of protection against challenged Ascaris suum lung-stage infection in BALB/c mice

Previous studies have shown that antigens from various life-cycle stages of Ascaris suum can induce host-protective immunity against challenge infections with infective eggs of A. suum. This study evaluated whether Escherichia coli-expressed recombinant 24-kDa antigen from A. suum (rAs24) was a suitable vaccine candidate for the control of Ascaris infections by examining its performance in a mouse model. Immunization of BALB/c mice in three consecutive doses with rAs24 in Freund's Complete Adjuvant (FCA) results in protection against challenge infections as manifested by a 58% reduction (P<0.001) in recovery and stunted development of A. suum lung-stage larvae at day 7 post-challenge. Sera obtained from immune protected mice had a significantly increased level of immunoglobulin G (IgG) (P<0.0001) but had no IgE response. Analysis of IgG-subclass profiles revealed that IgG1 (P<0.0001) showed the greatest increase followed by IgG2b (P<0.005), IgG2a (P<0.006) and IgG3 (P<0.04). Splenic T cells from rAs24-FCA immunized mice secreted significantly high levels of both Th1 cytokine gamma-interferon (P<0.005) and Th2 cytokine interleukin-10 (P<0.001) after stimulation with rAs24 in vitro. Interestingly, affinity purified anti-rAs24 IgG was shown to inhibit moulting of A. suum lung-stage L3 to L4 in vitro by 26%, indicating an in vivo function of the endogenous As24 in the moulting processes. An intense expression of endogenous As24 in the hypodermis and gut epithelium of A. suum lung-stage L3 by immunofluorescence supports a function for endogenous As24. These findings may contribute to the understanding of rAs24-induced Th1/Th2-mediated effector mechanisms required for the protection of A. suum lung-stage larval infection.

Molecular cloning and partial characterization of a nematode-specific 24 kDa protein fromAscaris suum

The cloning and molecular characterization of a cDNA encodingAscaris suum24 kDa antigen (As24) are described. The cDNA sequence consists of 853 bp with an open reading frame coding for a protein of 147 amino acids with an inferred signal peptide of 19 amino acids. The predicted molecular mass and pI were 16 kDa and 8·35 respectively. The endogenous protein in adultA. suumwas 24 kDa with the expected pI. A search of the public databases revealed over 50% homology with proteins from filarial parasites but not to other known proteins, suggesting that As24 is a nematode-specific protein. Immunohistochemical studies using polyclonal antibodies raised againstEscherichia coli-expressed recombinant As24 demonstrated that the endogenous As24 proteins were intensely localized in unembryonated eggs within the uterus, uterine and gut epithelium, muscle tissues and in the hypodermis of an adult femaleA. suum. Endogenous As24 was expressed throughoutA. suumdevelopment and was detected in the excretory/secretory products by immunoblot analysis. Importantly, a homologous protein(s) was detected inAscarisfrom human andToxocara canisfrom dog, suggesting that As24 is a nematode-specific protein.

Resistance against migrating ascaris suum larvae in pigs immunized with infective eggs or adult worm antigens

Resistance to Ascaris suum infections was investigated in 8- and 15-week-old Iberian pigs. Groups of 3 or 5 pigs were immunized weekly for 6 weeks with antigens of adult A. suum: a 97 kDa body wall (BW) fraction, a 42 kDa fraction of pseudocoelomic fluid (PF) or a 14 kDa PF-fraction; or were inoculated with increasing doses of infective eggs (500-20,000), with or without abbreviation by pyrantel pamoate. All immunized pigs and unimmunized control pigs, were challenged with 10,000 infective eggs 7 days after the last immunization. The number of liver lesions and lung larvae was substantially lower in the older pigs than in the younger ones 7 days after challenge, but the resistance in immunized pigs of both age groups was similar in comparison to the challenge controls of the same age. The highest degree of resistance against lung larvae was observed in pigs immunized with A. suum eggs (97-99%). The pigs immunized with the 14 kDa and 42 kDa PF-fractions were also well protected (67-93%), while no protection was produced by the 97 kDa BW fraction (0-49%). The reduction of white spots following immunization was less evident, with a maximum of 82% reduction in egg-inoculated young pigs.

Pharmacotherapy of ascariasis

Ascaris lumbricoides, the most frequent human intestinal nematode, is the causative agent of ascariasis, with an estimated worldwide prevalence of over one billion people, especially in moist tropical and subtropical regions, but also in cooler climates. Although characterised with low morbidity and mortality rates, the global prevalence of ascariasis still results in approximately 20,000 deaths annually, primarily as a consequence of intestinal obstruction. In humans, transmission usually occurs by hand-to-mouth route by way of contaminated agricultural products and food, or from dirty hands. Three phases of ascariasis may be present, namely, the pulmonary, intestinal and the complications stage. Although generally asymptomatic, heavy infestation may cause serious pulmonary disease, or partial or complete obstruction of biliary or intestinal tracts. Anthelminthic chemotherapy is required to eradicate the parasites and prevent potentially serious complications. Mebendazole, albendazole and pyrantel pamoate are the most widely used agents to treat ascariasis. Preventive chemotherapy delivered to communities in endemic regions may serve as an affordable and cost-effective strategy to reduce the prevalence and morbidity in endemic regions. Under unusual circumstances, Ascaris suum, the cause of helminthic infection in pigs, may also cause disease in humans.