Inhibitory role of antibodies in the development of Taenia solium and Taenia crassiceps toward reproductive and pathogenic stages

Anti-GK1 antibodies damage Taenia crassiceps cysticerci through complement activation

Taeniasis-cysticercosis, a zoonosis caused by Taenia solium, is prevalent in underdeveloped countries, where marginalization promotes its continued transmission. Pig cysticercosis, an essential stage for transmission, is preventable by vaccination. An efficient multiepitope vaccine against pig cysticercosis, S3Pvac, was developed. Previous studies showed that antibodies against one of the S3Pvac components, GK-1, are capable of damaging T. solium cysticerci, inhibiting their ability to transform into the adult stage in golden hamster gut. This study is aimed to evaluate one of the mechanisms that could mediate anti-GK-1 antibody-dependent protection. To this end, pig anti-GK-1 antibodies were produced and purified by using protein A. Proteomic analysis showed that the induced antibodies recognized the respective native cysticercal protein KE7 (Bobes et al. Infect Immun 85:e00395-17, 2017) and two additional T. solium proteins (endophilin B1 and Gp50). A new procedure to evaluate cysticercus viability, based on quantifying the cytochrome c released after parasite damage, was developed. Taenia crassiceps cysticerci were cultured in the presence of differing amounts of anti-GK-1 antibody and complement in a saturating concentration, along with the respective controls. Cysticercus viability was assessed by recording parasite motility, trypan blue exclusion, and cytochrome c levels in cysticercal soluble extract. Anti-GK-1 antibody significantly increased cysticercus damage as measured by all three methods. Parasite evaluation by electron microscopy after treatment with anti-GK-1 antibody plus complement demonstrated cysticercus damage as shorter, capsule-severed microtrichia; a decrease in glycocalyx length with respect to untreated cysts; and disaggregated desmosomes. These results demonstrate that anti-GK-1 antibodies damage cysticerci through classic complement activation.

Development of the S3Pvac vaccine against porcine Taenia solium cysticercosis: a historical review

Herein we present a review of our research dealing with vaccination against experimental and naturally acquired porcine Taenia solium cysticercosis using Taenia crassiceps-derived antigens. Results strongly support that the different versions of S3Pvac vaccine are indeed effective against porcine T. solium cysticercosis. Immunological results related to vaccination prove that protection is at least partially mediated by specific immunity. The data also support the validity of T. crassiceps murine cysticercosis as an effective tool to identify vaccine candidates against some metacestode infections.

Development of the S3Pvac vaccine against murine Taenia crassiceps cysticercosis: a historical review

Our work of the last 25 yr was concerned with the development of a vaccine aimed to prevent porcine Taenia solium cysticercosis and was based on cross-reacting Taenia crassiceps antigens that had proved protective against experimental intraperitoneal murine T. crassiceps cysticercosis (EIMTcC). In recent times the efficacy of the vaccine has been considered in need of confirmation, and the use of EIMTcC has been questioned as a valid tool in screening for vaccine candidates among the many antigens possibly involved. A review of our work divided in 2 parts is presented at this point, the first dealing with EIMTcC and the second with porcine T. solium cysticercosis (presented in this issue). Herein, we revise our results using EIMTcC as a measure of the protective capacity of T. crassiceps complex antigen mixtures, of purified native antigens, and of S3Pvac anti-cysticercosis vaccine composed by 3 protective peptides: GK-1, KETc1, and KETc12 either synthetic or recombinantly expressed and collectively or separately, by diverse delivery systems when administered at different doses and by different routes. Statistical analyses of the data lead confidently to the strong inference that S3Pvac is indeed an effective vaccine against EIMTcC via specific and non-specific mechanisms of protection.

Renewed hope for a vaccine against the intestinal adult Taenia solium

Review of experimental and observational evidence about various cestode infections of mammalian hosts revives hope for the development of an effective vaccine against adult intestinal tapeworms, the central protagonists in their transmission dynamics. As for Taenia solium, there are abundant immunological data regarding cysticercosis in humans and pigs, but information about human taeniasis is scarce. A single publication reporting protection against T. solium taeniasis by experimental primo infection and by vaccination of an experimental foster host, the immunocompetent female hamster, kindles the hope of a vaccine against the tapeworm to be used in humans, its only natural definitive host.

Clinical heterogeneity of human neurocysticercosis results from complex interactions among parasite, host and environmental factors

Human neurocysticercosis (NC) is endemic in most countries of Latin America, Asia and Africa and is re-emerging in some industrialized nations. Both within and among endemic countries, NC is very variable in its clinical and radiological features, as well as in the intensity of the immuno-inflammatory reactions of the hosts. This review, focusing on the Mexican experience, describes and interprets the heterogeneity of NC as the result of different combinations among factors associated with the parasite, host and environment. The review may serve to foster similar descriptive efforts in other endemic areas of the world in order to facilitate the identification of the distinct factors that participate in the complex pathogenesis and diverse clinical outcomes of NC. In particular, it is necessary to understand the precise physiopathology of the inflammatory reaction associated with NC, as inflammation is one of the characteristics of those NC cases that are clinically more severe and less responsive to current treatments. Devising new medical interventions through the use of molecular regulators of the innate and adaptive immune responses of the host is a largely unexplored approach that could improve the existing forms of treatment.

Serological responses in porcine cysticercosis: a link with the parasitological outcome of infection

An oral infection model with Taenia solium whole proglottids was used to study host-parasite relationships and the mechanisms underlying resistance to infection in pigs. In addition, an attempt was made to link the parasitological findings to serological data. Groups of six piglets aged 1, 3 and 5 months were infected and slaughtered 3 months p.i. Circulating antibody and antigen levels were monitored weekly. At autopsy total cyst counts were performed. Although the detailed carcass dissection at necropsy revealed a high variation in the number of cysts, the trend was that the number of viable cysts decreased with the age at which the animals were infected. The kinetics of the antigen levels throughout the course of the infection differed markedly between the three age groups of the experimental infection model. In the younger animals, a fast increase in titres of circulating antigen was observed in most animals, reaching a plateau as early as 2 weeks p.i. Besides its faster increase, antigen levels in pigs infected at younger ages also reached higher levels than in older animals and were associated with weaker antibody responses. Results also demonstrated that a relationship exists between the number of cysts and the titre of circulating antigen. This is promising in view of the development of an assay to quantify the progress of an active T. solium infection and would be a useful tool in epidemiological studies to assess the infection burden and the risk of transmission of the disease. The use of specific antibody-detection assays combined with circulating antigen detection could improve our understanding of this relationship.

The immune response in Taenia solium cysticercosis: protection and injury

This article reviews current knowledge on the innate and acquired immune responses in human Taenia solium neurocysticercosis, highlighting the conditions that appear to be favourable for the survival or destruction of the parasite and for the benefit or injury to its host.

Improvement of the synthetic tri-peptide vaccine (S3Pvac) against porcine Taenia solium cysticercosis in search of a more effective, inexpensive and manageable vaccine

Vaccination of pigs may curtail Taenia solium transmission by reducing the number of cysticerci, the precursors of adult intestinal tapeworms in humans. Several antigen preparations induce protection against porcine cysticercosis in experimental settings but only one subunit vaccine (S3Pvac) has been tested and proved effective in the field against naturally acquired disease. Besides improving of the vaccine's effectiveness, significant reductions in production costs and in the logistics of its administration are necessary for the feasibility of nationwide control programs. This review highlights the development of several versions of S3Pvac aimed to increase effectiveness, reduce costs and increase feasibility by novel delivery systems and alternative routes of administration.

Effective Protection Against Experimental Taenia solium Tapeworm Infection in Hamsters by Primo-Infection and by Vaccination with Recombinant or Synthetic Heterologous Antigens

The disease caused by Taenia solium is progressively being recognized as a growing global threat for public human health and pig husbandry that requires the development of effective control measures. A central participant in the taeniasis/cysticercosis transmission network is the human carrier of the adult tapeworm because of its great potential in spreading the infection. Herein, evidence is presented that a primary infection of golden hamsters with orally administered T. solium cysticerci improved the host's resistance against a secondary infection. Likewise, previous vaccination increased the hamster's resistance. Similar high levels of protection (> 78%) were induced by systemic or oral vaccination with the S3Pvac anticysticercosis synthetic peptide vaccine or the highly immunogenic recombinant chimera based on the protective peptide KETc1 bound to Brucella spp. lumazine synthase (BLS-KETc1). Increased resistance after primo-infection and vaccination possibly results from changes in the immune conditions prevailing in the host's intestine. The contribution to protection from the KETc1 and BLS epitopes in a chimeric vaccine is under study. Preventive vaccination of definitive hosts of T. solium against the tapeworm, the most relevant step in the taeniasis/cysticercosis transmission, may greatly impact the dynamics of endemic disease and has not been studied or tried previously.

Therapeutic capacity of the synthetic peptide-based vaccine against Taenia solium cysticercosis in pigs

The S3Pvac synthetic vaccine composed of three peptides (GK1, KETc1 and KETc12) effectively protect against pig cysticercosis. Preliminary results point to an additional cysticidal capacity induced by S3Pvac or GK1 immunization. Herein, clear evidences of the cysticidal effect of S3Pvac but not of GK1 are presented. S3Pvac immunization of already experimentally infected pigs induced a reduction in the parasite load, in the vesicular cysticerci and in their viability. It also substantially increases the percent of histological damaged cysticerci more importantly in muscles than in brains, with a concomitant reduction in the antibody levels. Thus, S3Pvac represents a powerful means of controlling cysticercosis infection in pigs.

Recombinant bacteriophage-based multiepitope vaccine against Taenia solium pig cysticercosis

The aim of this study was to test the capacity of recombinant phages to deliver antigens for vaccination against porcine cysticercosis. Thus, three peptides (KETc1, KETc12, GK1) and a recombinant antigen KETc7, previously proven to induce high levels of protection against pig cysticercosis, were expressed on the surface of the M13 bacteriophage at multiple copies. The pool of these four recombinant phages induced high levels of protection against an experimental murine cysticercosis. The immunogenicity of the phage vaccine preparation was therefore, tested in pigs, the natural host of Taenia solium. Subcutaneous or oral vaccination with these phages induced antigen-specific cellular immune responses in pigs. Preliminary data also points to the protective capacity of this recombinant phage vaccine against pig cysticercosis. The immunogenicity of these recombinant phages, together with the low cost of their production, make them a realistic candidate to be tested in pigs as an anti-cysticercus phage vaccine for field trials. This is the first report describing the application of a filamentous bacteriophage as a vaccine in large animals such as pigs, the only intermediate hosts of T. solium, a parasite of major medical importance in developing countries. The potential application of phages as a modern platform for vaccines for human and animal diseases is discussed.

Th1 and Th2 indices of the immune response in pigs vaccinated against Taenia solium cysticercosis suggest various host immune strategies against the parasite

Kinetics of the production of serum antibody levels and Th1 (IL-2, IFN-gamma) and Th2 (IL-4, IL-10) cytokines was studied in five pigs vaccinated with a synthetic tri-peptide vaccine (S3Pvac) against Taenia solium, a vaccine that has been shown protects pigs against naturally acquired infection. Healthy pigs of mixed genetic background, similar to those bred in rural villages of Mexico, were vaccinated with S3Pvac or with adjuvant alone, kept in sanitary conditions and bled at different times after vaccination to study the development of their specific immune response. Peripheral blood mononuclear cells (PBMCs) of vaccinated pigs showed a significant increment in the production of Th1 cytokines (IL-2 and IFN-gamma) but not of Th2 cytokines (IL-4 and IL-10) after specific PBLs stimulation with all the individual peptides. A Th1-inclined cytokine profile leading to an exacerbated local inflammation at the early installation stage of the cysticercus may possibly interfere with their successful establishment in the serum antibodies against total cysticercus antigens and against each of the three different peptides comprising S3Pvac were detected 7-51 days after vaccination. Antibodies against GK-1 interfered with the cysticerci development into intestinal tapeworms in prednisolone-treated hamsters. The sub-lethal crippling effect of anti-GK-1 antibodies upon cysticerci indicates to a therapeutic application of S3Pvac in infected pigs having potential epidemiological consequences, as it could aid in decreasing the number of tapeworms expected to develop from the few cysticerci that survive in the vaccinated pigs.

CD4+ and CD19+ splenocytes undergo apoptosis during an experimental murine infection with Taenia crassiceps

The Taenia crassiceps cysticercus is a cestode that naturally and experimentally infects rodents in which it reproduces by budding. In the laboratory, a persistent cellular immunosuppression with a concomitant increasing load of parasites has been observed in experimentally infected BALB/cAnN mice. In this study, enhanced apoptosis was found in spleen cells from 30-day infected mice with a typical "ladder-patterned" DNA fragmentation and an increase in phosphatidylserine expression. A characteristic poly-(ADP-ribose) polymerase cleavage indicates that this cell death is caspase-mediated. Apoptosis was detected in the CD4(+) and CD19(+) splenocytes of infected mice after in vitro stimulation with cysticercal antigens. Considering previous results on the crucial role that CD4(+) T cells play in controlling the extent of infection, apoptosis in this T-lymphocyte subpopulation induced by T. crassiceps cysticerci could be responsible for the immunosuppression that underlies parasite success.

Immune response and protection elicited by DNA immunisation against Taenia cysticercosis

The study evaluated DNA vaccination in Taenia solium cysticercosis prevention by using cDNA of an antigen (cC1) from T. solium metacestode. pcDNA3-cC1 DNA vaccine was constructed by inserting the cDNA into the eukaryotic expression plasmid pcDNA3. Positive expression of the pcDNA3-cC1 product was confirmed by its transfection into COS7 cell and enzyme-linked immunoabsorbent assay using serum of pigs infected with T. solium metacestode. Immunisation of BALB/c mice with three injections of pcDNA3-cC1 induced antigen-specific immune responses of the Th1 phenotype. Inoculation of new-born pigs induced protection against challenge with T. solium by 73.3% reduction of the metacestode number. Antibodies elicited by DNA immunisation with pcDNA3-cC1 specifically reacted with native cC1 protein, which was mainly restricted to the cyst wall of T. solium metacestode. Positive apoptosis signals were also detected in the cyst wall cells of metacestode slices from pigs immunised with pcDNA3-cC1 by TUNEL staining method. Those suggested that apoptosis played a role in protecting pigs immunised with pcDNA3-cC1 nucleic acid vaccine from pathogen challenge.

New approaches to improve a peptide vaccine against porcine Taenia solium cysticercosis

Cysticercosis caused by Taenia solium frequently affects human health and rustic porciculture. Cysticerci may localize in the central nervous system of humans causing neurocysticercosis, a major health problem in undeveloped countries. Prevalence and intensity of this disease in pigs and humans are related to social factors (poor personal hygiene, low sanitary conditions, rustic rearing of pigs, open fecalism) and possibly to biological factors such as immunity, genetic background, and gender. The indispensable role of pigs as an obligatory intermediate host in the life cycle offers the possibility of interfering with transmission through vaccination of pigs. An effective vaccine based on three synthetic peptides against pig cysticercosis has been successfully developed and proved effective in experimental and field conditions. The well-defined peptides that constitute the cysticercosis vaccine offer the possibility to explore alternative forms of antigen production and delivery systems that may improve the cost/benefit of this and other vaccines. Encouraging results were obtained in attempts to produce large amounts of these peptides and increased its immunogenicity by expression in recombinant filamentous phage (M13), in transgenic plants (carrots and papaya), and associated to bacterial immunogenic carrier proteins.

Two epitopes shared by Taenia crassiceps and Taenia solium confer protection against murine T. crassiceps cysticercosis along with a prominent T1 response

Taenia crassiceps recombinant antigens KETc1 and KETc12 have been shown to induce high level of protection against experimental murine T. crassiceps cysticercosis, an experimental model successfully used to test candidate antigens for use in vaccination against porcine Taenia solium cysticercosis. Based on the deduced amino acid sequence, KETc1 and KETc12 were chemically synthesized in linear form. Immunization with KETc1 induced 66.7 to 100% protection against murine cysticercosis, and immunization with KETc12 induced 52.7 to 88.1% protection. The elicited immune response indicated that both peptides contain at least one B-cell epitope (as demonstrated by their ability to induce specific antibodies) and one T-cell epitope that strongly stimulated the proliferation of T cells primed with either the free peptide or total cysticercal T. crassiceps antigens. The high percentage of spleen cells expressing inflammatory cytokines points to the likelihood of a T1 response being involved in protection. The protective capacity of the peptides and their presence in all developmental stages of T. solium point to these two epitopes as strong candidates for inclusion in a polyepitopic synthetic vaccine against T. solium pig cysticercosis.