DNA vaccine encoding the Toxoplasma gondii bradyzoite-specific surface antigens SAG2CDX protect BALB/c mice against type II parasite infection

The surface antigens SAG2C, SAG2D, and SAG2X, which expressed specifically on bradyzoite stage of Toxoplasma gondii, have been demonstrated to be important for persistence of cyst in the brain. In this study, DNA vaccines expressing SAG2C, SAG2D, and SAG2X of T. gondii were constructed and their protective efficacy were evaluated in BALB/c mice. Mice vaccinated with pVAX1-SAG2C (pSAG2C), pVAX1-2D (pSAG2D) or pVAX1-2X (pSAG2C) showed higher levels of serum IgG antibodies and lymphocyte proliferation response compared to PBS and pVAX1 treated mice (p < 0.05). The immune response was characterized by a strong Th1 response and increased cytokine production of IL-2 and IFN-γ. Vaccinated mice displayed significant protection against the challenge with the cyst of T. gondii genotype II strain of PRU (cyst-forming in mouse). A significant reduction in the brain cyst burden was detected in the mice immunized with pSAG2C (72%), pSAG2D (23%), pSAG2X (69%) alone and even more reduction rate, 77%, was achieved in the combination group compared to PBS treated mice. The results implied that immunization with DNA vaccines expressing SAG2C, SAG2D, and SAG2X, and, in particular, a combination of all three DNA plasmids, could effectively protect the mice against T. gondii chronic infection.     

Delivery of antigenic candidates by a DNA/MVA heterologous approach elicits effector CD8T cell mediated immunity against Trypanosoma cruzi

In this study, we have characterized the immune mechanisms elicited by antigenic candidates, TcG2 and TcG4, delivered by a DNA-prime/MVA-boost approach, and evaluated the host responses to Trypanosoma cruzi infection in C57BL/6 mice. Immunization of mice with antigenic candidates elicited antigen-specific, high-avidity, trypanolytic antibody response (IgG2b > IgG1) and CD8⁺T cells that exhibited type-1 cytolytic effector (CD8⁺CD107a⁺IFN-γ⁺Perforin⁺) phenotype. The extent of TcG2-dependent type 1 B and T cell immunity was higher than that noted in TcG4-immunized mice, and expanded accordingly in response to challenge infection with T. cruzi. The progression of chronic phase in immunized mice was associated with persistence of IgGs, 55–90% reduction in the frequency of proinflammatory (IFN-γ⁺ or TNF-α⁺) CD8⁺T cells, and an increase or emergence of immunoregulatory (IL-10⁺) CD4/CD8 T cells. The tissue parasitism, infiltration of inflammatory infiltrate, parasite persistence, and fibrosis were decreased by 82–92% in heart and skeletal muscle of immunized/chronically infected mice. Control mice exhibited a significantly low antibody response, consistent activation of effector CD8⁺T cells dominated by pro-inflammatory phenotype and mixed cytokine profile (IFN-γ + TNF-α > IL-4 + IL-10), parasite persistence and pathologic damage in chagasic hearts. We conclude that delivery of TcG2 or TcG4 by DNA-rMVA approach elicits effective antibody and CD8⁺T cell mediated immunity against T. cruzi and Chagas disease. The emergence of type 2 cytokine and T cell response in chronic phase was indicative of prevention of clinical disease.     

Protective immunity induced by a DNA vaccine expressing eIF4A of Toxoplasma gondii against acute toxoplasmosis in mice

Toxoplasma gondii is an obligate intracellular protozoan parasite infecting humans, mammals and birds. Eukaryotic translation initiation factor (eIF4A) is a newly identified protein associated with tachyzoite virulence. To evaluate the protective efficacy of T. gondii eIF4A, a DNA vaccine (pVAX-eIF4A) encoding T. gondii eIF4A (Tg-eIF4A) gene was constructed. The expression ability of this recombinant DNA plasmid was examined in Marc145 cells by IFA. Then, Kunming mice were intramuscularly immunized with pVAX-eIF4A and followed by challenge infection with the highly virulent T. gondii RH strain. The results showed that vaccination with pVAX-eIF4A elicited specific humoral responses, with high IgG antibody titers and specific lymphocyte proliferative responses. The cellular immune response was associated with significant production of IFN-γ, IL-2 in Kunming mice, and a mixed IgG1/IgG2a response with predominance of IgG2a production, indicating that a Th1 type response was elicited after immunization with pVAX-eIF4A. In addition, the increase of the percentage of CD8+ T cells in lymphoid in mice suggested the activation of MHC class I restricted antigen presentation pathways. After lethal challenge, the mice vaccinated with the pVAX-eIF4A showed a significantly prolonged survival time (23.0 ± 5.5 days) compared with control mice which died within 7 days of challenge (P < 0.05). These results demonstrate that pVAX-eIF4A could elicit strong humoral, Th1-type cellular immune responses and increase survival time of immunized mice, suggesting that eIF4A is a promising vaccine candidate against acute T. gondii infection in mice.     

Toxoplasma gondii microneme protein 6 (MIC6) is a potential vaccine candidate against toxoplasmosis in mice

Infection with the intracellular protozoan parasite Toxoplasma gondii causes serious public health problems and is of great economic importance worldwide. Microneme proteins which are responsible for adhesion and invasion have been implicated as vaccine candidates. In this study, we constructed a DNA vaccine expressing microneme protein 6 (MIC6) of T. gondii, and evaluated the immune response it induced in Kunming mice. The gene sequence encoding MIC6 was inserted into the eukaryotic expression vector pVAXI. We immunized Kunming mice intramuscularly. After immunization, we evaluated the immune response using lymphoproliferative assay, cytokine and antibody measurements, and the survival times of mice challenged lethally. The results showed that the group immunized with pVAX-MIC6 developed a high level of specific antibody responses against T. gondii lysate antigen (TLA), 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 phosphate-buffered saline, respectively. These results demonstrate that pVAX-MIC6 induces significant humoral and cellular Th1 immune responses. After lethal challenge, the mice immunized with the pVAX-MIC6 showed an increased survival time (13.3 ± 1.2 days) compared with control mice died within 7 days of challenge. Our data demonstrate, for the first time, that MIC6 triggered a strong humoral and cellular response against T. gondii, and that the antigen is a potential vaccine candidate against toxoplasmosis, worth further development.     

Protective effect against toxoplasmosis in mice induced by DNA immunization with gene encoding Toxoplasma gondii ROP18

Toxoplasma gondii is an obligate intracellular protozoan parasite infecting mammals and birds including humans. Rhoptry protein 18 has been implicated as an important virulence factor. In this study, we constructed a DNA vaccine expressing rhoptry protein 18 (ROP18) of T. gondii, and evaluated the immune response and protective immunity in Kunming mice. The gene sequence encoding ROP18 was inserted into the eukaryotic expression vector pVAX I. Intramuscular immunization of mice with pVAX-ROP18 elicited specific humoral responses and stimulated lymphoproliferation (P < 0.05). The cellular immune response was associated with the production of IFN-γ, indicating that a Th1 type response was elicited, which was confirmed by the production of large amounts of IgG2a (P < 0.05). By the expression of the CD69, an activation marker of CD4+ and CD8+ T cells, we found that pVAX-ROP18 enhanced the activation of CD4+ and CD8+ T cells in lymphoid in mice. After lethal challenge, the mice immunized with the pVAX-ROP18 showed a significantly increased survival time (27.9 ± 15.1 days) compared with control mice which died within 7 days of challenge (P < 0.05). Our results show for the first time, that a ROP18 vaccine construct can enhance the T. gondii-specific CTL. Th1 responses and increased survival suggested that ROP18 is a promising vaccine candidate against infection with T. gondii.     

The virulence-related rhoptry protein 5 (ROP5) of Toxoplasma Gondii is a novel vaccine candidate against toxoplasmosis in mice

Infections with the intracellular protozoan parasite Toxoplasma gondii pose a serious public health problem and are of great economic importance worldwide. The parasite rhoptry protein 5 (ROP5) has been implicated as a major virulence factor that reduces the accumulation of immunity-related GTPases (IRG) in parasitophorous vacuole membrane (PVM), which maintains PVM integrity and evades IFNγ-mediated killing by intracellular parasites. To study the immunoprotective value of ROP5, BALB/c mice were immunized with a recombinant form of the protein administered alone or in combination with another promising vaccine antigen, rSAG1. All mice vaccinated with the recombinant antigens developed a high level of specific antibody responses against soluble tachyzoite antigens (STAg), a statistically significant increase of the splenocyte proliferation response, and significant levels of IFN-γ and IL-2 production. In contrast to rSAG1, which only stimulated the release of IFN-γ and IL-2, rROP5 induced the specific production of IL-10, the Th2-type cytokine, in addition to IFN-γ and IL-2. These results demonstrated that rROP5 could induce significant cellular and humoral (Th1/Th2) immune responses. Moreover, mice immunized with rROP5 displayed a prolonged survival time against a lethal challenge with the T. gondii RH strain. Additionally, vaccination with the mixture of rROP5 + rSAG1 resulted in higher levels of T. gondii-specific IgG antibodies and lymphocyte proliferative responses and conferred more efficient protection against T. gondii challenge compared to immunization with rROP5 or rSAG1 alone. Our studies show that recombinant ROP5 antigen may be a promising vaccine candidate against toxoplasmosis. To our knowledge, this is the first report to evaluate the immunoprotective value of ROP5.     

Transgenic Neospora caninum strains constitutively expressing the bradyzoite NcSAG4 protein proved to be safe and conferred significant levels of protection against vertical transmission when used as live vaccines in mice

At present, there is no effective treatment or vaccine to prevent vertical transmission or abortion associated with Neospora caninum infection in cattle. Different vaccine formulations have been assayed, and live vaccines have shown the most promising results in terms of protection. Previously, transgenic N. caninum tachyzoites expressing the bradyzoite stage-specific NcSAG4 antigen in a constitutive manner (Nc-1 SAG4^c) were obtained and showed a reduced persistence of parasite in inoculated mice. Thus, the present study evaluates the Nc-1 SAG4^c1.1 and Nc-1 SAG4^c2.1 transgenic strains and the Nc-1 wild-type (WT) strain to determine their protective efficacy against vertical transmission and cerebral neosporosis in mice. Consequently, dams were immunized twice with 5 × 10⁵ tachyzoites of each strain and challenged with 2 × 10⁶ tachyzoites of a heterologous and virulent isolate at 7-10 days of gestation. The Nc-1 SAG4^c1.1 strain offered less protection than the other transgenic strain (Nc-1 SAG4^c2.1) or their ancestor (Nc-1 WT). Indeed, 40%, 7% and 5.6% of the postnatal deaths corresponded to pups from dams vaccinated with Nc-1 SAG4^c1.1, Nc-1 SAG4^c2.1 and Nc-1 (WT) strains, respectively. In comparison, the non-immunized challenge group had a 100% mortality rate. In addition, mice were protected against congenital transmission; vertical transmission rates were 45%, 11.1% and 10.8% in the Nc-1 SAG4^c1.1, Nc-1 SAG4^c2.1 and Nc-1 WT immunized groups, respectively, vs. 94.9% in the non-vaccinated infected group. However, this protection against the postnatal mortality and the vertical transmission was not associated with a consistent Th1 or Th2-type immune response. Nonetheless, the Nc-1 SAG4^c2.1 strain appears to be the best candidate for use as a live vaccine, as evidenced by results demonstrating its high levels of protection against vertical transmission and its lower persistence in mice, making this transgenic strain safer than Nc-1 WT.     

Evaluation of protective effect of pVAX-TgMIC13 plasmid against acute and chronic Toxoplasma gondii infection in a murine model

Toxoplasma gondii is a significant zoonotic parasite which can cause congenital infection and abortion in warm-blooded animals and humans. Microneme protein 13 (MIC13) plays an important role in attachment and penetration of the host cell by T. gondii. In this study, a DNA vaccine expressing mic13 of T. gondii was constructed and its protective efficacy was evaluated in Kunming L615^H2k mice. Immunization with pVAX-TgMIC13 induced a strong immune responses demonstrated by significant lymphocyte proliferation, cytokine production and antibody responses. Immunized mice showed increased survival time (21.3 ± 11.3 days) and reduced number of cysts in brain of mice (57.14%) after challenge with tachyzoites of the virulent T. gondii RH strain and cysts of the T. gondii PRU strain, respectively, demonstrating that T. gondii MIC13 is a potential vaccine candidate, worth being included in future vaccine development against acute and chronic T. gondii infection.     

Evaluation of the adjuvant properties of Astragalus membranaceus and Scutellaria baicalensis GEORGI in the immune protection induced by UV-attenuated Toxoplasma gondii in mouse models

Human vaccines are not available and current anti-toxoplasma treatment is disappointing. To investigate the possible adjuvant effect of aqueous extracts obtained from medicinal herbs of Astragalus membranaceus (Am) and Scutellaria baicalensis GEORGI (Sb) on the immune response to Toxoplasma gondii in the mouse models induced by ultraviolet (UV)-attenuated T. gondii, this paper studies the possible vaccination strategies to help combat infections with Toxoplasma and looking towards developing new vaccine and approaches. We used UV-attenuated T. gondii (UV-T.g) of RH strain as a vaccine and the extracts of Am (AmE) and Sb (SbE) as adjuvant. Mice were infected by intraperitoneal (i.p.) injection of 10² RH tachyzoites alone (infected controls), infected and treated with AmE (T.g + AmE) and SbE (T.g + SbE), respectively; and mice immunized i.p. with UV-T.g alone, UV-T.g co-administrated with AmE (UV-T.g + AmE) or SbE (UV-T.g + SbE), and then challenged with T.g, respectively. The animal survival time, parasite burden in peritoneal lavage fluids, liver histopathological analysis, and levels of serum antibodies among the groups were compared after either infection or challenge. The results showed that, compared to infected controls, infected mice treated with AmE or SbE, or vaccinated mice and then challenged, had significantly prolonged survival time, decreased parasite burden, improved liver histopathological score, and increased Th1-type cellular immune response; furthermore, vaccinated mice co-administrated with AmE or SbE had even longer survival, lower parasite burden, lower liver histopathological score, and higher Th1 response after challenge. Our data demonstrated that the protective immunity of UV-attenuated T. gondii could be markedly enhanced by AmE or SbE co-administration, which suggests that both AmE and SbE may have the potential to be used as effective vaccine adjuvant.     

Identification of T. gondii epitopes,adjuvants, and host genetic factors that influence protection of mice and humans

Toxoplasma gondii is an intracellular parasite that causes severe neurologic and ocular disease in immune-compromised and congenitally infected individuals. There is no vaccine protective against human toxoplasmosis. Herein, immunization of L^d mice with HF10 (HPGSVNEFDF) with palmitic acid moieties or a monophosphoryl lipid A derivative elicited potent IFN-γ production from L^d-restricted CD8⁺ T cells in vitro and protected mice. CD8⁺ T cell peptide epitopes from T. gondii dense granule proteins GRA 3, 6, 7, and Sag 1, immunogenic in humans for HLA-A02⁺, HLA-A03⁺, and HLA-B07⁺ cells were identified. Since peptide repertoire presented by MHC class I molecules to CD8⁺ T cells is shaped by endoplasmic reticulum-associated aminopeptidase (ERAAP), polymorphisms in the human ERAAP gene ERAP1 were studied and associate with susceptibility to human congenital toxoplasmosis (p < 0.05). These results have important implications for vaccine development.     

MyD88-dependent protective immunity elicited by adenovirus 5 expressing the surface antigen 1 from Toxoplasma gondii is mediated by CD8(+) T lymphocytes

Toxoplasma gondii is an intracellular parasite widely spread around the world. The surface antigens (SAG) 1, 2 and 3 are the main proteins expressed on the surface of T. gondii tachyzoites. Replication-defective adenovirus serotype 5 (rAd5) is one of the most potent recombinant viral vectors for eliciting T cell-mediated immunity in mice and humans. Here we show that vaccination with rAd5 expressing SAG1 (AdSAG1), but neither SAG2 nor SAG3, induces protective immunity in the highly susceptible C57BL/6 mice challenged with T. gondii. Furthermore, we evaluated different immunological components involved on viral induced protective immunity. We observed that host protection elicited by AdSAG1 is highly dependent on IL-12, IFN-γ and CD8⁺ T lymphocytes. Importantly, the induction of protective immunity (T cell-derived IFN-γ) was also dependent on Myeloid Differentiation Factor 88 (MyD88), and thus, likely to involve Toll-like Receptors. We conclude that protective parasite specific-CD8⁺ T cells are elicited by a mechanism that involves MyD88-dependent induction of IL-12.     

Induction of protective Th1 immune responses in mice by vaccination with recombinant Toxoplasma gondii nucleoside triphosphate hydrolase-II

The Toxoplasma gondii nucleoside triphosphate hydrolase (TgNTPase) has apyrase activity, degrading ATP to the di- and mono-phosphate forms and may be used by the parasite to salvage purines from the host cell for survival and replication. To study the immune-protective value of TgNTPase-II, BALB/c mice were immunized with a recombinant form of the antigen rTgNTPase-II combined with alum. All immunized mice produced specific anti-rTgNTPase-II immunoglobulins, with high IgG antibody titers and a mixed IgG1/IgG2a response, with predominance of IgG2a production. The cellular immune response was associated with the production of IFN-γ and IL-2 cytokines and the increase of the percentage of CD8+ T cells. Vaccinated mice displayed significant protection against acute infection with the virulent RH strain (P < 0.05 in survival rate) and also chronic infection with PRU cyst (62.9% and 57.6% reduction in brain parasite load for rTgNTPase-II + alum and rTgNTPase-II alone vaccinated groups) compared to the non-vaccinated control group. In conclusion, rTgNTPase-II elicits a strong specific Th1 immune response providing partial protection against both T. gondii acute and chronic infection.     

Protection in mice immunized with a heterologous prime-boost regime using DNA and recombinant pseudorabies expressing TgSAG1 against Toxoplasma gondii challenge

An effective vaccine of animals can block transmission of Toxoplasma gondii to humans. In this study, mice have been protected against lethal T. gondii challenge by a prime-boost vaccination strategy using DNA vaccine pVAX/TgSAG1 and recombinant pseudorabies virus rPRV/TgSAG1, both expressing the major immunodominant surface antigen of T. gondii (TgSAG1). High levels of splenocyte proliferative responses and significant levels of IFN-γ resulted, with strong cytotoxic T lymphocyte (CTL) responses in vitro. After lethal challenge, prime-boost vaccinated mice showed an increased survival time (15.4 ± 5.0 days) and a 40% survival rate compared with controls who all died within 11 days of challenge. Results of the present study indicated that this novel immunization strategy is useful in enhancing immune protection in mice against lethal T. gondii infection, which would provide foundation for the development of effective vaccines against T. gondii.     

Intragastric administration of attenuated Salmonella typhimurium harbouring transmissible gastroenteritis virus (TGEV) DNA vaccine induced specific antibody production

Attenuated Salmonella typhimurium was selected as a transgenic vehicle for the development of live mucosal vaccines against transmissible gastroenteritis virus (TGEV). A 2.2 kb DNA fragment, encoding for N-terminal domain glycoprotein S of TGEV, was amplified by RT-PCR and cloned into eukaryotic expression vector pVAX1. The recombinant plasmid pVAX-S was transformed by electroporation into attenuated S. typhimurium SL7207, the expression and translation of the pVAX-S delivered by recombinant S. typhimurium SL7207 (pVAX-S) was detected in vitro and in vivo respectively. BALB/c mice were inoculated orally with SL7207 (pVAX-S) at different dosages, the bacterium was safe to mice at dosage of 2 × 10⁹ CFU and eventually eliminated from the spleen and liver at week 4 post-immunization. Mice immunized with different dosages of SL7207 (pVAX-S) elicited specific anti-TGEV local mucosal and humoral responses as measured by indirect ELISA assay. Moreover, the immunogenicity of the DNA vaccine was highly dependent on the dosage of the attenuated bacteria used for oral administration, 10⁹ CFU dosage group showed higher antibody response than 10⁸ CFU and 10⁷ CFU dosages groups during week 4–8 post-immunization. The results indicated that attenuated S. typhimurium could be used as a delivery vector for oral immunization of TGEV DNA vaccine.     

Induction of protection in mice against a respiratory challenge by a vaccine formulated with the Chlamydia major outer membrane protein adjuvanted with IC31®

IC31^®, a novel adjuvant, has been shown to be effective by increasing the levels of IFN-γ in animal models when delivered with several antigens. Here, we tested the ability of IC31^®, to enhance the protective ability of the Chlamydia trachomatis native major outer membrane protein (nMOMP). BALB/c mice were immunized by the intramuscular (i.m.) and subcutaneous (s.c.) routes with nMOMP + IC31^®. Another group of animals was immunized with nMOMP + Alum and as a negative control mice were immunized with ovalbumin (Ova) + IC31^®. Animals immunized with nMOMP + IC31^® developed high Chlamydia-specific IgG titers. The serum levels of IgG1 were higher than those of the IgG2a. T cells, from the spleens of mice immunized with IC31^®-adjuvanted nMOMP demonstrated a strong lymphoproliferative reaction to Chlamydia elementary bodies (EB) compared with the groups immunized with nMOMP + Alum or Ova + IC31^®. A similar comparison between these groups of mice revealed that the levels of IFN-γ in the supernatants from stimulated T-cells were significantly higher in animals immunized with nMOMP + IC31^®. Following an intranasal challenge with C. trachomatis, the mice immunized with IC31^®-adjuvanted nMOMP showed significant protection. The change in body weight, an indication of the severity of the infection, was significantly less reduced in mice immunized with nMOMP + IC31^®. Furthermore, the weight of the lungs, as well as the pulmonary Chlamydia burden, was significantly lower in the animals immunized with nMOMP + IC31^® when compared with the groups immunized with nMOMP + Alum or with Ova + IC31^®. In conclusion, these results provide the rationale for further preclinical testing of IC31^® using other chlamydial antigens, and support the potential evaluation of this adjuvant in human vaccines against Chlamydia.     

Oligomannose-coated liposome-entrapped dense granule protein 7 induces protective immune response to Neospora caninum in cattle

Neospora caninum is an intracellular protozoan parasite that causes abortion in cows. Vaccination is an important strategy for control of neosporosis, and a safe and effective vaccine suitable for cattle is required. Dense granule protein 7 of N. caninum (NcGRA7) is a secretory protein with high antigenicity in hosts. We demonstrated previously that NcGRA7 entrapped in liposomes coated with mannotriose (M3-NcGRA7) could induce a parasite-specific T-helper type 1 immune response and produce humoral antibodies that resulted in increased offspring survival and decreased infection in the brains of mice dams. In the present study, the efficacy of M3-NcGRA7 as a vaccine candidate against N. caninum has been evaluated in cattle (n = 12). Cattle were immunized with M3-NcGRA7 containing 50 μg (n = 4) or 200 μg NcGRA7 (n = 4) subcutaneously twice with a 4-week interval and all cattle including the non-immunized controls (n = 4) were inoculated with 10⁷ tachyzoites of Nc-1 strain 27 days after the second immunization and euthanized at 85–87 days post infection (dpi). In immunized cattle, NcGRA7-specific antibody production and IFN-γ production in PBMC was induced before challenge. At 3 dpi, body temperature and concentration of serum IFN-γ tended to be higher in control cattle than in the immunized cattle. Furthermore, the parasite load in the brain significantly decreased in cattle immunized with 50 μg M3-NcGRA7 compared with controls. These results suggest that M3-NcGRA7 can induce protective immune responses to N. caninum tachyzoites in cattle, which could lead to practical application of safe and effective subunit vaccines.     

A recombinant bivalent fusion protein rVE confers active and passive protection against Yersinia enterocolitica infection in mice

In the present study, a bivalent chimeric protein rVE comprising immunologically active domains of Yersinia pestis LcrV and YopE was assessed for its prophylactic abilities against Yersinia enterocolitica O:8 infection in murine model. Mice immunized with rVE elicited significantly higher antibody titers with substantial contribution from the rV component (3:1 ratio). Robust and significant resistance to Y. enterocolitica infection with 100% survival (P < 0.001) was seen in rVE vaccinated mice when intra peritoneal (I.P.) challenged with 10⁸ CFU of Y. enterocolitica O:8 against the 75%, 60% and 75% survival seen in mice immunized with rV, rE, rV + rE, respectively. Macrophage monolayer supplemented with anti-rVE polysera illustrated efficient protection (89.41% survival) against challenge of Y. enterocolitica O:8. In contrast to sera from sham-immunized mice, immunization with anti-rVE polysera provided complete protection to BALB/c mice against I.P. challenge with 10⁸ CFU of Y. enterocolitica O:8 and developed no conspicuous signs of infection in necropsy. The histopathological analysis of microtome sections confirmed significantly reduced lesion size or no lesion in liver and intestine upon infection in anti-rVE immunized mice. The findings from this study demonstrated the fusion protein rVE as a potential candidate subunit vaccine and showed the functional role of antibodies in protection against Y. enterocolitica infections.     

Prime and boost immunization with influenza and adenovirus encoding the Toxoplasma gondii surface antigen 2 (SAG2) induces strong protective immunity

In this work, we explored an original vaccination protocol using recombinant influenza and adenovirus. We constructed recombinant influenza viruses harboring dicistronic NA segments containing the surface antigen 2 (SAG2) from Toxoplasma gondii under control of the duplicated 3′ promoter. Recombinant influenza viruses were able to drive the expression of the foreign SAG2 sequence in cell culture and to replicate efficiently both in cell culture and in lungs of infected mice. In addition, mice primed with recombinant influenza virus and boosted with a recombinant adenovirus encoding SAG2 elicited both humoral and cellular immune responses specific for SAG2. Moreover, when immunized animals were challenged with the cystogenic P-Br strain of T. gondii, they displayed up to 85% of reduction in parasite burden. These results demonstrate the potential use of recombinant influenza vectors harboring the dicistronic segments in the development of vaccines against infectious diseases.     

Protective immunity against Toxoplasma challenge in mice by coadministration of T. gondii antigens and Eimeria profilin-like protein as an adjuvant

Toll-like receptor (TLR) ligands are attractive adjuvant candidates in vaccine development. Eimeria tenella profilin-like protein has recently been shown to be a potent agonist of the innate immune system through its recognition by Toll-like receptor-11. In this report, we studied the systemic and mucosal adjuvant activity of Eimeria profilin-like protein within a vaccinal strategy against Toxoplasma gondii in mice. Using intraperitoneal (i.p.) immunization, we observed that coadministration of the recombinant Eimeria antigen (rEA) with T. gondii antigen (TAg) effectively elevates plasma levels of IL-12p70 and consequently induced both enhanced specific humoral and Th1 cellular immune responses. The co-administration of TAg plus rEA by i.p route significantly enhanced the protection against T. gondii infection (62% brain cyst reduction) in comparison with control mice and with mice immunized with TAg alone (only 36% brain cyst reduction). After intranasal immunization, humoral and cellular responses were weak. However mice immunized nasally with TAg plus rEA were significantly protected with 50% of brain cyst reduction, conversely TAg immunized mice did not present any brain cyst reduction.These results indicate that Eimeria profilin-like protein would serve as an efficacious systemic and mucosal adjuvant inducing protective immune response against chronical stage of T. gondii infection through TLR11 activation.     

Protection against an intranasal challenge by vaccines formulated with native and recombinant preparations of the Chlamydia trachomatis major outer membrane protein

To compare the ability of a native and a recombinant preparation of the major outer membrane protein of Chlamydia trachomatis mouse pneumonitis (MoPn; Ct-nMOMP and Ct-rMOMP) to protect against an intranasal (i.n.) challenge, BALB/c mice were vaccinated by the intramuscular (i.m.) and subcutaneous (s.c.) routes using CpG-1826 and Montanide ISA 720 as adjuvants. Animals inoculated i.n. with live elementary bodies (EB) of Chlamydia served as a positive control. Negative control groups were immunized with either Neisseria gonorrhoeae recombinant porin B (Ng-rPorB) or with minimal essential medium (MEM-0). Mice immunized with Ct-rMOMP, Ct-nMOMP and EB developed a strong immune response as shown by high levels of Chlamydia specific antibodies in serum and a strong T-cell lymphoproliferative response. Following the i.n. challenge with 10⁴ inclusion forming units (IFU) of C. trachomatis, mice immunized with Ct-nMOMP or Ct-rMOMP lost significantly less weight than the negative control animals immunized with Ng-rPorB or MEM-0 (P < 0.05). However, mice vaccinated with the Ct-nMOMP lost less weight than those immunized with the Ct-rMOMP (P < 0.05). Mice were euthanized at 10 days following the challenge, their lungs weighed and the number of IFU of Chlamydia determined. Based on the lung weight and number of IFU recovered, significant protection was observed in the groups of mice immunized with both Ct-nMOMP and the Ct-rMOMP (P < 0.05). Nevertheless, significantly better protection was achieved with the Ct-nMOMP in comparison with the Ct-rMOMP (P < 0.05). In conclusion, vaccination with a preparation of the nMOMP elicited a more robust protection than immunization with rMOMP, suggesting that the conformational structure of MOMP is critical for inducing strong protection.