Maturation of human dendritic cells with Saccharomyces cerevisiae (yeast) reduces the number and function of regulatory T cells and enhances the ratio of antigen-specific effectors to regulatory T cells

We compared the effects of yeast-treated human dendritic cells (DCs) with CD40L-matured human DCs for the induction of effector cells and the number and functionality of CD4⁺CD25⁺CD127⁻FoxP3⁺ regulatory T cells (Tregs). DCs were treated with yeast or CD40L and cocultured with isolated autologous CD4⁺ T cells. CD4⁺CD25⁺CD127⁻ T cells isolated from the coculture of CD4⁺ T cells plus yeast-treated DCs (yeast coculture) had a lower expression of FoxP3 and decreased suppressive function compared to CD4⁺CD25⁺CD127⁻ T cells isolated from the coculture of CD4⁺ T cells plus CD40L-treated DCs (CD40L coculture). Also, compared to the CD40L coculture, the yeast coculture showed increases in the ratio of CD4⁺CD25⁺ activated T cells to Tregs and in the production of Th1-related cytokines (IL-2, TNF-α, IFN-γ) and IL-6. In addition, yeast-treated DCs used as antigen-presenting cells (APCs) incubated with the tumor antigen CEA enhanced the proliferation of CEA-specific CD4⁺ T cells compared to the use of CD40L-matured DCs used as APCs. This is the first study to report on the role of yeast-treated/matured human DCs in reducing Treg frequency and functionality and in enhancing effector to Treg ratios. These results provide an additional rationale for the use of yeast as a vector in cancer vaccines.     

CD8 T cell immunity to Plasmodium permits generation of protective antibodies after repeated sporozoite challenge

Individuals living in malaria endemic areas are subject to repeated infections yet fail to develop sterilizing immunity, however, immunization of mice with attenuated sporozoites or subunit vaccines has shown the ability to protect mice against a sporozoite challenge. We recently reported that mice primed with dendritic cells coated with the dominant circumsporozoite CD8 T cell epitope from Plasmodium berghei followed by a boost with recombinant Listeria monocytogenes expressing the same epitope exhibited sterile immunity against a sporozoite challenge for more than one year. In this report we show those mice do not contain protective antibodies and that depletion of CD4 T cells in the immunized mice did not affect sterile immunity. In contrast, CD8 T cell depletion eliminated protection. Thus, protective immunity generated by this immunization approach is entirely memory CD8 T cell-dependent. We also show here that mice initially protected by circumsporozoite-specific memory CD8 T cells develop sterilizing sporozoite-specific antibodies after repeated asymptomatic challenges with physiologic numbers of viable sporozoites. Therefore, initial protection by a CD8 T cell-targeted liver stage subunit vaccine allows the generation of enhanced sterilizing immune responses from repeated exposure to Plasmodium parasites.     

CD4+ and CD8+ T cell- and IL-17-mediated protection against Entamoeba histolytica induced by a recombinant vaccine

Amebiasis in the murine model can be prevented by vaccination with the Gal/GalNAc lectin through a T cell-dependent mechanism. In this work we further decipher the mechanism of this protection. Mice vaccinated with the recombinant “LecA” fragment of the Gal/GalNAc lectin with alum were capable of transferring protection to naïve recipients by both CD4+ T cells and surprisingly CD8+ T cells. We then examined the cytokine profile of these cells. CD4+ T cells from PBMC of LecA-alum vaccinated mice were observed to be a major source of IFN-γ, known to be a protective cytokine with this vaccine. In contrast, CD8+ T cells produced relatively little IFN-γ but more IL-17 than the CD4 compartment. We thus examined the role of IL-17 in vaccine mediated protection and found through neutralization experiments that this cytokine contributed to LecA-alum vaccine protection. In addition we examined whether these cells exhibited direct amebicidal activity in vitro and found that both populations had amebicidal activity at high concentrations (1000:1) but CD8+ T cells appeared more potent, capable of cytotoxicity at a 100:1 ratio. In conclusion, both CD4 and CD8 T cells exert protection with this amebiasis vaccine. The mechanism of CD8 T cell-mediated protection may include direct amebicidal activity and/or IL-17 production. Both IL-17 and IFN-γ are useful surrogates for immune protection.     

CD4 T-cell responses among adults and young children in response to Streptococcus pneumoniae and Haemophilus influenzae vaccine candidate protein antigens

We characterized cytokine profiles of CD4⁺ T-helper (h) cells in adults and young children to ascertain if responses occur to next-generation candidate vaccine antigens PspA, PcpA, PhtD, PhtE, Ply, LytB of Streptococcus pneumonia (Spn) and protein D and OMP26 of non-typeable Haemophilus influenzae (NTHi). Adults had vaccine antigen-specific Th1 and Th2 cells responsive to all antigens evaluated whereas young children had significant numbers of vaccine antigen-specific CD4⁺ T cells producing IL-2, (p = 0.004). Vaccine antigen-specific CD4⁺ T-cell populations in adults were largely of effector (T_EM) and/or central memory (T_CM) phenotypes as defined by CD45RA⁻CCR7⁺ or CD45RA⁻CCR7⁻ respectively; however among young children antigen-specific IL-2 producing CD4⁺ T cells demonstrated CD45RA⁺ expression (non-memory cells). We conclude that adults have circulating memory CD4⁺ T cells (CD45RA⁻) that can be stimulated by all the tested Spn and NTHi protein vaccine candidate antigens, whereas young children have a more limited response.     

Protection of cattle against a natural infection of Fasciola hepatica by vaccination with recombinant cathepsin L1 (rFhCL1)

The liver fluke, Fasciola hepatica causes liver fluke disease, or fasciolosis, in ruminants such as cattle and sheep. An effective vaccine against the helminth parasite is essential to reduce our reliance on anthelmintics, particularly in light of frequent reports of resistance to some frontline drugs. In our study, Friesian cattle (13 per group) were vaccinated with recombinant F. hepatica cathepsin L1 protease (rFhCL1) formulated in mineral-oil based adjuvants, Montanide™ ISA 70VG and ISA 206VG. Following vaccination the animals were exposed to fluke-contaminated pastures for 13 weeks. At slaughter, there was a significant reduction in fluke burden of 48.2% in the cattle in both vaccinated groups, relative to the control non-vaccinated group, at p ≤ 0.05. All vaccinated animals showed a sharp rise in total IgG levels to rFhCL1 post-vaccination which was maintained over the course of the 13-week challenge infection and was significantly higher than levels reached in the control group. Arginase levels in the macrophages of vaccinated cattle were significantly lower than those of the control cattle, indicating that the parasite-induced alternative-activation of the macrophages was altered by vaccination. The data demonstrate the potential for recombinant FhCL1 vaccine in controlling fasciolosis in cattle under field conditions.     

卵巢癌患者外周血CD4~+ CD25~(high)调节性T细胞及Foxp3的检测及临床意义

目的:检测CD4+CD25high调节性T细胞(Treg)及Foxp3在卵巢癌患者外周血单个核细胞(PBMC)中的表达,探讨其在抗肿瘤免疫调节中的作用及临床意义。方法:采用流式细胞术检测75例卵巢癌患者PBMC中CD4+CD25+/CD4+、CD4+CD25high/CD4+T细胞百分比以及CD4+CD25+及CD4+CD25highT细胞中Foxp3+T细胞的表达,并与73例正常对照组进行比较。结果:卵巢癌患者治疗前PBMC中CD4+CD25+/CD4+、CD4+CD25high/CD4+T细胞百分比及Foxp3表达水平均较正常对照组增高(P<0.05),治疗后上述指标较治疗前减低(P<0.05)。结论:卵巢癌患者外周血调节性T细胞增高可能是其免疫异常的主要原因之一,定期检测外周血中上述指标的变化有助于了解卵巢癌患者的病情变化及判断预后。     

Phenotype of the anti-Rickettsia CD8 T cell response suggests cellular correlates of protection for the assessment of novel antigens

The obligately intracellular bacteria Rickettsia infect endothelial cells and cause systemic febrile diseases that are potentially lethal. No vaccines are currently available and current knowledge of the effective immune response is limited. Natural and experimental rickettsial infections provide strong and cross-protective cellular immunity if the infected individual survives the acute infection. Although resistance to rickettsial infections is attributed to the induction of antigen-specific T cells, particularly CD8⁺ T cells, the identification and validation of correlates of protective cellular immunity against rickettsial infections, an important step toward vaccine validation, remains a gap in this field. Here, we show that after a primary challenge with Rickettsia typhi in the C3H mouse model, the peak of anti-Rickettsia CD8⁺ T cell-mediated responses occurs 7 days post-infection (dpi), which coincides with the beginning of rickettsial clearance. At this time point, both effector-type and memory-type CD8⁺ T cells are present, suggesting that 7 dpi is a valid time point for the assessment of CD8⁺ T cell responses of mice previously immunized with protective antigens. Based on our results, we suggest four correlates of cellular protection for the assessment of protective rickettsial antigens: (1) production of IFN-γ by antigen-experienced CD3⁺CD8⁺CD44^high cells, (2) production of Granzyme B by CD27^lowCD43^low antigen-experienced CD8⁺ T cells, (3) generation of memory-type CD8⁺ T cells [Memory Precursor Effector Cells (MPECs), as well as CD127^highCD43^low, and CD27^highCD43^low CD8⁺ T cells], and (4) generation of effector-like memory CD8⁺ T cells (CD27^lowCD43^low). We propose that these correlates could be useful for the general assessment of the quality of the CD8⁺ T cell immune response induced by novel antigens with potential use in a vaccine against Rickettsia.     

Antigen-specific B memory cell responses to lipopolysaccharide (LPS) and invasion plasmid antigen (Ipa) B elicited in volunteers vaccinated with live-attenuated Shigella flexneri 2a vaccine candidates

We evaluated B memory responses in healthy adult volunteers who received one oral dose of live-attenuated Shigella flexneri 2a vaccine. LPS-specific B_M cells increased from a median of 0 at baseline to 20 spot forming cells (SFC)/10⁶ expanded cells following vaccination (p = 0.008). A strong correlation was found between post-vaccination anti-LPS B_M cell counts and peak serum anti-LPS IgG titers (rs = 0.95, p = 0.0003). Increases in B_M specific for IpaB approaching significance were also observed. In sum, oral vaccination with live-attenuated S. flexneri 2a elicits B_M cells to LPS and IpaB, suggesting that B_M responses to Shigella antigens should be further studied as a suitable surrogate of protection in shigellosis.     

Evaluation of a multisubunit recombinant polymorphic membrane protein and major outer membrane protein T cell vaccine against Chlamydia muridarum genital infection in three strains of mice

An efficacious vaccine is needed to control Chlamydia trachomatis infection. In the murine model of Chlamydia muridarum genital infection, multifunctional mucosal CD4 T cells are the foundation for protective immunity, with antibody playing a secondary role. We previously identified four Chlamydia outer membrane proteins (PmpE, PmpF, PmpG and PmpH) as CD4 T cell vaccine candidates using a dendritic cell-based immunoproteomic approach. We also demonstrated that these four polymorphic membrane proteins (Pmps) individually conferred protection as measured by accelerated clearance of Chlamydia infection in the C57BL/6 murine genital tract model. The major outer membrane protein, MOMP is also a well-studied protective vaccine antigen in this system. In the current study, we tested immunogenicity and protection of a multisubunit recombinant protein vaccine consisting of the four Pmps (PmpEFGH) with or without the major outer membrane protein (MOMP) formulated with a Th1 polarizing adjuvant in C57BL/6, Balb/c and C3H mice. We found that C57BL/6 mice vaccinated with PmpEFGH + MOMP elicited more robust cellular immune responses than mice immunized with individual protein antigens. Pmps elicited more variable cellular immune responses than MOMP among the three strains of mice. The combination vaccine accelerated clearance in the three strains of mice although at different rates. We conclude that the recombinant outer membrane protein combination constitutes a promising first generation Chlamydia vaccine construct that should provide broad immunogenicity in an outbred population.     

Effectiveness of intranasal vaccination against Angiostrongylus costaricensis using a serine/threonine phosphatase 2 A synthetic peptide and recombinant antigens

Intranasal immunization was assayed in C57BL/6 mice against Angiostrongylus costaricensis using a synthetic and a recombinant peptide belonging to the catalytic region of the serine/threonine phosphatase 2 A (PP2A) of the parasite. Immunization was carried out with the synthetic peptide (SP) polymerized either with itself or with the β fraction of the cholera toxin (CTB) and then enclosed in nanocapsules of phosphatidyl choline, cholesterol and Quil A (ISCOM). Another group of mice was immunized with recombinant peptide. Immunization consisted of two intranasal inoculations at two-week intervals, and the challenge with L3 larvae was made one month after the last vaccination.     

CD8 T cell independent immunity after single dose infection-treatment-vaccination (ITV) against Plasmodium yoelii

Sporozoite vaccination of both humans and rodents elicits potent anti-malarial immunity, but the dose of sporozoites and the number of immunizations required varies with vaccination approach. Here we examine the immunological basis for superior protection afforded from single-dose vaccination with virulent sporozoites administered under prophylatic chloroquine-cover, referred to as infection-treatment-vaccination (ITV), compared to the well-studied approach of administering radiation-attenuated Plasmodium sporozoites (RAS). Earlier rodent studies utilizing ITV and RAS vaccination suggested a major role of CD8 T cells in reducing liver parasite burden after sporozoite challenge in a BALB/c mouse model. Consistent with this, we find that in C57Bl/6 mice ITV elicits substantially higher parasite-specific CD8 T cell responses than RAS vaccination and enhances immunity against P. yoelii infection. However, we show ITV-induced CD8 T cells are not necessary for protection following liver-stage sporozoite or blood-stage parasite challenge. Mechanistically, we found protection afforded from single-dose ITV is associated with low grade, transient parasitemia shortly following cessation of chloroquine treatment and generation of potent antibody responses to blood-stage parasites. Collectively, our data show the mechanistic basis for enhanced protective immunity against P. yoelli elicited by ITV in highly susceptible C57Bl/6 mice is independent of CD8 T cells. These studies may be relevant in understanding the potent immunity observed with ITV in humans.     

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.     

Ovalbumin lipid core peptide vaccines and their CD4 and CD8 T cell responses

The lipid core peptide (LCP) system has successfully been used in development of peptide-based vaccines against cancer and infectious diseases (such as group A streptococcal infection). CD8⁺ T cells are important targets for vaccines, however developing a vaccine that activates long-lasting immunity has proven challenging. The ability of LCP vaccines to activate antigen-specific CD8⁺ and/or CD4⁺ T cell responses was tested using compounds that contained two or four copies of OVA_257–264 and/or OVA_323–339 peptides conjugated to LCP, which are recognised by OTI (CD8⁺ specific) and OTII (CD4⁺ specific) T cells, respectively. The LCP–ovalbumin vaccines developed in this study were synthesised in 30% yields and showed no significant haemolytic effect on red blood cells (below 4% haemolysis when tested with compounds at up to 100 μM concentrations). Promising in vivo data in mice suggested that this LCP–ovalbumin vaccine system could act as a novel and potent vehicle for the stimulation of robust antigen-specific CD8⁺ T cell responses.     

Recombinant pro-apoptotic Mycobacterium tuberculosis generates CD8 T cell responses against human immunodeficiency virus type 1 Env and M. tuberculosis in neonatal mice

Mycobacterium bovis BCG is an attractive vaccine vector against breast milk HIV transmission because it elicits Th1-type responses in newborns. However, BCG causes disease in HIV-infected infants. Genetically attenuated Mycobacterium tuberculosis (Mtb) mutants represent a safer alternative for immunocompromised populations. In the current study, we compared the immunogenicity in mice of three different recombinant attenuated Mtb strains expressing an HIV envelope (Env) antigen construct. Two of these strains (ΔlysA ΔpanCD Mtb and ΔRD1 ΔpanCD Mtb) failed to induce significant levels of HIV Env-specific CD8⁺ T cell responses. In striking contrast, an HIV-1 Env-expressing attenuated ΔlysA Mtb containing a deletion in secA2, which encodes a virulence-related secretion system involved in evading adaptive immunity, generated consistently measurable Env-specific CD8⁺ T cell responses that were significantly greater than those observed after immunization with BCG expressing HIV Env. Similarly, another strain of ΔlysA ΔsecA2 Mtb expressing SIV Gag induced Gag- and Mtb-specific CD8⁺ T cells producing perforin or IFNγ, and Gag-specific CD4⁺ T cells producing IFNγ within 3 weeks after immunization in adult mice; in addition, IFNγ-producing Gag-specific CD8⁺ T cells and Mtb-specific CD4⁺ T cells were observed in neonatal mice within 1 week of immunization. We conclude that ΔlysA ΔsecA2 Mtb is a promising vaccine platform to construct a safe combination HIV-TB vaccine for use in neonates.     

Vaccination of koalas (Phascolarctos cinereus) with a recombinant chlamydial major outer membrane protein adjuvanted with poly I:C,a host defense peptide and polyphosphazine,elicits strong and long lasting cellular and humoral immune responses

Chlamydial infections are wide spread in koalas across their range and a solution to this debilitating disease has been sought for over a decade. Antibiotics are the currently accepted therapeutic measure, but are not an effective treatment due to the asymptomatic nature of some infections and a low efficacy rate. Thus, a vaccine would be an ideal way to address this infectious disease threat in the wild. Previous vaccine trials have used a three-dose regimen; however this is very difficult to apply in the field as it would require multiple capture events, which are stressful and invasive processes for the koala. In addition, it requires skilled koala handlers and a significant monetary investment. To overcome these challenges, in this study we utilized a polyphosphazine based poly I:C and a host defense peptide adjuvant combined with recombinant chlamydial major outer membrane protein (rMOMP) antigen to induce long lasting (54 weeks) cellular and humoral immunity in female koalas with a novel single immunizing dose. Immunized koalas produced a strong IgG response in plasma, as well as at mucosal sites. Moreover, they showed high levels of C. pecorum specific neutralizing antibodies in the plasma as well as vaginal and conjunctival secretions. Lastly, Chlamydia-specific lymphocyte proliferation responses were produced against both whole chlamydial elementary bodies and rMOMP protein, over the 12-month period. The results of this study suggest that a single dose rMOMP vaccine incorporating a poly I:C, host defense peptide and polyphosphazine adjuvant is able to stimulate both arms of the immune system in koalas, thereby providing an alternative to antibiotic treatment and/or a three-dose vaccine regime.     

Role of antibody dependent cell mediated cytotoxicity (ADCC) in Sm-p80-mediated protection against Schistosoma mansoni

Schistosomiasis is a major health problem in the developing world and for international travelers to the endemic countries. Existing strategies to control schistosomiasis have had limited successes so far. The addition of an effective vaccine in existing control measures would be greatly beneficial in reducing the impact of the disease. In this regard, Sm-p80 mediated protection against intestinal schistosomiasis caused by Schistosoma mansoni has been observed to be promising in two animal models of infection and disease. In this study, the role of antibody dependent cell mediated cytotoxcity (ADCC) was deciphered in Sm-p80-mediated protection especially in the elimination of lung stage schistosomula. This was achieved using lung lavage cells and lung cells that were isolated from mice immunized with and without Sm-p80 formulated in a recombinant vaccine formulation. Significant differences were observed in cytotoxicity assays using immune sera with the lung lavage cells which showed 51% more killing of schistosomula and elevated levels of nitric oxide in the supernatants were detected compared to controls.     

The in vivo expressed Mycobacterium tuberculosis (IVE-TB) antigen Rv2034 induces CD4 T-cells that protect against pulmonary infection in HLA-DR transgenic mice and guinea pigs

Tuberculosis (TB) remains a life-threatening infectious disease of global proportions with serious negative health and economic consequences. The lack of sufficient protection induced by Mycobacterium bovis BCG, the current vaccine for TB, as well as the impact of HIV co-infection and the emergence of drug resistant Mycobacterium tuberculosis (Mtb) strains all urge for improved vaccines against TB.     

Outer membrane protein A (OmpA) from Shigella flexneri 2a: A promising subunit vaccine candidate

Shigellosis is the leading cause of childhood mortality and morbidity. Despite many years of extensive research a practical vaccine is not yet available against the disease. Recent studies illustrate that bacterial outer membrane proteins are budding target as vaccine antigen. Outer membrane proteins A (OmpA) are among the most immunodominant antigens in the outer membrane of gram negative bacteria and possess many characteristics desired of a vaccine candidate. We observe that OmpA of Shigella flexneri 2a is crossreactive and common antigen among Shigella spp. and the epitope is widely exposed on the cell surface as well as capable of evoking protective immunity in mice. The protective immunity involves participation of both the humoral and cellular immune responses, since OmpA boosts rapid induction of IgG and IgA in both the systemic and mucosal compartments and also activates Th1 cells. The immunopotentiating activity of OmpA is mediated by its ability to bind and stimulate macrophages and up-regulate the surface expression of MHCII, CD80 and CD40, leading to activation of CD4⁺ T cells to secrete cytokines and express chemokine receptor and IL-12Rβ2, thereby orchestrating the bridge between innate and adaptive immune responses. This ability is dependent on Toll-like receptor 2 (TLR2), as demonstrated by lack of response by TLR2 knockdown macrophages to OmpA. Hence this property of OmpA to link innate and adaptive immunity via TLR2 offers a novel vista to develop vaccine against shigellosis.     

支气管哮喘患者外周血CD4+ CD25+调节性T细胞水平及Foxp3 mRNA表达的分析

目的 观察支气管哮喘(哮喘)患者外周血单个核细胞(PBMCs)中CD4+ CD25+调节性T细胞(Treg)水平及叉状头/翅膀状螺旋转录因子(Foxp3)mRNA表达的变化,探讨CD4+ CD25+ Treg在哮喘发病中的作用.方法采用流式细胞仪检测78例哮喘患者(急性发作期组30例,慢性持续期组25例,缓解期组23例)和29例健康志愿者(正常对照组)PBMCs中CD4+ CD25+ Treg的比例;反转录-聚合酶链反应(RT-PCR)检测PBMCs中Foxp3 mRNA的表达.结果 急性发作期组和慢性持续期组PBMCs中CD4+ CD25+ Treg的比例及Foxp3 mRNA的表达明显低于缓解期组和正常对照组(P＜0.05);缓解期组CD4+ CD25+ Treg的比例及Foxp3 mRNA的表达虽亦低于正常对照组,但差异无统计学意义(P＞0.05);急性发作期组CD4+ CD25+ Treg的比例及Foxp3 mRNA的表达低于慢性持续期组(P＜0.05).结论 哮喘患者外周血中具有免疫抑制活性的CD4+ CD25+ Treg数量减少,功能下降,可能参与哮喘的发生和发展.     

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.