Genetic immunization of BALB/c mice with a plasmid bearing the gene coding for a hybrid merozoite surface protein 1-hepatitis B virus surface protein fusion protects mice against lethal Plasmodium chabaudi chabaudi PC1 infection

A DNA Vaccine Encoding Plasmodium falciparum PfRH5 in Cationic Liposomes for Dermal Tattooing Immunization

Vaccines are the primary means of controlling and preventing pandemics and outbreaks of pathogens such as bacteria, viruses, and parasites. However, a major drawback of naked DNA-based vaccines is their low immunogenicity and the amount of plasmid DNA necessary to elicit a response. Nano-sized liposomes can overcome this limitation, enhancing both nucleic acid stability and targeting to cells after administration. We tested two different DNA vaccines in cationic liposomes to improve the immunogenic properties. For this, we cloned the coding sequences of the Plasmodium falciparum reticulocyte binding protein homologue 5 (PfRH5) either alone or fused with small the small hepatitis virus (HBV) envelope antigen (HBsAg) encoding sequences, potentially resulting in HBsAg particles displaying PfRH5 on their outside. Instead of invasive intraperitoneal or intramuscular immunization, we employed intradermal immunization by tattooing nano-encapsulated DNA. Mice were immunized with 10 μg encapsulated DNA encoding PfRH5 alone or in fusion with HBsAg and this elicited antibodies against schizont extracts (titer of 10⁴). Importantly, only IgG from animals immunized with PfRH5-HBs demonstrated sustained IgG-mediated inhibition in in vitro growth assays showing 58% and 39% blocking activity after 24 and 48 h, respectively. Intradermal tattoo-vaccination of encapsulated PfRH5-HBsAg coding plasmid DNA is effective and superior compared with an unfused PfRH5-DNA vaccine, suggesting that the HBsAg fusion may be advantageous with other vaccine antigens.

Protective immunity induced by a DNA vaccine cocktail expressing TgSAG1, TgROP2, and the genetic adjuvant HBsAg against Toxoplasma gondii infection

Toxoplasma gondii is an intracellular obligate parasitic protozoon that can infect all warm-blooded animals, causing zoonotic toxoplasmosis. So far, there is no commercial toxoplasmosis vaccine for human use. In the present study, we constructed a DNA vaccine cocktail which includes the surface protein (SAG1) and the rhoptry protein ROP2 denoted as pEGFP-N1-SAG1-ROP2. In order to improve the efficacy, HBsAg was used as a genetic adjuvant to construct pEGFP-N1-HBsAg-SAG1-ROP2. Two eukaryotic plasmids were transiently transfected into HEK293T cells and the expression was examined using fluorescence microscopy and western blotting. We then immunized Kunming mice intramuscularly with the DNA vaccine. After three immunizations, the immune response was evaluated by measuring antibody levels, cytokine production, percentages of CD4⁺ and CD8⁺ T lymphocytes, and the survival times of the T. gondii RH strain challenged mice. The results showed that the two DNA vaccines stimulated Th1 responses, and had a higher antibody titer, IL-2, IL-12, and IFN-γ levels, and percentage of CD4⁺ and CD8⁺ T lymphocytes than the control group. In addition, mice immunized with the pEGFP-N1-HBsAg-SAG1-ROP2 vaccine showed increased survival times compared with pEGFP-N1-SAG1-ROP2.

DNA-Loaded Cationic Liposomes Efficiently Function as a Vaccine against Malarial Proteins

The delivery of antigens as DNA vaccines is an efficient alternative to induce immune responses against antigens, which are difficult to produce in recombinant form. However, the delivery of naked DNA is ineffective or relies on sophisticated ballistic devices. Here, we show a combination of liposome application and naked DNA vaccine that successfully overcomes these problems. Upon entrapment of plasmids encoding different antigens in cationic particles, transfection efficiencies similar to commercial kits were achieved in in vitro cell cultures. The liposome-based approach provided strong humoral responses against three malarial antigens, namely the Circumsporozoite protein and the C terminus of merozoite surface protein 1 from Plasmodium vivax (titers 10⁴ or 10³–10⁴, respectively) and P. falciparum Rhoptry antigen 5 from Plasmodium falciparum (titers 10³–10⁴). When employed in P. falciparum growth-inhibition assays, antibodies demonstrated consistent reinvasion-blocking activities that were dose dependent. Liposome-formulated DNA vaccines may prove useful when targets cannot be produced as recombinant proteins and when conformation-dependent and highly specific antibodies are mandatory.

Immunogenicity of a plasmid DNA vaccine encoding 42kDa fragment of Plasmodium vivax merozoite surface protein-1

Plasmodium vivax is the second major human malaria parasite that inflicts debilitating morbidity and consequent economic impact in South-East Asian countries. The relapsing nature of P. vivax along with the emergence of drug-resistant P. vivax strains has emphasized the urgent need for a vaccine. However, the development of an effective vivax vaccine is seriously hampered due to the diversity and variation in parasite antigens and non-availability of suitable animal models. DNA based vaccines represent an alternative approach in inducing immunity to multiple targets from different stages of malaria parasite. DNA prime-boosting strategies induce both antibody mediated and cell-mediated immune responses that are the major mechanisms of protection against malaria parasites. We have earlier studied the immunogenicity and protective efficacy of the soluble and refolded forms of recombinant 42kDa fragment of Plasmodium vivax merozoite surface protein-1 (PvMSP-142) using P. cynomolgi rhesus monkey model. In the present study, we have constructed a recombinant DNA vaccine encoding 42kDa fragment of P. vivax MSP-1 and studied the immunogenicity of PvMSP-142 DNA vaccine construct in mice. The 42kDa gene fragment of PvMSP-1 was PCR amplified using gene specific primers and subcloned into pcDNA 3.1 (+) eukaryotic expression vector. In vitro expression of PvMSP-142 plasmid construct was checked by transfection in COS-1 cell line. Indirect immunofluorescence of transfected COS-1 cells probed with monoclonal antibodies against PvMSP-142 exhibited positive fluorescence. Immunization of BALB/c mice with PvMSP-142-pcDNA vaccine construct revealed the immunogenicity of recombinant vaccine plasmid that can be enhanced by prime boosting with recombinant protein corresponding to the DNA vaccine as evidenced by significant elevation of antibody and the cytokines responses.

Murine granulocyte-macrophage colony-stimulating factor expressed from a bicistronic simian immunodeficiency virus-based integrase-defective lentiviral vector does not enhance T-cell responses in mice

As a prelude to immunization studies in nonhuman primates, we compared in mice the immunogenicity of a simian immunodeficiency virus (SIV)-based integrase (IN)-defective lentiviral vector (IDLV) encoding the model antigen-enhanced green fluorescence protein (eGFP) in the presence or absence of the murine granulocyte-macrophage colony-stimulating factor (mGM-CSF) expressed from an internal ribosomal entry site (IRES) sequence. BALB/c mice were immunized once intramuscularly with IDLV expressing eGFP alone or eGFP and mGM-CSF and immune responses were evaluated up to 90 days from the single intramuscular immunization. Results indicated that the mGM-CSF was unable to improve the magnitude and quality of the immune response against the eGFP transgene in the context of the SIV-based IDLV, as evaluated by enzyme-linked immunosorbent spot (ELISPOT) assays for interferon-γ (IFN-γ) and by intracellular cytokine staining for IFN-γ, interleukin-2 (IL-2), and tumor necrosis factor-alpha (TNF-α). These findings suggest that for vaccination purposes, the presence of mGM-CSF expressed after the IRES in a SIV-based IDLV system does not favor the improvement of the immunological response against the transgene of interest. Further studies should investigate whether the selection of a different cytokine gene might improve the immune response against the transgene.

Construction and identification of Complex DNA vaccine of hepatitis B and Toxoplasma gondii

OBJECTIVE

To construct and identify multi-gene recombinant expression vector pcDNA3-HBsAg-p30-ROP2.

METHOD

Primers were designed according to the gene sequences of restriction enzyme cutting site of recombinant pcDNA3-p30-ROP2 and hepatitis B surface antigen (HBsAg). The target fragment of HBsAg was amplified and cloned to expression vector pcDNA3-p30-ROP2 by restriction enzyme digestion and ligation. The recombinant expression vector pcDNA3-HBsAg-p30-ROP2 was identified by PCR detection, followed by enzyme restriction and sequencing.

RESULTS

The target fragment of HBsAg was successfully amplified, and the multi-gene eukaryotic expression vector pcDNA3-HBsAg-p30-ROP2 was established. PCR detection and restriction enzyme digestion showed that the length of the target fragment was consistent with the theoretical value. The recombinant expression vector contained the complete sequences of p30-ROP2 compound gene and HBsAg.

CONCLUSION

Multi-gene recombinant expression vector pcDNA3-HBsAg-p30-ROP2 was successfully established. The constructed expression vector could be used to develop multi-gene nucleic acid vaccines.

A fusion DNA vaccine encoding middle version of HBV envelope protein fused to interleukin-21 did not enhance HBV-specific immune response in mice

DNA vaccination can generate both humoral and cellular immunity, resulting in potential prophylactic and therapeutic vaccines in variety of conditions, including hepatitis B virus (HBV) infection. Fusion of cytokine gene is one of the ways to increase the immunogenicity of DNA vaccine. Interleukin (IL)-21 has been demonstrated to play an immunomodulatory role in HBV infection. Thus, we aimed to investigate the ability of IL-21 in the regulation of middle version of HBV envelop protein (MS) DNA vaccine. Fusion plasmid encoding IL-21 linked with MS was constructed. Normal and HBV transgenic mice were immunized by plasmid. pcDNA-IL-21/S2S induced a comparable level of anti-HBs antibody and HBsAg-specific CD8+ T-cell response with pcDNA-S2S. Furthermore, the level of circulating HBsAg was decreased by induction of anti-HBs antibody and HBsAg-specific CD8+ T-cell response to both pcDNA-IL-21/S2S and pcDNA-S2S vaccination in HBV transgenic mice. Thus, immunization with DNA vaccine encoding HBV MS protein induced both T- and B-cell response by targeting the specific antigen. Furthermore, it was also revealed that MS DNA vaccination could break immune tolerance in HBV transgenic mice. But IL-21 did not strengthen immune response induced by HBV DNA immunization. Our study suggested that MS-expressing plasmid may be useful for both preventive and therapeutic methods in HBV infection. However, IL-21 does not improve the immunogenicity and efficacy of MS DNA vaccination, and thus may not be used as a therapeutic marker for chronic hepatitis B.

Clinical trial in healthy malaria-naïve adults to evaluate the safety, tolerability, immunogenicity and efficacy of MuStDO5, a five-gene, sporozoite/hepatic stage Plasmodium falciparum DNA vaccine combined with escalating dose human GM-CSF DNA

When introduced in the 1990s, immunization with DNA plasmids was considered potentially revolutionary for vaccine development, particularly for vaccines intended to induce protective CD8 T cell responses against multiple antigens. We conducted, in 1997−1998, the first clinical trial in healthy humans of a DNA vaccine, a single plasmid encoding Plasmodium falciparum circumsporozoite protein (PfCSP), as an initial step toward developing a multi-antigen malaria vaccine targeting the liver stages of the parasite. As the next step, we conducted in 2000–2001 a clinical trial of a five-plasmid mixture called MuStDO5 encoding pre-erythrocytic antigens PfCSP, PfSSP2/TRAP, PfEXP1, PfLSA1 and PfLSA3. Thirty-two, malaria-naïve, adult volunteers were enrolled sequentially into four cohorts receiving a mixture of 500 μg of each plasmid plus escalating doses (0, 20, 100 or 500 μg) of a sixth plasmid encoding human granulocyte macrophage-colony stimulating factor (hGM-CSF). Three doses of each formulation were administered intramuscularly by needle-less jet injection at 0, 4 and 8 weeks, and each cohort had controlled human malaria infection administered by five mosquito bites 18 d later. The vaccine was safe and well-tolerated, inducing moderate antigen-specific, MHC-restricted T cell interferon-γ responses but no antibodies. Although no volunteers were protected, T cell responses were boosted post malaria challenge. This trial demonstrated the MuStDO5 DNA and hGM-CSF plasmids to be safe and modestly immunogenic for T cell responses. It also laid the foundation for priming with DNA plasmids and boosting with recombinant viruses, an approach known for nearly 15 y to enhance the immunogenicity and protective efficacy of DNA vaccines.

Viral vectored granulocyte-macrophage colony stimulating factor inhibits vaccine protection in an SIV challenge model: protection correlates with neutralizing antibody

In a previous vaccine study, we reported significant and apparently sterilizing immunity to high-dose, mucosal, simian immunodeficiency virus (SIV) quasi-species challenge. The vaccine consisted of vectors based on vesicular stomatitis virus (VSV) expressing simian immunodeficiency virus (SIV) gag and env genes, a boost with propagating replicon particles expressing the same SIV genes, and a second boost with VSV-based vectors. Concurrent with that published study we had a parallel group of macaques given the same doses of vaccine vectors, but in addition, we included a third VSV vector expressing rhesus macaque GM-CSF in the priming immunization only. We report here that addition of the vector expressing GM-CSF did not enhance CD8 T cell or antibody responses to SIV antigens, and almost completely abolished the vaccine protection against high-dose mucosal challenge with SIV. Expression of GM-CSF may have limited vector replication excessively in the macaque model. Our results suggest caution in the use of GM-CSF as a vaccine adjuvant, especially when expressed by a viral vector. Combining vaccine group animals from this study and the previous study we found that there was a marginal but significant positive correlation between the neutralizing antibody to a neutralization resistant SIV Env and protection from infection.

Genetic linkage of autologous T cell epitopes in a chimeric recombinant construct improves anti-parasite and anti-disease protective effect of a malaria vaccine candidate

We have reported the design of polyvalent synthetic and recombinant chimeras that include promiscuous T cell epitopes as a viable delivery system for pre-erythrocytic subunit malaria vaccines. To further assess the ability of several Plasmodium T cell epitopes to enhance vaccine potency, we designed a synthetic gene encoding four Plasmodium yoelii merozoite surface protein 1 (PyMSP1) CD4(+) promiscuous T cell epitopes fused in tandem to the homologous carboxyl terminal PyMSP1(19) fragment. This Recombinant Modular Chimera (PyRMC-MSP1(19)) was tested for immunogenicity and protective efficacy in comparative experiments with a recombinant protein expressing only the PyMSP1(19) fragment. Both proteins induced comparable antibody responses. However PyRMC-MSP1(19) elicited higher anti-parasite antibody titers and more robust protection against both hyper-parasitemia and malarial anemia. Most importantly, passive transfer of anti-PyRMC-MSP1(19), but not anti-PyMSP1(19) antibodies protected against heterologous challenge. These studies show that protective efficacy can be significantly improved by inclusion of an array of autologous promiscuous T cell epitopes in vaccine constructs.

Enhanced immune responses of mice inoculated recombinant adenoviruses expressing GP5 by fusion with GP3 and/or GP4 of PRRS virus

Porcine reproductive and respiratory syndrome (PRRS) is one of the most important causes of economic losses of the swine industry. PRRS virus (PRRSV) infection poses a challenge to current vaccination strategies. In this study, three replication-defective adenovirus recombinants expressing fusion protein GP3-GP5, GP4-GP5, or GP3-GP4-GP5 were developed as potential vaccine against PRRSV in a mouse model. Six groups of BALB/c mice (24mice per group) were inoculated subcutaneously twice at 2-week intervals with above mentioned recombinants and other adenoviruses expressing single GP3, GP4, or GP5 protein. The results showed that the mice inoculated with recombinant adenoviruses developed PRRSV-specific antibodies, cellular immune response by 2 weeks post-boost-immunization. However, mice immunized with recombinant adenoviruses rAd-GP3-GP5, rAd-GP4-GP5, and rAd-GP3-GP4-GP5 developed significantly higher titers of neutralizing antibodies to PRRSV and produced stronger lymphocyte proliferation responses compared to mice immunized with rAd-GP3, rAd-GP4 or rAd-GP5 alone. It was also found that mice immunized with rAd-GP3-GP5 and rAd-GP3-GP4-GP5 were primed for significant higher levels of anti-PRRSV CTL responses than mice immunized with rAd-GP3 and rAd-GP5. These findings suggested that the recombinant adenoviruses expressing fusion proteins GP3-GP5 or GP3-GP4-GP5 might be an attractive candidate vaccine for preventing PRRSV infection.

Immunogenicity of hybrid DNA vaccines expressing hepatitis B core particles carrying human and simian immunodeficiency virus epitopes in mice and rhesus macaques

An effective HIV vaccine will likely need to induce broad and potent CTL responses. Epitope-based vaccines offer significant potential for inducing multi-specific CTL, but often require conjugation to T helper epitopes or carrier moieties to induce significant responses. We tested hybrid DNA vaccines encoding one or more HIV or SIV CTL epitopes fused to a hepatitis B core antigen (HBcAg) carrier gene as a means to improve the immunogenicity of epitope-based DNA vaccines. Immunization of mice with a HBcAg-HIV epitope DNA vaccine induced CD8(+) T cell responses that significantly exceeded levels induced with DNA encoding either the whole HIV antigen or the epitope alone. In rhesus macaques, a multi-epitope hybrid HBcAg-SIV DNA vaccine induced CTL responses to 13 different epitopes, including 3 epitopes that were previously not detected in SIV-infected macaques. These data demonstrate that immunization with hybrid HBcAg-epitope DNA vaccines is an effective strategy to increase the magnitude and breadth of HIV-specific CTL responses.

Recombinant adenovirus expressing GP5 and M fusion proteins of porcine reproductive and respiratory syndrome virus induce both humoral and cell-mediated immune responses in mice

Porcine reproductive and respiratory syndrome virus (PRRSV) is one of the most important contagious agents of swine in the world. PRRSV infection poses a challenge to current vaccination strategies. In this study, three replication-defective adenovirus recombinants were developed as potential vaccine against PRRSV in a mouse model. Three groups of BALB/c mice (24 mice per group) were inoculated subcutaneously twice at 2-week intervals with the recombinants expressing PRRSV GP5 (rAd-GP5), M (rAd-M), and M-GP5 fusion protein (rAd-M-GP5). Two additional groups were injected with wild-type adenovirus (wtAd) or PBS as control. The results showed that the mice inoculated with recombinant adenoviruses developed PRRSV-specific antibodies, cellular immune response by 2 weeks post second inoculation. However, only mice immunized with recombinant adenovirus rAd-M-GP5 developed significantly higher titers of neutralizing antibodies to PRRSV and produced stronger lymphocyte proliferation responses compared to mice immunized with rAd-M or rAd-GP5 alone. It was also found that mice immunized with rAd-M-GP5 were primed for significant higher levels of anti-PRRSV CTL responses than mice immunized with rAd-M. Mice receiving rAd-GP5 also mounted PRRSV-specific response, but levels were lower. It suggested that the recombinant adenovirus expressing M-GP5 fusion protein might be an attractive candidate vaccine to be tested for preventing PRRSV infection.

Peptides delivered by immunostimulating reconstituted influenza virosomes

Vaccines have been well accepted and used effectively for more than 100 years. Traditional vaccines are generally composed of whole inactivated or attenuated microorganisms that have lost their disease-causing properties. These classical prophylactic live vaccines evoke protective immune responses, but have often been associated with an unfavorable safety profile, as observed, for example, for smallpox and polio myelitis vaccines [1,2]. First improvements were subunit vaccines that do not focus on attenuation of whole organisms but concentrate on particular proteins. These vaccines are able to generate protective immune responses (e.g. diphtheria, tetanus, pertussis)3. However, next generation vaccines should focus on specific antigens (e.g. proteins, peptides), since the requirements by regulatory authorities to crude biological material are becoming more stringent over time. An increasing number of such antigens capable of inducing protective humoral or cellular immune responses have been identified in the last few years. But most of these are weak immunogens. This reemphasizes the need for adjuvants to promote a potent immune response and also for delivery antigens to the immune system in an appropriate way (carrier capability). Here we review a new approach for prophylactic and therapeutic vaccines, which focuses on the induction of highly specific immune responses directed against antigen-derived peptides using a suitable carrier system.

Immunization with the hybrid protein vaccine, consisting of Leishmania major cysteine proteinases Type I (CPB) and Type II (CPA), partially protects against leishmaniasis

Cysteine proteinases (CPs) are enzymes that belong to the papain superfamily, which are found in a number of organisms from prokaryotes to mammals. On the parasitic protozoan Leishmania, extensive studies have shown that CPs are involved in parasite survival, replication and the onset of disease, and have, therefore, been considered as attractive drugs and/or vaccine targets for the control of leishmaniasis. We have previously shown that cysteine proteinases, Type I (CPB) and Type II (CPA), in Leishmania major (L. major), delivered as recombinant proteins or in plasmid DNA, induce partial protection against infection with the parasite in BALB/c mice. We had shown that the level of protection was greater if a cocktail of cpa and cpb containing DNA constructs was used. Therefore, to reduce the costs associated with the production of these vaccine candidates, a construct was developed, whereby the cpa and cpb genes were fused together to give rise to a single hybrid protein. The genes were fused in tandem where the C-terminal extension (CTE), encoding region of CPB, was located at the 3' of the fused genes, and ultimately expressed in the bacterial expression construct pET-23a. The expression of the CPA/B hybrid protein (60 kDa) was verified using rabbit anti-CPA and anti-CPB antibodies by SDS-PAGE and immunoblotting. The protective potential of the CPA/B hybrid protein against the infection with Leishmania was then assessed in BALB/c mice. The animals were vaccinated with CPA/B, challenged with live L. major promastigotes, and the degree of protection was examined by measuring footpad lesion sizes. It was found that there was a delay in the expansion of lesions size compared to control groups. Furthermore, an immunological analysis of antibody isotypes, before and after infection, showed high levels of IgG2a compared to IgG1 (more than five-fold) in the CPA/B hybrid protein vaccinated group. In addition, a predominant Th1 immune response characterized by in vitro IFN-gamma production was observed, along with little, if any, IL-5 production. This finding indicates that the hybrid CPA/B is able to elicit a protective immune response against L. major in the mice model. In addition, 54% of individuals tested, who had recovered from cutaneous leishmaniasis, produced more than 50 pg/ml IFN-gamma, in response to the CPA/B hybrid protein in an in vitro assay, demonstrating the importance of cysteine proteinases as targets of immune response in humans.

Current status of malaria vaccine development

There is an urgent need to develop an effective vaccine against malaria--a disease that has approximately 10% of the world population at risk of infection at any given time. The economic burden this disease puts on the medico-social set-up of countries in Sub-Saharan Africa and South East Asia is phenomenal. Increasing drug resistance and failure of vector control strategies have necessitated the search for a suitable vaccine that could be integrated into the extended program of immunization for countries in the endemic regions. Malaria vaccine development has seen a surge of activity in the last decade or so owing largely to the advances made in the fields of genetic engineering and biotechnology. This revolution has brought sweeping changes in the understanding of the biology of the parasite and has helped formulate newer more effective strategies to combat the disease. Latest developments in the field of malaria vaccine development will be discussed in this chapter.

Gene gun-based co-immunization of merozoite surface protein-1 cDNA with IL-12 expression plasmid confers protection against lethal Plasmodium yoelii in A/J mice

The carboxyl-terminal region of the merozoite surface protein-1 (MSP1) is a leading candidate for a vaccine against malaria in the erythrocytic stage. In this study, we investigated the utility of interleukin-12 (IL-12) cDNA as an adjuvant for malaria DNA vaccine in a mouse challenge model. We found that co-immunization of expression plasmids encoding a C-terminal 15-kDa fragment of MSP1 (MSP1-15) with the IL-12 gene using a gene gun significantly increased the protective immunity against malaria as compared with MSP1-15 DNA immunization alone. Co-immunization of IL-12 DNA potentiated MSP1-15-specific T helper (Th)1-type immune responses as evaluated by in vivo antibody (Ab) responses and in vitro cytokine profiles. After the Plasmodium yoelii challenge, mice immunized with MSP1-15 plus IL-12 DNA showed a higher level of interferon gamma (IFN-gamma) production than did other groups of mice. In vivo neutralization of IFN-gamma or depletion of CD4(+) T cells completely abolished this protective immunity. Macrophages, but not nitric oxide (NO), were found to play an important role in this effector mechanism. The sera from mice in which the infection had been cleared by the vaccination showed strong protection against P. yoelii infection. Thus, in addition to cellular immune responses, Abs against parasites induced in the course of infection are essential for protection against P. yoelii. The results indicate that combined vaccination with DNA encoding antigenic peptides plus IL-12 DNA provides a strategy for improving the prophylactic efficacy of a vaccine for malaria infection.

Evaluation of the murine immune response to Leishmania meta 1 antigen delivered as recombinant protein or DNA vaccine

The meta 1 gene of Leishmania is conserved across the genus and encodes a protein upregulated in metacyclic promastigotes. Meta 1 constitutive overexpressing mutants show increased virulence to mice. In this paper, both meta 1 recombinant protein and plasmids bearing the meta 1 gene were tested for their antigenicity and potential for inducing protective immunity in mice. Vaccination with the recombinant protein induced a predominant Th2-type of response and did not result in protection upon challenge with live parasites. Surprisingly, the expected reversal to a CD4(+) Th1-type of response upon genetic immunisation by the intramuscular route was not observed. Instead, vaccination with either the meta 1 gene alone or in fusion with the monocyte chemotactic protein (MCP)-3 cDNA induced a Th2-type of response that correlated with lack of protection against infection.