DNA prime and peptide boost immunization protocol encoding the Toxoplasma gondii GRA4 induces strong protective immunity in BALB/c mice

Abstract

BackgroundToxoplasma gondii is a widespread intracellular parasite, which infects most vertebrate animal hosts and causes zoonotic infection in humans. Vaccine strategy remains a promising method for the prevention and control of toxoplasmosis. T. gondii GRA4 protein has been identified as a potential candidate for vaccine development. In our study, we evaluated the immune response induced by four different immunization vaccination strategies encoding TgGRA4.MethodsBALB/c mice were intramuscularly (i.m.) immunized four times according to specific immunization schedules. Generally, mice in experimental groups were immunized with polypeptide, pGRA4, peptide/DNA, or DNA/peptide, and mice in the control groups were injected with PBS or pEGFP. After immunization, the levels of IgG antibodies and cytokine productions were determined by enzyme-linked immunosorbent assays (ELISA). The survival time of mice was also evaluated after challenge infection with the highly virulent T. gondii RH strain.ResultsThe results showed that mice vaccinated with different immunization regimens (polypeptide, pGRA4, peptide/DNA, or DNA/peptide) elicited specific humoral and cellular responses, with high levels of total IgG, IgG2a isotype and gamma interferon (IFN-γ), which suggested a specific Th1 immunity was activated. After lethal challenge, an increased survival time was observed in immunized mice (11.8 ± 4.8 days) compared to the control groups injected with PBS or pEGFP (P < 0.05). Mice injected with PBS or pEGFP died within 8 days, and there was no significant difference in the protection level in two groups (P > 0.05).ConclusionsThese results demonstrated that this DNA prime and peptide boost immunization protocol encoding the TgGRA4 can elicit the highest level of humoral and cellular immune responses compared to other immunized groups, which is a promising approach to increase the efficacy of DNA immunization.

Protection via a ROM4 DNA vaccine and peptide against Toxoplasma gondii in BALB/c mice

“…Prime-boost vaccination strategies have been used to enhance immune responses of some DNA vaccines [5, 22]. The first immunization primes the immune response and subsequent immunizations trigger the further expansion of antigen specific cells and selection of cells with high antigen avidity [40].…”

“…Synthetic MAP contains a high concentration of the relevant antigen to induce immune responses to predefined epitopes and leads to protective immunity [25, 41]. Meng et al [5] used the DNA prime-peptide boost vaccination regimen to enhance the effectiveness of T. gondii DNA vaccines, which produced a stronger immune response and better protection compared to priming with polypeptide and boosting with DNA.…”

“…Tachyzoites were extracted from human foreskin fibroblast cells 1 h before injection to ensure freshness prior to challenge. About 8 × 10 9 tachyzoites were used to create soluble tachyzoite antigens (STAg) after isolation by centrifugation, and resuspended in sterile PBS as previously described [5], while about 8 × 10 6 tachyzoites were used to extract total RNA with TRIzol Reagent (Life Technologies, Carlsbad, CA, USA). After tachyzoites were lysed with 1 ml TRIzol, 0.2 ml chloroform was added, and the homogenate was separated into three layers after centrifugation.…”

“…When the host immune function is compromised, bradyzoites transform to tachyzoites [3]. Current drugs are effective for the treatment of toxoplasmosis (acute or reactivated) but they cause many side effects, especially in the fetus, and have no effect on cysts and bradyzoites [5]. Therefore, a safe and effective vaccine is important for the prevention and control of toxoplasmosis.…”

Vaccination with toxofilin DNA in combination with an alum-monophosphoryl lipid A mixed adjuvant induces significant protective immunity against Toxoplasma gondii

“…Besides, they can’t prevent reinfection [6]. Therefore, the development of an effective and safe vaccine against toxoplasmosis is of great importance to prevent the continued spread of this disease.…”