Induction of Protective Immune Responses by a Multiantigenic DNA Vaccine Encoding GRA7 and ROP1 of Toxoplasma gondii

Abstract

c Toxoplasma gondii is distributed worldwide and infects most species of warm-blooded animals, including humans. The heavy incidence and severe or lethal damage caused by T. gondii infection clearly indicates the need for the development of a vaccine. To evaluate the protective efficacy of a multiantigenic DNA vaccine expressing GRA7 and ROP1 of T. gondii with or without a plasmid encoding murine interleukin-12 (pIL12), we constructed DNA vaccines using the eukaryotic plasmids pGRA7, pROP1, and pGRA7-ROP1. Mice immunized with pGRA7, pROP1, or pGRA7-ROP1 showed significantly increased serum IgG2a titers; production of gamma interferon (IFN-␥), IL-10, and tumor necrosis factor alpha (TNF-␣); in vitro T cell proliferation; and survival, as well as decreased cyst burdens in the brain, compared to mice immunized with either the empty plasmid, pIL12, or vector with pIL12 (vector؉pIL12). Moreover, mice immunized with the multiantigenic DNA vaccine pGRA7-ROP1 had higher IgG2a titers, production of IFN-␥ and TNF-␣, survival time, and cyst reduction rate compared to those of mice vaccinated with either pGRA7 or pROP1 alone. Furthermore, mice immunized with either a pGRA7-ROP1؉pIL12 or a single-gene vaccine combined with pIL12 showed greater Th1 immune response and protective efficacy than the single-gene-vaccinated groups. Our data suggest that the multiantigenic DNA antigen pGRA7-ROP1 was more effective in stimulating host protective immune responses than separately injected single antigens, and that IL-12 serves as a good DNA adjuvant.

Toxoplasma gondii GRA7-Induced TRAF6 Activation Contributes to Host Protective Immunity

“…gondii infection and parasite burden in the brain in vivo. Cysts of T. gondii strain Me49 were obtained from the brains of infected mice and purified as described previously (6). BALB/c mice (six per group) were immunized intraperitoneally with rGRA7 (100 g/kg of body weight) once a week for 4 weeks.…”

“…Cell culture supernatants and mouse sera were analyzed for cytokine content with a BD OptEIA ELISA set (BD Pharmingen) for the detection of TNF-␣, IL-6, IL-12p40, IFN-␥, IL-4, and IL-10. T. gondiispecific serum IgG, IgG1, and IgG2a Ab levels were determined by ELISA as described previously (6). All assays were performed as recommended by the manufacturers.…”

“…Dense granule antigen (GRA) is a secretory vesicular organelle present in all infectious forms of T. gondii. Among the GRA proteins, GRA7 induces a strong antibody (Ab) response during acute infection (6) and is a target antigen in the intracerebral immune response during the chronic phase of infection (7). Importantly, GRA7 has the ability to stimulate significant humoral and cellular immune responses to T. gondii (1,6,7).…”

“…Among the GRA proteins, GRA7 induces a strong antibody (Ab) response during acute infection (6) and is a target antigen in the intracerebral immune response during the chronic phase of infection (7). Importantly, GRA7 has the ability to stimulate significant humoral and cellular immune responses to T. gondii (1,6,7). Transmembrane GRA7 proteins are released as soluble proteins and then trafficked to the parasitophorous vacuole membrane (PVM) and/or the intravacuolar network, a structure that forms at the posterior end of the parasite and unfolds throughout the lumen of the vacuole (1,4), and play important roles in interaction with the host.…”

Relevant aspects of human toxoplasmosis

“…As future perspectives, vaccines development studies against T. gondii have demonstrated that heterologous DNA priming and recombinant adenovirus boost strategy may provide protective immunity against T. gondii infection [57] and multiantigenic DNA antigen pGRA7-ROP1 was more effective in stimulating host protective immune responses than separately injected single antigens, and that IL-12 serves as a good DNA adjuvant [58].…”