Protective Efficacy Of Recombinant Canine Adenovirus Type-2 Expressing TgROP18 (CAV-2-ROP18) Against Acute And Chronic Toxoplasma Gondii Infection In Mice

Toxoplasmosis caused by T.gondii, an obligate intracellular parasite, is an important zoonosis with a worldwide distribution. The WHO and FAO have recently established it as a foodborne parasite infection causing global concern. Toxoplasmosis not merely caused huge economic losses to animal husbandry, but it also threatened the safety of human beings(especially AIDS patients, accepting the treatment of cancer patients and organ transplant patients), posed austere challenges to the public health security of the world. Since there are no safe and effective drugs to completely eliminate the parasite in vivo, vaccines against toxoplasmosis should be an optimal option.Besides being highly efficient for transgene expression “in vivo” and being safe for administration, adenoviral vectors also have intrinsic adjuvant properties capable of activating an innate immune response via TLR and NLR receptors. The use of recombinant viral vectors expressing T.gondii antigens is a safe and efficient approach to induce immune response against the parasite, as well as a valuable tool for vaccine development. We have previously prolonged the survival time of mice challenged with RH strain of T. gondii by immunizing the mice with an eukaryotic vector expressing the protein ROP18 of T. gondii. We are now looking for ways to improve this vaccination strategy and enhance protection.In this study, we constructed and identified a novel recombinant virus canine adenovirus type 2 expressing ROP18(CAV-2-ROP18) of T.gondii by cytopathic effect(CPE) and indirect immunofluorescence assay(IFA) following transfection into MDCK cells. Intramuscular immunization of Kunming mice with CAV-2-ROP18 was carried out to evaluate humoral and cellular immune responses.Vaccination with CAV-2-ROP18 elicited antibody production against ROP18 including high levels of a mixed Ig G1/Ig G2 a and significant production of IFN-γ or IL-2, and displaying a significant bias toward a helper T cell type 1(Th1) profile in mice immunized with CAV-2-ROP18. Furthermore, the presence of T. gondii-specific IFN-γ-production and TNF-α-production T cells was elicited in both CD4+ and CD8+ T cells compartments. Again, significantly higher survival rates(40%) were developed in the experimental group. A reduction in brain cyst burden was detected in mice vaccinated with CAV-2-ROP18(57.3%), CAV-2(6.6%), and PBS(3.4%).This results demonstrate the potential use of CAV vector harboring the ROP18 in the development of vaccine against acute and chronic toxoplamosis.