Encapsulation of chimeric protein rSAG1/2 into poly(lactide-co-glycolide) microparticles induces long-term protective immunity against Toxoplasma gondii in mice.

In the present study, the poly(lactide-co-glycolide) (PLG) polymer was used as an adjuvant to encapsulate the chimeric protein rSAG1/2 for preparing a microparticle vaccine against Toxoplasma gondii. The resulting PLG-encapsulated rSAG1/2 (PLG-rSAG1/2) microparticles, 1.27-1.65μm in diameter, showed 72-83% entrapment efficiency. The amount of released rSAG1/2 protein from microparticles gradually increased over a long 56-day period and the protein still retained its antigenicity. Intraperitoneal immunization with the microparticles in BALB/c mice elicited significant long-term (10weeks) humoral and cell-mediated immune responses, accompanied by secretion of a large amount of IFN-γ, to achieve strong protection (83%) against a lethal subcutaneous tachyzoite challenge. In conclusion, we have successfully encapsulated rSAG1/2 with the PLG polymer to produce stable microparticles that can effectively induce not only long-term immunity but also high protection against T. gondii. These crucial data would be advantageous for developing long-term Toxoplasma vaccines for future use in humans and animals.