Sustained release of recombinant surface antigen 2 (rSAG2) from poly(lactide-co-glycolide) microparticles extends protective cell-mediated immunity against <i>Toxoplasma gondii</i> in mice

Abstract

Current development efforts of subunit vaccines against <i>Toxoplasma gondii</i>, the aetiological agent of toxoplasmosis, have been focused mainly on tachyzoite surface antigens (SAGs) such as SAG2, due to their attachment roles in the process of host-cell invasion. In the present study, we aimed to produce poly(lactide-co-glycolide) (PLG) microparticles (MPs) containing recombinant SAG2 (rSAG2) to induce improved immunity against <i>T. gondii</i>. The resulting PLG-encapsulated rSAG2 (PLG-rSAG2) MPs, 2·14-3·63 <i>μ</i>m in diameter, showed 74-80% entrapment efficiency and gradually released antigenic rSAG2 protein (88·3% of the total protein load) for a long 33-day period. Peritoneal immunization with PLG-rSAG2 MPs in BALB/c mice resulted in not only sustained (10 weeks) lymphocyte proliferation and IFN-<i>γ</i> production but also an improved protective capacity (87%) against a lethal subcutaneous challenge of 1×10⁴ live tachyzoites of <i>T. gondii</i> (RH strain). In conclusion, the sustained release of rSAG2 protein from PLG-rSAG2 MPs extends Th1 cell-mediated immunity (lymphocyte proliferation and IFN-<i>γ</i> production) and induces improved protection against <i>T. gondii</i> tachyzoite infection in mice.