Induction of protective immunity against toxoplasmosis in mice by immunization with Toxoplasma gondii RNA.

Toxoplasma gondii enters the mucosal surfaces of the host, and so immunity at these sites is of major interest. Due to the compartmentalization of the immune response, systemic immunization does not induce high levels of immunity at mucosal surfaces. Intranasal immunization has been shown to be very effective in inducing both systemic and mucosal immune responses. Immunization with mRNA can induce both humoral and cell-mediated immune responses, both of which are important in conferring immunity to T. gondii. The efficacy of RNA vaccination by the nasal route with T. gondii RNA was evaluated. We assessed the percentage of cumulative survival after an oral challenge with a lethal dose of T. gondii cysts (40 cysts), and the number of brain cysts following a challenge with a sublethal dose of T. gondii 76 K cysts (15 cysts). Vaccinated mice were found to be significantly better protected than non-immunized mice after a challenge with a lethal dose of cysts; and a challenge with a sublethal dose also resulted in fewer brain cysts than in non-immunized mice. Sera and intestinal secretions of immunized mice recognized T. gondii antigens, suggesting that a specific humoral immune response may occur. Moreover, a specific lymphoproliferative response observed in cervical lymph nodes may confer protection. These preliminary findings suggest that RNA vaccination by a mucosal route could be feasible.