Induction of protective mixed Th-1/Th-2 responses in mice by oral vaccination with chloroplast-expressed Toxoplasma gondii GRA4

YACONO, M. L.; LAGU¨ªA BECHER, M.; MART¨ªN, V.; FARRAN, I.; VERAMINDI, J.; CLEMENTE, M.

Mar del Plata

Congreso; IX Congreso de Protozoolog¨ªa y Enfermedades Parasitarias; 2011

SAP

Induction of protective mixed Th-1/Th-2 responses in mice by oral vaccination with chloroplast-expressed Toxoplasma gondii GRA4 Y¨¢cono, ML; Lagu¨ªa-Becher, M; Mart¨ªn, V; Farran, I; Veramendi, J; Clemente, M. Toxoplasma gondii, the causal agent of toxoplasmosis, can infect most mammals and birds. Treatment of this disease is difficult due to toxic effects of available drugs and re-infection occurs rapidly. Thus, the development of an effective vaccine would be of great value to human and veterinary medicine. Given that T. gondii invasion occurs through the intestinal mucosa of the host, the route of vaccine delivery is relevant to the development of vaccines. Plant expression systems have been intensively studied to provide an attractive alternative for oral vaccine production. Particularly, chloroplast transformation offers a potential alternative for the expression of vaccine antigens in plants. GRA4 antigen is a potential candidate for oral vaccination against T. gondii. This antigen is able to induce both humoral and systemic immune responses. In this study, we evaluate the immune response and the grade of protection generated by oral administration of chloroplast-expressed GRA4 (chlGRA4) in a murine model. C57BL/6 (H-2d) mice were orally immunized with chlGRA4 plants (chlGRA4 group), wild-type plants (control group), or PBS (PBS group). Two weeks after the last immunization, we evaluated the humoral immune response. Significant levels of specific anti-GRA4 IgGt, IgG2b and IgG1 were observed in sera from chlGRA4 vaccinated mice. Also, this group showed a specific mucosal immune response characterized by the production of anti-GRA4 IgA in intestinal lavages. To further characterize the immune response generated by this antigen produced in transplastomic plant, cytokine profiles were determined in supernatants of spleen and lymph node cells after in vitro stimulation with ESA. Significant amounts of secreted IFN-¦Ã (Th-1), IL10 and IL-4 (Th-2) were found in the supernatants of both cell types from chlGRA4 vaccinated mice when compared to the control and PBS groups. Finally, to evaluate the immune protective value of chlGRA4 against T. gondii infection, two weeks after the vaccination schedule was completed, mice were orally challenged and the number of T. gondii brain cysts was analyzed. The chlGRA4 group showed a significant reduction in the brain cyst burden (56%) compared to the control and PBS groups. The results obtained in this study showed that the GRA4 antigen expressed in transplastomic tobacco is able to induce mucosal and systemic humoral and cellular immune responses, with a balanced Th-1/Th2 profile. In addition, this vaccine confers partial protection against a challenge with the parasite.