Plant Hsp90 is a novel adjuvant that elicits a strong humoral and cellular immune response against B- and T-cell epitopes of a Toxoplasma gondii SAG1 peptide

SÁNCHEZ LÓPEZ, EDWIN F; CORIGLIANO, MARIANA G.; ALBARRACÍN, ROMINA M; SANDER, VALERIA A; LEGARRALDE, ARIEL C; BENGOA LUONI, SOFIA A; CLEMENTE, MARINA

PARASITES AND VECTORS

BIOMED CENTRAL LTD

Lugar: Londres; Año: 2019

1756-3305

Background: The 90-kDa heat-shock protein (Hsp90) from Nicotiana benthamiana (NbHsp90.3) is apromising adjuvant, especially for those vaccines that require a T cell-mediatedimmune response. Toxoplasma gondii SAG1is considered one of the most important antigens for the development ofeffective subunit vaccines. Some epitopes located in the SAG1 C-terminus regionhave showed a strong humoral and cellular immune response. In the present study,we aimed to assess the efficacy of NbHsp90.3 as carrier/adjuvant ofSAG1-derived peptide (SAG1HC) in a T. gondii infection murine model. Methods: In the present study, C57BL/6 mice were intraperitoneal. immunized withthe NbHsp90.3-SAG1HC fusion protein (NbHsp90.3-SAG1HCgroup), mature SAG1 (SAG1m group), NbHsp90.3 (NbHsp90.3 group) or PBS buffer 1X(PBS group). The levels of IgG antibodies and the cytokine profile weredetermined by ELISA. Two weeks after the last immunization, all mice wereorally challenged with 20 cysts of T.gondii Me49 strain and the number of brain cysts was determined. Inaddition, both humoral and cellular immune responses were also evaluated duringthe acute and chronic phase of T. gondiiinfection by ELISA.Results: The characterization of the immune response generated after vaccinationwith NbHsp90.3 as an adjuvant showed that rNbHsp90.3-SAG1HC-immunizedmice produced antibodies that were able to recognize not only rSAG1m but alsothe native SAG1 present in the total lysate antigen extract (SAG1TLA)from T. gondii tachyzoites, whilecontrol groups did not. Furthermore, anti-rSAG1m IgG2a/2b antibodies weresignificantly induced. In addition, only the spleen cell cultures from NbHsp90.3-SAG1HC-immunizedmice showed a significantly increased production of IFN-γ. During the chronicphase of T. gondii infection, theantibodies generated by the infection were unable to detect the recombinantprotein, but they did react with TLA extract. In addition, splenocytes from allgroups showed a high production of IFN-γ when stimulated with rGRA4, but only thosefrom NbHsp90.3-SAG1HC group stimulated with rSAG1m showed highproduction of IFN-γ. Finally, NbHsp90.3-SAG1HC-immunized miceexhibited a significant reduction in the cyst load (56%) against T. gondii infection. Conclusions: We demonstrated that NbHsp90.3 enhances the humoraland cell-mediated immune response through a Th1 type cytokine production. Micevaccinated with NbHsp90.3-SAG1HC exhibited a partial protectionagainst T. gondii infection and it wascorrelated with the induction of memory immune response. For the first time, wedeveloped and validated a vaccine formulation which, to our knowledge, for thefirst time includes the NbHsp90.3 protein covalently fused to a peptide from T. gondii SAG1 protein that contains T-and B-cell epitopes.