Abstract
BackgroundThe 90-kDa heat-shock protein (Hsp90) from Nicotiana benthamiana (NbHsp90.3) is a promising adjuvant, especially for those vaccines that require a T cell-mediated immune response. Toxoplasma gondii SAG1 is considered one of the most important antigens for the development of effective subunit vaccines. Some epitopes located in the SAG1 C-terminus region have showed a strong humoral and cellular immune response. In the present study, we aimed to assess the efficacy of NbHsp90.3 as carrier/adjuvant of SAG1-derived peptide (SAG1HC) in a T. gondii infection murine model.MethodsIn the present study, C57BL/6 mice were intraperitoneal immunized with the NbHsp90.3-SAG1HC fusion protein (NbHsp90.3-SAG1HC group), mature SAG1 (SAG1m group), NbHsp90.3 (NbHsp90.3 group) or PBS buffer 1× (PBS group). The levels of IgG antibodies and the cytokine profile were determined by ELISA. Two weeks after the last immunization, all mice were orally challenged with 20 cysts of T. gondii Me49 strain and the number of brain cysts was determined. In addition, both humoral and cellular immune responses were also evaluated during the acute and chronic phase of T. gondii infection by ELISA.ResultsThe characterization of the immune response generated after vaccination with NbHsp90.3 as an adjuvant showed that NbHsp90.3-SAG1HC-immunized mice produced antibodies that were able to recognize not only rSAG1m but also the native SAG1 present in the total lysate antigen extract (SAG1TLA) from T. gondii tachyzoites, while control groups did not. Furthermore, anti-rSAG1m IgG2a/2b antibodies were significantly induced. In addition, only the spleen cell cultures from NbHsp90.3-SAG1HC-immunized mice showed a significantly increased production of IFN-γ. During the chronic phase of T. gondii infection, the antibodies generated by the infection were unable to detect the recombinant protein, but they did react with TLA extract. In addition, splenocytes from all groups showed a high production of IFN-γ when stimulated with rGRA4, but only those from NbHsp90.3-SAG1HC group stimulated with rSAG1m showed high production of IFN-γ. Finally, NbHsp90.3-SAG1HC-immunized mice exhibited a significant reduction in the cyst load (56%) against T. gondii infection.ConclusionsWe demonstrated that NbHsp90.3 enhances the humoral and cell-mediated immune response through a Th1 type cytokine production. Mice vaccinated with NbHsp90.3-SAG1HC exhibited a partial protection against T. gondii infection and it was correlated with the induction of memory immune response. We developed and validated a vaccine formulation which, to our knowledge, for the first time includes the NbHsp90.3 protein covalently fused to a peptide from T. gondii SAG1 protein that contains T- and B-cell epitopes.
Highlights
The 90-kDa heat-shock protein (Hsp90) from Nicotiana benthamiana (NbHsp90.3) is a promising adju‐ vant, especially for those vaccines that require a T cell-mediated immune response
Sánchez‐López et al Parasites Vectors (2019) 12:140 validated a vaccine formulation which, to our knowledge, for the first time includes the NbHsp90.3 protein covalently fused to a peptide from T. gondii SAG1 protein that contains T- and B-cell epitopes
We developed and validated a vaccine formulation which, to our knowledge, for the first time includes the NbHsp90.3 protein covalently fused to a peptide from T. gondii SAG1 protein that contains T- and B-cell epitopes
Summary
The 90-kDa heat-shock protein (Hsp90) from Nicotiana benthamiana (NbHsp90.3) is a promising adju‐ vant, especially for those vaccines that require a T cell-mediated immune response. Some epitopes located in the SAG1 C-terminus region have showed a strong humoral and cellular immune response. SAG1 is able to stimulate the production of IFN-γ of T cells in seropositive individuals [3] For this reason, this antigen has been suggested as an excellent candidate for vaccine development in the prevention of toxoplasmosis. Many studies have identified different short peptides present in SAG1 that would have promising immunogenic properties and could be used in the development of acellular vaccines [9,10,11,12]. Godard et al [9] observed that the C-terminus of SAG1 is the dominant antigenic and immunogenic region and, in particular, the SAG1238–256 peptide is an important T-cell epitope. Cardona et al [11] found that B-cell epitopes of SAG1 enclosed in the SAG1301–320 position show the highest reactivity against human sera from T. gondii-infected patients
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