Oral immunization with a plant HSP90-SAG1 fusion protein produced in tobacco elicits strong immune responses and reduces cyst number and clinical signs of toxoplasmosis in mice

SANCHEZ LOPEZ, E.; CORIGLIANO, M.; OLIFERUK, SONIA; RIVERA, M.; RAMOS DUARTE, V.; MENDOZA MORALES, L.F.; ANGEL, S. O.; SANDER, V.; CLEMENTE, M.

Congreso; 32nd Annual Molecular Parasitology Meeting; 2021

Genetics Society of America

Plant 90 kDa heat shock protein (Hsp90) is a potent adjuvant that increases both humoral and cellular immune responses to diverse proteins and peptides. In this study, we explored the immune effects of a Toxoplasma gondii surface antigen 1 (SAG1)?Hsp90 construct transiently expressed in Nicotiana benthamiana. We obtained two constructs containing SAG1 sequences (aa221 to aa319 [SAG1HC], containing only the B and T cell antigenic epitopes; and aa77 to aa323 [SAG1m], the mature antigen) fused to Arabidopsis thaliana Hsp90 (AtHsp81.2). AtHsp81.2?SAG1HC had the highest expression levels of the two fusion proteins (80 to 120 μg/g of fresh weight). Mice were orally immunized with AtHsp81.2?SAG1HC-infiltrated fresh leaves (pAtHsp81.2?SAG1HC), recombinant AtHsp81.2?SAG1HC purified from infiltrated leaves (rAtHsp81.2?SAG1HC), non-infiltrated fresh leaves (control), or phosphate buffered saline (PBS). Serum samples from pAtHsp81.2?SAG1HC-immunized mice had significantly higher levels of immunoglobulin (Ig)Gt, IgG2a and IgG2b anti-rSAG1m antibodies than serum from rAtHsp81.2?SAG1HC, control and PBS groups. The number of cysts per brain in the pAtHsp81.2?SAG1HC-immunized mice was significantly reduced, and the parasite load in brain tissue was also lower in this group compared with the remaining groups. In an immunoblot assay, plant-expressed AtHsp81.2-SAG1HC was shown to react with antibodies from T. gondii-infected people. The incorporation of plant Hsp90 as a carrier/adjuvant in formulations against T. gondii could substantially improve vaccine efficacy in humans; plants may therefore be a suitable and powerful biotechnological system for antigen expression against toxoplasmosis.