Safe plant Hsp90 adjuvants elicit an effective immune response against Sars-CoV-2 derived RBD antigen

RAMOS DUARTE, V. A.; ORLOWSKI, A.; JAQUENOD DE GIUSTI, C.; CORIGLIANO, M.G.; MENDOZA MORALES, L.F.; SANCHEZ, M.A.; LEGARRALDE, A.; SANDER, V.A.; ANGEL, S. O.; CLEMENTE, M.

Buenos Aires

Congreso; Frontiers Biosciences 4; 2023

CONICET

Previously, we suggest that two plant Heat Shock Proteins (Hsp90) using as adjuvants, woulddifferentially modulate the immune response. In order to better understand the role of plantHsp90 in the immune response modulation, we proposed to use the Receptor Binding Domain(RBD) of the Spike protein of SARS-CoV2 and the main candidate in the design of subunitvaccines. We evaluated the humoral and cellular response against RBD trough the strategyprotein mixture (Adjuvant + Antigen). Thirty C57 mice were randomly separated into sevengroups and intramuscularly immunized with AtHsp81.2 (Arabidopsis thaliana), NbHsp90.3(Nicotiana benthamiana), or RBD as control groups, RBD+AtHsp81.2, RBD+NbHsp90.3 orRBD+Aluminium as vaccinated groups. A PBS group was also included. The humoral responseanalysis showed a significant increase in anti-RBD IgGt, which persisted between 21 and 42 dpi.In addition, the RBD+AtHsp81.2 group showed a significant increase in anti-RBD IgG1 like thecontrol RBD+Aluminium group, while the RBD+NbHsp90.3 group showed a significant increasein anti-RBD IgG2b. The cellular immune response analysis showed that just the spleen cellcultures from RBD + NbHsp90.3 immunized mice showed a significantly increased production ofIFN-γ. By contrast, the spleen cell cultures from RBD+AtHsp81.2-immunized mice showed asignificant increase in IL-4 levels. These results suggest that both isoforms are able to modulatethe humoral and cellular response, but each of them would do so from a different profile; whileAtHsp81.2 triggered a Th2-type immune response, NbHsp90.3 would trigger a Th1-typeresponse. Finally, we evaluated the serum capacity to neutralize lentiviral vectors pseudotypedwith Spike glycoprotein. The sera obtained at 42 dpi from mice immunized with RBD+AtHsp81.2and RBD+NbHsp90.3 showed the potential to neutralize viral infection. Interestingly, thedifferential profile of both isoforms in the triggered immune response would not modify theneutralizing capacity of the antigens contained in both vaccine formulations.