PRECLINICAL IMMUNOGENICITY STUDIES OF A RECOMBINANT VACCINE FORMULATION AGAINST COVID-19

AGOSTINA DEMARÍA; LORENA CORIA; CELESTE PUEBLAS CASTRO; LAURA BRUNO; ELIANA CASTRO; LUCAS SAPOSNIK; MAYRA RÍOS MEDRANO; VALERIA KRUM; IGNACIO DREHE; MARIANA LI CAUSI; JOHANNA SIDABRA; JONATHAN BAQUÉ; CRISTIAN PAYES; BRENDA HEINRICH; ANALÍA DE NICHILO; FRANCISCO ZURVARRA; DIEGO ALVAREZ; KARINA PASQUEVICH; JULIANA CASSATARO

Congreso; LXX REUNIÓN ANUAL DE LA SOCIEDAD ARGENTINA DE INMUNOLOGÍA (SAI); 2022

In this work, we studied the immunogenicity of vaccine formulationsbased on the receptor binding domain (RBD) of the spike proteinfrom SARS-CoV-2. BALB/c mice were immunized by intramuscularroute with two vaccine formulations that contained different antigen(Ag) doses. Induction of Ag-specific IgG antibody titers were deter-mined in sera of immunized animals. Results showed that both for-mulations induced high but similar anti-RBD IgG titers. Evaluation ofAg-specific IgG subclasses showed that both vaccine formulationsinduced higher titers of IgG1 than IgG2a. Interestingly, independent-ly of the Ag dose specific IgG antibody titers against RBD remainedelevated until 253 days post prime vaccination. Virus neutralizationcapacity of antibodies induced by these vaccines was evaluated in alive virus neutralization assay. Results indicate that both vaccine for-mulations elicited antibodies that have neutralizing activity againstancestral, gamma, alpha, lambda and delta SARS-CoV-2 variants.Finally, to determine T-cell-mediated immune responses, spleno-cytes from immunized mice were stimulated in vitro with completemedium or the Ag and cytokine levels were measured in superna-tants by ELISA. Splenocytes from all vaccinated mice induced sig-nificant levels of IFN-γ and IL-5 upon antigen stimulation (p<0.05).Moreover, intracellular flow cytometry analysis revealed that stim-ulated splenocytes from both groups of vaccinated mice inducedAg-specific IFN-y and TNF-α producing CD4+ T cells (p<0.05) whileonly the high dose of Ag could induce CD8+ T cells that produceIFN-y and TNF-α (p<0.05). These results indicate that the vaccineformulation with the higher dose of Ag has a better performance:induces high levels of specific antibodies with broad neutralizing ac-tivity against different SARS-CoV-2 variants and specific CD4+ andCD8+ T cell responses. Based on these results we selected the highdose Ag formulation to continue our actual preclinical studies.