Preclinical immunogenicity studies of a recombinant vaccine formulation against COVID-19

DEMARIA, MARÍA AGOSTINA; CORIA, LORENA; CASTRO, CELESTE PUEBLAS; BRUNO L; CASTRO, ELIANA; SAPOSNIK, LUCAS; MEDRANO, MAYRA RIOS; KRUM, VALERIA; DREHE, IGNACIO; LI CAUSI, MARIANA; SIDABRA, JOHANNA E.; BAQUÉ, JONATHAN A.; PAYES, CRISTIAN J.; BRENDA HEINRICH; DE NICHILO, ANALIA V.; ZURVARRA, FRANCISCO M.; ALVAREZ, DIEGO; KARINA A. PASQUEVICH; CASSATARO JULIANA

Mar del Plata

Congreso; Reunión Conjunta de Sociedades de Biociencias (SAIC); 2022

In this work, we evaluated recombinant receptor binding domain (RBD)-based vaccine formulation prototypes with potential for further clinical development. RBD was formulated with aluminum hydroxide (alum) and two different formulations were assessed: RBD Gamma (P.1) 5 µg plus alum and RBD P.1 10 µg plus alum. Recombinant BALB/c mice received two doses at day 0 and 14 via intramuscular route. Specific IgG antibody titers for RBD wt and RBD P.1 were determined. Results show that, immunization with RBD P.1 5µg+alum or RBD P.1 10µg+alum induced high anti-RBD IgG titers (GMT at day 42: 691,200 and 921,600, respectively for anti-RBD wt; 1,177,600 and 691,200, respectively for anti-RBD P.1). RBD-specific IgG subclasses were evaluated 1 month after last immunization. Results show that both vaccine formulations induced higher titer of IgG1 than IgG2a. Levels of RBD P.1- specific IgG1 were higher in the group that received RBD 5 µg+alum than in the group that received RBD 10 µg+alum. As for anti-RBD IgA, immunization with RBD 10 µg induced significant higher levels of IgA than immunization with RBD 5 µg, for both cases, RBD wt and P.1. Besides, for animals immunized with RBD 10 µg, results show higher levels of anti-RBD P.1 IgA than anti-RBD wt IgA. When we assessed both formulation prototypes in another experiment, long term results showed that specific IgG antibody titers against RBD wt and RBD P.1 remain high at least up to 253 days post prime vaccination (GMT at day 253: for RBD P.1 5 µg+alum: 92,800 for anti-RBD wt and 156,800 for anti-RBD P.1; for RBD P.1 10 µg+alum: 76,800 for anti-RBD wt and 128,000 for anti-RBD P.1). Moreover, the neutralization capacity of the antibodies induced by the vaccine was evaluated using the ancestral SARS-CoV-2 (wt) or Gamma variant. Results confirm that the formulations RBD P.1 5µg+alum or RBD P.1 10µg+alum induce high neutralizing activity against ancestral and gamma variant (GMT at day 41: 182.1 for RBD P.1 5ug+Alum vs SARS-CoV-2 wt, 347.5 for RBD P.1 5ug+Alum 100 vs Gamma, 253.7 for RBD P.1 10ug+Alum 100 vs SARS-CoV-2 wt and 299.1 for RBD P.1 10ug+Alum 100 vs Gamma). Also, both formulations induce high neutralizing antibodies titers against prevalent circulating variants in our region: wt, Alpha, Gamma, Delta and Lambda. Finally, to determine T-cell-mediated immune responses, splenocytes from RBD 5µg+alum or RBD 10µg+alum immunized mice were stimulated with RBD wt, RBD P.1 or medium alone, and then, cytokines levels in the supernatants were measured. Both formulations could induce the secretion of IFN-γ and IL-5 in significative levels after the in vitro stimulation, demonstrating their potential to induce a Th1/Th2 cellular immune response in spleen. Overall, these results indicate that both formulations induce: significant neutralization activity against SARS-CoV-2 wt and many others variants of concern, and a Th1/Th2 profile in the spleens, which has recently allowed these vaccine prototypes to break through a phase 1 clinical trial.