Fig. 2: Gamma RBD-adapted vaccine induces a high and broad antibody response and specific-B cells.

a Immunization protocol scheme. BALB/c mice were immunized on day 0 and day 14 via i.m. with: Ancestral RBD + Alum (red) or Gamma RBD + Alum (blue). Serum samples were obtained at indicated time points for ELISA and neutralization assays. b Kinetics of RBD-specific IgG endpoint titers in sera of immunized animals by ELISA. Points are means ± SEM. n = 5 mice per group. c RBD-specific (Gamma, Ancestral or Omicron BA.4/5) IgG titers in sera of immunized animals at days 14 and 42 post prime immunization. Error bars are GMT ± SD. GMT values are shown above the bar. n = 5 mice per group. Two-sided Mann Whitney test. *p < 0.05, **p < 0.01. Exact P values are shown. d Gamma SARS-CoV-2 (circles) or Ancestral SARS-CoV-2 (triangles) Neutralizing-antibody titers in sera were determined by authentic PRNT SARS-CoV-2 assay for each group of vaccinated mice at different time points. The lines represent the geometric mean (GMT) of all data points. n = 5 mice per group. Titers correspond to the 50% of virus neutralization (NT50). e BALB/c mice were immunized at day 0 and day 14 via i.m. with: Ancestral RBD + Alum (n = 5 mice, blue circles), Gamma RBD + Alum (n = 5 mice, red circles) or placebo (n = 3 mice, black circles). Flow cytometry analysis of different B-cell populations in spleen of vaccinated mice were performed using anti-CD19, anti-B220, anti-IgD, anti-IgG, anti-CD138, anti-GL7, and anti-CD95 antibodies. Specific-B cells were determined by binding to fluorescent RBD (Ancestral and Gamma versions). Results are presented as percentage of RBD⁺ B cells (CD19⁺ B220⁺ IgD⁻ RBD⁺), RBD⁺ IgG⁺ B cells (CD19⁺ B220⁺ IgD⁻ IgG⁺ RBD⁺) or RBD⁺ plasmablasts (B220⁺ CD19⁺ IgD⁻ CD138⁺ RBD⁺). Bars are means ± SEM. Kruskal Wallis test. *p < 0.05, **p < 0.01. Exact P values are shown. f BALB/c mice were immunized at day 0 and day 14 via i.m. with: Ancestral RBD + Alum (n = 5 mice, red circles), Gamma RBD + Alum (n = 5 mice, blue circles) or placebo (n = 3 mice, black circles). Frequency of germinal center B cells (B220⁺ CD19⁺ GL7⁺ CD95⁺) in each group of vaccinated mice. Bars are means ± SEM. Kruskal Wallis test. *p < 0.05, ns (not significant). Exact P value is shown. g BALB/c mice were immunized at day 0 and day 14 via i.m. with: Ancestral RBD + Alum (n = 5 mice, red circles), Gamma RBD + Alum (n = 5 mice, blue circles) or placebo (n = 3 mice, black circles). Frequency of T follicular helper cells (CD4⁺ CXCR5⁺ PD-1⁺) in spleen of vaccinated mice. Bars are means ± SEM. Kruskal Wallis test. Results are representative of three independent experiments. Source data are provided as a Source Data file.