Figure 6.

Generation of cross-reactive memory B cells and long-lived plasma cells in mice immunized with GM9 or GM14. (A) Schematic overview of the experimental design. (B) The cross-reactivity of CoV-2 RBD-specific memory B cells (CD138⁻B220⁺IgG⁺CD38⁺GL7⁻ CoV-2 RBD[APC]⁺ CoV-2 RBD[PE-Cy7]⁺) with CoV-1 RBD from spleen of mice 1 mo after boost immunization with each antigen was assessed by flow cytometry. The plots are representative of finding from two independent experiments (left). Frequency of CoV-1 and CoV-2 RBD cross-reactive memory B cells (middle) and quantification of absolute numbers of total CoV-2 RBD-specific memory B cells (right) from multiple mice in one experiment. Results are representative of two independent experiments. CoV-2 RBD WT (n = 5); GM9 (n = 5); GM14 (n = 5). (C) ELISPOT analysis of CoV-1 RBD– (left) or CoV-2 RBD– (right) specific IgG1 ASC responses of bone marrow (BM) cells from preimmune (Pre-imm) mice, or mice 1 mo after boost immunizations with each antigen. Results are representative of two independent experiments. Preimmune (n = 1); CoV-2 RBD WT (n = 4); GM9 (n = 4); GM14 (n = 4). Horizontal lines indicate mean values; each symbol indicates one mouse. *, P < 0.05; **, P < 0.01; ***, P < 0.001; unpaired Student’s t test.