Fig. 6. SARS-CoV-2 SApNP vaccines induce robust long-lived germinal centers.

(A) Top: Representative immunohistological images of germinal centers at week 2 after a single-dose injection of the S2GΔHR2-presenting I3–01 SApNP vaccine (10 μg/injection, 40 μg/mouse). Bottom: Germinal center B cells (GL7⁺, red) adjacent to FDCs (CD21⁺, green) in lymph node follicles (left) and T_fh cells in the light zone (LZ) of germinal centers (right). Scale bars of 500 μm and 50 μm are shown for a complete lymph node and an enlarged image of a follicle, respectively. (B, C) Quantification of germinal center reactions using immunofluorescent images: GC/FDC ratio and sizes of germinal centers 2, 5, and 8 weeks after (B) single-dose or (C) prime-boost injections (n = 4–7 mice/group). The GC/FDC ratio is defined as whether the germinal center formation is associated with an FDC network (%). (D, E) Representative immunohistological images of germinal centers in mice immunized using S2GΔHR2 spike or S2GΔHR2-presenting E2p and I3–01 SApNP vaccines at week 8 after (D) single-dose or (E) prime-boost injections, with a scale bar of 50 μm shown for each image. (F, G) Quantification of germinal center reactions using flow cytometry: percentage and number of germinal center B cells and T_fh cells 2, 5, and 8 weeks after (F) single-dose or (G) prime-boost injections. The data points are shown as mean ± SD. The data were analyzed using one-way ANOVA followed by Tukey’s multiple comparison post hoc test for each timepoint. ns (not significant), *p < 0.05, **p < 0.01, ***p < 0.001, ****p < 0.0001.