Fig. 3: Combo#5-TM mRNA-LNP immunization regime boosts B cell responses.

a Flow cytometric contour plots showing the proportion of plasma cells (PCs; gated as live B220^loCD138⁺CD98⁺) in the spleen at day seven post-final vaccination. Frequency of total PCs within the total B cells cell gate are shown. b Frequency (left) and total number (right) of PCs in the spleen at day seven post-final vaccination. c Flow cytometric contour plots showing the proportion of germinal center (GC) B cells (live B220⁺CD138^-CD38^loCD95^hi) in the spleen at day seven post-final vaccination. d Frequency (left) and total number (right) of GC B cells in the spleen at day seven post-final vaccination. e Representative flow cytometric contour plots show the gating strategy employed to identify follicular helper T (Tfh) cells and non-Tfh cells in the spleen at day seven post-final vaccination. Geometric mean fluorescence intensity (gMFI) of Bcl-6 for each subset are shown. f Frequency (left) and total number (right) of Tfh cells in the spleen at day seven post-final vaccination. Tfh cells were identified as live CD45⁺CD3⁺TCRβ⁺CD4⁺PD1⁺CXCR5⁺ cells. g Representative flow cytometry contour plot showing immunoglobulin class-switched (IgM^-) and IgM⁺ memory B cells (MBC; defined as live B220^hi/loCD138^-CD38^hiCD95^loIgD^lo). h Total number of IgM⁺ (left) and class-switched (right) MBC in the spleen at day seven post-final vaccination. i Contour plot showing CD80 and PD-L2 expression switched memory B cells in the spleen at day seven post-final vaccination. j Total number of PD-L2⁺ single positive (PD-L2 SP), PD-L2⁺CD80⁺ double positive (DP), CD80⁺ single positive (CD80 SP) and PD-L2^-CD80^- double negative (DN) memory B cell subsets in the spleen at day seven post-final vaccination. Data in a–i represent findings from two independent experiments. Data in b–j are pooled from two independent experiments (n = 6 mice/group/experiment, equal numbers of males and females). Each dot represents one mouse and bars indicate the median. Statistical analyses were performed using a Kruskal-Wallis test followed by Dunn’s test for multiple comparisons. P-values for comparisons between the PBS/PBS and Combo#5-TM or M1/alum versus Combo#5-TM groups are indicated. Source data are provided as a Source Data file.