Fig. 4: Flow cytometric analysis of antigen-specific ASCs and ASC subsets in BCMA-KOΔ3 mice upon prime/boost immunization with the mRNA vaccine mRNA-1273.

A Schematic illustration of the experimental setup. Mice were intramuscularly immunized and boosted on day 42 with 5 µg mRNA-1273 each and analyzed on day 126. B RBD-specific IgG serum concentrations were determined by ELISA for wildtype (WT, black, n = 7) and BCMA-KOΔ3 mice (KOΔ3, gray, n = 9). Flow cytometric quantification of (C) RBD-specific CD138⁺TACI⁺ ASCs in the bone marrow (n = 7 WT and 8 KOΔ3) and (D) total ASC numbers in bone marrow, spleen, and mLN (n = 7 WT and 9 KOΔ3). E IgH isotype-specific total and RBD-specific ASC counts in the bone marrow were determined by flow cytometry and visualized in a stacked bar diagram. F Concentration of total serum IgM, IgG, and IgA and feces IgA in BCMA-KOΔ3 and wildtype mice at day 126 (n = 8 WT and 9 KOΔ3). Bar diagrams show mean and SD with each dot indicating one mouse. Statistical analysis in B and E was performed using a two-way ANOVA with Šídák’s multiple comparisons test. Statistical analysis (C, D, F) was performed with unpaired t-tests. Exact p-values, mouse sex, and ages are provided in the Source Data file. G, H Transcriptome analysis of bone marrow ASCs isolated of mRNA-1273 immunized BCMA-KOΔ3 and wildtype mice (WT) on day 126 after primary immunization. Principal component analysis visualizes sample similarities (G), and differential gene expression is documented in the MA plot (H). In BCMA-KOΔ3 ASCs, no upregulated genes were detected; the only downregulated gene (Tnfrsf17) is colored in blue. ASC antibody-secreting cells, RBD receptor binding domain of the SARS-CoV-2, i.m. intramuscular, ns not significant, mLN mesenteric lymph node, ^*p ≤ 0.05, ^**p ≤ 0.01, ^****p ≤ 0.0001.