Figure 6

Induction of long-term immunity in mice administered S-910823 plus A-910823. (a) Study schedule schematic. On Day 0 and Day 14, female mice were intramuscularly administered 1 μg of S-910823 with or without A-910823 (n = 5/group). Spleens and bone marrow were collected on Day 83. (b) Flow cytometric analysis of the percentage of receptor-binding domain (RBD)-specific B-cells among CD73⁺CD19⁺ B-cells. Each circle represents the percentage of cells in an individual mouse. The bars represent mean values, while error bars indicate standard deviation. (c) Detection of vaccine-induced antibody-secreting cells (ASCs) in bone marrow. Bone marrow cells were cultured for 2.5 h in an enzyme-linked immunospot (ELISPOT) assay plate wells which had been coated with SARS-CoV-2 spike protein. Results indicate the number of antigen-specific ASCs among 10⁶ bone marrow cells. (d, e) Percentage of cytokine-producing T cells in the spleen. Splenocytes were restimulated ex vivo with or without SARS-CoV-2 spike-protein-derived peptides for 16 h. Levels of IL-2, IFN-γ, TNF-α, IL-4, and IL-5 from CD44⁺CD4⁺ T cells (d) and levels of IFN-γ from CD44⁺CD8⁺ T cells (e) were evaluated using cell-surface and intracellular staining and examined using flow cytometry. The open bars indicate non-stimulated splenocytes [peptide ( −)], while the solid bars indicate splenocytes stimulated with SARS-CoV-2 spike protein peptides [peptide ( +)]. The gray bars represent mice administered vehicle or S-910823 without adjuvant A-910823, while the rose bars represent mice administered S-910823 with A-910823. The open and solid circles represent the results of individual mice. The error bars indicate the standard deviation.