Fig. 4

RBD_XBB.1.5-HR vaccine induces long-term protective immune response. a The schematic representation of immunization schedule. NIH mice were intramuscularly injected with 10 μg of RBD_XBB.1.5-HR proteins three times at 0, 3, and 6 weeks, the mice were sacrificed and the spleen, lymph node and bone marrow samples were collected at 43 weeks after the first immunization. b Neutralizing antibodies against a variety of pseudoviruses in serum samples from vaccinated mice (n = 6 mice per group). The Visual representations (c) and quantitative analysis (d) of RBD-specific IgG antibody secreting cells (ASCs) in bone marrow and spleen tissues (n = 5 mice per group). e The representative images and percentage of LLPCs in the bone marrow (n = 5 mice per group). f The percentage of MBCs in spleen and lymph nodes (n = 5 mice per group). The percentages of splenic IFN-γ- (g) and TNF-α- (h) secreting CD4⁺/CD8⁺ and CD44⁺ memory T cells after stimulation with peptide pools covered full-length spike proteins of XBB.1.5 variant (n = 5 mice per group). Data are presented as geometric mean values with SD in (b), and presented as mean with SEM in (d–h). LLPCs, long-lived plasma cells; P values in (d) were performed by the Two-way ANOVA followed by Sidak’s multiple comparisons test, and in (e–h) were conducted by Unpaired Student’s t-tests. ns, not significant. ****P < 0.0001; ***P < 0.001; **P < 0.01; *P < 0.05