Fig. 4: MPV/S-2P immunization induced S-specific B cells in the blood that are restimulated after boosting.

Peripheral blood monocytic cells (PBMC) were stained with fluorochrome-labeled monoclonal antibodies and fluorochrome-labeled SARS-CoV-2 receptor binding domain (RBD) and S-2P probes to identify spike (S)-specific B cells (RBD⁺/S-2P⁺ or RBD⁻/S-2P⁺, see Fig. S3A for gating strategy). A, D, F Dot plots from representative MPV/S-2P- or MPV (A only) immunized macaques showing the frequency of RBD⁺ and RBD⁻ S-specific B cells. B Frequency of S-specific B cells from MPV primed (n = 4), MPV/S-2P primed (n = 8) and boosted (n = 4) macaques [medians (lines), min and max (whiskers), 25th to 75th quartiles (boxes) on indicated days]. C Median frequencies with ranges of S-specific B cells in the blood of MPV/S-2P immunized macaques that are RBD⁺ (dark purple) or RBD⁻ (light purple) on indicated days (prime n = 8; boost n = 4 macaques). Isotype class of RBD⁺ and RBD⁻ S-specific B cells. D Representative dot plots from an MPV/S-2P-immunized macaque. E Median frequencies with ranges of IgM (gray), IgA (red) and IgG (blue) RBD⁺ (left) and RBD⁻ (right) S-specific B cells at the indicated day pi (prime n = 8; boost n = 4 macaques). F, G Activated memory (AM; CD21⁻/CD27⁺; yellow), resident memory (RM; CD21⁺/CD27⁺; green), CD27⁻ RM (CD21⁺/CD27⁻; brown) or tissue-resident like memory (TLM; CD21⁻/CD27⁻; white) phenotypes of S-specific IgM⁺, IgA⁺, and IgG⁺ B cells of MPV/S-2P-immunized macaques. G Median frequencies with ranges (prime n = 8; boost n = 4 macaques). Source data are provided in the Source Data file.