Fig. 3: Prime/boost regimen of MPV/S-2P induced high level of serum anti-S antibodies with increased avidity, breadth and ADCP activity.
Anti-spike (S) and receptor binding domain (RBD)-specific serum IgG (A) and IgA (B) measured by ELISA or DELFIA (limit of detection: 3.0 log10, dotted line). Antibody avidity to S, determined by ELISA with or without NaSCN, which strips low-affinity antibodies; avidity index (AI), calculated as ratio of NaSCN-treated vs. PBS-treated serum IgG or IgA titers. C Antibody-dependent cellular phagocytosis (ADCP), determined by incubating biotinylated S protein complexed to neutravidin-labeled fluorescent beads with macaque sera, followed by measurement of the phagocytic activity of THP-1 monocytes [ref. 41, modified as described in Supplementary Methods 2]. Data are expressed as the 50% inhibitory concentration (IC50) corresponding to the dilution of serum that resulted in 50% of THP-1 cells being FITC positive for binding and/or phagocytosing the S protein. D 50% SARS-CoV-2 serum neutralizing-antibody titers (ND50) against the WA1/2020, B.1.1.7, and B.1.351 isolates; serum MPV neutralizing-antibody titers, determined by 60% plaque reduction neutralization tests (PRNT60). E Inhibition of binding of soluble, tagged angiotensin converting enzyme 2 receptor (ACE2) to indicated purified S proteins by serum antibodies, expressed as % inhibition relative to no-serum control (see also Fig. S2B). A–E Medians (lines), min and max values (whiskers), 25th to 75th quartile (boxes), and individual values are shown for MPV primed (n = 4), MPV/S-2P primed (n = 8) and boosted (n = 4) macaques; two-way ANOVA with Sidak post-test; exact p values are indicated for levels of significance p < 0.05 unless p < 0.0001 (****). Source data are provided in the Source Data file.
