Fig. 6. INO-4800 immunized mouse and guinea pig sera compete with ACE2 receptor for SARS-CoV-2 Spike protein binding.

a Soluble ACE2 receptor binds to CoV-2 full-length spike with an EC₅₀ of 0.025 µg/ml. b Purified serum IgG from BALB/c mice (n of 5 per group) after second immunization with INO-4800 yields significant competition against ACE2 receptor. Serum IgG samples from the animals were run in triplicate. c IgGs purified from n = 5 mice day 7 post second immunization with INO-4800 show significant competition against ACE2 receptor binding to SARS-CoV-2 S 1 + 2 protein. The soluble ACE2 concentration for the competition assay is ~0.1 µg ml⁻¹. Bars represent the mean and standard deviation of AUC for curves displayed in Supplementary Fig. 1. d Hartley guinea pigs were immunized on Day 0 and 14 with 100 µg INO-4800 or pVAX-empty vector as described in the methods. Day 28 collected sera (diluted 1:20) was added SARS-CoV-2 coated wells prior to the addition of serial dilutions of ACE2 protein. Detection of ACE2 binding to SARS-CoV-2 S protein was measured. Sera collected from 5 INO-4800-treated and 3 pVAX-treated animals were used in this experiment. e Serial dilutions of guinea pig sera collected on day 21 were added to SARS-CoV-2 coated wells prior to the addition of ACE2 protein. Detection of ACE2 binding to SARS-CoV-2 S protein was measured. Sera collected from 4 INO-4800-treated and 5 pVAX-treated guinea pigs were used in this experiment.