Fig. 3: Humoral and cellular immune responses to pNTC-spike vaccination in rabbits.

a An overview of the immunization strategy in New Zealand white rabbits. Animals received three immunization of 125 µg pNTC-Spike at 2 week intervals delivered either as a 100 µL intradermal dose using a needle-and-syringe (N = 3) or the needle-free PharmaJet® Tropis ID device (N = 4) or as a 500 µL intramuscular dose using the needle-free PharmaJet® Stratis IM device (N = 5). b Temporal end-point titers of IgG antibodies specific for the SARS-CoV-2 spike ectodomain and receptor-binding domain (RBD). c 50% virus-neutralizing antibody titer against a SARS-CoV-2 clinical isolate as determined in a live virus microneutralization assay. d Correlation analysis between the level of SARS-CoV-2 spike-specific binding IgG and virus neutralization. e Interferon gamma (IFNγ) responses measured by ELISA and ELISpot following restimulation of immunized rabbit splenocytes with the SARS-CoV-2 spike ectodomain and RBD. Cell culture medium and concanavalin A (ConA) served as antigen negative and positive controls, respectively. f Percentage body weight change from baseline (day 0) of animals measured daily for 4 days after each intramuscular immunization and every 2 day thereafter. g Body temperature measured on the day of each intramuscular immunization (0 and 6 h) and daily thereafter. A temperature above 40 °C constitutes a fever (dotted line). Bar graphs indicate the median with interquartile range. Rabbit silhouette created with BioRender.com.