Figure 2. Varied vaccination regimens elicit neutralizing antibodies that target different regions of the MERS-CoV Spike glycoprotein.

Immunization with different vaccine regimens elicited neutralizing antibodies that target the Spike glycoprotein within and outside the RBD. (a) Cell adsorption assay. Sera from mice immunized with MERS-CoV S DNA-only, S DNA prime and S1 protein plus Ribi adjuvant, or S1 protein plus Ribi adjuvant prime and boost were evaluated for neutralization activity against pseudotyped MERS-CoV England1 after adsorption with HEK 293T cell-surface-expressed MERS-CoV Spike proteins: S, RBD, S1, S2. Serum neutralization was tested at a single dilution. Sera adsorbed with untransfected HEK 293T cells served as controls and retained 95% of neutralization activity. Each bar represents the mean of triplicate assays with s.e.’s. The experiment was repeated once to ensure reproducible results; one of the two experiments is shown. (b) Protein competition neutralization assay. Sera at a single dilution from the immunized mice were also assayed for neutralization of MERS-CoV England1 pseudovirus in the presence of soluble MERS-CoV RBD, S1 and S2 proteins at concentrations of 0.016–50 μg ml⁻¹. Each data point represents the mean of triplicate assays with s.e.’s. The experiment was repeated once to ensure reproducible results; one of the two experiments is shown.