Administration of a second booster dose further enhances antibody response and neutralization capacity of mCuMVTT-RBM
In a next step, we compared the efficacy of vaccinating mice with a total of 2 doses of mCuMVTT-RBM (Prime/Boost) versus 3 doses (Prime/Boost/Boost) as illustrated in Figure 6A.
The results showed no significant difference in the induced RBD-specific antibody titers following the 2nd dose in comparison to sera following the 3rd dose (Fig. 6B and C). Furthermore, the avidity of the induced antibodies induced after the 3rd dose did not show a higher value when compared to the ones induced following the 2nd dose (Fig. 6D and E).
To test the capacity of the induced antibodies to neutralize the real virus, we have performed cytopathic effect (CPE) using 100 TCID50 of SARS-CoV-2/ABS/NL20. Titers are expressed as the highest dilution that inhibits formation of CPE 100%. In contrast to ELISA titers, a significant difference in neutralization capacity was seen when comparing day 42 sera of vaccinated mice vs the control group (p = 0.0014). However, sera from mice after the 3rd dose of the vaccine (day 63) showed further enhanced neutralization titer when compared to the control group (p . <0.00001) or the group received only the 2nd dose (p . 0.0021) (Fig. 6F). The obtained results show the capacity of the vaccine candidate to completely block the cytopathic effect of the virus.