Marked enhancement of neutralizing antibody and IFN-γ T-cell responses by GX-19N DNA booster in mice primed with inactivated vaccine

In response to the COVID-19 pandemic, an unprecedented level of vaccine development has occurred. As a result, various COVID-19 vaccines have been approved for use. Among these, inactivated virus particle (VP) vaccines have been widely used worldwide, but additional vaccination strategies are needed because of the short duration of immune responses elicited by these vaccines. Here, we evaluated homologous and heterologous prime–boost regimens using a VP vaccine and GX-19N DNA vaccine for their ability to enhance the protective immune response against SARS-CoV-2. We demonstrated that a heterologous prime–boost regimen with the VP vaccine and GX-19N DNA vaccine resulted in enhanced S _RBD - & N-specific antibody responses, compared to the homologous VP vaccine prime–boost vaccination. In addition, the neutralizing antibody response was significantly improved with the heterologous VP prime–DNA boost regimen, and the neutralizing antibody induced with the heterologous prime–boost regimen did not decrease against the SARS-CoV-2 variant of concern (VOC). The heterologous VP prime–DNA boost regimen not only significantly increased S- and N-specific IFN-γ T-cell responses, but also induced an equivalent level of T-cell response against SARS-CoV-2 VOCs. Our results provide new insights into prophylactic vaccination strategies for COVID-19 vaccination.