Immunogenicity of COVID-eVax Delivered by Electroporation Is Moderately Impacted by Temperature and Molecular Isoforms

Abstract

DNA integrity is a key issue in gene therapy and genetic vaccine approaches based on plasmid DNA. In contrast to messenger RNA that requires a controlled cold chain for efficacy, DNA molecules are considered to be more stable. In this study, we challenged this concept by characterizing the immunological response induced by a plasmid DNA vaccine delivered using electroporation. As a model, we used COVID-eVax, a plasmid DNA-based vaccine that targets the receptor binding domain (RBD) of the SARS-CoV-2 spike protein. Increased nicked DNA was produced by using either an accelerated stability protocol or a lyophilization protocol. Surprisingly, the immune response induced in vivo was only minimally affected by the percentage of open circular DNA. This result suggests that plasmid DNA vaccines, such as COVID-eVax that have recently completed a phase I clinical trial, retain their efficacy upon storage at higher temperatures, and this feature may facilitate their use in low-/middle-income countries.

DNA Vaccines for Epidemic Preparedness: SARS-CoV-2 and Beyond

“…An anecdotal report additionally noted DNA vaccine stability at +25 °C for 1 year and at 37 °C for a month [ 29 ]. A study of accelerated degradation conditions comparing structural stability and Immunogenicity for the COVIDe-Vax SARS-CoV-2 vaccine stored frozen at −20 °C versus vaccines kept at 23 °C, 45 °C, and 65 °C [ 30 ]. Whereas exposure to 45 °C caused the almost complete conversion from supercoiled to open circle forms, gene expression and binding antibody and T cell responses were unaffected in contrast to storage at 65 °C, which resulted in the linearization of the DNA and a significant reduction in gene expression, resulting in the almost complete loss of T cell responses and decreased B cell responders [ 30 ].…”

“…A study of accelerated degradation conditions comparing structural stability and Immunogenicity for the COVIDe-Vax SARS-CoV-2 vaccine stored frozen at −20 • C versus vaccines kept at 23 • C, 45 • C, and 65 • C [30]. Whereas exposure to 45 • C caused the almost complete conversion from supercoiled to open circle forms, gene expression and binding antibody and T cell responses were unaffected in contrast to storage at 65 • C, which resulted in the linearization of the DNA and a significant reduction in gene expression, resulting in the almost complete loss of T cell responses and decreased B cell responders [30]. Our group is conducting a 2-year long-term accelerated stability study of the GLS-5310 SARS-CoV-2 vaccine and have similarly noted no loss of immunogenicity for vaccines held at 25 • C for a year, 32.5 • C for 6 months, and 37 • C for 3 months (unpublished data).…”