SARS-CoV-2 DNA Vaccine INO-4800 Induces Durable Immune Responses Capable of Being Boosted in a Phase 1 Open-Label Trial

Abstract Background Additional SARS-CoV-2 vaccines that are safe and effective as both primary series and booster remain urgently needed to combat the COVID-19 pandemic. Here we describe the safety and durability of the immune response from two doses of a DNA vaccine (INO-4800) targeting the full-length Spike antigen and a subsequent homologous booster dose. Methods INO-4800 was evaluated in 120 healthy participants across three dose groups (0.5 mg, 1.0 mg and 2.0 mg), each stratified by age. INO-4800 was injected intradermally followed by electroporation at 0 and 4 weeks followed by an optional booster dose 6-10.5 months following the second dose. Results INO-4800 was well-tolerated, with no treatment-related serious adverse events reported. Most adverse events were mild in severity and did not increase in frequency with age and subsequent dosing. A durable antibody response was observed 6 months following the second dose; a homologous booster dose significantly increased immune responses. Cytokine producing T cells and activated CD8+T cells with lytic potential were detected in the 2.0 mg dose group. Conclusion INO-4800 was well-tolerated as a 2-dose series and as a homologous booster dose in all adults, including the elderly. These results support further development of INO-4800 as a primary series and as a booster.