[Immunization of Mice with the pVAXrbd DNA Vaccine by Jet Injection Induces a Stronger Immune Response and Protection...

During the COVID-19 pandemic, it became clear that, to ensure global health security, it is essential to have a developed platform that can be used to develop a safe, low-cost, effective vaccine quickly. DNA vaccines have several advantages over other platforms, including rapid development and ease of production. They are more stable than mRNA vaccines. Unlike viral vector-based vaccines, DNA vaccines do not induce antivector immunity. One of the disadvantages of DNA vaccines is their relatively low immunogenicity. This problem can be solved using jet injection. Here, we evaluated and confirmed the efficiency of an inexpensive, simple, and safe method for delivering the naked DNA vaccine pVAXrbd encoding the receptor-binding domain (RBD) of the SARS-CoV-2 spike (S) protein using a spring-loaded jet injector. Based on the results of histological analysis, optimal conditions were determined that ensure low tissue trauma in laboratory animals upon administration of pVAXrbd. An optimized immunization protocol for BALB/c mice was used to compare the immunogenicity of pVAXrbd with two different administration schemes: using a jet injector under the skin and into the adjacent muscle layers or intramuscularly using a syringe with a needle. Mice immunized with "naked" pVAX-RBD were shown to produce high levels of specific virus-neutralizing antibodies. The vaccine also induced a strong RBD-specific T-cell response. As shown by quantitative PCR analysis of viral RNA, vaccinated mice infected with the Gamma variant of SARS-CoV-2 developed a protective immune response; moreover, it was more pronounced in animals to which the DNA-vaccine was administered using a jet injector compared to those immunized intramuscularly. Thus, the introduction of a DNA-vaccine using jet injection effectively activates both types of immune response and leads to a decrease in the viral load. Jet injection is a promising method for delivering DNA vaccines, characterized by low cost, simplicity, technological administration, and minimal pain for the patient.