Plasmid DNA vaccines: where are we now?

DNA vaccines are considered as third-generation vaccines. The recombinant DNA technology plays an important role in the production of DNA vaccines. These vaccines are intended to increase DNA insertion and translation in the cell, activate CD4+ T cells, and enhance cytotoxic T-lymphocyte induction and antibody production. DNA vaccines are safe with few side effects in humans and animals. Their immunogenicity can be improved by the use of suitable adjuvants and proper delivery systems. In recent years, strategies have been developed to increase the efficacy of DNA vaccines through electroporation, as well as the use of cytokines, genetically engineered vectors, liposomes, and micro- or nanoparticles. In the last decade, significant advances have been made in the field of DNA immunization. Strategies such as the use of DNA vaccines in combination with genetic adjuvants and prime-boost immunization increase the protective response and decrease the doses of DNA vaccines. Vaccine efficacy is influenced by the route of immunization, with intracutaneous injection of the plasmid having been found to be more effective than intramuscular or subcutaneous injection even at lower doses. DNA vaccines are useful in both humans and animals against infectious diseases, allergies and even cancer. This review elaborates on the current status of DNA immunization in the medical and veterinary fields.