Minicircle DNA Vaccines: Overcoming Delivery and Expression Barriers in Next-Generation Immunization.

DNA vaccines have emerged as a promising immunization platform, offering key advantages over conventional vaccine approaches, including superior stability, a favorable safety profile, rapid and flexible antigen design, and scalable manufacturing. However, their clinical efficacy has remained limited, primarily due to inefficient cellular uptake, poor endosomal escape, and degradation of the plasmid DNA within host cells. Recent advances have highlighted minicircle DNA (mcDNA) as a next-generation alternative to conventional plasmid vectors. mcDNA constructs are compact, backbone-free episomal vectors containing only the expression cassette, including the promoter, transgene, and polyadenylation signal, while lacking bacterial sequences such as antibiotic resistance genes and origins of replication. This reduced vector size reduced vector-driven innate immune activation and susceptibility to epigenetic silencing, thereby improving transfection efficiency and supporting more sustained transgene expression in both dividing and non-dividing cells. This review provides a comprehensive overview of mcDNA technology in the context of vaccine development, discussing its structural design and production principles, mechanistic advantages over conventional plasmid DNA, and current applications across infectious disease and cancer vaccine platforms. In addition, we explore recent delivery strategies to enhance mcDNA transfection and immunogenicity, summarize existing limitations that hinder translation into applications, and outline future directions to optimize mcDNA-based vaccine technologies.