DNA vaccination is the direct introduction of genetic material (containing DNA or RNA) into the host cell via injection, oral administration or particle bombardment [
1]. The coding sequence of a protective antigenic gene is incorporated into the plasmid DNA, which will allow its expression in the host cells. DNA vaccination can elicit both humoral and cellular immune responses, and give protection against a variety of pathogens, tumor antigens and allergens [
2,
3]. DNA vaccine potentially has several advantages over traditional vaccines, cheaper and easier to produce, have less adverse side effects, has been developing rapidly in recent years. However, the application of DNA vaccine is largely limited by its susceptibility to intercellular or extracellular endonucleases degradation. So far, several strategies have been attempted to address this issue, but none has been complete successful [
4,
5].
The principle of DNA vaccine is similar to viral infection mechanisms inside the host. Both viral and non-viral vector systems have been used for DNA delivery in clinical trials [
6,
7]. Superior gene delivery vectors using eukaryotic viruses including adenovirus, adeno-associated virus, retrovirus, and lentivirus have been frequently reported [
8]. Also, a variety of non-viral systems have been developed, such as lipids, liposomes [
9], polymers, polymersomes, cell-penetrating peptide and inorganic nanoparticles [
10‐
14]. Bacteriophages are the most prospective biological nanomaterials, have attracted increasingly more attention as a novel DNA delivery system. Phage vectors have several advantages over viral and non-viral DNA delivery systems due to a number of promising characteristics. Bacteriophage is a nano-sized natural system capable of harboring foreign DNA insertion and efficient packaging. Most importantly, phages are safe, and have been used for treatment of bacterial infections, both in human and animals, with no safety concerns being identified [
15]. Moreover, large-scale production and purification of phage particles are simple and economical. Among bacteriophages, lambda phage have been suggested as a good candidate for delivering DNA vaccine into eukaryotic cells [
16,
17]. Lambda phages carrying DNA vaccine expression cassette, consisting of an eukaryotic promoter, antigen gene and polyadenylation site, can be propagated and purified for immunization against hepatitis B [
18]. In addition, lambda phage particles expressing heterologous gene from eukaryotic expression cassettes have also been used for tumor therapy in a mice model [
19]. Filamentous phages have been used as DNA vaccine delivery vehicle against human syncytial virus [
20]. Although bacteriophages have no tropism for mammalian cells, they can be modified to display targeting ligands on the particle surface as fusion coat proteins without disrupting the phage structure [
21‐
24]. The surface displayed targeting ligands then guide the binding and internalization of the phage particles into cells. Moreover, transfection efficacy is directly related to the copy number of the targeting ligands [
25,
26].
T7 phage possesses a 55-nm diameter icosahedral head that encapsulates a 40 kb double stand DNA genome coding for 55 proteins. Under optimal conditions, T7 phages have a multiplication cycle of 11 min and produce about 10
13 offspring particles in 1 h of replication cycle [
27], and thus are suitable for large-scale production. The two main capsid proteins (10A and 10B) of T7 phages have been engineered for surface display systems that can display peptides up to about 50 amino acids in size in high copy number (415 per phage). However, T7 phage delivering genetic material has not been previously reported. In this study, we herein engineered a T7 phage as a DNA vaccine targeting delivery vector, with surface displaying Tat peptide and genome insertion eukaryotic expression box.