Biotechnology and Bioinformatics (1+1)

4.3.10.1. DNA vaccines

DNA vaccines consist of a suspension of bacterial plasmids carrying the gene coding for the immunogenic protein under the control of eukaryotic promoter.

• The basic attributes of a DNA vaccine include an origin of replication suitable for producing high yields of plasmid in E. coli, an antibiotic -resistant gene to confer antibiotic-selected growth in E. coli, a strong enhancer/promoter and an mRNA transcript termination/polyadenylation sequence for directing expression in mammalian cells.
• The plasmids hence construct ed are grown in E. coli, purified and suspended in saline and introduced into the host either by intramuscular injection or using a gene gun.
• DNA vaccines have been used in fishes with very encouraging results. Strong expression of reporter gene s in muscle cells following intramuscular injection of plasmid constructs carrying gene of interest and reporter gene have been reported.
• When plasmids carrying luciferase gene under the control of cytomegalovirus immediate early gene promoter is injected to rainbow trout at a dose of 50µg of DNA, maximum activity is seen at 5 to 7 day post-injection and the activity of luciferase remains for 115 days.
• Combined injection of plasmids carrying VHSV and IHNV glycoprotein genes shows plasmid DNA to remain in the muscle cells up to 45 days.

DNA immunization induced specific as well as non-specific immune response in the recipient host. High level of protection in clinical animal model has been observed due to the generation of specific antibodies and priming of T-cell responses. Significant protection of rainbow trout is observed against IHNV challenged following the injection of construct encoding the IHNV G protein.

Apart from introducing a part of the genome of pathogen coding for immunogenic protein, it is possible to introduce a gene coding for an antibody that can target and destroy the pathogen.