Practice question

DNA vaccines deliver genetic instructions as circular plasmid DNA rather than protein antigen or RNA. Plasmid constructs typically contain bacterial origin pUC, antibiotic resistance for selection during manufacturing, and eukaryotic expression cassette comprising strong promoter cytomegalovirus CMV immediate early with intron A enhancing transcription, codon optimized antigen gene, polyadenylation signal bovine growth hormone BGH or SV40 preventing mRNA degradation. Plasmids produced in Escherichia coli fermentation high copy number, purified supercoiled isoform removing endotoxin via chromatography. Upon intramuscular delivery with electroporation needles delivering brief electrical pulses increasing membrane permeability or needle free jet injector, plasmid enters myocytes and antigen presenting cells, translocates nucleus independently of cell division, transcribed by RNA polymerase II into mRNA exported then translated. Resulting antigen triggers both humoral and cellular immunity. Advantages include exceptional thermostability stable at room temperature months facilitating transport without stringent cold chain, simple large scale manufacturing, lack of anti-vector immunity permitting homologous boosting, ability to encode multiple antigens single plasmid. Limitations include relatively low transfection efficiency in humans requiring devices, theoretical rare integration at frequencies less than 10^-7 per plasmid. World's first approved ZyCoV-D COVID DNA vaccine India uses three dose regimen.