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#gene delivery

6 public questions tagged with this topic.

Vaccine

DNA vaccines deliver genes in the form of:

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.

Ref: Wolff et al. Science 1990 DNA vaccines plasmid; Plotkin DNA vaccines; WHO DNA plasmid.

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Gene Therapy

Target cells in cardiovascular gene therapy include:

Endothelial cell central therapeutic target cardiovascular gene therapy because monolayer regulates vascular homeostasis via eNOS converting L-arginine to nitric oxide stimulating soluble guanylate cyclase raising cGMP relaxing smooth muscle, prostacyclin via COX2 inhibiting platelet aggregation, barrier integrity VE-cadherin junctions, leukocyte adhesion E-selectin VCAM1. Dysfunction oxidative stress uncoupling eNOS drives atherosclerosis hypertension ischemia. Ischemic peripheral artery disease refractory angina benefit proangiogenic factors VEGF-A165, FGF4, HGF, HIF1-alpha delivered AAV1 or plasmid catheter-based intracoronary or intramuscular promoting collateral vessel formation endothelial proliferation migration MAPK ERK and PI3K Akt pathways. Heart failure SERCA2a therapy improves cardiomyocyte calcium handling but endothelial transduction improving perfusion upstream essential. Promoters Tie2, VE-cadherin, endothelin enhancer confer specificity limiting off-target expression reducing neointimal hyperplasia after percutaneous coronary intervention. Restoration barrier reduces thrombogenicity and inflammatory infiltration critical for long-term graft patency. This mechanistic insight guides vector optimization, dosing strategies, and clinical safety monitoring essential for translational development and regulatory evaluation. This mechanistic insight guides vector optimization, dosing strategies, and clinical safety monitoring essential for translational development and regulatory evaluation.

Ref: Circ Res Cardiovascular Gene Therapy Endothelial Targets 2022; NHLBI Vascular Gene Therapy Overview; Lodish Vascular Biology Endothelial Function Chap 22.

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Gene Therapy

Which method directly delivers naked DNA into cells?

Electroporation applies brief high-intensity electric fields to transiently permeabilize lipid bilayer enabling direct cytosolic entry naked nucleic acids without chemical carriers. Square-wave pulses 100-1500 V/cm for microseconds to tens milliseconds generate transmembrane potential exceeding dielectric strength 0.2-1 V causing rearrangement lipids forming aqueous pores water intrusion between headgroups. Polyanionic DNA driven electrophoretically toward anode migrates through pores reaching cytoplasm within milliseconds before rapid resealing seconds mediated lateral diffusion and calcium-dependent exocytosis. Efficiency depends buffer conductivity, osmolality, cell diameter affecting induced potential proportional radius, pulse number, DNA concentration. Nuclear entry limiting but mitosis or nuclear localization signals improve. In vivo devices needle array electrodes deliver 50-500 V intramuscularly achieving DNA vaccine uptake myofibers and dendritic cells triggering MHC I and II presentation. Ex vivo clinical-scale electroporators transfect primary human T cells CD34 stem cells with mRNA or Cas9 RNP achieving 80 percent efficiency preserving viability avoiding insertional mutagenesis and viral manufacturing complexity suitable repeated applications.

Ref: FDA Guidance Electroporation Devices 2021; Molecular Therapy Methods Electroporation Protocol; NCERT Biotechnology Ch 11 Electroporation Principles.

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Gene Therapy

Non-viral vectors include:

Non-viral delivery uses chemically defined materials condensing nucleic acids avoiding viral capsid immunity and packaging limits. Cationic liposomes DOTAP, DOTMA, helper DOPE facilitating hexagonal phase transition, and cholesterol stabilizing bilayer electrostatically interact with negatively charged phosphate backbone plasmid DNA or mRNA condensing into lipoplexes 100-300 nm diameter positive zeta potential promoting binding anionic proteoglycans initiating endocytosis via clathrin and caveolae. Modern LNPs employ ionizable lipids DLin-MC3-DMA neutral at physiological pH 7.4 minimizing toxicity but cationic upon protonation acidic endosomal lumen pH 5.5-6.0 destabilizing endosomal membrane via inverted hexagonal structure releasing RNA into cytosol for ribosomal translation. Absence viral proteins eliminates insertional mutagenesis permits repeated dosing, scalability via microfluidic mixing, and accommodation large plasmids >10 kb. Transient expression suits vaccination and Cas9 provision where permanent integration undesirable, reducing oncogenesis. Cytotoxicity from cationic lipids at high doses managed by optimization lipid:DNA ratio and inclusion PEG-lipid shielding reducing opsonization and prolonging circulation enabling targeted delivery.

Ref: Lodish Molecular Cell Biology Non-viral Vectors Chap 9; NIH Non-viral Gene Delivery Liposomes Review; Alberts Membrane Fusion Liposome Mechanism.

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