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DNA Vaccines

Mechanism of Action

  • DNA vaccines are circular or linear plasmids that encode pieces of viral genes of interest.
  • After the vaccine is injected into patients the plasmid is taken up by cells at the site of injection.
  • Inside the cell, the viral genes are expressed into proteins. For gene expression to occur a stretch of genetic code called the promoter is necessary.
  • The viral proteins are degraded into small peptide fragments, which are then presented by MHC class I and class II molecules on the cell surface where T cells recognizing these complexes generate an immune response..

DNA vaccines represent a favored vaccine strategy because they are safe, stable, easy to engineer and produce, and immune responses generated pose no interference against later boost immunizations. However, DNA vaccines need to be improved significantly as they do not induce sufficient levels of immune responses in humans and non-human primates.

Strategies for enhancing DNA vaccines include improving gene expression and delivery methods, and adding molecular adjuvants:

  • Gene expression is increased by optimizing both the coding sequence and the gene regulatory elements.
  • Traditionally DNA has been delivered by injection or gene gun into muscles or skin, or administration into nasal or oral cavity. Novel delivery technologies include use of bacterial and viral vectors; particle-mediated delivery into antigen presenting cells using lipid polymers and gold microparticles that encapsulate and condense the DNA allowing slow release; and physical delivery methods such as electroporation, and needle-free devices such as epidermal patches.
  • Immune responses are modulated by addition of co-stimulatory molecules such as ICAM-1 and CD40L; genes encoding cytokines such as IL-12 and GM-CSF; chemokines such as RANTES and MIP-1a; and TLR ligands such as CpG oligonucleotides and heat-shock proteins.

Regulatory Aspects

Outside of clinical trials, no DNA vaccines have yet been approved for use in humans by the Food and Drug Administration, the U.S. regulatory agency responsible for ensuring safety of food, drugs and medical devices.

View the FDA guidance on DNA vaccines.

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Last Updated January 14, 2010