The Emerging Role of DNA Vaccines

W. Michael McDonnell, MD, Western Washington Medical Group, and Frederick K. Askari, MD, PhD, University of Michigan.

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DNA Vaccines Result in MHC Class I Presentation and Cell-Mediated Immunity

DNA vaccines are made of nucleotides, usually contained in a DNA plasmid or "naked DNA;" there is no protein component.[4]They stimulate a cellular immune response (cell-mediated immunity) in addition to an antibody response (humoral immunity). Generally, cellular immunity is better able to fight viruses and parasites.

DNA vaccines are able to generate cellular immunity because the foreign protein they induce production of is processed intracellularly and presented to the immune system in the context of the MHC class I system. Traditional vaccines are processed via the MHC class II system and therefore are poor immunogens for cell-mediated immunity. Some researchers are using non-DNA vectors in an attempt to induce cell-mediated immunity through MHC I presentation. These non-DNA vectors consist of peptide epitopes attached to liposomes.[5,6]

Naked plasmid DNA vaccine technology is easily applied to many different infectious agents. Using a standard DNA plasmid, genes from any pathogen can be "cut and pasted" into the plasmid, creating a new vaccine. The peptides made intracellularly in response to DNA vaccines (expressed epitopes) more closely resemble native viral epitopes and thus may be more effective. Additionally, the peptides are presented to the immune system in ways that may be more effective in producing cell-mediated immunity, as stated above. A vaccine that effectively stimulates a cellular immune response could be used to treat patients already infected with chronic viral illness such as HIV, hepatitis C virus (HCV), HBV, and HSV, and could also be used to fight cancer cells.

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