DNA vaccines raise immune responses by expressing proteins in vaccinated hosts. Responses are raised by nanogram levels of protein expression. Popular methods of DNA delivery include intramuscular (i. m.) injections of DNA in saline and gene gun delivery of DNA-coated gold beads to the epidermis. Professional antigen-presenting cells derived from the bone marrow present DNA-expressed antigens to T-cells. Following gene gun immunizations directly transfected dendritic cells present antigens, whereas following i.m. immunizations both directly transfected dendritic cells and macrophages can present antigen. For both methods of DNA delivery, non-lymphoid cells can serve as factories of antigen for professional antigen presenting cells. Gene gun immunizations depend on antigen expression at the skin target whereas i.m. immunizations are largely independent of DNA expression in the muscle target. For both methods, antigen expression capable of initiating an immune response persists for about one month. intramuscular deliveries of DNA tend to raise type 1 T-cell help for intracellular and plasma membrane antigens but type 2 T-cell help for secreted antigens. Gene gun immunizations tend to raise type 2 T-cell help for both cell-associated and secreted antigens. In mice, DNA-raised immune responses can be equivalent to those raised by viral infections for both the height and longevity of antibody and cytotoxic T-cell responses.

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