DNA vaccines: Basic mechanism and immune responses (Review)

DNA vaccines raise immune responses by expressing proteins in vaccinated ho sts. 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. Pro fessional antigen-presenting cells derived from the bone marrow present DNA -expressed antigens to T-cells. Following gene gun immunizations directly t ransfected dendritic cells present antigens, whereas following i.m. immuniz ations both directly transfected dendritic cells and macrophages can presen t antigen. For both methods of DNA delivery, non-lymphoid cells can serve a s 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 targe t. For both methods, antigen expression capable of initiating an immune res ponse persists for about one month. Intramuscular deliveries of DNA tend to raise type 1 T-cell help for intracellular and plasma membrane antigens bu t 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 vir al infections for both the height and longevity of antibody and cytotoxic T -cell responses.