T-cell responses. In skeletal muscle, striated muscle cells are most frequently transfected, but seem to be unimportant in immune response. Instead, IM inoculated DNA “washes” into the draining lymph node within minutes, where distal dendritic cells are transfected and then initiate an immune response. Transfected myocytes seem to act as a “reservoir” of antigen for trafficking professional APCs. Maintenance of immune response DNA vaccination generates an effective immune memory via the display of antigen-antibody complexes on follicular dendritic cells (FDC), which are potent B-cell stimulators. T-cells can be stimulated by similar, germinal centre dendritic cells. FDC are able to generate an immune memory because antibodies production “overlaps” long-term expression of antigen, allowing antigen-antibody immunocomplexes to form and be displayed by FDC. Interferons Both helper and cytotoxic T-cells can control viral infections by secreting interferons. Cytotoxic T cells usually kill virally infected cells. However, they can also be stimulated to secrete antiviral cytokines such as IFN-γ and TNF-α, which do not kill the cell, but limit viral infection by down-regulating the expression of viral components. DNA vaccinations can be used to curb viral infections by non-destructive IFN-mediated control. This was demonstrated for hepatitis B. IFN-γ is critically important in controlling malaria infections and is a consideration for anti-malarial DNA vaccines. Immune response modulation Cytokine modulation An effective vaccine must induce an appropriate immune response for a given pathogen. DNA vaccines can polarise T-cell help towards TH1 or TH2 profiles and generate CTL and/or antibody when required. This can be accomplished by modifications to the form of antigen expressed (i.e. intracellular vs. secreted), the method and route of delivery or the dose. It can also be accomplished by the co-administration of plasmid DNA encoding immune regulatory molecules, i.e. cytokines, lymphokines or co-stimulatory molecules. These “genetic adjuvants” can be administered as a: mixture of 2 plasmids, one encoding the immunogen and the other encoding the cytokine single bi- or polycistronic vector, separated by spacer regions plasmid-encoded chimera, or fusion protein In general, co-administration of pro-inflammatory agents (such as various interleukins, tumor necrosis factor, and GM-CSF) plus TH2-inducing cytokines increase antibody responses, whereas pro-inflammatory agents and TH1-inducing cytokines decrease humoral responses and increase cytotoxic responses (more important in viral protection). Co-stimulatory molecules such as B7-1, B7-2 and CD40L are sometimes used. This concept was applied in topical administration of pDNA encoding IL-10. Plasmid encoding B7-1 (a ligand on APCs) successfully enhanced the immune response