[Naked DNA vaccines]

Although still in a developmental stage, naked DNA vaccines are already the most important advancement in the history of vaccinology. Both the injection of plasmid DNA in experimental animals by different routes and preclinical studies, demonstrate the induction of protective immunity against different pathogens. Therapeutic application of DNA vaccines are well under way. In spite of the growing understanding about methods and routes of immunisation, both the early mechanisms by which DNA dependent immunisation occurs as well as the transfected cell types remain poorly understood. There is abundant experimental evidence that myocytes, keratinocytes and dendritic cells play an important role in the induction of the immune response. There is also an ongoing controversy on the relative importance of each one of these cell types. The aim of this paper is to review the current state of affairs regarding the understanding of the cell types participating in an immune response to the injection of a plasmid DNA vaccine. It is probably unlikely that only one and the same cell type would be the transfected cell and the one presenting the immunising peptide on MHC class II and I. An important step towards the understanding of DNA immunising mechanisms would be to elucidate plasmid DNA transfection. Is there a cell type that has specific receptors capturing the plasmid, expressing it and transferring its products to the antigen-presenting cell?