| This dissertation examines strategies for improving DNA vaccines. Despite their many advantages and the considerable promise shown in small animal models, poor immunogenicity resulting from low transfection efficiency and transient transgene expression limits the effectiveness of DNA vaccines in humans. Methods for circumventing transient transgene expression as well as for directly manipulating T cell responses are explored. Chapters 2 and 3 of this thesis study the use of minicircle (MC) DNA as a vaccine. In chapter 2, a MC DNA vaccine is shown to generate larger CD8+ T cell responses and confer superior protection against an infectious challenge than a conventional plasmid DNA vaccine. Chapter 3 investigates the mechanism by which MC DNA elicits superior CD8+ T cell responses. In particular, the role of prolonged antigen expression is explored and found to be an important component of MC DNA vaccine efficacy. Chapter 4 proposes a method for targeted gene delivery to T cells in general, or to antigen-specific T cells. The targeting mechanism uses a streptavidin platform modified with positively charged peptides to enable binding to nucleic acid. Targeting is mediated by addition of biotinylated targeting moieties, either an anti-CD7 antibody for targeting of T cells or peptide-MHC molecules for targeting of antigen-specific T cells. We find that such an approach is promising, as it mediates uptake of both fluorescently labeled siRNA and DNA. However, gene expression did not occur, indicating that further modifications to the approach are needed. |
