Accell particle-mediated DNA immunization elicits humoral, cytotoxic, and protective immune responses

Accell particle-mediated gene delivery technology was employed for the intracellular delivery of antigen-encoding expression vectors in epidermal tissues in laboratory animals. Delivery of plasmid DNA-coated gold microparticles using the Accell gene delivery system resulted in de novo antigen expression in epidermal cells that stimulated the induction of antigen-specific humoral and cytotoxic cellular immune responses. Optimal DNA delivery conditions favoring maximal humoral responses required the delivery of 5 x 10(7) micron-sized gold particles containing 300 plasmid copies per particle (80 ng of vector total) into a 4-cm2 area of abdominal skin. Comparison of immune responses between animals that received intramuscular injections of relatively large quantities of vector DNA (100 micrograms) and those that received intracellular deliveries of submicrogram quantities of the same DNA to the epidermis demonstrated that the latter approach was considerably more effective at eliciting strong humoral responses. In addition, cytotoxic cellular immune responses were elicited to HIV-1 gp120 following epidermal delivery of HIV-1 gp160 or gp120 expression constructs. A qualitative shift from predominantly cytotoxic cellular to predominantly humoral immune responses with continued immunization indicated the potential for optimizing delivery conditions to favor specifically one type of response over the other.