Examination of parameters affecting the elicitation of humoral immune responses by particle bombardment-mediated genetic immunization.

A human growth hormone expression construct was delivered intracellularly into the abdominal skin of mice by particle bombardment-mediated gene transfer. Using this technology, the in vivo delivery of antigen-encoding expression vectors affixed to gold microprojectiles results in de novo antigen production in target skin and development of specific antibody responses. In this study, we examined the contribution of various delivery parameters to the resultant protein expression and related antibody responses. The highest levels of both protein expression and antibody production were correlated with particle delivery to the epidermis while deliveries extending into the dermis resulted in decreased protein and antibody production. Optimal immune responses were also shown to be dependent upon the delivery of a sufficient number of DNA-coated gold particles, indicating that a dose-response relationship exists between the number of particles delivered and the resultant protein expression and antibody production. Further, maximal protein expression and associated antibody titers were elicited with surprisingly small amounts of DNA. The practicality of targeting skin and the use of three to four orders of magnitude less DNA than is typically required in direct DNA inoculation studies demonstrates the potential utility of this emerging technology for the rapid production of antibodies in laboratory animals, and in the development of a new class of human clinical vaccines based upon direct, intracellular DNA delivery.