Preclinical safety assessment of a DNA vaccine using particle-mediated epidermal delivery in domestic pig, minipig and mouse.

DNA vaccination involves the direct injection of genes coding for specific antigenic proteins. One technique known as particle-mediated epidermal delivery (PMED) is a practical approach for epidermal delivery and provides a strong immune response. An important aspect of the preclinical safety assessment of DNA vaccines is the selection of a pharmacologically relevant animal model for the assessment of antigen expression, optimization of delivery and formulation of the plasmid. This paper describes a comparative study of domestic pig, minipig and mouse in regard to local tolerance and antigen expression of HIV immunotherapeutic using PMED. Pig/minipig is considered a good model for the safety assessment of DNA vaccines due to the similarity to human skin. Local reactions were evaluated at 10 min, 4, 24 and 48 h. Histology of administration sites revealed epidermal necrosis with associated dermal inflammation at 10 min and 4h, and subsequent regeneration with repair at 24 and 48 h. The degree and extent of these changes varied according to species. Domestic pig and minipig showed superficial epidermal necrosis and complete repair, while the mouse showed full-thickness epidermal necrosis and partial repair. Expression of HIV antigen was confirmed using immunohistochemistry in all three species at 4, 24 and 48 h. The results showed that PMED is an effective system for DNA vaccine delivery as demonstrated by the antigen expression seen as early as 4 h.