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Vaccines 2013, 1(3), 384-397; doi:10.3390/vaccines1030384
Article

Elucidating the Kinetics of Expression and Immune Cell Infiltration Resulting from Plasmid Gene Delivery Enhanced by Surface Dermal Electroporation

1, 1, 1, 1, 2, 1, 1 and 1,*
1 Inovio Pharmaceuticals Inc., 1787 Sentry Parkway West, Building 18, Suite 400, Blue Bell, PA 19422, USA 2 The Scripps Research Institute, Core Microscopy Facility, 10550 North Torrey Pines Rd, La Jolla, CA 92037, USA
* Author to whom correspondence should be addressed.
Received: 16 July 2013 / Revised: 13 August 2013 / Accepted: 21 August 2013 / Published: 28 August 2013
(This article belongs to the Special Issue DNA Vaccines)
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Abstract

The skin is an attractive tissue for vaccination in a clinical setting due to the accessibility of the target, the ease of monitoring and most importantly the immune competent nature of the dermal tissue. While skin electroporation offers an exciting and novel future methodology for the delivery of DNA vaccines in the clinic, little is known about the actual mechanism of the approach and the elucidation of the resulting immune responses. To further understand the mechanism of this platform, the expression kinetics and localization of a reporter plasmid delivered via a surface dermal electroporation (SEP) device as well as the effect that this treatment would have on the resident immune cells in that tissue was investigated. Initially a time course (day 0 to day 21) of enhanced gene delivery with electroporation (EP) was performed to observe the localization of green fluorescent protein (GFP) expression and the kinetics of its appearance as well as clearance. Using gross imaging, GFP expression was not detected on the surface of the skin until 8 h post treatment. However, histological analysis by fluorescent microscopy revealed GFP positive cells as early as 1 h after plasmid delivery and electroporation. Peak GFP expression was observed at 24 h and the expression was maintained in skin for up to seven days. Using an antibody specific for a keratinocyte cell surface marker, reporter gene positive keratinocytes in the epidermis were identified. H&E staining of treated skin sections demonstrated an influx of monocytes and granulocytes at the EP site starting at 4 h and persisting up to day 14 post treatment. Immunological staining revealed a significant migration of lymphocytic cells to the EP site, congregating around cells expressing the delivered antigen. In conclusion, this study provides insights into the expression kinetics following EP enhanced DNA delivery targeting the dermal space. These findings may have implications in the future to design efficient DNA vaccination strategies for the clinic.
Keywords: intradermal; DNA vaccine; electroporation; kinetics; infiltration intradermal; DNA vaccine; electroporation; kinetics; infiltration
This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

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Mendoza, J.M.; Amante, D.H.; Kichaev, G.; Knott, C.L.; Kiosses, W.B.; Smith, T.R.F.; Sardesai, N.Y.; Broderick, K.E. Elucidating the Kinetics of Expression and Immune Cell Infiltration Resulting from Plasmid Gene Delivery Enhanced by Surface Dermal Electroporation. Vaccines 2013, 1, 384-397.

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