(283d) Electroporation-Mediated Delivery of mRNA in the Skin Using a Low-Cost Handheld Electroporator

Recent examples of rapid development and distribution of mRNA-based COVID vaccines, in addition to the safety and effectiveness of these vaccines, have proven their prowess over other types of vaccination. Furthermore, mRNA vaccination has also enabled nucleic acid-based vaccines to be at the forefront of vaccine development and distribution for future endemics and pandemics. The epidermis and dermis layers of skin offer large populations of antigen-presenting cells (APCs) associated with improved immune responses to skin vaccination compared to vaccines administered to muscle. However, for nucleic acid-based vaccines, intradermal drug delivery has been an outstanding challenge due to lower cell transfection. Large molecules of mRNA have been delivered inside the cell using non-viral carriers (e.g., lipid nanoparticles) or electroporation. In electroporation, micro- to milli-seconds duration electric pulses transiently permeabilize the cell membrane which allows the mRNA molecules to pass into the cell for transfection. However, commercial electroporators are bulky and expensive. Here, we present a low-cost (< $1 USD) handheld device (ePatch) for electroporation which consists of a microneedle electrode array and a hand-operated piezoelectric pulser.

We used adult female Wistar rats for the animal study. Firefly luciferase-encoded mRNA (5 µg/25 µl) injections were administered intradermally using insulin syringes. A microneedle electrode array (MEA) was then immediately applied to the skin to deliver the electric pulses to the epidermis for electroporation of keratinocytes and other cells in the epidermis. IVIS bioluminescence imaging was performed to quantify the protein expression for up to two weeks.

Here, we show that the ePatch pulser, when discharged in air, generated a peak voltage of up to 23 kV and resulted in a spark discharge. When connected to the MEA and applied to skin, the peak voltage was measured to be 250–300 V, in the form of a rapidly decaying oscillating waveform with a characteristic time of approximately 10 microseconds and a total duration of approximately 100 microseconds. Furthermore, we found that a force of 14.7-19.8 N was optimal for proper insertion of microneedles into the skin and to deliver electric pulses with a peak voltage of ~300 V, which is sufficient for electroporation purposes. Expression kinetics after intradermal drug delivery showed that mRNA delivered with lipid nanoparticles showed the highest protein expression, followed by electroporation-mediated delivery of naked mRNA delivered with an RNase inhibitor and electroporation-mediated delivery of naked mRNA alone. Ongoing studies are addressing the effect of mRNA concentration and formulation, as well as parameters related to the electroporation pulse characteristics on in vivo protein expression of naked and self-amplifying mRNA.